Growth Hormone In Man Research Articles

Growth hormone and prolactin--molecular and functional evolution.

Growth hormone, prolactin, the fish hormone, somatolactin, and related mammalian placental hormones, including placental lactogen, form a family of polypeptide hormones that share a common tertiary structure. They produce their biological effects by interacting with and dimerizing specific single transmembrane-domain receptors. The receptors belong to a superfamily of cytokine receptors with no intrinsic tyrosine kinase, which use the Jak-Stat cascade as a major signalling pathway. Hormones and receptors are thought to have arisen as a result of gene duplication and subsequent divergence early in vertebrate evolution. Mammalian growth hormone and prolactin show a slow basal evolutionary rate of change, but with episodes of accelerated evolution. These occurred for growth hormone during the evolution of the primates and artiodactyls and for prolactin in lineages leading to rodents, elephants, ruminants, and man. Placental lactogen has probably evolved independently on three occasions, from prolactin in rodents and ruminants and from growth hormone in man. Receptor sequences also show variable rates of evolution, corresponding partly, but not completely, with changes in the ligand. A principal biological role of growth hormone, the control of postnatal growth, has remained quite consistent throughout vertebrate evolution and is largely mediated by insulin-like growth factors. Prolactin has many and diverse roles. In relation to lactation, the relative roles of growth hormone and prolactin vary between species. Correlation between the molecular and functional evolution of these hormones is very incomplete, and it is likely that many important functional adaptations involved changes in regulatory elements, for example, altering tissue of origin or posttranscriptional processing, rather than change of the structures of the proteins themselves.

Multifactorial control of the elimination kinetics of unbound (free) growth hormone (GH) in the human: regulation by age, adiposity, renal function, and steady state concentrations of GH in plasma.

To evaluate the principal determinants of the MCR and plasma t1/2 of unbound (free) GH in man, we performed steady state infusions of 3 doses of recombinant human GH during pharmacological suppression (iv octreotide) of endogenous GH secretion in 24 healthy adults and 12 patients (6 adults and 6 children) with chronic renal failure (CRF). Free plasma GH was calculated from total plasma GH (measured by immunoradiometric assay) and GH-binding protein activity (radioligand assay). The MCR of free GH was determined from free plasma GH and the rate of recombinant human GH infusion. The t1/2 of free plasma GH, and the concentration and the in vivo dissociation constant (Kd) of GH-binding protein (GHBP) were estimated by dynamic modeling of the postinfusion total plasma GH concentration decay curves. The MCR of free GH decreased and the plasma GH t1/2 increased significantly with increasing plasma GH concentrations. The MCR of free GH over its physiological concentration range was positively correlated with the body mass index as a measure of relative obesity and negatively related to age, but only at supraphysiological GH concentrations. In the adult patients with CRF, the MCR of free GH was decreased at each infusion rate by 25-38%, and the t1/2 was increased by 80-170%. Children with CRF showed a significantly lower MCR and higher t1/2 of plasma free GH than adult patients. Modeling and direct measurements of the off-rate of GH from its high affinity GHBP indicated normal dissociation rate constants but decreased molar concentrations of the GHBP in uremic plasma. We conclude that the rate of elimination of free GH from plasma in man is controlled by 1) plasma total free GH concentrations, 2) relative obesity, and 3) renal function within the physiological GH concentration range, whereas 4) age is a negative predictor of MCR only at supraphysiological GH concentrations.

Metabolic actions of growth hormone in man.

GH continues to be produced after the cessation of childhood growth and is the most abundant pituitary hormone in the adult pituitary. There is strong evidence that GH continues to exert significant biological effects on body metabolism in adult humans. The actions of GH may be direct or indirectly mediated by IGF-1. The direct actions of GH impart major effects on glucose, lipid and sodium homeostasis. GH administration causes hyperinsulinaemia and impairs the ability of insulin to suppress hepatic glucose production and to stimulate glucose uptake and oxidation. GH enhances fat utilisation by stimulating lipolysis and fat oxidation. The significance of these effects is reflected in the finding of increased adiposity in GH deficiency (GHD) and reduced fat mass in acromegaly. GH causes sodium retention which occurs in part through activation of the renin-angiotensin system. Extracellular water volume is diminished in GHD and increased in relation to the extent of GH excess in acromegaly. Lean body mass is reduced in GHD and restored by GH treatment. The anabolic actions of GH are mediated by IGF-1. Studies of whole body protein metabolism show that this occurs through the stimulation of protein synthesis, reduction in protein oxidation but not inhibition of protein breakdown. GH plays an important role in the regulation of substrate metabolism and body composition in man.

Improved early bone-implant integration in transgenic mice overexpressing bovine growth hormone

Titanium implants were inserted in transgenic mice overexpressing bovine growth hormone. Four weeks after insertion the implants were cut out en bloc with the surrounding bone. The undecalcified specimens were cut and ground to a thickness of approximately 10 μm. Histomorphometry demonstrated significantly more direct bone to metal contact for the transgenic mice than for the non-transgenic littermates. The results indicate that endogenous high levels of bovine growth hormone result in improved early bone-implant integration. This study indicate that it may be possible to systemically administrate growth hormone in man, in the early healing in phase, to improve implant integration.

Effects of diurnal sleep on secretion of cortisol, luteinizing hormone, and growth hormone in man.

Evidence has been provided for an influence of nocturnal sleep on the secretion of cortisol, LH, and GH in man. Although nocturnal sleep inhibits cortisol secretion during the first hours, it augments the secretion of LH and GH. To separate the effects of circadian rhythm from those of sleep, the present experiments examined the influence of diurnal sleep on the release of cortisol, LH, and GH in 12 young men. Subjects slept on 2 different occasions. After a night of wakefulness, subjects were assigned to bed at 0800 h the following morning. Lights were turned off either at 1100 or 1500 h to enable sleep. Effects of diurnal sleep were evaluated by comparing blood hormone concentrations during the interval from 1100-1500 h between subjects when sleeping and awake. Comparing hormonal concentrations during the 4 h of sleep after 1100 h with those during the 4-h sleep interval after 1500 h provided evidence for an influence of circadian rhythm on cortisol and LH release. Diurnal sleep, as has been shown for nocturnal sleep, augmented the secretion of LH and GH. However, in contrast to nocturnal sleep, diurnal sleep failed to suppress cortisol release, suggesting that sleep does not inhibit cortisol release at any point of its circadian rhythm, but only within a limited range of entrainment.

Effects of diurnal sleep on secretion of cortisol, luteinizing hormone, and growth hormone in man

Effects of diurnal sleep on secretion of cortisol, luteinizing hormone, and growth hormone in man

In vivo activation of circulating monocytes by exogenous growth hormone in man

Animal studies have shown that administration of growth hormone improves wound healing. Monocyte activation is a prerequisite for optimal repair of damage. In vitro, human recombinant growth hormone was shown to be a potent human monocyte chemoattractant. It induced random migration and chemotaxis at picomolar concentrations of recombinant human growth hormone; combinations of growth hormone with other chemoattractants deactivated the chemotactic response. Other functions of monocytes that are activated by growth hormone include release of superoxide anion and production of cytokines. In order to test activation of human monocytes by growth hormone in vivo, we investigated the effects of recombinant human growth hormone administration on monocyte migration in nine healthy young adults. After a single dose of recombinant human growth hormone (4 IU subcutaneously injected), random migration of circulating monocytes significantly increased, whereas chemotaxis of monocytes that was maximally stimulated with f-Meth-Leu-Phe decreased ( p < .05). The alterations paralleled the concomitantly measured plasma levels of growth hormone. After recombinant human growth hormone administration, no changes were seen in plasma levels of proinflammatory cytokines. These in vivo data on monocyte migration are comparable to effects of growth hormone on monocyte migration in vitro and strongly suggest that recombinant human growth hormone can activate circulating monocytes in man.

Pharmacokinetics and short-term metabolic effects of mammalian cell-derived biosynthetic human growth hormone in man.

The pharmacokinetics and acute effects of an authentic recombinant DNA-derived human growth hormone (rhGH) produced by genetically engineered mammalian cells were determined in 12 healthy volunteers following intravenous (i.v.), intramuscular (i.m.) and subcutaneous (s.c.) administration of 4 IU (1.3 mg) hGH/m2 body surface area. Following i.v. administration, apparent elimination half-life of rhGH was 18 min. Following i.m. administration, a mean peak serum concentration of 36.9 ng/ml (range 13-61 ng/ml) occurred at 3 h, and following s.c. administration, more sustained but lower serum concentrations occurred, with mean peak concentrations of 16.4 and 16.3 ng/ml at 4 and 6 h (ranges 9.0-27.5 ng/ml and 6.5-35.5 ng/ml at 4 and 6 h, respectively). The mean area under the curves was lower after s.c. (134 +/- 48 ng.h.ml-1) than after i.m. (194 +/- 48 ng.h.ml-1) injections (p < 0.03). Comparable results were obtained for the same dose of rhGH given subcutaneously in concentrations of either 4 IU/ml or 10 IU/ml. Both i.m. and s.c. administrations caused similar increases in free fatty acids at 4 h and insulin-like growth factor I at 24 h. Insulin, C-peptide and blood glucose were almost unchanged during the first 4 h after administration, whereas leukocytes increased significantly (p < 0.0001). Local and systemic tolerance were good, and no adverse reactions were observed. In a GH-deficient child, hGH serum levels between 10 and 20 ng/ml were demonstrated for a period of 8 h after s.c. administration of 0.07 IU rhGH/kg body weight.

Delta-Opioid receptors and the secretion of growth hormone in man: effect of opioid delta-receptor agonist deltorphin on GH responses to GH-releasing hormone and insulin-induced hypoglycemia.

To investigate the role of delta-opioid receptors in the modulation of growth hormone (GH) secretion, we compared in normal subjects the effect of the highly selective delta-opioid receptor agonist Deltorphin (DT) on the GH secretion responses to pituitary (GH-releasing hormone, GHRH)- and hypothalamic (insulin-induced hypoglycemia, IIH)-mediated stimuli. DT blunted the GH response to IIH, whereas it had no effect on the GH response to GHRH. It is concluded that in man DT-induced activation of delta-opioid receptors exerts an inhibitory action on hypoglycemia-stimulated GH secretion. Based on the lack of an effect of DT on the GH response to GHRH, we suggest that DT may modulate the secretion of GH through suprapituitary mechanisms.

Characterization of the insulin-antagonistic effect of growth hormone in man

The insulin-antagonistic effect of growth hormone was characterized by infusing the hormone at three different infusion rates (6, 12 or 24 mU.kg-1.min-1) for one h in 11 healthy subjects. The insulin effect was measured with the euglycaemic clamp technique combined with D-(3-3H)-glucose infusion to evaluate glucose production and utilization. A control study with NaCl (154 mmol.l-1) infusion was also performed. The insulin levels during the clamps were similar in all studies (36 +/- 0.2 mU.l-1). Peak growth hormone levels were reached at 60 min (growth hormone 6 mU.kg-1.h-1: 31 +/- 5; growth hormone 12 mU.kg-1.h-1: 52 +/- 4 and growth hormone 24 mU.kg-1.h-1; 102 +/- 8 mU.l-1). The insulin-antagonistic effect of growth hormone started after approximately 2 h, was maximal after 4-5 h (approximately 39% inhibition of glucose infusion rate between control and growth hormone 24 mU.kg-1.h-1) and lasted for 6-7 h after peak levels. The resistance was due to a less pronounced insulin effect both to inhibit glucose production and to stimulate glucose utilization. Growth hormone infusion of 12 mU.kg-1.h-1 induced a similar insulin-antagonistic effect as the higher infusion rate whereas 6 mU.kg-1.h-1 induced a smaller response with a duration of 1 h between 3-4 h after peak levels of growth hormone. The present study demonstrates that growth hormone levels similar to those frequently seen in Type 1 (insulin-dependent) diabetic patients during poor metabolic control or hypoglycaemia, have pronounced insulin-antagonistic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Thirty-Second Sampling of Plasma Growth Hormone in Man: Correlation with Sleep Stages*

Both fasting and sleep increase the secretion of human GH and, therefore, might explain its predominantly nocturnal release. To study the precise temporal relationship between GH secretory episodes and cortical activity, GH measurements and electroencephalogram sleep stage recordings were performed every 30 s for 8 h in six young male volunteers fasted for 24 h. GH was measured in two drops of whole blood, which were directly sampled into the assay tube using a continuous blood withdrawal pump and a fraction collector. Concomitant serum sampling during a GH-releasing hormone test (n = 4) revealed a high correlation (r = 0.98) between GH measurements in serum and whole blood. GH pulses were objectively identified with Cluster analysis, and GH secretion rates were calculated with a waveform-independent deconvolution algorithm. When data were analyzed as replicates with 1-min intervals, the nocturnal pulse frequency was 1.2 pulses/h. Elimination of data points demonstrated 43% and 64% reductions in the number of GH pulses detected for 5- and 20-min sampling intervals, respectively. Mean GH concentrations and secretory rates were significantly higher during stage 3 and 4 sleep compared to stage 1, 2, and rapid eye movement sleep. GH secretory rates and peripheral GH concentrations were maximally correlated with sleep stage, with lags of 4.5 and 16 min, respectively, suggesting that maximal GH release occurs within minutes of the onset of stage 3 or 4 sleep. This temporal coincidence between pituitary GH secretion and delta sleep is consistent with cortical control over hypothalamic-pituitary function.

The antinatriuretic action of biosynthetic human growth hormone in man involves activation of the renin-angiotensin system

Previous studies using human pituitary extracts have not resolved whether the sodium retaining effects of human growth hormone (hGH) are mediated in part by increased aldosterone secretion. We have studied the effects of an authentic biosynthetic GH (bio-hGH) preparation on sodium metabolism and on the activity of the renin-angiotensin system. Six young men were administered this preparation at 0.2 U/kg/d subcutaneously for five consecutive days. Twenty-four-hour urine collections were obtained for measurement of sodium excretion and osmolality and blood collected for quantitating changes in sodium, osmolality, plasma renin activity (PRA), aldosterone, and arginine vasopressin (AVP) concentrations. Bio-hGH administration resulted in a fall in 24-hour urinary sodium excretion (197 ± 38 to 42 ± 20 mmol, mean ± SD, P < .005), a reduction in urine volume (1,652 ± 182 to 848 ± 348 mL, P < .05) but not osmolality. PRA increased significantly from 1,118 ± 73 to 3,608 ± 1,841 fmol angiotensin 1 L/s ( P < .005), which was associated with a sevenfold increase in plasma aldosterone concentration (52 ± 12 to 402 ± 99 pg/mL, P < .001). Plasma osmolality and AVP concentrations did not change significantly. The results show that Bio-GH-induced retention of sodium involves the activation of the renin-angiotensin system. This mechanism may explain in part the occurrence of plasma volume expansion and hypertension in acromegaly and suggests a risk of fluid retention and possibly hypertension in subjects receiving supraphysiological doses of bio-hGH for treatment of short stature.

The Somatostatin Analog Octreotide Inhibits the Secretion of Growth Hormone (GH)-Releasing Hormone, Thyrotropin, and GH in Man*

The effects of the somatostatin analog octreotide on plasma GH, TSH, and immunoreactive GH-releasing hormone (IR-GHRH) were studied in 10 normal men. After morning sc administration of 50 or 100 micrograms octreotide or placebo, plasma GH, TSH and GHRH were measured frequently for 6 h. Plasma GH or IR-GHRH concentrations did not change after placebo injection, but plasma TSH levels gradually decreased, in conformity with a circadian rhythm during the morning. The mean plasma GH levels after sc injection of 50 or 100 micrograms octreotide declined, and no spontaneous GH pulses occurred for 5 h. Plasma TSH decreased rapidly after both doses of octreotide and was significantly lower than the level after placebo treatment from 90-315 min (P less than 0.05) and 60-360 min (P less than 0.05 or P less than 0.01), respectively. Plasma IR-GHRH levels also were significantly lower from 30-360 min (P less than 0.05) in the group given 100 micrograms octreotide compared with the value in the placebo group. We conclude that octreotide inhibits not only GH and TSH secretion from the pituitary, but also GHRH release from the hypothalamus and/or peripheral tissues. These findings suggest that somatostatin controls GH secretion not only by suppressing pituitary secretion of GH but also by suppressing GHRH release from the hypothalamus.

The circulating growth hormone (GH)-binding protein complex: a major constituent of plasma GH in man.

The recent discovery of a specific binding protein for human GH (hGH) in human plasma suggests that hGH circulates in part as a complex in association with the binding protein(s). However, the magnitude of the complexed fraction prevailing under physiological conditions is unknown because of 1) dissociation of the complex during analysis and 2) potential differences in the binding characteristics of radiolabeled and native hGH. We conducted experiments designed to minimize dissociation during analysis (gel filtration in prelabeled columns, frontal analysis, and batch molecular sieving) with both native and radioiodinated hGH. All three methods yielded similar estimates for the complexed fraction. In normal plasma the bound fraction for 22 K hGH averaged 50.1% (range, 39-59%), that for 20 K hGH averaged 28.5% (range, 26-31%). Above a hGH level of about 20 ng/ml the bound fraction declines in concentration-dependent manner due to saturation of the binding protein. We conclude that a substantial part of circulating hGH is complexed with carrier proteins. This concept has important implications for the metabolism, distribution, and biological activity of hGH.

Evidence for a GABAergic control of the exercise-induced rise in GH in man.

The effect of the GABAergic drug sodium valproate (SV) on the exercise-induced release of growth hormone (GH) was investigated in 10 healthy males. The exercise test consisted of using a stationary bicycle ergometer at 450 kg/min for 20 min. SV 600 mg blunted the increase in GH induced by the exercise, suggesting GABAergic regulation of GH secretion in man, at least under certain physiological conditions.

Stature and weight in chronic granulomatous disease

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Effect of age and obesity on fasting levels of glucose, insulin, glucagon, and growth hormone in man.

The influence of age and obesity on glucose homeostasis may be mediated via changes in basal levels of the main glucoregulatory hormones, insulin, glucagon, and growth hormone. Fasting plasma levels of these hormones and of glucose were measured in 186 normal male volunteers, 23 to 93 years old. Obesity was assessed as obesity index and by a more accurate anthropometric method as percentage of fat. Age and obesity index had a significant but low linear correlation (r = -.16, p less than .05). Age was not significantly correlated to any other metabolic variable. Percentage of fat was, however, significantly related to the fasting plasma levels of glucose (r = .27, p less than .001), insulin (r = .26, p less than .01), and glucagon (r = .16 less than .05). Fasting glucose was significantly correlated to insulin (r = .30 , p less than .001). These significant correlations persisted when age was held constant. In the basal state the main glucoregulatory hormones are not influenced by age, but plasma glucose, insulin, and glucagon levels are influenced by obesity.

The ketotic effects of glucocorticoid and growth hormone in man.

The ketotic effects of both glucocorticoid and growth hormone were assessed in normal man. Experimental protocols, previously shown to induce marked ketosis in diabetic man, were utilized to explore the metabolic effects of these two stress hormones in subjects with normal insulin secretory capacity. Glucocorticoid was administered orally as 1 mg of dexamethasone at 24 and 8 h prior to study. Growth hormone was administered subcutaneously at a dosage of 1 mg, 12 h prior to study. During the 90-min study of the ketotic activity of these hormones, plasma nonesterified fatty acids were acutely increased by heparin administration to support hepatic ketogenesis. This technique permitted an assessment of the ketotic activity of glucocorticoid and growth hormone independent of their lipolytic activity. The results of this study demonstrate that glucocorticoid may cause minimal hyperketonemia in spite of hyperinsulinemia in normal man. However, this effect is accompanied by a glucocorticoid-induced instability in basal ketone body and nonesterified fatty acid concentration. In contrast, no effect of growth hormone on plasma ketone body concentration or insulin levels was observed. These results in normal man contrast to the marked ketosis previously induced by these two stress hormones in diabetic man.

Influence of bupropion HCL (Wellbatrin®), a novel antidepressant, on plasma levels of prolactin and growth hormone in man and rat

Bupropion HCl (Wellbatrin®), a non-tricyclic compound with antidepressant effects in man, was evaluated for effects on plasma prolactin (PRL) and growth hormone (GH) levels in normal human subjects, and for effects on plasma PRL levels in a series of pharmacological studies in normal rats. Single oral doses of 50, 100 or 200 mg of bupropion given to male (n=6) and female (n=12) subjects produced a marked suppression (80% decrease) of PRL. Incomplete PRL recovery was observed at the end of 24 hours. One hour after drug administration there was a +0.56 correlation of percent decrease in PRL levels with bupropion plasma levels. GH showed only small and erratic changes in plasma levels at 1–4 hours post-dose. In the rat, single bupropion doses of 25 mg/kg, i.p., failed to lower basal PRL levels. Bupropion, however, significantly decreased PRL in rats in which plasma PRL was elevated by pretreatment with alphamethyltyrosine, 5-hydroxytryptophan or quipazine. Bupropion, on the other hand, did not counteract the PRL-elevating effect of haloperidol. Results in man and rat are consistent with the view that bupropion has significant dopamine mimetic properties. Whether bupropion is a direct dopamine receptor-stimulator or an indirectly acting agonist cannot be determined from the present results.

Metabolic clearance rates of isohormones of human growth hormone in man.

The charge isomers of human GH (/GH), isohormones C, D, and E, which result from limited proteolytic cleavage exhibit enhanced biological activity in the rat and in man compared to the intact polypeptide and most abundant form, isohormone B. The mechanism leading to enhanced activity is unknown. To examine the possibility that different in vivo metabolism may represent one such mechanism, the MCRs of radioiodinated hGH-B, -C, and -D were measured in seven normal adults. Significant differences in metabolic clearance were found between isohormones (hGH-B, 108.4; hGH-C, 67.9; hGH-D, 55.7 liters/m2-day). It is concluded that in man, the enzymatically cleaved hGH isohormones are cleared more slowly than hGH-B. Slower metabolism may be a factor responsible for the enhanced biological activity of proteolytically cleaved hGH isohormones.