Insulin-like Growth Factor I Generation Research Articles

Are the Effects of Oral and Vaginal Contraceptives on Bone Formation in Young Women Mediated via the Growth Hormone-IGF-I Axis?

Purpose: Combined hormonal contraceptive therapy has been associated with negative bone mineral density outcomes that may be route-dependent [i.e., combined oral contraception (COC) vs. contraceptive vaginal ring (CVR)] and involve the hepatic growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. The objective of the pilot study was to assess the impact of route of contraceptive administration on IGF-I and procollagen type I N-terminal propeptide (PINP) responses to an IGF-I Generation Test. We hypothesized that the peak rise in IGF-I and PINP concentration and area under the curve (AUC) would be attenuated following COC, but not CVR, use.Methods: Healthy, premenopausal women not taking hormonal contraception were recruited. Women were enrolled in the control group (n = 8) or randomly assigned to COC (n = 8) or CVR (n = 8) for two contraceptive cycles. IGF-I Generation Tests were used as a probe to stimulate IGF-I release and were completed during the pre-intervention and intervention phases. Serum IGF-I and PINP were measured during both IGF-I Generation Tests. The study was registered at ClinicalTrials.gov (NCT02367833).Results: Compared to the pre-intervention phase, peak IGF-I concentration in response to the IGF-I Generation Test in the intervention phase was suppressed in the COC group (p < 0.001), but not the CVR or Control groups (p > 0.090). Additionally, compared to the pre-intervention phase, PINP AUC during the intervention phase was suppressed in both COC and CVR groups (p < 0.001), while no difference was observed in the control group (p = 0.980).Conclusion: These data suggest that changes in recombinant human GH-stimulated hepatic IGF-I synthesis in response to combined hormonal contraception (CHC) use are dependent on route of CHC administration, while the influence on PINP is route-independent. Future research is needed to expand these results with larger randomized control trials in all age ranges of women who utilize hormonal contraception.Clinical Trial Registration: www.ClinicalTrials.gov registration NCT02367833.

Significance of Direct Confirmation of Growth Hormone Insensitivity for the Diagnosis of Primary IGF-I Deficiency.

Primary insulin-like growth factor-I (IGF-I) deficiency is a synonym of growth hormone (GH) insensitivity (GHI), however the necessity of direct confirmation of GH resistance by IGF-I generation test (IGF-GT) is discussed. GHI may disturb intrauterine growth, nevertheless short children born small for gestational age (SGA) are treated with GH. We tested the hypothesis that children with appropriate birth size (AGA), height standard deviation score (SDS) <−3.0, GH peak in stimulation tests (stimGH) ≥10.0 µg/L, IGF-I <2.5 centile, and excluded GHI may benefit during GH therapy. The analysis comprised 21 AGA children compared with 6 SGA and 20 GH-deficient ones, with height SDS and IGF-I as in the studied group. All patients were treated with GH up to final height (FH). Height velocity, IGF-I, and IGF binding protein-3 (IGFBP-3) concentrations before and during first year of treatment were assessed. Effectiveness of therapy was better in GHD than in IGF-I deficiency (IGFD), with no significant difference between SGA and AGA groups. All but two AGA children responded well to GH. Pretreatment IGF-I and increase of height velocity (HV) during therapy but not the result of IGF-GT correlated with FH. As most AGA children with apparent severe IGFD benefit during GH therapy, direct confirmation of GHI seems necessary to diagnose true primary IGFD in them.

Idiopathic short stature and growth hormone sensitivity in prepubertal children.

We compared growth hormone sensitivity to an insulin-like growth factor I (IGF-I) generation test in children with idiopathic short stature (ISS) and of normal stature (NS) across the birthweight range. Forty-six prepubertal children (~7.1years) born at term were studied: ISS (n=23; 74% boys) and NS (n=23; 57% boys). Children underwent a modified IGF-I generation test with recombinant human growth hormone (rhGH; 0.05mg/kg/d) over four consecutive days. Hormonal concentrations were measured at baseline and day 5. Children with idiopathic short stature were 1.90 SDS lighter (P<0.0001) but had 4.5% more body fat (P=0.0007) than NS children. Overall, decreasing birthweight SDS across the normal range (-1.9 to +1.5 SDS) was associated with lower percentageIGF-I response to rhGH stimulation in univariable (r=0.45; P=0.002) and multivariable models (β=24.6; P=0.006). Plasma IGF-I concentrations rose in both groups with rhGH stimulation (P<0.0001). GHBP levels (P=0.002) were suppressed in ISS children (-19%; P=0.029) but increased among NS children (+18%; P=0.028), with contrasting responses also observed for leptin and IGFBP-1. Further, the increase in insulin concentrations in response to rhGH stimulation was ~3-fold greater in NS children (142% vs 50%; P=0.006). A progressive decrease in birthweight SDS was associated with a reduction in GH sensitivity in both NS and ISS children. Thus, the lower IGF-I response to rhGH stimulation in association with decreasing birthweight indicates that the ISS children at the lower end of the birthweight spectrum may have partial GH resistance, which may contribute to their poorer growth.

Pharmacogenomics of insulin-like growth factor-I generation during GH treatment in children with GH deficiency or Turner syndrome

Individual responses to growth hormone (GH) treatment are variable. Short-term generation of insulin-like growth factor-I (IGF-I) is recognized as a potential marker of sensitivity to GH treatment. This prospective, phase IV study used an integrated genomic analysis to identify markers associated with 1-month change in IGF-I (ΔIGF-I) following initiation of recombinant human (r-h)GH therapy in treatment-naïve children with GH deficiency (GHD) (n=166) or Turner syndrome (TS) (n=147). In both GHD and TS, polymorphisms in the cell-cycle regulator CDK4 were associated with 1-month ΔIGF-I (P<0.05). Baseline gene expression was also correlated with 1-month ΔIGF-I in both GHD and TS (r=0.3; P<0.01). In patients with low IGF-I responses, carriage of specific CDK4 alleles was associated with MAPK and glucocorticoid receptor signaling in GHD, and with p53 and Wnt signaling pathways in TS. Understanding the relationship between genomic markers and early changes in IGF-I may allow development of strategies to rapidly individualize r-hGH dose.

The changing face of acromegaly—advances in diagnosis and treatment

Acromegaly is a chronic disease characterized by the presence of a pituitary growth hormone (GH)-producing tumour, excessive secretion of growth hormone, raised levels of insulin-like growth factor I (IGF-I) and characteristic clinical presentation of acral enlargement. Over the past two decades, major advances have occurred in the understanding of some aspects of acromegaly--such as the biology of pituitary tumours, the physiology, molecular mechanisms of GH secretion and IGF-I generation, and the pathogenesis of comorbidities. Moreover, new approaches to diagnosis and surveillance (both in terms of screening and follow-up) of acromegaly have led to increases in the number of patients diagnosed with active disease, many of whom would previously have been missed. The development of sensitive assays for detecting plasma GH and IGF-I levels, as well as the widespread use of MRI for visualization of small tumours, have been major contributing factors to these improvements. Treatment advances have resulted in improved cure rates and disease control through novel neurosurgical techniques and pharmacological approaches. This Review summarizes and discusses the changes in our understanding of the epidemiology, diagnosis, treatment, and follow-up of acromegaly and its comorbidities.

The insulin-like growth factor-I (IGF-I) generation test as an indicator of growth hormone status

The aim of the study was to evaluate the IGF-I generation test (IGF-I gen) as a possible indirect test of Growth Hormone (GH) secretory status. Sixty-five GH deficient (GHD 1 and 2) and 86 control children were studied. Children in the GHD-1 subgroup (n=33) had low GH values (<10 microg/L) after clonidine and levo-dopa while those in the GHD-2 subgroup (n=32) had normal GH values after pharmacologic provocation but low 24-hour GH secretory rates compared to 187 Normal Statured (NS) children. Of the 86 controls, who underwent IGF-I gen,50 were NS and 36 Short-Statured (SS). Serum IGF-I was measured prior to and daily during hGH administration (hGH 0.033 mg/kg/dayx4 days). The prepubertal and pubertal GHD-1 and GHD-2 children had low baseline IGF-I values but their peak IGF-I values during the IGF-I gen reached those of the controls. The percent increase of IGF-I during the test was greater in the GHD groups than in the controls; in the prepubertal groups: 516+/-58% in the GHD-1, 433+/-50% in the GHD-2, 106+/-12% in the NS, and 102+/-18% in the SS (p=0.001); in the pubertal groups: 191+/-28% in the GHD-1, 141+/-20% in the GHD-2, 48+/-8% in the NS, and 61+/-17% in the SS (p=0.003). The IGF-I response during the IGF-I gen seems to reflect the GH status in children.

Growth and Factors Affecting it in Thalassemia Major

In our thalassemic (T) cohort, 45% of them had height standard deviation score (HtSDS) less than −2 and 56% of them had growth velocity standard deviation score (GVSDS) less than −1. Their mid-arm circumference and triceps skin-fold thickness were decreased versus normal controls. Their circulating insulin-like growth factor-I (IGF-I) concentrations were significantly lower than normal children. Growth hormone (GH) response to provocation with clonidine and glucagon was defective in half of the short T children (peak GH < 7 ng/dL). Some of the short T children, with normal GH response to provocation, had defective spontaneous nocturnal GH secretion. IGF-I generation after one GH injection was reduced in T children than those with GH deficiency (GHD) and constitutional delay of growth and puberty (CDGP). GH therapy for a year significantly increased IGF-I concentrations, GV, and HtSDS in T children but to a lower level compared to those with GHD or CDGP, suggesting partial GH insensitivity. Pubertal induction with human chorionic gonadotropin in T adolescents was associated with increased IGF-I concentrations, GV, and HtSDS.

Growth hormone, IGF-I and insulin and their abuse in sport.

There is widespread anecdotal evidence that growth hormone (GH) is used by athletes for its anabolic and lipolytic properties. Although there is little evidence that GH improves performance in young healthy adults, randomized controlled studies carried out so far are inadequately designed to demonstrate this, not least because GH is often abused in combination with anabolic steroids and insulin. Some of the anabolic actions of GH are mediated through the generation of insulin-like growth factor-I (IGF-I), and it is believed that this is also being abused. Athletes are exposing themselves to potential harm by self-administering large doses of GH, IGF-I and insulin. The effects of excess GH are exemplified by acromegaly. IGF-I may mediate and cause some of these changes, but in addition, IGF-I may lead to profound hypoglycaemia, as indeed can insulin. Although GH is on the World Anti-doping Agency list of banned substances, the detection of abuse with GH is challenging. Two approaches have been developed to detect GH abuse. The first is based on an assessment of the effect of exogenous recombinant human GH on pituitary GH isoforms and the second is based on the measurement of markers of GH action. As a result, GH abuse can be detected with reasonable sensitivity and specificity. Testing for IGF-I and insulin is in its infancy, but the measurement of markers of GH action may also detect IGF-I usage, while urine mass spectroscopy has begun to identify the use of insulin analogues.

Linear Growth, Growth-Hormone Secretion and IGF-I Generation in Children with Neglected Hypothyroidism Before and After Thyroxine Replacement

We studied growth hormone (GH) stimulation and insulin-like growth factor -I (IGF-I) generation tests in 15 children with neglected congenital hypothyroidism (CH) (age = 6.4 +/- 4.2 years) and measured their growth parameters for >1 years after starting thyroxine (T4) replacement. One year after treatment, height SDS (HtSDS) increased from -4.3 +/- 2.5 to -2.7 +/- 2.3. Peak GH response to clonidine increased from 3.2 +/- 1.2 ng ml(-1) to 7.62 +/- 1.38 ng ml(-1) after treatments. Basal and peak IGF-I response to GH increased from (34.66 +/- 17.3 ng ml(-1) and 58.4 +/- 36.99 ng ml(-1), respectively) before treatment to (130.6 +/- 97.8 ng ml(-1) and 193.75 +/- 122.5 ng ml(-1), respectively). HtSDS increments were correlated significantly with basal free T4 concentrations (r = 0.622, P < 0.01). In summary, after long period of hypothyroidism, T4 replacement produced significant, although incomplete, catch-up growth through a partial recovery of GH- IGF-I axis.

Growth Hormone and Testosterone: Effects on Whole Body Metabolism and Skeletal Muscle in Adolescence

The characteristic changes in human puberty – increased muscle bulk, increased linear growth, and the mineralization of the skeleton – are due, in part, to the combined effects of growth hormone (GH), insulin-like growth factor I (IGF-I), sex hormones and insulin. GH and testosterone, but not oestrogen, are highly protein-anabolic in vivo, and the combined administration of GH and testosterone has synergistic effects on these measures, both in children and adults. GH has no significant effect on enhancing skeletal muscle strength in humans; however, testosterone is highly ergogenic and is largely responsible for the differences in muscle bulk apparent in late puberty between the genders. The results of recent detailed metabolic studies suggest that boys have higher rates of protein synthesis and IGF-I generation than girls, given comparable doses of GH. In patients with a constitutional delay in growth and maturation, relative deficiencies in testosterone and lower IGF-I concentrations are associated with greater rates of total energy expenditure, suggesting that this relatively hormone-insufficient state is associated with a hypermetabolic state. Whether added nutritional supplements, alone or in combination with GH, could improve the growth pattern and final height of these children deserves further study. In conclusion, the metabolic effects of GH and testosterone are complex and they synergize in puberty. These hormones could be of use as protein-anabolic agents in selected catabolic conditions.

Insulin-Like Growth Factor (IGF) Parameters and Tools for Efficacy: The IGF-I Generation Test in Children

Serum levels of growth hormone (GH)-dependent peptides could provide important and valuable measures of GH sensitivity and, potentially, responsiveness. In normal individuals, serum insulin-like growth factor I (IGF-I) concentrations are dependent on the dose of GH given, with IGF-I responsiveness not decreasing with age. Individuals heterozygous for the E180 GH receptor (GHR) splice mutation have normal IGF-I generation, but those homozygous for the E180 splice mutation have very low basal and stimulated IGF-I concentrations. Similar results are observed for the serum IGF-binding protein 3 (IGFBP-3) response to GH, with a correlation between changes in serum concentrations of IGF-I and changes in IGFBP-3 in normal, heterozygotic, GH-insensitive and GH-deficient participants. In individuals with the E180 splice mutation, IGF-I and IGFBP-3 tests show sensitivity and specificity for detecting GH insensitivity (GHI). In children with idiopathic short stature, it appears that some individuals have selective resistance to GH, with their ability to generate IGF-I more impaired than their ability to generate other GH-dependent peptides. This heterogeneous group may require individualization of GH dosage. IGF generation tests remain the best short-term, in vivo test for classic GHI, although diagnostic tests will undoubtedly require further modification to identify milder pathophysiologic abnormalities.

Pegvisomant in the treatment of acromegaly

Epidemiological studies have highlighted the need for tight control of growth hormone (GH) and insulin-like growth factor I (IGF-I) in patients with acromegaly. Studies highlighting the events involved in GH receptor signaling have allowed the development of a pegylated GH receptor antagonist (pegvisomant) for use in humans, which has been designed to outcompete GH for the GH receptor, but which contains a position 120 amino acid substitution that prevents recruitment of a second GH receptor. This process of receptor dimerisation is crucial for signal transduction and IGF-I generation. Clinical trials of pegvisomant suggest it is the most effective treatment for acromegaly to date, as this therapy is capable of normalising serum IGF-I in up to 97% of patients when doses of 40 mg per day are used. This paper reviews the development of pegvisomant and the clinical experience in patients with acromegaly to date.

Reproducibility in Patterns of IGF Generation with Special Reference to Idiopathic Short Stature

Background/Aim: Insulin-like growth factor I (IGF-I) and insulin-lke growth factor binding protein 3 (IGFBP-3) generation tests are both sensitive and specific measures of growth hormone (GH) sensitivity. Recently, the question of reproducibility of IGF generation tests has been raised. We report our analysis of the correlation of low- and high-dose GH IGF-I and IGFBP-3 generation tests among patients with GH deficiency, GH insensitivity, and idiopathic short stature. Methods: A total of 198 subjects were randomized to either high- or low-dose GH for 7 days; the alternate dose was received after a 2-week washout period. Samples were collected at baseline and on days 5 and 8 of GH administration. Results: The serum concentrations of IGF-I and IGFBP-3 correlated significantly from one test to the other, regardless of the diagnosis. In normal subjects and patients with GH insensitivity and GH deficiency, the delta over baseline in IGF-I and IGFBP-3 in the low-dose test was highly predictive of the delta values in the high-dose test. The delta correlation was greatly diminished, however, in the patient population having idiopathic short stature. Conclusions: These observations support partial GH insensitivity effecting IGF-I generation specifically, as a possible etiology for idiopathic short stature, and thus such patients may warrant appropriate biochemical and/or molecular evaluation for partial GH insensitivity.

Growth Hormone Insensitivity: Pathophysiology, Diagnosis, Clinical Variation and Future Perspectives

The study of genetic growth hormone (GH) insensitivity is an evolving field. GH insensitivity syndrome (GHIS), otherwise known as Laron syndrome, is a heterogeneous disorder. Biochemical features consist of severe insulin-like growth factor I (IGF-I) and IGF-binding protein 3 (IGFBP-3) deficiency and elevated GH secretion. In a heterogeneous ‘European’ cohort of GHIS patients, features varied from classical to moderate abnormalities of phenotype and endocrine disturbance. A study of facial features within this series showed that a mild subgroup existed with normal facies, mild short stature and moderate biochemical abnormalities. Overlap with idiopathic short stature (ISS) exists, with heterozygous mutations of the GH receptor demonstrated to cause impaired growth. This ‘partial’ GHIS has not yet been defined endocrinologically. GH sensitivity, measured by IGF-I and IGFBP-3 responses in the IGF-I generation test, may reveal abnormalities in ISS, although it is likely that the dose of recombinant human GH and frequency of sampling in the test need to be modified.

The Effects of Treatment and the Individual Responsiveness to Growth Hormone (GH) Replacement Therapy in 665 GH-Deficient Adults

Data from 665 adults with GH deficiency (GHD; 332 women; 169 childhood-onset GHD; mean age, 44 yr) were analyzed to determine the efficacy of and individual responsiveness to GH replacement therapy. GH replacement was started at enrolment into KIMS (Pharmacia & Upjohn, Inc. International Metabolic Database). Mean maintenance doses of GH after 6 and 12 months were 0.43 and 0.53 mg/day (1.3 and 1.6 IU/day) for men and women, respectively. Serum insulin-like growth factor I (IGF-I) sd score increased from −2.2 and− 4.2 in men and women, respectively, to 1.8 and −0.9 at 6 months and 0.8 and −0.7 at 12 months. The waist/hip ratio decreased after 6 and 12 months, with the changes more pronounced in men. The waist/hip ratio was not influenced by age of onset of GHD, severity of hypopituitarism, or gonadal status. Total cholesterol decreased significantly in men, and high density lipoprotein cholesterol increased in women. Systolic blood pressure was unchanged during GH therapy, but diastolic blood pressure decreased in women. Quality of life, determined by a specific questionnaire for assessment of GHD in adults, improved after 6 and 12 months of GH therapy; this was more pronounced in adult-onset than in childhood-onset GHD, but was not influenced by gender, severity of hypopituitarism, or gonadal status. In 80% of patients, the starting dose of GH was 0.27 mg/day or less. This and the absence of a correlation between body weight and change in IGF-I were consistent with a dose-titration approach, which would tend to obscure individual variations in responses (determined by IGF-I levels). Nonetheless, the increase in IGF-I was significantly higher in men than in women on similar mean GH doses. Weak correlations were observed between the maintenance dose of GH and the change in IGF-I in men and women receiving sex steroid replacement, but not in patients with untreated hypogonadism or an intact gonadotropin reserve. Similarly, the increment in IGF-I was not related to the severity of GHD, as determined by the number of additional pituitary hormone deficiencies. Differences in IGF-I generation may partly explain the gender differences in reduction of central adiposity. These data highlight the value of large longitudinal surveillance databases in defining the optimum dose regimen for GH replacement and indicate that women may need a higher replacement dose of GH than men.

The effects of treatment and the individual responsiveness to growth hormone (GH) replacement therapy in 665 GH-deficient adults. KIMS Study Group and the KIMS International Board.

Data from 665 adults with GH deficiency (GHD; 332 women; 169 childhood-onset GHD; mean age, 44 yr) were analyzed to determine the efficacy of and individual responsiveness to GH replacement therapy. GH replacement was started at enrolment into KIMS (Pharmacia & Upjohn, Inc. International Metabolic Database). Mean maintenance doses of GH after 6 and 12 months were 0.43 and 0.53 mg/day (1.3 and 1.6 IU/day) for men and women, respectively. Serum insulin-like growth factor I (IGF-I) SD score increased from -2.2 and -4.2 in men and women, respectively, to 1.8 and -0.9 at 6 months and 0.8 and -0.7 at 12 months. The waist/hip ratio decreased after 6 and 12 months, with the changes more pronounced in men. The waist/hip ratio was not influenced by age of onset of GHD, severity of hypopituitarism, or gonadal status. Total cholesterol decreased significantly in men, and high density lipoprotein cholesterol increased in women. Systolic blood pressure was unchanged during GH therapy, but diastolic blood pressure decreased in women. Quality of life, determined by a specific questionnaire for assessment of GHD in adults, improved after 6 and 12 months of GH therapy; this was more pronounced in adult-onset than in childhood-onset GHD, but was not influenced by gender, severity of hypopituitarism, or gonadal status. In 80% of patients, the starting dose of GH was 0.27 mg/day or less. This and the absence of a correlation between body weight and change in IGF-I were consistent with a dose-titration approach, which would tend to obscure individual variations in responses (determined by IGF-I levels). Nonetheless, the increase in IGF-I was significantly higher in men than in women on similar mean GH doses. Weak correlations were observed between the maintenance dose of GH and the change in IGF-I in men and women receiving sex steroid replacement, but not in patients with untreated hypogonadism or an intact gonadotropin reserve. Similarly, the increment in IGF-I was not related to the severity of GHD, as determined by the number of additional pituitary hormone deficiencies. Differences in IGF-I generation may partly explain the gender differences in reduction of central adiposity. These data highlight the value of large longitudinal surveillance databases in defining the optimum dose regimen for GH replacement and indicate that women may need a higher replacement dose of GH than men.

Dehydroepiandrosterone sulfate enhances natural killer cell cytotoxicity in humans via locally generated immunoreactive insulin-like growth factor I.

Experimental and clinical investigations suggest the hypothesis that dehydroepiandrosterone sulfate (DHEAS) can positively influence natural killer (NK) immunity via locally produced insulin-like growth factor I (IGF-I) from NK cells. In the present study, the NK cell cytotoxicity (NKCC) and IGF-I levels in the supernatant of NK cells were studied at baseline and after exposure to various molar concentrations of DHEAS (from 10(-5)-10(-8) mol/L x mL/7.75 x 10(6) NK cells) in healthy subjects of young and old age. DHEAS-induced NKCC was also determined after DHEAS coincubation with somatostatin-14 (10-6) mol/L x mL/7.75 x 10(6) NK cells) and with interleukin-2 (IL-2; 100 IU/mL x 7.75 x 10(6) NK cells). NK cells were previously isolated by Ficoll-Hypaque density gradient and then by immunomagnetic procedure; the purity obtained was 97 +/- 1%. NKCC was determined against K562 tumoral targets. We observed that the increase in NKCC after DHEAS exposure was dose dependent and was correlated with the amount of IGF-I released in the supernatant of cultured NK cells. NKCC and IGF-I generation from NK cells were more elevated in healthy elder subjects than in healthy young subjects. The coincubation of DHEAS with somatostatin-14 significantly suppressed NKCC and IGF-I release from NK in both groups, whereas higher NKCC was found after DHEAS plus IL-2 exposure than after incubation with DHEAS alone. Taken together, this study suggests a role for NK-generated IGF-I in the modulation of NKCC by DHEAS in humans. Although DHEAS may contribute to the IL-2-mediated NKCC, its activity on NK cytolytic function can be dependent on a autocrine mechanism (IGF-I-mediated), probably independent of cytokine activation. The higher NKCC response to DHEAS found in old subjects than in younger might counterbalance the age-dependent decline in circulating DHEAS, thus contributing to maintain the pattern of NK immunity during aging.

Effects of Growth Hormone and Insulin-Like Growth Factor-I on Radiation Enteritis

The effect of growth hormone (GH) and insulin-like growth factor-I (IGF-I) on intestinal mucosal integrity and bacterial translocation after abdominal radiation was studied in rats. Animals were divided into the following groups: I (control), II (radiation), III (radiation plus GH) and IV (radiation plus IGF-I). Radiation (1,100 cGy) was administered on the 1st day to groups II, III and IV. GH [0.25 mg/kg body weight (BW) s.c. once daily] was administered on days 1, 2 and 3 to group III, and IGF-I (0.1 mg/kg BW s.c. twice daily) was given on days 1, 2 and 3 to group IV. On day 4, animals were sacrificed. Cultures of the mesenteric lymph nodes (MLN) and blood cultures from aorta and portal vein were performed. The number of villi per centimeter (V/cm), the villus height (Vh), mitoses per crypt (M/C) and protein and DNA contents of the mucosa were evaluated in samples from the terminal ileum. Radiation increased the number of positive MLN cultures, while treatment with GH and IGF-I reduced them significantly. V/cm, Vh, M/C, protein and DNA contents were significantly increased in all irradiated animals treated with GH and IGF-I. In conclusion both GH and IGF-I are not only capable of improving the mucosal integrity but also to reduce the bacterial translocation that follows intestinal radiation. In small doses IGF-I could reproduce the effects of GH and in some parameters the effects were more pronounced, although not statistically significant. This suggests that the effects of GH on intestine could be mediated through the local and systemic generation of IGF-I.

Fuel metabolism in growth hormone-deficient adults

Apart from being a stimulator of longitudinal growth, growth hormone (GH) regulates fuel metabolism in children and adults. A halfmark is mobilization of lipids, which involves an inhibition of lipoprotein lipase activity in adipose tissue and activation of the hormone sensitive lipase. Suppression of basal glucose oxidation and resistance to insulin are other important effects. This may cause concern during GH substitution in GH-deficient adults, some of whom may present with insulin resistance due to concomitant abdominal obesity. However, there are data to suggest that the GH-induced reduction in fat mass and increase in lean body mass may offset the insulin antagonistic actions of the hormone. The nitrogen-retaining effects of GH seem to involve a direct stimulation of protein synthesis in addition to secondary effects such as generation of insulin-like growth factor-I (IGF-I), hyperinsulinemia, and promotion of lipolysis. Thus, during periods of substrate affluence, GH acts in concert with insulin and IGF-I to promote protein anabolism. Postabsorptively, GH is primarily lipolytic and thereby indirectly protein-sparing. This effect becomes further accentuated with more prolonged fasting. In that sense, GH is unique by its preservation of protein during both feast and famine. These fuel metabolic effects add merit to the principle of GH substitution in hypopituitary adults.

Growth hormone receptor messenger ribonucleic acid expression in leiomyoma and surrounding myometrium

OBJECTIVE: Uterine leiomyomas are the most common pelvic tumors, occurring in one of four women, and they represent the single most common indication for hysterectomy. The genesis and growth-promoting factors responsible for their development are poorly understood. We speculate that growth hormone may play a role in the initiation of these tumors; women with acromegaly have a higher incidence of leiomyomas and growth hormone promotes uterine growth in rats, with or without the addition of estradiol. We evaluated the presence of growth hormone receptor messenger ribonucleic acid in the human uterus and leiomyomas to investigate whether growth hormone might act directly rather than by hepatic generation of insulin-like growth factor-I. STUDY DESIGN: Paired samples of leiomyomas and adjacent normal myometrium from nine premenopausal women (32 to 52 years old) were collected at surgery. Three patients received a gonadotropin-releasing hormone agonist for 3 months before the surgical procedure; six did not receive any adjuvant therapy. We used a digoxigenin-labeled oligoprobe sharing no homology to the growth hormone-binding protein or to the prolactin receptor, to investigate whether growth hormone receptor messenger ribonucleic acid was present in tissue sections or amplified complementary deoxyribonucleic acid from leiomyoma and the surrounding myometrium. RESULTS: The ratios of growth hormone receptor/reduced glyceraldehyde-phosphate dehydrogenase in leiomyomas and the surrounding myometrium as assessed by densitometry analysis of polymerase chain reaction products were similar and were not altered by gonadotropin-releasing hormone agonist treatment. In situ hybridization localized the growth hormone receptor messenger ribonucleic acid to the nuclei and cytoplasm of leiomyoma and myometrium. CONCLUSION: The presence of growth hormone receptor messenger ribonucleic acid suggests that the human uterus is a target tissue for growth hormone action. Future investigations are needed to investigate further the role of growth hormone in the development of leiomyomas.