Growth hormone response to human pancreatic growth hormone releasing factor in cattle

The effects of a growth hormone releasing factor, human pancreatic growth hormone releasing factor-44 (hpGRF-44), on growth hormone (GH) secretion in calves, heifers and cows were studied. A single intravenous (iv) injection of 0.1, 0.25, 0.5 or 1.0 microgram of synthetic hpGRF-44 per kg of body weight (bw) in calves significantly elevated the circulating GH level within 2-5 min, while no increase in plasma GH was observed in saline injected control calves. The plasma GH level increased proportionally to the log dose of hpGRF-44, and reached a peak at 5-10 min (p less than 0.01). Subcutaneous injection of hpGRF-44 also elevated the plasma GH level, but the peak value at 15 min was 37% of that of iv injection (p less than 0.05). Intravenous injection of 0.25 microgram of hpGRF-44 per kg of bw to female calves, heifers, and cows significantly elevated mean the GH levels from 8.5, 2.3, and 1.6 ng/ml at 0 time to peak values of 97, 26, and 11.6 ng/ml, respectively (p less than 0.01). The plasma GH response and basal level in calves were significantly higher than those of heifers or cows (p less than 0.025). The plasma GH response to hpGRF-44 as well as the basal level decreased with advancing age. The plasma GH response to hpGRF-44 and basal GH in male calves were significantly greater than those in female calves (p less than 0.001). These results indicate that synthetic hpGRF-44 is a potent secretogogue for bovine GH, and suggest its usefulness in the assessment of GH secretion and reserve in cattle.     

In vitro pituitary hormone releasing activity of 40 residue human pancreatic tumor growth hormone releasing factor

The hypophysiotropic activities of a synthetic human pancreatic growth hormone releasing factor (hpGRF) with 40 residues was examined in vitro using rat pituitary halves. At concentrations from 10(-10) M to 10(-7) M the peptide stimulated GH release in a dose-dependent manner with the ED50 being 1.2 x 10(-9) M. The concentration of 10(-10) M hpGRF is comparable to the basal hypophyseal portal blood levels of other known hypothalamic hypophysiotropic hormones. However, GH release was enhanced three-fold by concentration as low as 10(-12) M, though no dose-response relationship was observed up to 10(-10) M. Thus, this peptide not only stimulates the release of GH in a dose-dependent manner, but at lower concentrations also maintains elevated GH levels. The release of ACTH, beta-endorphin, LH, and FSH was not affected by hpGRF at any of the concentrations tested. At hpGRF concentrations less than 10(-7) M, the release of TSH and PRL were unaffected. However, at 10(-6) M, TSH release was enhanced about 2.5 fold and prolactin release was elevated slightly.     

Effects of corticotropin releasing factor and growth hormone releasing factor on pituitary hormone secretion in patients with congenital thyrotropin deficiency. Abnormal response of growth hormone to corticotropin releasing factor

Blood concentrations of anterior pituitary hormones, ACTH, GH, TSH, PRL, LH, and FSH were determined in corticotropin releasing factor (CRF) test (synthetic ovine CRF 1.0 microgram per kg body weight) and growth hormone releasing factor (GRF) test (synthetic human pancreatic GRF-44 100 micrograms) in 2 female sibling patients with congenital isolated TSH deficiency, in their mother, in 2 patients with congenital primary hypothyroidism and in 8 normal controls. The patients with isolated TSH deficiency showed normally increased plasma ACTH and serum GH after CRF and GRF, respectively, and also showed an abnormal GH response to CRF. The serum GH showed a rapid increase to maximum levels (12.9 ng/ml) within 30 to 60 min followed by decrease. The possibility of secretion of abnormal GH could be excluded by the fact that on serum dilution, GH value gave a linear plot passing through zero. In addition, serum PRL, LH and FSH levels after CRF administration in case 1 and PRL after GRF in case 2 were also slightly increased but these responses were marginal. The mother of the patients, patients with congenital primary hypothyroidism, and normal healthy controls showed normal responses of pituitary hormones throughout the experiment. Data from the present study and a previous report show that abnormal GH response to the hypothalamic hormones (CRF, TRH and LHRH) may be observed in patients with congenital isolated TSH deficiency.     

Stimulation of growth hormone release in dwarf and normal chickens by thyrotrophin releasing hormone (TRH) or human pancreatic growth hormone releasing factor (hpGRF)

The effect of thyrotrophin releasing hormone (TRH) or human pancreatic growth hormone releasing factor (hpGRF) on growth hormone (GH) release was studied in both dwarf and normal Rhode Island Red chickens with a similar genotype except for a sex-linked dw gene. Both TRH (10 micrograms/kg) and hpGRF (20 micrograms/kg) injections stimulated plasma GH release within 15 min in young and adult chickens. The increase in GH release was higher in young cockerels than that in adult chickens. The age-related decline in the response to TRH stimulation was observed in both strains, while hpGRF was a still potent GH-releaser in adult chickens. The maximal and long acting response was observed in young dwarf chickens, suggesting differences in GH pools releasable by TRH and GRF in the anterior pituitary gland. The pituitary gland was stimulated directly by perifusion with hpGRF (1 microgram/ml and 10 micrograms/ml) or TRH (1 microgram/ml). Repeated perifusion of GRF at 40 min intervals blunted further increase in GH release, but successive perifusion with TRH stimulated GH release. The results suggest the possibility that desensitization to the effects of hpGRF occurs in vitro and that the extent of response depends on the number of receptors for hpGRF or TRH and/or the amount of GH stored in the pituitary gland.     

Growth hormone and prolactin response to thyrotropin releasing hormone and growth hormone releasing factor in the immature turkey

Synthetic thyrotropin releasing hormone (TRH) and human pancreatic growth hormone releasing factor (hpGRF) stimulated growth hormone (GH) secretion in 6- to 9-week-old turkeys in a dose-related manner. TRH and hpGRF (1 and 10 micrograms/kg, respectively) each produced a sixfold increase in circulating GH levels 10 min after iv injection. Neither TRH nor hpGRF caused a substantial change in prolactin (PRL) secretion in unrestrained turkeys sampled through intraatrial cannulas. However, some significant increases in PRL levels, possibly related to stress, were noted.     

Somatocrinin,growth hormone releasing factor,stimulates secretion of growth hormone in anesthetized rats

The synthetic replicate of a 44 amino acid peptide isolated from a human pancreatic tumor which had caused acromegaly possesses high specific activity to release growth hormone (GH) in anesthetized male rats. The GH secretion induced by this peptide is dose-dependent from 50 ng to 1 μg, with plasma GH concentrations increasing more than 10-fold within 5 min of iv administration at the higher doses. Two enzymatic degradation products of the 44 residue peptide were also isolated and consist of the first 37 and 40 amino acids. All three peptides appear to possess similar potency, on a molar basis, $\text{in}\text{vivo}$, contrary to $\text{in}\text{vitro}$ results. The specificity of these peptides on GH release was shown by their failure to alter plasma concentrations of prolactin (PRL), thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and corticosterone. Based on these $\text{in}\text{vivo}$ results, the three peptides with serve as powerful tools with which to investigate the mechanisms of GH secretion.     

Corticotropin releasing factor stimulates growth hormone secretion in neonatal rats

Corticotropin releasing factor (CRF) both stimulates ACTH secretion from the pituitary and inhibits secretion of growth hormone (GH) in adult rats through actions in the CNS. The purpose of the present study was to evaluate these pituitary and central actions of CRF in neonatal rats, in which the hypothalamo- pituitary adrenal (HPA) axis is relatively hypo-functional. The results of this study show that central or peripheral administration of CRF evokes a marked dose-related rise in serum corticosterone in 6-day old rats. The same doses of CRF stimulate, rather than inhibit GH secretion. These results suggest that CRF has unique central actions early in ontogeny.     

The influence of age on human pancreatic growth hormone releasing hormone stimulated growth hormone secretion

63 non-obese healthy subjects aged 18 to 95 years were investigated for age-dependence of GHRH-stimulated GH-secretion. In addition, priming of GH-secretion with three oral doses of propranolol (3 x 80 mg, the last dose 2 hours prior to the second GHRH-bolus) was carried out in 15 subjects below 40 years and 13 subjects older than 70 years. We found that mean maximal incremental GH-levels were inversely correlated with chronological age (r = -0.44, P = 0.001) of the probands. Propranolol premedication caused a significant rise of both basal and peak GHRH-induced relative increases in all subjects tested, whereas GHRH-induced relative increases of GH remained unchanged. In a well selected group of non-obese healthy subjects stimulated GH-secretion is found to undergo an aging process that is supposed to be of pituitary and suprapituitary origin. Priming GH-secretion with a beta-Blocker is possible both in young and very old healthy subjects and is likely to affect the basal GH secretory tone and not GHRH-stimulated GH-secretion.     

The growth hormone secretory response to growth hormone releasing factor in the developing rhesus monkey.

We studied the development of the GH response to growth hormone releasing hormone (GHRH) using two doses of GHRH. The newborns demonstrated higher baseline GH and responses to GHRH than animals of any older age. There was no difference noted between the rise in GH in male and female subjects with 10 mcg/kg vs 1 mcg/kg. Serum cortisol concentrations did not correlate with serum GH concentrations. These developmental patterns of serum GH are similar to those known in the human being.     

Changing responsiveness to growth hormone releasing factor in the perinatal sheep

Synthetic human pancreatic growth hormone releasing factor 1-44-amide was administered (8 micrograms/kg iv bolus) to chronically catheterised fetal sheep between 77 and 135 days of gestation and to infant sheep. At all ages human pancreatic growth hormone releasing factor induced a significant growth hormone response. In fetuses less than 120 days the integrated growth hormone response to human pancreatic growth hormone releasing factor (n = 5) was 250 +/- (SE) 50 ng X hr X ml-1 compared (p less than 0.001) to -22.8 +/- 8.6 ng X hr X ml-1 in saline treated controls (n = 7). In fetuses older than 120 days (n = 5), the response to human pancreatic growth hormone releasing factor was 110.8 +/- 15.6 ng X hr X ml-1 compared to -12.0 +/- 17.6 ng X hr X ml-1 in saline treated controls (n = 4 p less than 0.001). In 4 infant lambs (4-12 days) the response to human pancreatic growth hormone releasing factor (56.5 +/- 14.5 ng X hr X ml-1) was greater than in 6 control injected lambs (0.95 +/- 1.5 ng X hr X ml-1). The magnitude of the response to growth releasing factor decreased progressively with increasing postconceptual age (r = -0.80, p less than 0.001). These observations demonstrate that the fetal somatotrope can respond to exogenous growth releasing factor from at least 77 days of gestation. The progressive decrease in responsiveness may reflect the gradual development of somatostatin mediated inhibitory control or altered responsiveness of the somatotrope.     

Plasma growth hormone responses to repetitive administrations of growth hormone releasing factor in patients with pituitary dwarfism

Plasma growth hormone (GH) responses to the repetitive administrations of synthetic human pancreatic growth hormone releasing factor (hpGRF-44) were studied in 15 patients with GH deficiency (11 diagnosed as idiopathic and 4 diagnosed as secondary to hypothalamo-pituitary tumor). hpGRF-44 was administered by single iv bolus (2 micrograms/kg), repetitive im (100 micrograms, twice a day), and/or repetitive iv infusion (2.5 micrograms/min for 90 min, once a day) for three to six consecutive days. Three of the eleven idiopathic GH deficient patients had plasma GH responses to both single iv bolus injection and repetitive administrations by im, or iv infusion of hpGRF. In four of the remaining eight, who had not had peak plasma GH levels above 5 ng/ml to a single iv bolus of the peptide, repetitive administrations of hpGRF-44 by im injection and/or iv infusion induced GH responses to the peptide. In the four patients with secondary GH deficiency, three had plasma GH response to hpGRF administration but one patient, who had indications of pituitary disorder, did not show any plasma GH response to either single iv injection or repetitive administrations of hpGRF-44. These data show that repetitive administrations of hpGRF-44 can induce plasma GH responses in some GH deficient patients who do not respond to a single iv bolus of the peptide.     

Synthetic human pancreatic growth hormone releasing factor (GRF) stimulates growth hormone secretion in the domestic fowl (Gallus domesticus)

Synthetic human pancreatic Growth Hormone-Releasing Factor (hpGRF) elevated the plasma concentration of growth hormone (GH) in young and adult domestic fowl. This in vivo effect of hpGRF appeared to be largely similar for both the 32 amino-acid (hpGRF 1-32) or 40 amino-acid (hpGRF 1-40) polypeptide, although the effect of hpGRF 1-32 was more prolonged than that of hpGRF 1-40 in adult domestic fowl. The increase in plasma GH concentrations following hpGRF administration (10 micrograms/kg) was somewhat greater in young than adult chickens (the increase in plasma concentration of GH being 230 ng/ml at 1 week old, 282 ng/ml at 6 week old, 241 ng/ml at 10 weeks and 150 ng/ml in adults). In the adult domestic fowl hpGRF stimulated a greater increase in the plasma concentration of GH than did thyrotropin-releasing hormone (TRH). However in the young chicks TRH was more active. The in vitro release of GH from dispersed chicken pituitary cells was elevated by hpGRF (1-32) and hpGRF (1-40).     

Ectopic corticotrophin-releasing-factor and growth hormone releasing factor secretion: diagnosis using human pituitary cell culture

Cell culture of human pituitary tissue has been used to diagnose a patient with Cushing's syndrome due to ectopic secretion of corticotrophin-releasing factor (CRF; case 1) and a case of acromegaly associated with ectopic secretion of a growth-hormone releasing factor (GRF; case 2). In both patients a pituitary tumour was not detected. Case 1 had a small cell carcinoma and symptoms of the ectopic ACTH syndrome, but in culture the carcinoma failed to secrete detectable ACTH. However, the culture medium used to maintain this carcinoma in vitro was found to contain a substance which stimulated ACTH secretion by human pituitary corticotrophs in cell culture. Radioimmunoassays and HPLC indicated that this substance had similar elution characteristics to human CRF and cross-reacted with antiserum to ovine CRF. Case 2 was found to have a lung tumour, the removal of which led to regression of her acromegalic symptoms. In culture, this tumour did not secrete GH, but did secrete a GRF. We conclude that the Cushing's syndrome and acromegaly, in cases 1 and 2, respectively, were due to ectopic secretion of CRF and GRF leading to hyperstimulation of the pituitary gland.     

Characterization of growth hormone releasing factor analog expression in Saccharomyces cerevisiae.

An analog of growth hormone releasing factor (GRF), [Leu27]GRF(1-40)-OH, has been expressed and secreted in Saccharomyces cerevisiae under the control of the alpha-factor gene promoter and prepro sequence. A single pair of consecutive basic residues served as a processing site between the alpha-factor sequences and the GRF sequences. [Leu27]GRF(1-40)-OH from fermentor broth containing 20-30 mg/L of immunoreactive peptides was shown to be correctly processed and to possess biological activity as measured in vitro and in vivo. Additional peptides purified from broth appear to result from proteolytic degradation of the original translation product. Analysis of the amino acid compositions and sequences of these peptides suggests that processing enzymes may be responsible for some of the degradation.     

Isolation and characterization of the porcine hypothalamic growth hormone releasing factor

A 44 amino acid peptide with high intrinsic growth hormone releasing activity was isolated from 2500 porcine hypothalami by means of acid extraction, immunoaffinity chromatography, gel filtration, and 2 steps of reverse phase HPLC. The growth hormone releasing factor was structurally characterized by gas phase sequence analyses of the intact peptide and its carboxyl terminal cyanogen bromide digestion fragment. Reverse phase liquid chromatography of the native peptide and synthetic replicates showed that the molecule possesses an amide rather than a free acid at its carboxyl terminus. The structure of the peptide was established as: Tyr-Ala-Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Met-Ser-Arg-Gln-Gln-Gly-Glu-Arg-Asn-Gln-Glu-Gln-Gly-Ala-Arg-Val-Arg-Leu-NH2 using approximately 6 nmol of material.     

Increased growth hormone responses to growth hormone releasing hormone and thyrotropin releasing hormone in patients with metastatic testicular cancer

In 16 patients with metastatic testicular cancer and 10 age matched male control subjects growth hormone (GH) responses to growth hormone releasing hormone (GHRH; 1 microgram/kg body weight iv.) and thyrotropin releasing hormone (TRH; 200 micrograms iv.) were measured. Basal GH levels and GH levels following stimulation with GHRH or TRH were significantly increased in cancer patients compared to control subjects. 9 patients with testicular cancer were studied both in the stage of metastatic disease and after they had reached a complete remission. In complete remission GH responses to GHRH tended to decrease but the differences did not reach statistical significance. Our data suggest an alteration of hypothalamic and/or pituitary regulation of GH secretion in patients with metastatic testicular cancer.