Basal Plasma Growth Hormone Concentrations Research Articles

Use of basal and TRH-stimulated plasma growth hormone concentrations to differentiate between primary hypothyroidism and nonthyroidal illness in dogs.

BackgroundA low plasma total thyroxine (TT4) concentration in combination with a plasma TSH concentration within reference range does not distinguish between hypothyroidism and nonthyroidal illness (NTI) in dogs. Hypothyroidism is associated with TSH‐releasing hormone (TRH)‐induced increased release of growth hormone (GH).HypothesisBasal and TRH‐induced plasma GH concentrations can be used to distinguish hypothyroid dogs from NTI dogs.AnimalsTwenty‐one dogs with signs consistent with hypothyroidism, a low plasma TT4 concentration, and a plasma TSH concentration within reference interval.MethodsCase control study. Thyroid scintigraphy was performed to classify dogs as having hypothyroidism or NTI. All dogs underwent a TRH stimulation test with measurement of plasma concentrations of GH and TSH before and 30 and 45 minutes after IV administration of TRH.ResultsEleven of the dogs were classified as hypothyroid and 10 as having NTI. Basal plasma GH concentration in the hypothyroid dogs (3.2 μg/l; range, 2.0 to 12.5 μg/l) was significantly higher (p<0.001) than that in the NTI dogs (.73 μg/l; range, .45 to 2.3 μg/l), with minimal overlap, and increased (p=.009) after TRH administration in hypothyroid dogs, whereas it did not change in NTI dogs. At T=45, plasma GH concentrations in hypothyroid dogs and NTI dogs did not overlap. The plasma TSH concentration did not change significantly after TRH administration in hypothyroid dogs, whereas it increased (p<.001) in NTI dogs. At T=45, there was no overlap in percentage TSH increase from baseline between hypothyroid dogs.Conclusions and Clinical ImportanceMeasurement of basal plasma GH concentration and concentrations of GH and TSH after TRH stimulation can distinguish between hypothyroidism and NTI in dogs.

Evaluation of growth hormone response to insulin-induced hypoglycaemia in dairy cattle during a 670-day lactation

Plasma growth hormone secretion in response to insulin-induced hypoglycaemia was evaluated in cows undergoing an extended lactation. Twelve multiparous Holstein-Friesian cows that calved in late winter and were managed for a 670-day lactation by delaying mating. Four experimental periods of 40 days commenced at ~73, 217, 422 and 520 (±9.1; mean ± s.d.) days in milk (DIM) during which cows were individually offered a diet of perennial ryegrass (73 and 422 DIM) or pasture hay and pasture silage (217 and 520 DIM) supplemented with either 1 kg DM grain (CONT) or 6 kg DM grain (GRAIN). Cows were fitted with jugular catheters during the final week of each experimental period. Seven blood samples over a 24-h period were collected and an insulin tolerance test was performed on each cow using a dose of 0.12 µU insulin/kg liveweight at ~100, 250, 460 and 560 DIM. This resulted in an increase in plasma growth hormone concentration occurring at 100 DIM, an intermediate and delayed response at 250 DIM, and no response at both 460 and 560 DIM. Cows in the CONT treatment had higher basal plasma growth hormone concentrations and tended to have a greater peak growth hormone response than GRAIN cows. The growth hormone response at 100 and 250 DIM is likely a homeorhetic mechanism to support milk yield during early-mid lactation. These observations are consistent with the known actions of growth hormone to promote lipid mobilisation, hepatic glucose production and an overall state of catabolism. With further research, the insulin tolerance test may be a useful tool to identify cows with greater growth hormone secretory response and increased milk production or persistency.

Evaluation of pulsatile plasma concentrations of growth hormone in healthy dogs and dogs with dilated cardiomyopathy

To evaluate plasma concentrations of growth hormone (GH) and insulin-like growth factor I (IGF-I) in healthy dogs and large-breed dogs with dilated cardiomyopathy (DCM). 8 dogs with DCM and 8 healthy control dogs of comparable age and body weight. Blood samples for determination of the pulsatile plasma GH profile were collected from all dogs at 10-minute intervals between 8:00 am and 8:00 pm. Plasma IGF-I concentration was determined in the blood sample collected at 8:00 am. No significant differences in plasma IGF-I concentrations, basal plasma GH concentration, GH pulse frequency, area under the curve above the zero line and above the baseline for GH, and GH pulse amplitude were found between dogs with DCM and control dogs. Results did not provide evidence for an association between DCM in dogs and a reduction in plasma concentrations of GH or IGF-I. Therefore, reported positive effects of GH administration are most likely attributable to local effects in the heart.

Thyrotropin-releasing hormone-induced growth hormone secretion in dogs with primary hypothyroidism

Primary hypothyroidism in dogs is associated with increased release of growth hormone (GH). In search for an explanation we investigated the effect of intravenous administration of thyrotropin-releasing hormone (TRH, 10 μg/kg body weight) on GH release in 10 dogs with primary hypothyroidism and 6 healthy control dogs. The hypothyroid dogs had a medical history and physical changes compatible with hypothyroidism and were included in the study on the basis of the following criteria: plasma thyroxine concentration <2 nmol/l and plasma thyrotropin (TSH) concentration >1 μg/l. In addition, 99mTcO 4 − uptake during thyroid scintigraphy was low or absent. TRH administration caused plasma TSH concentrations to rise significantly in the control dogs, but not in the hypothyroid dogs. In the dogs with primary hypothyroidism, the mean basal plasma GH concentration was relatively high (2.3 ± 0.5 μg/l) and increased significantly ( P = 0.001) 10 and 20 min after injection of TRH (to 11.9 ± 3.5 and 9.8 ± 2.7 μg/l, respectively). In the control dogs, the mean basal plasma GH concentration was 1.3 ± 0.1 μg/l and did not increase significantly after TRH administration. We conclude that, in contrast to healthy control dogs, primary hypothyroid dogs respond to TRH administration with a significant increase in the plasma GH concentration, possibly as a result of transdifferentiation of somatotropic pituitary cells to thyrosomatotropes.

Ovariectomy during the luteal phase influences secretion of prolactin, growth hormone, and insulin-like growth factor-I in the bitch

A decline in circulating progesterone concentration plays an important role in the ethiopathogenesis of pseudopregnancy in the bitch. Because growth hormone (GH) and prolactin (PRL) are essential for normal mammogenesis and the secretion of these hormones is influenced by changes in the circulating progesterone concentration, the purpose of this study was to investigate the effects of mid-luteal phase ovariectomy on the 6-h pulsatile plasma profiles of GH and PRL and the basal plasma concentrations of GH, PRL, and insulin-like growth factor-I (IGF-I) in six beagle bitches. Ovariectomy was followed by only mild or covert signs of pseudopregnancy. The sharp decrease of the plasma progesterone concentration was accompanied by decreased basal plasma concentrations of GH and IGF-I and a rise in basal plasma PRL concentration. GH and PRL were secreted in a pulsatile fashion both prior to and after ovariectomy. The mean basal plasma GH concentration was significantly higher before ovariectomy than on days 1 and 7 after ovariectomy. The mean area under the curve above the zero level (AUC 0) for GH was significantly higher before than at 7 days after ovariectomy. The mean area under the curve above basal level (AUC b) and the frequency of GH pulses at 7 days after ovariectomy were significantly higher than before and 1 day after ovariectomy. Both the mean basal plasma PRL concentration and the mean AUC 0 for PRL increased after ovariectomy. In conclusion, ovariectomy of bitches in the mid-luteal phase stops progesterone-induced GH release from the mammary gland, as evidenced by the lowering of basal plasma GH levels, the recurrence of GH pulsatility, and the lowering of circulating IGF-I levels. The sudden lowering of plasma progesterone concentration is probably a primary cause of a prolonged increase in PRL secretion. These observations underscore the importance of similar, albeit less abrupt, hormonal changes in the cyclical physiological alterations in the mammary gland and in the development of pseudopregnancy.

Somatostatin treatment affects testicular function in stallions

This study investigated the regulation of growth hormone (GH) release in stallions and tested the hypothesis that the somatotrophic axis influences testicular function. Basal plasma GH concentrations, effects of an experimental decrease of GH release on testicular function and an opioidergic regulation of GH release were investigated in Shetland stallions ( n=6). No seasonal variations in plasma GH concentrations were found over a 12-month period. Treatment with the somatostatin analogue octreotid (100 mg twice daily over 10 days) caused a decrease in semen motility from 38.7±8.4% progressively motile spermatozoa before treatment to 18.3±5.4% on day 3 after end of treatment ( P<0.05). Values returned to 35.0±8.5% on day 5 after treatment. On the last day of octreotid treatment, a hCG stimulation test was performed (3000 IU hCG i.v.). The hCG-induced testosterone release was significantly higher in saline treated than in octreotid pretreated animals ( P<0.05). Neither plasma GH concentrations nor volume and density of ejaculates, total sperm count, or semen morphology were different between saline and octreotid treatments. Injection of the opioid antagonist naloxone (0.5 mg/kg) significantly increased GH release in June (from 1.1±0.3 ng/ml before to 3.7±2.2), while a minor and not significant increase occurred in January. In conclusion, our results indicate a non-seasonal basal GH release with a fine-modulation by season-dependent opioidergic mechanisms in the male horse. A transient decrease in semen motility and hCG-induced testosterone release following ocreotid treatment indicate a role of GH in the regulation of testicular function in stallions.

Pulsatile secretion pattern of growth hormone in dogs with pituitary-dependent hyperadrenocorticism

The amplitude and frequency of growth hormone (GH) secretory pulses are influenced by a variety of hormonal signals, among which glucocorticoids play an important role. The aim of this study was to investigate the pulsatile secretion pattern of GH in dogs in which the endogenous secretion of glucocorticoids is persistently elevated, i.e. in dogs with pituitary-dependent hyperadrenocorticism (PDH). Blood samples for the determination of the pulsatile secretion pattern of GH were collected at 10-min interval between 08:00 and 14:00 h in 16 dogs with PDH and in 6 healthy control dogs of comparable age. The pulsatile secretion patterns of GH were analyzed using the Pulsar program. GH was secreted in a pulsatile fashion in both dogs with PDH and control dogs. There was no statistical difference between the mean (±S.E.M.) basal GH level in dogs with PDH (0.7±0.1 μg/l) and the control dogs (0.6±0.1 μg/l). The mean area under the curve (AUC) for GH above the zero-level in dogs with PDH (4.6±0.6 μg/l per 6 h) was significantly lower than that in the control dogs (7.3±1.0 μg/l per 6 h). Likewise, the mean AUC for GH above the base-level in dogs with PDH (0.6±0.1 μg/l per 6 h) was significantly lower than that in the control dogs (3.7±1.0 μg/l per 6 h). The median GH pulse frequency in the dogs with PDH (2 pulses/6 h, range 0–7 pulses/6 h) was significantly lower ( P=0.04) than that (5 pulses/6 h, range 3–9 pulses/6 h) in the control group. The results of this study demonstrate that PDH in dogs is associated with less GH secreted in pulses than in control dogs, whereas the basal plasma GH concentrations were similarly low in both groups. It is discussed that the impaired pulsatile GH secretion in dogs with PDH is the result of alterations in function of pituitary somatotrophs and changes in supra-pituitary regulation.

Pulsatile secretion pattern of growth hormone during the luteal phase and mid-anoestrus in beagle bitches

The pulsatile secretion pattern of growth hormone was investigated during four stages of the luteal phase and during mid-anoestrus in six cyclic beagle bitches. Plasma samples were obtained via jugular venepuncture at 10 min intervals for 12 h at 19 +/- 2 (mean +/- SEM; luteal phase 1), 38 +/- 2 (luteal phase 2), 57 +/- 2 (luteal phase 3), 78 +/- 2 (luteal phase 4) and 142 +/- 4 days (mid-anoestrus) after ovulation. During all stages, growth hormone was secreted in a pulsatile fashion. The mean basal plasma growth hormone concentration during luteal phase 1 (2.2 +/- 0.3 microgram l(-1)) was significantly higher than that during luteal phase 4 (1.5 +/- 0.1 microgram l(-1)) and mid-anoestrus (1.4 +/- 0.2 microgram l(-1)). The mean area under the curve (AUC) above zero during luteal phase 1 (27.3 +/- 2.7 microgram l(-1) in 12 h) tended to be higher than that during luteal phase 4 (20.8 +/- 1.8 microgram l(-1) in 12 h) and mid-anoestrus (19.2 +/- 2.5 microgram l(-1) in 12 h). In contrast, the mean AUCs above the baseline during luteal phase 1 (1.1 +/- 0.5 microgram l(-1) in 12 h) and luteal phase 2 (1.2 +/- 0.5 microgram l(-1) in 12 h) were significantly lower than that during luteal phase 4 (2.8 +/- 0.5 microgram l(-1) in 12 h). In conclusion, the pulsatile secretion pattern of growth hormone changes during the luteal phase in healthy cyclic bitches: basal growth hormone secretion is higher and less growth hormone is secreted in pulses during stages in which the plasma progesterone concentration is high. It is hypothesized that this change is caused by a partial suppression of pituitary growth hormone release by progesterone-induced growth hormone production in the mammary gland. The progesterone-induced production of growth hormone in the mammary gland may promote the physiological proliferation and differentiation of mammary gland tissue during the luteal phase of the bitch by local autocrine-paracrine effects. In addition, progesterone-induced mammary growth hormone production may exert endocrine effects, such as hyperplastic changes in the uterine epithelium and insulin resistance.

Growth hormone secretion and pituitary gland weight in suckling lambs from genetically lean and fat sheep

Previous studies have found that weaned lambs from Coopworth sheep selected for low (lean) backfat depth have higher mean plasma growth hormone (GH) levels and heavier pituitary glands than those selected for high (fat) backfat depth. This study examined whether these differences between genotypes occurred in young suckling lambs. Six ewes from each genotype which were suckling a male/female set of twins were kept indoors. Four weeks after birth, ewes and lambs were blood‐sampled for 6 hours at 10 minute intervals and plasma GH levels measured. Lambs were then slaughtered and carcass composition determined. Subcutaneous fat depth was lower in lean than fat lambs at four of the five different sites measured (P < 0.05). Lean lambs and ewes had greater mean and basal plasma GH concentrations and a greater amplitude of GH pulses than fat sheep (P < 0.05). Plasma IGF‐I levels did not differ (P < 0.05) between genotype for either ewes or lambs. Pituitary glands were heavier (P< 0.001) in lean than fat genotype lambs (0.29 versus 0.19, SED = 0.017 g). It is concluded that differences between genotypes in body composition, plasma GH, and pituitary gland weight occur at an early age. An investigation of foetal development patterns may be required to elucidate the relationship between these parameters.

Dopamine function in obsessive—compulsive disorder: Growth hormone response to apomorphine stimulation

Indirect observations suggest that the dopaminergic system may be involved in the pathophysiology of obsessive-compulsive disorder (OCD). The dopaminergic function of 15 patients with OCD and 15 age/sex-matched controls was evaluated by measuring the growth hormone (GH) responses to stimulation with the dopaminergic agonist apomorphine (APO), which increases growth hormone-releasing hormone (GHRH), GH, and somatomedine C (SMD-C) secretions. Therefore, we measured basal plasma GH and SMD-C concentrations and GH responses to GHRH stimulation to exclude that a downstream pathology of the somatotropic axis could obscure the significance of the results of the APO test. The response of prolactin (PRL) to APO inhibition were also measured. Basal plasma levels of GH, SMD-C, and PRL, GH responses to GHRH stimulation, and PRL responses to APO inhibition did not differ in the two groups of subjects. GH responses to APO stimulation were blunted in obsessive-compulsive (OC) patients. The emetic response to the same stimulation was stronger in patients than in controls. These responses suggest that in our OC patients there is a dysregulation of the dopaminergic system, which is possibly expressed in different ways in the various areas of the central nervous system.

Plasma insulin-like growth factor-I response to cold exposure in barrows.

Information about the plasma IGF-I concentrations in domestic animals in a cold environment is still limited. And mechanisms to change plasma IGF-I concentrations in cold environments are not fully elucidated. In this study, plasma insulin-like growth factor-I (IGF-I) in relation to plasma growth hormone (GH) and metabolite concentrations was investigated in pigs living at 20 degrees C and at 4 degrees C. Six pigs (Landrase breed; barrows, 118 days old, 51.0 +/- 3.5 kg body weight) were maintained for 2 weeks at 20 degrees C in a climatic room. Then a placebo or recombinant bovine GH (100 micrograms/kg body weight) was injected subcutaneously. Blood samples were taken through a catheter at -2, 0, 1, 2, 3, 4, 5, 6, 9, 12, 22, and 24 h after the injections. The same experiments were conducted on days 5 and 6 after the room temperature was changed to 4 degrees C. Mean (+/- SD) basal plasma GH concentrations in pigs without bovine GH administration living at 20 degrees C and at 4 degrees C were 4.8 +/- 1.7 ng/ml and 4.6 +/- 2.8 ng/ml, respectively. There were no significant differences between GH concentrations. On the other hand, the mean plasma IGF-I concentrations were 80.8 +/- 25.1 ng/ml and 57.3 +/- 14.3 ng/ml respectively. Plasma IGF-I concentrations in pigs living at 4 degrees C were significantly lower than in pigs living at 20 degrees C (P < 0.05). Plasma glucose and non-esterified fatty acid (NEFA) concentrations in pigs at 4 degrees C were significantly higher than in pigs at 20 degrees C (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Growth and growth hormone kinetics in Holstein steer calves

Average daily gain (ADG), basal plasma growth hormone (GH) concentration, and plasma GH kinetics following a bolus injection of GH were determined at birth and at 75, 150, 250, 350 and 450 kg body weight in 19 Holstein steer calves. From 100 kg body weight, calves were fed one of three diets: 85% grass hay and 15% concentrate; 85% grass hay and 15% concentrate with rumen undegradable protein (formaldehyde-treated canola meal); and, 85% concentrate and 15% grass hay. Addition of rumen undegradable protein to the hay-based diet did not (P &gt; 0.05) increase ADG. However, ADG were higher (P &lt; 0.001) for calves on the 85% concentrate diet. Calf basal plasma GH concentrations, plasma GH clearance rates, and GH secretion rates were not affected by either diet or ADG adjusted for the effect of diet. In contrast, body weight had a large effect on basal plasma GH concentration and plasma GH kinetics. As body weight increased, basal plasma GH concentration and GH half-life decreased. Growth hormone steady state volume of distribution, metabolic clearance rate and secretion rate per kg of body weight all decreased as calves became heavier. Key words: Steer growth, growth hormone, GH, basal GH, clearance, secretion

Plasma growth hormone and prolactin responses to graded levels of acute exercise and to a lactate infusion.

The effect of acute exercise at three graded intensities on plasma growth hormone (GH) and prolactin (PRL) concentrations was examined in three groups of healthy male volunteers. According to their training status these subjects were divided into untrained, moderately trained and highly trained. A clear response of GH to exercise was registered already at an intensity of 50% of maximal oxygen uptake (VO2max) with a maximal response at 70% VO2max and no further effect at 90% VO2max. In contrast, no PRL response was observed at 50% VO2max, a small PRL rise was seen at 70% VO2max and the highest response occurred at 90% VO2max. Basal and exercise-stimulated plasma GH and PRL concentrations were similar in the three groups tested at similar relative workloads, suggesting that physical training induces adaptive changes whereby higher absolute workloads induce similar hormonal and metabolic changes. To examine a potential causative role of lactate in inducing the GH and PRL responses, sodium L-lactate was infused intravenously to normal sedentary volunteers at doses producing plasma lactate concentrations within the range of those seen between 70 and 90% VO2max. This resulted in a significant elevation of plasma GH and PRL concentrations, which, however, were smaller than those obtained at an exercise-induced matched plasma lactate concentration. We conclude that physical training causes adaptive changes in highly trained runners so that identical GH and PRL responses to exercise are recorded at higher absolute workloads. Lactate may be involved in the exercise-induced GH and PRL response; however, it does not appear to play an exclusive role.

Central somatostatinergic regulation of growth hormone secretion in dwarf chickens

1. 1. Basal circulating growth hormone (GH) concentrations in sex-linked-dwarf (SLD) chickens were unaffected by the intracerebroventricular (icv) injection of 10, 50 or 100 μg somatostatin (SRIF). 2. 2. The GH response to systemic thyrotropin-releasing hormone (TRH; 10μg/kg, iv) was, however, ‘paradoxically’ enhanced 20 min after icv SRIF administration. 3. 3. A lower dose (1.0μg) of SRIF had no effect on basal or TRH-induced GH release. 4. 4. High-litre SRIF antisera (4μl) also had no acute effect on basal plasma GH concentrations, but augmented the GH response to TRH challenge. 5. 5. SRIF would appear to act at central sites to modulate stimulated GH secretion in SLD chickens.

Follow-up study of the heart in acromegaly: Pre- and post-operative evaluation.

Pre-operative and post-operative echocardiographic data were analyzed from 8 patients with acromegaly. Pre-operatively, end-diastolic diameter was greater than 55 mm in 5 patients (63%) and concentric left ventricular hypertrophy was observed in 3 patients (38%). However, left ventricular function was normal (fractional shortening of the left ventricle greater than 28%) in all patients except 1. All patients had increased left ventricular mass. There was no significant correlation between left ventricular mass and basal plasma growth hormone concentration. An average of 23.9 months after hypophysectomy, growth hormone concentration was significantly decreased. However, the abnormal echocardiographic findings remained. In conclusion, echocardiographic abnormalities (left ventricular dilatation and hypertrophy) are common in patients with acromegaly, but systolic function is, in general, maintained. These cardiac abnormalities persist after reduction of plasma growth hormone concentration.

Secretory patterns and metabolic clearance rate of porcine growth hormone in swine selected for growth.

Eleven Landrace pigs (six boars and five gilts, 50 kg) representing lines selected for three generations for maximum weight at 200 d of age were compared to eight pigs (four boars and four gilts, 50 kg) representing contemporary randomly selected Landrace controls to determine the effect of selection for growth on the metabolic clearance rate (MCR) and plasma concentrations of porcine growth hormone (GH). To estimate MCR of GH, the disappearance of a bolus of porcine GH was monitored over 120 min following its i.v. injection. Blood samples also were collected every 15 min over a 6-h period before injecting GH to determine baseline and overall mean GH concentrations, mean peak amplitude and number of GH secretory episodes. Boars exhibited greater overall mean GH concentrations (4.80 vs 3.11 ng/ml; P less than .05) and had greater maximum GH concentrations associated with secretory episodes (16.11 vs 10.80 ng/ml; P less than .05) than did gilts. There were no differences between boars and pigs exhibited greater baseline GH concentrations (2.04 vs 1.25 ng/ml; P less than .01) than did those from the unselected Landrace line. Selected and control pigs exhibited similar (P greater than .15) overall mean concentrations of GH, frequency of secretory episodes, amplitude of GH peaks and MCR. These data demonstrate that pigs selected for heavier weight at 200 d of age had greater basal plasma GH concentrations than did unselected control pigs.

Investigation of the criteria for assessing the outcome of treatment in acromegaly.

The outcome of treatment in acromegaly is usually assessed by measuring plasma concentrations of growth hormone (GH)--either basal spontaneous levels or during hyperglycaemia. There is no consensus on how cure should be defined. Many studies have considered basal plasma growth hormone concentrations below 20 mU/l (10 ng/ml) as proof of cure, although some recent studies have applied lower values. At present a limit of 10 mU/l (5 ng/ml) seems to be accepted as evidence of cure. We have studied 28 acromegalic patients after transsphenoidal adenomectomy. Plasma GH concentrations (basal and during hyperglycaemia) as well as plasma somatomedin C (SMC) concentrations were measured and compared to the clinical symptoms. There was a close correlation between plasma GH and SMC concentrations (except when plasma GH levels were low) and between the clinical assessment and SMC concentrations. Very low plasma GH levels (less than 1 mU/l or 0.5 ng/ml) were associated with normal SMC values and clinical cure, high GH levels (greater than 10 mU/l or 5 ng/ml) with elevated SMC levels and persisting acromegaly. Moderately elevated plasma GH concentrations (1.9-9.6 mU/l) did not allow any conclusions on the outcome of treatment as assessed from SMC determinations and clinical evaluation. It is concluded that the usual criteria for cure in acromegaly may not be sufficiently strict.

The effect of glucose on growth hormone (GH)-releasing hormone-mediated GH secretion in man.

The effect of glucose on GH-releasing hormone (GHRH)-mediated GH secretion was examined in six normal young men. In two paired experiments, the six men drank a 75-g glucose solution or an equal volume of water 30 min before receiving, iv, 100 micrograms of the 44-amino acid form of human pancreatic GHRH (hGHRH-44). One week later, the same men underwent an identical experimental protocol in a cross-over trial. Basal plasma GH concentrations before hGHRH-44 administration were not statistically different in the two experiments [glucose experiment, 2.1 +/- 0.1 (+/- SE) ng/ml; water experiment, 2.6 +/- 0.6 ng/ml]. The mean peak plasma GH level occurred 30 min after hGHRH-44 administration in both experiments. However, the mean GH response was significantly diminished when the men received glucose (8.12 +/- 1.12 ng/ml) compared to that when they received only water (23.70 +/- 8.46 ng/ml; P less than 0.01). Thus, hyperglycemia may exert an inhibitory effect on the plasma GH response to hGHRH-44.

Measurement of the 24 hour integrated plasma concentration of growth hormone, in assessing the response of acromegalic patients to treatment.

The integrated concentration of growth hormone (ICGH) has been measured in fourteen acromegalic patients, and compared with the basal plasma growth hormone concentration (BGH). Seven patients were treated by trans-sphenoidal pituitary surgery, and in these, similar percentage reductions of BGH and ICGH occurred after treatment. The other seven patients were treated with bromocriptine alone, and in these the percentage reduction of ICGH was significantly less than that of BGH. Measurements of basal plasma growth hormone concentration may be unreliable in assessing the response of acromegalic patients to treatment with bromocriptine. The ICGH can be measured easily on a single blood specimen obtained by continuous sampling over 24 h, and may be more reliable for this purpose.