Human pancreatic growth hormone-releasing factor stimulates release of growth hormone in conscious unrestrained male rabbits

The effect on GH secretion of GH-releasing factor (GRF), a 44-amino acid peptide recently isolated from a human pancreatic tumor (hpGRF), was examined in conscious male rabbits. During a 6-h period (1030-1630 h) of the control study individual rabbits exhibited pulsatile GH release with a surge at 1030-1200 h, a trough at 1200-1400 h, and a second peak at 1400-1630 h. Intravenous bolus injections of 1 and 10 micrograms hpGRF caused significant and dose-related increases in plasma GH during both the period of the trough (1300 h) and the surge (1530 h), although the GH responses were obviously higher during the latter than the former period. Passive immunization with anti-somatostatin (SRIF) sheep serum resulted in a prompt increase in plasma GH immediately after an injection of the antiserum. When 0.1, 1, and 10 micrograms hpGRF were successively injected iv at 1215, 1345, and 1515 h, respectively, maximum levels of plasma GH after hpGRF in anti-SRIF sheep serum-treated rabbits were significantly higher than in animals given normal sheep serum. The plasma GH responses to 10 micrograms hpGRF, given iv only once at 1515 h in normal sheep serum-treated animals, were not different from those to 10 micrograms hpGRF injected at 1515 h after the prior administration either of the smaller hpGRF dose (0.1 micrograms, 1215 h; 1 microgram, 1345 h), nor of the large dose (10 micrograms, 1100 h). These findings suggest the following: 1) that the secretion of GH is pulsatile in conscious, unrestrained male rabbits; 2) that hpGRF is a potent secretagogue for GH release in rabbits as well as other species; 3) that the magnitude of plasma GH response to hpGRF is different according to timing of the injection during the course of pulsatile GH secretion but is not influenced by the prior administration of hpGRF (no priming effect); and 4) that the responsiveness of plasma GH to hpGRF is affected by circulating endogenous SRIF.     

Detection of growth hormone abuse in sport.

OBJECTIVE: To develop a test for GH abuse in sport. DESIGN: A double blind placebo controlled study of one month's GH administration to 102 healthy non-competing but trained subjects. Blood levels of nine markers of GH action were measured throughout the study and for 56 days after cessation of GH administration. Blood samples were also taken from 813 elite athletes both in and out of competition. RESULTS: GH caused a significant change in the nine measured blood markers. Men were more sensitive to the effects of GH than women. IGF-I and N-terminal extension peptide of procollagen type III were selected to construct formulae which gave optimal discrimination between the GH and placebo groups. Adjustments were made to account for the fall in IGF-I and P-III-P with age and the altered distribution seen in elite athletes. Using a cut-off specificity of 1:10,000 these formulae would allow the detection of up to 86% of men and 60% of women abusing GH at the doses used in this study. CONCLUSIONS: We report a methodology that will allow the detection of GH abuse. This will provide the basis of a robust and enforceable test identifying those who are already cheating and provide a deterrent to those who may be tempted to do so.     

Technology insight: detecting growth hormone abuse in athletes

Athletes recognized the performance-enhancing potential of human growth hormone when it became available for treatment of short stature in growth-retarded children. Although no controlled clinical studies have demonstrated a significant benefit in highly trained adults with normal pituitary function, the practice of doping increased with the introduction of recombinant human growth hormone. Evidence of widespread abuse has been gathered by police and customs authorities or provided by former athletes. It has been difficult to develop a test to prove the administration of exogenous growth hormone in athletes because of its specific physiological and biochemical properties. Significant progress has only recently been made, particularly via two differing approaches. The 'marker approach' utilizes characteristic changes in concentrations of pharmacodynamic end points of growth hormone action, for example serum concentrations of insulin-like growth factor I and factors related to bone and soft tissue turnover. The 'isoform approach' detects changes in the molecular isoform composition of circulating growth hormone evoked by the administration of exogenous recombinant growth hormone. The isoform approach was applied at the Olympic Games in Athens in 2004 and in Turin in 2006. Used in a complementary way in an out-of-competition setting, these methods are a powerful tool with which to detect growth hormone abuse in sports.     

Human pituitary growth hormone (hGH) therapy in growth hormone deficiency

This review has attempted to answer a number of questions regarding human growth hormone therapy in growth hormone deficiency. I believe that the available data support several conclusions which form a suggested current approach to the clinical use of hGH. While these conclusions are derived from data obtained using pituitary growth hormone, it is likely that they are applicable to growth hormone manufactured by recombinant DNA technology, as well. Treatment should be begun as early as the diagnosis can be made in anticipation of a better initial and long-term response in younger patients. Growth hormone should be administered on the basis of body weight in an initial dose of 0.06-0.10 unit/kg 3 times a week. Growth hormone may be administered either intramuscularly or subcutaneously. Therapy should be continuous whenever possible. Treatment should be given until there is no further response which generally will reflect closure of the epiphyses. Associated hormone deficiencies should be adequately treated, and patients should be periodically evaluated for the development of additional deficiencies. Concomitant therapy is not indicated unless deficiencies are clearly demonstrated. Thyroid replacement should be at full dosage, while glucocorticoid replacement should probably not exceed 10-15 mg/m2 x day. Gonadal steroids should be used at the bone age when puberty is expected, and hGH should be continued during pubertal development. There is no general indication for giving anabolic/androgenic steroid in combination with hGH in prepubertal patients. If a waning effect of therapy is observed, the dose of hGH should be incrementally increased, and/or the addition of anabolic/androgenic steroid therapy should be considered. While most reports have focused on the effect of hGH on linear growth, changes in weight, bone age, body proportions, and body composition have also been observed. The effect on bone age is variable, but there is greater enhancement of linear growth than of epiphyseal development in the majority of treated patients. Bone age must be monitored during hGH administration whether or not anabolic/androgenic steroids are used concurrently. Growth hormone administration is remarkably free of side effects. However, neutralizing antibodies to hGH may develop and they should be sought in patients in whom an unexplained decrease in response is observed. Certainly the available incomplete data allow for different conclusions. The expanding supply of hGH should lead to a more systematic evaluation and provide more definite answers to the questions which this review has considered.     

The history of doping and growth hormone abuse in sport

The earliest records of doping in sport come from the Ancient Olympics games when athletes are reported to have taken figs to improve their performance. With the advent of modern pharmacology in the 19th century, many athletes began to experiment with cocktails of drugs to improve strength and overcome fatigue. As this practice was not illegal, there are good records of the lengths athletes would go to in order to win. Alongside the benefits, came the dangers and following several fatalities, a code to ban performance enhancing drugs was gradually developed.Growth hormone was first isolated from the human pituitary gland in the 1950s. Its anabolic effects were soon recognised and athletes had begun to abuse it by the early 1980s, at least a decade before it was used therapeutically by adult endocrinologists. A number of high profile athletes have admitted using growth hormone. Detection of its abuse has been challenging and the lack of an effective test has undoubtedly encouraged its abuse. Only now are methodologies being developed that should stem this tide.     

The UK Sport perspective on detecting growth hormone abuse

Background and objectivesHuman growth hormone (hGH) is seen as a doping risk in sport because of its possible anabolic and lipolytic effects. As a result of this hGH is prohibited for athletes to use both in and out-of-competition by the World Anti-Doping Agency (WADA) requiring Anti-Doping Organisations to work with research teams in identifying ways to detect hGH abuse.ApproachThis paper reviews and discusses the UK Sport perspective on the challenges faced in detecting hGH and in particular draws upon the experiences gained during the collaborative efforts with the GH-2004 research team in achieving the implementation of the Marker Method for hGH detection.ConclusionsIn 2008 significant progress has been made; there is one test for detecting HGH approved for use in anti-doping and a second detection method pending. This is a strong reflection of the ongoing research efforts in anti-doping and the progress being made by the Anti-Doping Organisations in reducing the risk that doping poses to sport.     

Human growth hormone stimulates liver regeneration in rats

To study the effect of human growth hormone (hGH) on liver regeneration in rats, 200 micrograms hGH was administered to partial hepatectomized rats twice a day for three days. The bw of hGH-treated rats was higher than that in untreated rats. After three day administration, the liver weight was 3.18 +/- 0.13 g, significant higher than that of untreated rats (2.68 +/- 0.17 g). Human GH also stimulated the mitosis in the liver. Serum insulin-like growth factor I (IGF-I) and albumin levels were significantly increased and urea nitrogen levels were significantly decreased in hGH-treated rats compared with those in untreated rats. When 120 micrograms/day IGF-I was continuously administered to partial hepatectomized rats for three days, the bw and the liver weight were not higher than those of controls. These data indicate that hGH directly stimulates liver regeneration and recover liver dysfunction in rats.     

In-vivo uptake of human growth hormone in male rat liver

125I-Labelled human GH (hGH) was injected i.v. to male rats and its subcellular distribution in the hepatocyte was examined using fractionation techniques. Uptake into liver homogenates was maximal by 15 min after injection and represented 24% of the injected radioactivity; it was markedly inhibited by coinjection of native hGH. 125I-Labelled hGH taken up by the liver underwent a time-dependent translocation process. The peak of specific labelling of plasma membranes occurred at 3 min whereas later on the radioactivity was concentrated in low-density structures present in Golgi-endosome fractions. To characterize the ligand-associated structures better, endosome-enriched fractions were prepared from a microsomal fraction by isopycnic centrifugation in a sucrose gradient and a Nycodenz gradient. The radioactivity was in one peak with a median density of 1.096 g/cm3 in the Nycodenz gradient fractions. The peak of radioactivity was distinct from that of galactosyltransferase activity which appeared at a median density of 1.114 g/cm3. The labelled material eluted from the various subcellular fractions appeared as intact hGH. Upon in-vivo interaction with male rat hepatocytes, 125I-Labelled hGH was internalized with a sequential association with plasma membranes and endocytic structures distinct from Golgi elements.     

Human growth hormone and somatomedin C suppress the spontaneous release of growth hormone in unanesthetized rats

To investigate the feedback control of GH secretion, we examined the effects of human GH (hGH) and somatomedin C (SmC) on spontaneous GH secretory surges in unanesthetized, freely moving rats. Under pentobarbital anesthesia a right atrial catheter and an intracerebroventricular cannula were placed 7-10 days before the experimentation. For iv studies, hGH (0.3 U/ml.h) was infused for 6 h after an iv loading dose (0.3 U) at the beginning of the experiments. For intraventricular injections, hGH (0.1 U/10 microliter) or SmC (500 ng/10 microliter) were injected into the lateral ventricle 2 h before the experiments. The equivalent dose of crystalline BSA diluted in the same vehicle solutions was administered to the same rat as a control on a separate day. Venous blood samples were collected every 20 min for 6 h. Intravenous and intraventricular administration of crystalline BSA did not affect the typical rat GH (rGH) surges which appeared about every 3 h and reached peak values of more than 300 ng/ml. The iv infusion of hGH significantly inhibited the amplitude of rGH surges compared to controls (planimetric areas under the secretory profile 752 +/- 172 vs. 1921 +/- 183, P less than 0.01, n = 6). rGH secretion was similarly inhibited by intraventricular hGH (701 +/- 127 vs. 2208 + 225, P less than 0.01, n = 6) and by intraventricular SmC (537 +/- 70 vs. 1503 +/- 114, P less than 0.01, n = 6). These findings suggest that both GH and SmC are active in the feedback regulation of rGH secretion.     

Human pituitary growth hormone cells in old age.

Pituitaries obtained at autopsy from 18 men and 17 women, over 80 years of age, who died of various acute illness, were investigated histologically by various staining procedures, including the immunoperoxidase technique. Compared with pituitaries of 10 male and 10 female subjects who died of short-lasting diseases between 20 and 56 years of age, no involution of growth hormone cells was found in pituitaries of the older group. Incidence, distribution, granulation and immunoreactivity of growth hormone cells showed no apparent differences related to age and sex. Lack of regression of growth hormone cells with advancing age indicates that the pituitary can produce growth hormone in old subjects.