GH Excretion Research Articles

Anomalies de l'axe somatotrope et usage abusif d'hormone de croissance (GH)

Aims. – To evaluate the effects of the doping by GH. Synthesis of facts. – If it is well known that GH treatment has benefic effects on body composition in GH deficient patients (decrease in fat mass and increase in muscle mass), nothing has been proved on doping effects in trained subjects, excepted perhaps to avoid protein catabolism. GH amounts use for doping might be supraphysiological doses and might potentiate other substances such as anabolic steroids. Adverse effects are not yet well described, but seem potentially important at vascular and tumoral levels. Recombinant human GH (rhGH) abuse in athletes is actually almost undetectable because rhGH has the same sequence than natural GH, with a very short biological half-life and important fluctuations in plasmatic concentration, moreover urinary GH excretion is modified by physical exercise. It is therefore needful to analyze GH concentration in plasma (22 and 20 kDa molecular forms, the 20 kDa secretion is inhibited by feedback by the exogenous recombinant 22 kDa GH) as well as secondary markers, including IGF1, IGFBP3 and ALS. Reference values should be established taken into account physical activity type, and age.

Serum insulin-like growth factor-I concentrations in late middle age: no association with birthweight in three UK cohorts.

Small body size at birth and during infancy is associated with an increased risk of adult osteoporosis and cardiovascular disease. Fetal programming of the growth hormone-insulin-like growth factor (GH-IGF) axis may provide a mechanism for these epidemiological findings. To determine whether measurements of GH and IGF-I in late middle age were related to size at birth and in infancy. Overnight urinary GH excretion and fasting serum IGF-I were measured in 309 men and 193 women from Hertfordshire (born 1920-1930) for whom birthweight and weight at 1 year were recorded. Serum IGF-I was measured in men and women from Preston (n=254, born 1935-1943) and Sheffield (n=215, born 1939-1940) whose birthweight and other birth measurements were recorded. Urinary GH and serum IGF-I were not related to birthweight, other measurements at birth, or weight at 1 year. In contrast to previous studies in children or young adults, these data do not support the hypothesis that IGF-I concentrations are programmed by intra-uterine events, as assessed by birthweight, in late middle age.

Insulin sensitivity and lipolysis in adolescent girls with poorly controlled type 1 diabetes: effect of anticholinergic treatment

Increased GH secretion could be one factor behind the impaired glycaemic control often seen in adolescent girls with type 1 diabetes. Because GH induces insulin resistance, treatment with anticholinergic agents, such as pirenzepine (PZP), has been used to reduce GH secretion. However, in a previous study of adolescent girls with type 1 diabetes, we observed an improvement in glycaemic control during 12 weeks of PZP therapy despite unchanged excretion of GH in urine. Considering the complex mechanisms behind urinary GH excretion, the effects of PZP on pituitary GH secretion or secretory pattern cannot be excluded. Thus, to assess the effect of anticholinergic treatment on metabolic control in adolescent girls with diabetes, we have investigated GH secretion, insulin sensitivity and lipolysis before and during treatment with PZP. Eleven adolescent girls with type 1 diabetes and poor metabolic control were investigated before and after treatment with PZP, 100 mg orally, twice a day for 3 weeks. Serum samples for analysis of haemoglobin A1c and IGF-I were obtained in addition to serum profiles of GH, insulin and IGFBP-1 before and after 3 weeks of PZP treatment. Effects on insulin sensitivity and lipolysis were also assessed. IGFBP-1 was measured every hour, whereas serum GH and insulin were measured every 20 min for 24 h. Insulin sensitivity was analysed with the hyperinsulinaemic euglycaemic clamp technique. The rate of lipolysis was assessed under basal conditions following a constant rate infusion of [1,1,2,3,3-2H5]-glycerol. In five girls, lipolysis was also estimated during the hyperinsulinaemic euglycaemic clamp. There was a significant reduction in haemoglobin A1c levels (9.9 +/- 0.2%vs. 9.1 +/- 0.2; P < 0.0001) during 3 weeks of PZP treatment. In additional, the glucose requirement during the euglycaemic hyperinsulinaemic clamp increased by more than 30% (72.5 +/- 4.9 vs. 96.8 +/- 8.5 mg/m2/min; P = 0.003). However, we could not demonstrate any significant changes in GH secretion (area under the curve, basal levels or peak amplitude) or in the GH secretory pattern (peak height, peak length or interpeak interval). Concordantly, the IGF-I levels were statistically unchanged, as were IGFBP-1 concentrations. The rate of lipolysis did not change under basal conditions (3.40 +/- 0.53 vs. 3.04 +/- 0.54 micro mol/kg/min, n = 11, P = 0.54) or during the hyperinsulinaemic euglycaemic clamp (1.58 +/- 0.21 vs. 2.08 +/- 0.26 micro mol/kg/min; n = 5, P = 0.32). Our observations of an increased glucose requirement during the clamp as well as a decrease in haemoglobin A1c demonstrate improved insulin sensitivity in the adolescent girls with diabetes following pirenzepine therapy. The mechanism behind the improvement is not clear, as neither secretion nor the secretory pattern of GH changed significantly. The persistently high levels of GH might explain the unaltered rate of lipolysis despite the improved insulin sensitivity. The observed improvement in glycaemic control in adolescent girls with type 1 diabetes following pirenzepine therapy is promising, although more studies on this topic are needed.

Baja sensibilidad del IGF-I, la IGFBP-3 y la GH urinaria en el diagnóstico de la insuficiencia de la hormona del crecimiento en niños y adolescentes varones con talla baja y velocidad de crecimiento disminuida

Se estudió la utilidad del IGF-I, la IGFBP-3 y la excreción urinaria de la hormona del crecimiento (GH) en el diagnóstico del retraso de crecimiento en niños y adolescentes varones con talla baja. Se enviaron a un laboratorio central las muestras de suero de dos pruebas farmacológicas de estímulo de la secreción de GH y dos muestras de orina de 24 h para determinar la GH sérica y urinaria, y las concentraciones séricas de IGF-I, IGFBP-3 y GHBP tanto en valores absolutos como estandarizados para sujetos de la misma edad y sexo (índice Z). Los niños con talla baja se clasificaron en dos grupos diagnósticos dependiendo de los resultados del pico de concentración de GH estimulada que se estableció arbitrariamente en 7,5 µg/l: deficitarios en hormona del crecimiento (DGH) (n = 25) (pico < 7,5 µg/l), y talla baja idiopática (TBI) (n = 54) (pico = 7,5 µg/l). Además, se incluyó un grupo de 15 niños y adolescentes varones con crecimiento normal. La velocidad de crecimiento estandarizada fue menor, y el índice de masa corporal mayor, en el grupo de DGH respecto al de TBI. Los valores estandarizados del IGF-I presentaron diferenciassignificativas entre los 3 grupos (p = 0,001). El análisis de regresión lineal múltiple, considerando la velocidad de crecimiento estandarizada como variable dependiente, reveló que el IGF-I estandarizado es el mejor factor de predicción, seguido de la respuesta máxima de la GH al estímulo con clonidina y de la excreción urinaria de GH. Las curvas ROC revelaron un nivel de corte óptimo para el diagnóstico de déficit de GH (DGH) de –2,05 para el IGF-I estandarizado (32% de sensibilidad y 90% de especificidad) y de –1,14 para la IGFBP-3 estandarizada (28% de sensibilidad y 94% de especificidad). Las mediciones de IGF-I e IGFBP-3 estandarizadas para sujetos de la misma edad y sexo resultaron muy eficientes sólo en el diagnóstico del DGH grave, pero tuvieron escasa sensibilidad para diagnosticar el DGH idiopático aislado, definido según una baja respuesta de la GH a las pruebas de estímulo. The usefulness of IGF-I, IGFBP-3, and the urinary GH excretion in the diagnostic evaluation of growth retardation in boys with short stature was studied. Serum samples from two GH-stimulation tests and two 24-h urine samples were sent to a Central Laboratory to measure serum and urinary GH, serum IGF-I, IGFBP-3 and GHBP, bothin absolute and standardized values (Z-score). Short children were classified as growth hormone deficient (GHD) (n = 25), and idiopathic short statured (ISS) (n = 54), on the basis of the peak stimulated GH concentration of < 7.5 µg/l or = 7.5 µg/l respectively. A group of 15 normally growing children and adolescents was also included. Height-velocity standard deviation score (HV)-SDS was lower and body mass index higher in GHD than ISS. Standardized IGF-I differed significantly by ANOVA among the three groups (p = 0.001). Multiple stepwise linear regression analysis with HV-SDS as dependent variable showed IGF-I SDS as the best predictor followed by peak GH clonidine response and uGH excretion. ROC curves showed optimum cut-off level for IGF-I SDS as –2.05 (sensitivity: 32%, specificity: 90%), and –1.14 for IGFBP-3 SDS (sensitivity: 28%, specificity: 94%). Standardized IGF-I and IGFBP-3 measurements were highly efficient only in diagnosis of severe GHD, but they show low sensitivity for the diagnosis of isolated idiopathic GHD as defined according to the low GH response to stimulation tests.

Integrity of the growth hormone/insulin-like growth factor system is maintained in patients with chronic fatigue syndrome.

GH deficiency states and chronic fatigue syndrome (CFS) share several characteristics, and preliminary studies have revealed aspects of GH dysfunction in CFS. This study assessed indexes of GH function in 37 medication-free CFS patients without comorbid psychiatric illness and 37 matched healthy controls. We also assessed GH function before and after treatment with low dose hydrocortisone, which has been shown recently to reduce fatigue in CFS. We measured basal levels of serum insulin-like growth factor I (IGF-I), IGF-II, IGF-binding protein-1 (IGFBP-1), IGFBP-2 and IGFBP-3 together with 24-h urinary GH excretion. We also performed 2 dynamic tests of GH function: a 100-microg GHRH test and an insulin stress test using 0.15 U/kg BW insulin. There were no differences between patients and controls in basal levels of IGF/IGFBP or in urinary GH excretion. GH responses to both the GHRH test and the insulin stress test were no different in patients and controls. CFS patients did have a marginally reduced suppression of IGFBP-1 during the insulin stress test. Hydrocortisone treatment had no significant effect on any of these parameters. There is no evidence of GH deficiency in CFS. At the doses used, hydrocortisone treatment appears to have little impact on GH function.

Evolution of GH secretion in urine during an in-patient slimming course in obese children.

To estimate the change in GH excretion in urine (GH-U) during a slimming course, and if increased, to assess the components of the course related to the increase in obese children. Observational follow-up study of patients admitted for primary obesity to an in-patient slimming course lasting at least 10 weeks. 48 complete observations out of 54 consecutive pre-pubertal patients admitted to a paediatric centre for treatment of primary obesity (BMI greater than the 90th percentile of the national reference curves). GH excretion in urine by immunoradiometric assay, at entry and after 10 weeks, various anthropometric measurements, nutritional intake and departure from the prescribed diet, time spent in physical activity, sleep duration. A mean decrease of 0.90 standard deviations for BMI was accompanied by a 34% increase of GH-U. Time spent in physical activity was the only component of the course found to be related to the magnitude of GH-U increase. The results of this observational study confirm that GH-U is increased after a slimming course in children, and suggest that physical activity is a major contributor to the restoration of normal GH-U levels.

Diagnostic efficiency of serum IGF-I, IGF-binding protein-3 (IGFBP-3), IGF-I/IGFBP-3 molar ratio and urinary GH measurements in the diagnosis of adult GH deficiency: importance of an appropriate reference population.

To analyse the diagnostic role of serum IGF-I, IGF-binding protein-3 (IGFBP-3), IGF-I/IGFBP-3 molar ratio and urinary GH (uGH) excretion in adult GH deficiency (GHD). Twenty-seven adults (age range: 18-71 years) with severe GHD, defined by a peak GH response to an insulin tolerance test below 3microg/l in patients with at least one additional pituitary hypofunction. Reference values were established from a selected age- and body mass index-matched population (154 healthy adults grouped in four age groups). IGF-I and IGFBP-3 were measured by RIA (Nichols) and results expressed as standard deviation (s.d.) scores from our reference population and assay normative data (s.d. score Nichols). uGH was measured by IRMA. Within the control group, IGF-I, IGFBP-3, IGF-I/IGFBP-3 ratio standardisation regarding our control population and IGF-I with respect to the assay normative data resulted in disappearance of age-related differences. However, IGFBP-3 s.d. score Nichols resulted in mean values between +1.4 and +2.5 s.d. score. Greatest diagnostic efficiency was for IGF-I standardised with respect to our controls (97.2%), followed by s.d. score IGFBP-3 (92.9%). s.d. score IGF/IGFBP-3 ratio and uGH showed poor diagnostic efficiency. Any combination of at least two abnormal parameters raised specificity to 100%. IGF-I standardised with respect to assay reference (s.d. score Nichols) showed similar diagnostic value (95.0%) whereas IGFBP-3 showed low sensitivity (33. 3%). Within the GHD patients, those with three or more additional deficiencies had lower s.d. score IGF-I than those with only two or one. We underline the importance of an appropriate reference population for correct interpretation of GH secretion markers. Considering our results, specificity obtained with two simultaneous abnormal parameters when referred to an adequate reference population may add valuable information to alternative GH stimulation tests to confirm adult GHD.

Comparison of monthly intramuscular injections of Sandostatin LAR with multiple subcutaneous injections of octreotide in the treatment of acromegaly; effects on growth hormone and other markers of growth hormone secretion

To compare the effects of monthly intra-muscular injections of a long acting preparation of octreotide, Sandostatin LAR, with multiple daily subcutaneous injections of octreotide and to study the interrelationships between mean 24 h growth hormone profile, serum total and free IGF-1 levels, 24 h urinary growth hormone levels and serum IGFBP-3. Patients were assessed by 24 h GH profile off octreotide or any other GH modifying drug therapy; on subcutaneous octreotide (200-600 micrograms daily in divided doses for six weeks); and 28 days after the second of two injections of Sandostatin LAR (20 mg by intra-muscular injection) administered 28 days apart. Serum total and free IGF-1, serum IGFBP-3 and 24 h urinary GH were also measured on each occasion. Sandostatin LAR was well tolerated. None of the patients reported any adverse effect and all completed the study uneventfully. Mean GH off treatment was 10.1 +/- 3.0 micrograms/l falling equally significantly (P < 0.05) during therapy with subcutaneous octreotide to 3.0 +/- 0.7 micrograms/l and Sandostatin LAR to 2.8 +/- 0.7 micrograms/l. Fasting 0900 h GH was significantly reduced (P < 0.05) on Sandostatin LAR (3.0 +/- 0.7 micrograms/l) compared with subcutaneous octreotide (5.1 +/- 1.2 micrograms/l). Mean total IGF-1 off treatment was 658.6 +/- 56.1 micrograms/l and was reduced to a comparable extent with subcutaneous octreotide and Sandostatin LAR (466.0 +/- 59.7 and 448.6 +/- 59.5 micrograms/l respectively; both P < 0.05). Free IGF-1 off treatment was 3.1 +/- 0.6 micrograms/l and was reduced equally by subcutaneous octreotide and Sandostatin LAR (1.2 +/- 0.2 and 1.2 +/- 0.2 micrograms/l; both P < 0.05). IGFBP-3 was reduced to a greater extent during Sandostatin LAR than during subcutaneous octreotide (4518.2 +/- 247.3 vs 5132.8 +/- 280.7 micrograms/l; P < 0.05). Twenty-four hour urinary GH excretion was reduced to a comparable extent with both therapies. Highly significant positive correlations were found between mean 24 h GH levels and free IGF-1 (r = 0.66, P < 0.0001) and 24 h urinary GH excretion (r = 0.94, P < 0.0001). The relationships between mean 24 h GH levels and total IGF-1 and IGFBP-3 although significant showed less powerful correlations. These results suggest that Sandostatin LAR is well tolerated and as effective as subcutaneous octreotide. In addition, urinary growth hormone and serum free IGF-1 may prove valuable for outpatient follow-up of acromegalic patients, as both correlate well with mean 24 h serum growth hormone levels.

Energy and water metabolism, body composition, and hormonal changes induced by 42 days of enforced inactivity and simulated weightlessness.

Inactivity causes profound deleterious changes. We investigated in eight healthy men the impact of a 42-day head-down bed rest (HDBR) on energy and water metabolism and their interrelationships with body composition (BC) and catabolic and anabolic hormones. Total energy expenditure (TEE), total body water, water turnover, and metabolic water formation were assessed by the doubly labeled water method 15 days before and for the last 15 days of HDBR. Resting energy expenditure was determined by indirect calorimetry, and BC was determined by dual energy x-ray absorptiometry. Urinary excretion of cortisol, GH, normetanephrine, metanephrine, urea, and creatinine were measured daily. HDBR resulted in significant reductions in body weight (2%), total body water (5%), metabolic water (17%), and lean body mass (LBM; 4%), but fat mass and water turnover did not change. Segmental BC showed a decreased LBM in legs and trunk, whereas fat mass increased, no significant changes were noted in the arms. The hydration of LBM was unchanged. TEE and energy intake decreased significantly (20% and 13%), whereas resting energy expenditure was maintained. Expenditure for physical activity dropped by 39%. Subjects were in energy balance during HDBR, whereas it was negative during the control period (-1.5 MJ/day). There were decreases in urinary normetanephrine (23%) and metanephrine (23%), but urinary cortisol (28%; weeks 2 and 3), GH (75%; weeks 2-4), and urea (15%; weeks 3 and 4) increased. It was concluded that during prolonged HDBR no relevant modifications in water metabolism were triggered. BC changes occurred in the nonexercised body segments, and the reduction in TEE was due to inactivity, not to LBM loss. Moreover, body weight alone does not accurately reflect the subject's energy state, and energy balance alone could not explain the body weight loss, which involves a transient metabolic stress.

Is growth hormone hypersecretion in diabetic adolescen_t girls also a daytime problem?

Glycaemic control often deteriorates during puberty in girls with insulin dependent diabetes mellitus (IDDM). This may be due in part to the normal psychosocial changes associated with adolescence. Puberty is, however, also characterized by rapid somatic development, orchestrated by hormonal changes. Some of these hormones play a major role in glucose homeostasis. We have examined the insulin-GH-IGF-I axis in 11 adolescent girls with poorly controlled insulin dependent diabetes and compared the data with those of 10 non-diabetic girls matched for age, pubertal stage and body mass index (BMI). Serum profiles of glucose, insulin, GH and IGF binding protein 1 (IGFBP1) were analysed in addition to IGF-I in serum and nocturnal urinary excretion of GH. Serum glucose, insulin and IGFBP1 were measured every hour for 24 h, whereas GH in serum was measured every 30 minutes during the same period. Nocturnal urinary GH was analysed as a mean of three consecutive nights. The insulin profiles of the IDDM patients were flat with low post-prandial peaks, corresponding to only one-third of the peaks of the non-diabetic girls. The integrated insulin levels, both during 24-h sampling and during daytime, were significantly lower in the diabetic group. There were no differences during night-time. The diabetic patients had elevated mean baseline levels of serum GH (IDDM 2.8 +/- 0.5 mU/l, controls 0.7 +/- 0.2; P < 0.001), a higher 24-h mean serum GH level (9.8 +/- 1.7 mU/l vs. 4.4 +/- 0.7; P < 0.001), significantly more peaks and a urinary GH excretion twice as high as in the non-diabetic group. An interesting observation was the finding of marked differences in daytime GH concentrations between the groups, both regarding overall integrated levels (GH AUC 103 +/- 15.8 and 35.9 +/- 7.1 mU/l x 12 h, respectively; P < 0.005) as well as baseline levels (3.8 +/- 0.6 mU/l vs. 0.7 +/- 0.2; P < 0.001). In contrast, during night-time only the mean basal levels of GH differed. The level of IGF-I was reduced in the diabetic group compared with the healthy controls (IDDM 233 +/- 19 micrograms/l vs. controls 327 +/- 21; P < 0.005). In addition, the IDDM patients had significantly increased concentrations of IGFBP 1, but kept a normal diurnal rhythm with a pronounced night peak. Hypoinsulinaemia in adolescent IDDM patients, particularly in the portal hepatic circulation, results in decreased IGF-I and increased IGFBP 1 production in the liver. High levels of IGFBP 1 may, in turn, reduce the bioactivity of IGF-I even further. Low levels of IGF-I will lead to increased GH secretion. Earlier studies on the relationship between GH and diabetic control have focused on elevated GH levels during the night. In this study we have observed markedly elevated levels of GH also during daytime in adolescent IDDM patients. This indicates increased insulin resistance and insulin demand also during the day in diabetic subjects. The increased insulin resistance may result in hyperglycaemia leading to additional insulin resistance. A vicious circle may thus be induced, accelerating metabolic impairment in poorly controlled adolescent IDDM girls.

Growth hormone-binding protein levels over one year in healthy prepubertal children: intraindividual variation and correlation with height velocity.

The role of GH-binding protein (GHBP) in growth regulation is still under debate. We investigated 29 prepubertal healthy children (13 girls/16 boys; mean age 9.3 y to study intraindividual variation in serum GHBP and to explore whether any such variation was related to changes in IGF-I, IGF-binding protein-3 (IGFBP-3) or urinary excretion of GH. The relationship between changes in GHBP concentrations, short-term height velocity, and changes in body composition was also studied. Blood samples were taken every month for 1 y, for measurements of GHBP, IGF-I, and IGFBP-3. The mean coefficient of variation in monthly GHBP concentrations in individual children was 18% (range, 6.7-33.0%). The values for each child were normalized by expressing the concentration as a ratio to the mean GHBP concentration. GHBP values were highest in January and lowest in August (22% difference). Maximal monthly changes in GHBP correlated with simultaneous changes in weight (rs = 0.38, p < 0.05) and IGF-I (rs = 0.38, p < 0.05). The mean GHBP concentration during the year correlated with height velocity (rs = 0.37, p < 0.05) and the mean serum concentration of IGF-I (rs = 0.42, p < 0.05) and IGFBP-3 (rs = 0.60, p < 0.001). We conclude that there is a significant monthly variation in GHBP concentrations in healthy prepubertal boys and girls, which is correlated to changes in weight and IGF-I. The mean GHBP concentration during the year is correlated with the mean serum concentrations of IGF-I, IGFBP-3, and with height velocity. Thus, the variation in GHBP concentrations appears to mirror GH sensitivity, because no parallel changes in urinary GH excretion were observed.

Overnight Urinary Growth Hormone in Normally Growing Prepubertal Children: Effect of Urine Volume

Growth hormone excretion can easily be measured in the urine using ultrasensitive methods. The large day-to-day variation has, however, restricted its diagnostic usefulness. The present study aimed to evaluate the individual variation of GH in the urine (uGH) during normal prepubertal growth. Eighty-four prepubertal normally growing children were followed monthly for 13 months. During this period, 3,207 overnight urine samples were collected. The urine collection time was unrelated to the uGH concentration (p > 0.05), while there was a significant negative correlation between the uGH concentration and urine volume (the Spearman correlation coefficient of –0.33, p < 0.0001), while the calculated excretion of GH in the urine showed a positive correlation with the urine volume (r = 0.35; p < 0.0001). A reference chart, based on SD scores, was developed in order to avoid this volume dependency and to optimally normalize the skewed distribution of the uGH concentrations. The use of this model reduced the individual day-to-day variation of uGH from a coefficient of variation of 43 to 21%. Differences in mean cross-sectional urinary GH concentration was found between different months exceeding the expected methodological variation. This variation showed no seasonal pattern. Only 0.2% of triplicate values (three consecutive overnight uGH values) were all below –2 SD scores and 0.1% were above +2 SD scores. The mean uGH SD score for the boys was 0.01 (SD = 0.98), which was similar to that for the girls (–0.04; SD = 1.06). We found that uGH excretion can be estimated in a more robust way, using a SD score based reference chart that handles both the positive correlation between urinary GH and urine volume and the skewed distribution of urinary GH. This model reduced the day-to-day variability of uGH by half. Overestimation of GH in large urine volumes may be due to increased gradient between GH in urine and serum following increased urine volumes.

A nitrogen-free hypocaloric diet and recombinant human growth hormone stimulate postoperative protein synthesis: Fasted and fed leucine kinetics in the surgical patient

Twelve otherwise healthy patients undergoing elective surgery for resection of rectosigmoid adenocarcinoma were randomly allocated to two groups: one group receiving intravenous dextrose 5% 600 to 800 kcal · d −1 (DX, n = 6) and the other group receiving the same amount of dextrose intravenously plus recombinant human growth hormone (DX + rGH, n = 6). Supplementation with rGH strated on the day of surgery and continued for 5 days after surgery. Protein kinetics were studied in the diet. This regimen was started 3 days before surgery and continued for 5 days after surgery. Protein kinetics were studied over a period of 8 hours in all patients. Following an overnight fast, a primed constant infusion of l-[1- 13C]leucine was maintained for 4 hours (fasted state) and continued for a further 4 hours (fed state) during which 5% beet dextrose (low 13C content) with or without rGH was administered. The isotope studies were performed on the day before surgery and 6 days after surgery. Other measurements included urinary nitrogen excretion, gaseous exchange, and plasma concentrations of insulin, GH, and insulin-like growth factor-I (IGF-I). Addition of rGH to the dextrose diet had a significant positive effect on protein synthesis ( P = .02). Surgery was responsible for a significant increase in postoperative whole-body protein breakdown and synthesis and leucine oxidation ( P < .01), although lesser changes were observed in the DX group. An interaction between rGH and surgery was associated with a significant increase in protein synthesis ( P = .009), but not with changes in either protein breakdown or leucine oxidation. Carbohydrate provision in the form of beet dextrose during the fed state of the isotopic study did not attenuate the significant decrease in protein synthesis ( P = 0.0) or breakdown ( P = .003) either before or after surgery, probably reflecting the absence of nitrogen in the diet. No significant interaction was found between rGH and feeding. These results of leucine kinetics indicate that addition of rGH to a low-dextrose intake in the absence of dietary nitrogen can actually promote protein synthesis. The low levels of leucine oxidation could be explained by the fact that amino acids resulting from protein degradation were directed preferentially toward resynthesis of new proteins rather than to oxidative pathways. There was a significant increase in plasma insulin and GH in the group receiving rGH ( P < .05). The postoperative plasma concentration of IGF-I did not change in the latter group compared with the DX group, in which IGF-I concentration decreased significantly ( P < .05) as part of the response to combined surgery and dietary restriction. Although both IGF-I and insulin are independently capable of stimulating protein synthesis, elevated levels of either hormone or GH itself may primarily modulate protein synthesis, even with a low intake to carbohydrates.

Urinary growth hormone following exercise to assess growth hormone production in adults

The insulin stress test (IST) is the most commonly used test to assess the GH reserve in children and adults. It is a time-consuming, expensive and potentially dangerous test. We investigated whether measurement of urinary growth hormone excretion following exercise would prove on reliable method to diagnose adult GH deficiency. Healthy volunteers underwent a standard IST to confirm GH secretion. Using a standardized exercise protocol on a treadmill, the urinary excretion of GH was measured. Three patients confirmed as GH deficient by an IST were exercised during the same exercise protocol and their urinary excretion of GH was measured. Ten healthy volunteers and three patients with hypopituitarism were evaluated. A standard IST was performed on both healthy volunteers and patients, with measurements of plasma GH and plasma cortisol. Urinary growth hormone and urinary GH/creatinine (GH/CR) ratios were measured before and after IST. On a separate visit, healthy volunteers and patients were exercised on the treadmill with measurements of plasma GH and cortisol. Urinary GH and GH/CR ratios were measured before and after exercise. There was at least a two-fold increase in urinary GH and GH/CR ratios following exercise in all healthy adults. By contrast, patients with GH deficiency showed no rise in urinary GH or urinary GH/CR ratios following exercise. Measurements of urinary GH following exercise can distinguish between GH-deficient adults and healthy volunteers. Urinary GH excretion can be measured over a timed interval following exercise or can be expressed as the GH/CR ratio. This can be measured on a single sample following exercise and can be used to diagnose GH deficiency. The exercise test employed for this study is arduous. We are therefore performing further studies with a less strenuous exercise protocol with a view to designing a 'patient-friendly' exercise test for GH deficiency in adults.

Biochemical tests in the diagnosis of childhood growth hormone deficiency.

GH stimulation tests are widely used in the diagnosis of GH deficiency (GHD), although they are associated with a high false positive rate. We have examined, therefore, the performance of other tests of the GH axis [urinary GH excretion, serum insulin-like growth factor I(IGF-I), and IGF-binding protein-3 (IGFBP-3) levels] compared with GH stimulation tests in identifying children defined clinically as GH deficient. Group I comprised 60 children (mean age, 10.3 +/- 4.8 yr) whose diagnosis of GHD was based on a medical history indicative of pituitary dysfunction (n = 43) or on the typical phenotypic features and appropriate auxological characteristics of isolated GHD (n = 17). Group II comprised 110 short children (mean age, 9.8 +/- 4 yr) in whom GHD was not suspected, but needed exclusion. The best sensitivity for a single GH test was 85% at a peak GH cut-off level of 10 ng/mL, whereas the best specificity was 92% at 5 ng/mL. The sensitivities of IGF-I, IGFBP-3, and urinary GH, using a cut-off of -2 SD score were poor at 34%, 22%, and 25%, respectively, with specificities of 72%, 92%, and 76% respectively. Only 2 of 21 pubertal children in group I and none of the 27 subjects with radiation-induced GHD had an IGFBP-3 SD score less than -1.5. We devised a scoring system based on the positive predictive value of each test, incorporating data from the GH test and the IGF-I and IGFBP-3 levels. A specificity of 94% could be achieved with a score of 10 or more (maximum 17) (sensitivity 34%). The latter could not be improved above 81% with a score of 5 points or more (specificity, 69%). A high score was, therefore, highly indicative of GHD, but was achieved by few patients. A normal IGFBP-3 level, however, did not exclude GHD, particularly in patients with radiation-induced GHD and those in puberty. A GH test with a peak level more than 10 ng/mL was the most useful single investigation to exclude a diagnosis of GHD.

Infradian rhythms in urinary growth hormone excretion.

All studies of urinary GH excretion in normal and disordered growth have revealed marked day to day (infradian) variation. We used serial overnight urinary GH estimations as an indirect measure of endogenous GH secretion in eight normal prepubertal children (aged 3.6-7.3 yr) over 90-365 days to determine whether longer term rhythms in GH output could exist. This study constitutes a first step in examining the potential relationship between GH excretion and growth. Urinary GH was measured by immunoradiometric assay after dialysis, expressed as the total amount excreted (nanograms per night) or as the GH/creatinine ratio (nanograms per mmol), and assessed by pulse counting techniques and time-series analysis. Variability in urinary GH excretion (median coefficient of variation, 46%) was significantly greater than creatinine (median coefficient of variation, 25%; P = 0.003). Additionally, there was marked month by month variation in baseline urinary GH in all children. High frequency pulses of urinary GH were defined in all children, with periods between 3-5 days. In the two children followed for 7 months or more, time-series analysis was also undertaken on urinary GH data divided into weekly series. This revealed significant rhythms present at 2.6 and 4.1 weeks. There were, therefore, three components to urinary GH excretion: long term basal fluctuation (over months), short term pulses (over days), and intermediate rhythms (over weeks). Further work is required to establish the relationship between these patterns of GH excretion and short term growth.

Metabolic clearance of recombinant human growth hormone in health and chronic renal failure

Despite the increasing therapeutic use of recombinant human growth hormone (rhGH), its metabolic clearance has not been investigated in detail. To evaluate the kinetics of rhGH as a possible function of GH plasma concentration and glomerular filtration rate (GFR), we investigated the steady state metabolic clearance rate (MCR), disappearance half-life, and apparent volume of distribution of rhGH at low and high physiological as well as supraphysiological plasma GH levels during pharmacological suppression of endogenous GH secretion in human subjects with normal and reduced renal function. GH in plasma and urine was determined by an immunoradiometric assay, and GFR by inulin clearance. In all subjects MCR decreased and plasma half-life increased with increasing plasma GH concentrations (P < 0.001). MCR of rhGH was approximately half in patients with chronic renal failure at each GH level and plasma half-life was increased by 25-50%. Allowing for the linear dependence of MCR on GFR and assuming single-compartment distribution, the estimated renal fraction of total MCR was 25-53 and 4-15% in controls and patients, respectively. Saturation of extrarenal disposal of GH was suggested by an inverse hyperbolic relationship between extrarenal MCR and plasma GH concentrations in all subjects. Fractional GH excretion was up to 1,000-fold higher in patients than in controls. We conclude that MCR of hGH is a function of plasma GH concentrations and GFR. Extrarenal elimination is saturable in the upper physiological range of GH concentrations, whereas renal MCR is independent of plasma GH levels. The kidney handles GH like a microprotein involving glomerular filtration, tubular reabsorption, and urinary excretion.

Assessment of GH status in acromegaly using serum growth hormone, serum insulin‐like growth factor‐I and urinary growth hormone excretion

It is still not clear what is the most suitable method for monitoring progress of acromegaly. The aim of this study was to assess the relative merits of serum GH, serum IGF-I and urinary GH (uGH) excretion in the follow-up of acromegalic subjects. Thirty-six acromegalic patients each had a GH day series performed consisting of five serum GH measurements, together with an estimate of serum IGF-I and uGH. The first sample taken for serum GH was fasting (basal) whilst the third (1430h) was arbitrarily chosen as a random value. uGH was measured from two overnight collections and the mean value used for subsequent data analysis. Serum GH and IGF-I were measured by radioimmunoassay whilst uGH was estimated by an immunoradiometric assay using commercially available reagents. There is a highly significant linear correlation between serum GH and IGF-I following log transformation of these two variables (r = 0.85; P < 0.0001). Analysis of the raw data shows that the relation is in fact curvilinear rendering IGF-I less useful as a surrogate for integrated GH secretion at high levels of serum GH. There is a strong linear correlation between both a singleton basal serum GH and uGH (r = 0.78; P < 0.001) and the mean of five measurements (day series) and uGH (r = 0.81; P < 0.0001). Both uGH and IGF-I are excellent predictors of those patients with persistent elevation of serum GH, identifying 95 and 96% respectively with serum GH > 5mU/l. We have identified a number of patients, however, with persistent elevation of IGF-I in the presence of serum GH < 5mU/l and normal uGH. Until the significance of these findings with respect to long-term outcome is known, serum GH should continue to be used in the follow-up of these patients. An alternative, which reflects integrated overnight GH secretion, is uGH which is convenient and easy to collect as an outpatient and correlates strongly with serum GH. Acromegalic patients can be conveniently followed on an outpatient basis using a combination of uGH and serum IGF-I. Measurements of serum GH can be reserved for those with discrepant results.

Massive weight loss restores 24-hour growth hormone release profiles and serum insulin-like growth factor-I levels in obese subjects.

In the present study, we 1) determined whether the impaired spontaneous 24-h GH secretion as well as the blunted GH response to provocative testing in obese subjects are persistent disorders or transient defects reversed with weight loss and 2) investigated 24-h urinary GH excretion and basal levels of insulin-like growth factor-I (IGF-I), IGF-binding protein-3 (IGFBP-3), as well as insulin in obese subjects before and after a massive weight loss. We studied 18 obese subjects (age, 26 +/- 1 yr; body mass index, 40.9 +/- 1.1 kg/m2); 18 normal age-, and sex-matched control subjects; and 9 reduced weight obese subjects after a diet-induced average weight loss of 30.3 +/- 4.6 kg. Twenty-four-hour spontaneous GH secretion was estimated by obtaining 3240 integrated 20-min blood samples using a constant blood withdrawal technique and computerized algorithms. Body composition was determined using anthropometric measurements and dual energy x-ray absorptiometry scanning (DXA). In the obese subjects, 24-h spontaneous GH release profiles and the GH responses to insulin-induced hypoglycemia and L-arginine as well as basal IGF-I levels and the IGF-I/IGFBP-3 molar ratio were decreased, whereas insulin levels were elevated compared to those in normal subjects. In obese subjects, 24-h spontaneous GH secretion and serum IGF-I levels were inversely related to abdominal fat (r = -0.67; P < 0.01) and percent body fat (r = -0.69; P < 0.01), respectively. The decreased 24-h spontaneous GH release profiles, the decreased GH responses to insulin-induced hypoglycemia and L-arginine, the decreased basal IGF-I levels and IGF-I/IGFBP-3 molar ratio, as well as the elevated insulin levels were returned to normal after a massive weight loss in the obese subjects. In conclusion, the present study has shown reversible defects in 24-h spontaneous GH release profiles, basal IGF-I levels, and the IGF-I/IGFBP-3 molar ratio in obese subjects. The recovery of the 24-h GH release points to an acquired transient defect rather than a persistent preexisting disorder.

Assessment of GH status in adults with GH deficiency using serum growth hormone, serum insulin-like growth factor-I and urinary growth hormone excretion.

The benefits of treating adults with GH deficiency are now well recognized although the criteria for deciding which patients to treat are still not clear. At present the 'gold standard' is the insulin stress test (IST) which is unpleasant and potentially dangerous, particularly in patients with hypopituitarism. The aim of this study was to determine whether alternative methods of assessing GH status are reliable in predicting GH deficiency. Forty-four patients with unequivocal GH deficiency (peak IST < 2 mU/l) and 17 with partial deficiency (peak IST 2-10 mU/l) were studied. Each patient was assessed clinically with respect to the number of other pituitary axes affected and biochemically with an estimate of urinary GH excretion (uGH) and serum IGF-I. These markers were then related to GH status as defined by insulin stress testing. Insulin stress tests were performed using 0.1 units/kg i.v. and accepted with a blood glucose < 2 mmol/l. Serum GH and IGF-I were measured by radioimmunoassay whilst uGH was estimated by an immunoradiometric assay using commercially available reagents. uGH was estimated from the mean of two overnight urine collections which consisted of all urine passed from last voiding through to the first morning sample. The presence of unequivocal GH deficiency (peak IST < 2 mU/l) was predictable if 2 or more other pituitary axes were affected (90%). uGH declined significantly with the level of peak IST response (P < 0.001) and almost so with the number of other deficient hypothalamic-pituitary axes affected (P = 0.057). Thus, uGH accurately reflected GH status and showed good separation from normal controls in patients less than 40 years (specificity 79%) and between 40 and 60 years (specificity 67%). Above this age the method is less specific (36%). Patients excreted significantly less GH than controls in all three age groups (P < 0.01). Subnormal levels of IGF-I were strongly predictive of unequivocal GH deficiency (91% with subnormal IGF-I have a peak IST GH < 2 mU/l) although a normal value does not reliably exclude the diagnosis. A diagnosis of adult GH deficiency can be reliably made without the need for an insulin stress test by using a combination of low urinary GH excretion, subnormal IGF-I levels and clinical assessment with regard to the number of other pituitary axes affected.