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.     

Plasma growth hormone secretion during constant growth hormone-releasing factor infusion

Synthetic human pancreatic growth hormone-releasing factor (hpGRF-44) was infused intravenously at a constant rate of 2.5 micrograms/min for 180 minutes in 3 normal boys of short stature. Plasma GH levels reached a peak at 60-120 min with a mean value (+/- SEM) of 69.1 +/- 14.3 ng/ml, and then, declined gradually in spite of continuous hpGRF-44 infusion up to 180 minutes. Similarly, constant infusion of hpGRF-44 at a rate of 2.5 micrograms/min in 5 normal but short boys for 90 minutes, together with an iv bolus injection of hpGRF-44 (2 micrograms/kg) administered at 0 and 90 minutes, elicited a prompt rise in plasma GH 15-30 minutes after the first bolus but no significant elevation of GH was observed after the second bolus. In contrast, when two iv bolus injections of hpGRF-44 (2 micrograms/kg) were given in 4 normal boys with short stature at 0 and 90 minutes, respectively, significant elevation of plasma GH was found after each bolus. These results suggest that under constant infusion of GRF the pituitary experiences a down-regulation after the initial peak of GH response, possibly due to desensitization to GRF.     

Plasma growth hormone, insulin-like growth factor-I, and milk production responses to exogenous human growth hormone-releasing factor analogs in dairy cows

Responses of plasma growth hormone (GH) and insulin-like growth factor-I (IGF-I), and milk production to subcutaneous (sc) injection(s) of two synthetic human growth hormone-releasing factor (hGRF) analogs were studied in dairy cows. Two mg of each hGRF analog dissolved in 5 ml saline per cow were injected into the shoulder area of each experimental animal, and jugular venous blood samples were collected via an indwelling catheter or by venipuncture. Plasma GH and IGF-I concentrations were measured by radioimmunoassay methods. In dry cows, the mean concentration of plasma GH after a single sc injection of hGRF analogs rose to 22.0-28.3 ng/ml at about 5 h from 1.4-1.7 ng/ml at 0 h (just before injection), and returned to the level before injection after 10-12 h. On the other hand, the plasma IGF-I began to increase after a lag of 4-6 h following a single injection of hGRF analogs, and reached maximum values of 71.1-89.4 ng/ml at 20 h from 43.7-46.4 ng/ml at 0 h. The IGF-I concentration at 24 h after a single injection of hGRF analogs was still higher than the value for the dry cows given saline. In lactating cows, the plasma concentration of GH at 2 h after daily sc injections of hGRF analogs during 14 consecutive days (an injection period) was higher than those for the lactating cows which received saline. Also, during the injection period, the concentration of IGF-I was higher in the lactating cows which received hGRF analog injections than in the cows which received saline injections. During the last 7 days of the injection period, the administration of hGRF analogs increased the mean milk yield by 11-19% in comparison with those for the saline injected cows. A positive correlation was observed between the mean plasma IGF-I concentration and the mean milk yield in the lactating cows treated with hGRF analogs throughout the injection and a postinjection (11 consecutive days after cessation of hGRF analog injection) periods. The results demonstrate that a single sc injection of hGRF analogs stimulates both GH release and the circulating level of IGF-I in dry cows, and that daily sc injections of hGRF analogs over 14 days enhance milk production, and plasma GH and IGF-I levels in lactating cows.     

Plasma growth hormone (GH) response to GH-releasing factor (SM-8144) in children of short stature and patients with GH deficiency

Synthetic human GRF (hGRF (1-44) NH2; SM-8144) was administered as an iv bolus to 141 normal children of short stature (NSC), 73 patients with severe idiopathic GH deficiency (IGD; group A), 30 patients with mild idiopathic GH deficiency (IGD; group B), 29 patients with secondary GH deficiency, 3 patients with primary hypothyroidism, 21 patients with Turner's syndrome and 25 patients with various other disease. Their height was below normal for their age and sex, and they were all below 25 years old without obesity. The maximal GH responses (M+SEM) were 39.5 +/- 2.2, 7.2 +/- 0.9, 27.2 +/- 3.7, 5.2 +/- 0.8, 9.7 +/- 4.4, 25.1 +/- 2.8 and 32.3 +/- 4.8 ng/ml, respectively (significance from the NSC, ; p less than 0.05, ; p less than 0.001). The GH responses to hGRF were greater than those elicited by standard pharmacological tests. There was a negative correlation between bone age and peak plasma GH response to hGRF in patients with idiopathic GH deficiency (IGD) but not in normal children (NSC). In twenty-two percent of the patients with IGD in group A the response was above 10 ng/ml and in 57% of the patients with IGD in group B the response was above 20 ng/ml, suggesting that a large percentage of patients with idiopathic GH deficiency lack hypothalamic GRF. The side effect of flushing was observed in 15.2% of all subjects. These results indicate the potential usefulness of hGRF (1-44) NH2 (SM-8144) in inducing GH release from the pituitary.     

Interactions between growth hormone-releasing hormone and glucocorticoids in male rats

While chronic glucocorticoid treatment increases pituitary growth hormone (GH) content in rats and primates and increases pituitary GH release in response to growth hormone-releasing hormone (GHRH) in rats, it also inhibits somatic growth. We investigated these opposite actions in rats using the synthetic glucocorticoid dexamethasone. Seven days of dexamethasone treatment (40 micrograms/animal per day) did not alter the frequency of spontaneous GH pulses in conscious, freely-moving animals. The amplitude of the GH pulses in saline and dexamethasone-treated rats was different (P less than 0.01), the latter group having a higher incidence of GH levels less than 95 ng/ml, a lower incidence of GH levels between 96 and 251 ng/ml, and a higher incidence of GH values greater than 480 ng/ml. A 20 microgram/kg per day dose of dexamethasone was sufficient to significantly inhibit growth but was inadequate in enhancing the GH response to an acute injection of GHRH in anesthetized animals. These results support the concept that glucocorticoids exert their catabolic effects on somatic growth in peripheral tissues and not at the pituitary level.     

Human growth hormone-releasing hormone (hGH-RH; hGRF) treatment of four patients with GH deficiency

Four patients with GH deficiency aged 6-14 years old were treated with hGRF for 6 months. Before the treatment maximal plasma GH responses to 50 micrograms iv hGRF administration were 48.6, 12.1, 24.3 and 13.0 ng/ml, respectively. Human GRF was administered at a dosage of 50-100 micrograms twice a day subcutaneously. In two patients, the growth rate was increased from 2.4 and 2.0 cm/year to 8.2 and 9.8 cm/year, respectively. In the other two patients, the growth rate did not change with hGRF treatment. Plasma somatomedin C levels increased in one patient but did not change in the other three. Antibody to hGRF was observed in two patients during the treatment, but the presence of antibody did not affect the growth rate.     

Continuous infusion of GnRH reduces the LH response to an intravenous GnRH injection but does not inhibit endogenous LH secretion in cows

Plasma LH concentrations were monitored in 6 Hereford X Friesian suckled cows at about 80 days post partum, before and during a 14-day period of continuous s.c. infusion of GnRH (20 micrograms/h). Blood samples were collected at 10-min intervals on Days -2, -1, 1, 2, 3, 4, 7, 10, 13 and 14 (Day 1 = start of infusion). Plasma LH concentrations rose from mean pretreatment levels of 1.3 +/- 0.20 ng/ml to a maximum of 17.1 +/- 3.09 ng/ml within the first 8 h of GnRH infusion, but returned to pretreatment levels by Day 2 or 3. In 4/6 animals, the initial increase was of a magnitude characteristic of the preovulatory LH surge. In all animals, an i.v. injection of 10 micrograms GnRH, given before the start and again on the 14th day of continuous infusion, induced an increase in LH concentrations but the increase to the second injection was significantly (P less than 0.01) less (mean max. conc. 6.4 +/- 0.76 and 2.3 +/- 0.19 ng/ml). Mean LH concentrations (1.0 +/- 0.08, 1.1 +/- 0.08 and 0.9 +/- 0.06 ng/ml) and LH episode frequencies (3.3,4.3 and 3.2 episodes/6 h) did not differ significantly on Days -2,7 and 13. However, the mean amplitude of LH episodes was significantly lower (P less than 0.05) on Day 13 (1.3 +/- 0.10 ng/ml) than on Day -2 (1.8 +/- 0.16 ng/ml). Therefore, although the elevation in plasma LH concentrations that occurs in response to continuous administration of GnRH is short-lived and LH levels return to pre-infusion values within 48 h of the start of infusion, these results show that the pituitary is still capable of responding to exogenous GnRH, although the LH response to an i.v. bolus injection of GnRH is reduced. In addition, this change in pituitary sensitivity is not fully reflected in endogenous patterns of episodic LH secretion.     

Growth hormone response of bull calves to growth hormone-releasing factor

Three experiments were conducted to determine serum growth hormone (GH) response of bull calves (N = 4; 83 kg body wt) to iv injections and infusions of human pancreatic GH-releasing factor 1-40-OH (hpGRF). Peak GH responses to 0, 2.5, 10, and 40 micrograms hpGRF/100 kg body wt were 7 +/- 3, 8 +/- 3, 18 +/- 7, and 107 +/- 55 (mean peak height +/- SEM) ng/ml serum, respectively. Only the response to the 40-microgram dose was greater (P less than 0.05) than the 0-microgram dose. Concentrations of prolactin in serum were not affected by hpGRF treatment. In calves injected with hpGRF (20 micrograms/100 kg body wt) at 6-hr intervals for 48 hr, GH increased from a mean preinjection value of 3.1 ng/ml serum to a mean peak response value of 70 ng/ml serum. Differences in peak GH response between times of injection existed within individual calves (e.g., 10.5 ng/ml vs 184.5 ng/ml serum). Concentrations of GH in calves infused continuously with either 0 or 200 micrograms hpGRF/hr for 6 hr averaged 7.4 +/- 3 and 36.5 +/- 11 ng/ml serum, respectively (P less than 0.05). Concentrations of GH oscillated markedly in hpGRF-infused calves, but oscillations were asynchronous among calves. We conclude that GH response of bull calves to hpGRF is dose dependent and that repeated injections or continuous infusions of hpGRF elicit GH release, although magnitude of response varies considerably. We hypothesize that differences in GH response to hpGRF within and among calves, and pulsatile secretion in the face of hpGRF infusion may be related to the degree of synchrony among exogenous hpGRF and endogenous GRF and somatostatin.     

Generation of growth hormone pulsatility in women: evidence against somatostatin withdrawal as pulse initiator

To test whether endogenous hypothalamic somatostatin (SRIH) fluctuations are playing a role in the generation of growth hormone (GH) pulses, continuous subcutaneous octreotide infusion (16 microg/h) was used to create constant supraphysiological somatostatinergic tone. Six healthy postmenopausal women (age 67 +/- 3 yr, body mass index 24.7 +/- 1.2 kg/m(2)) were studied during normal saline and octreotide infusion providing stable plasma octreotide levels of 2,567 +/- 37 pg/ml. Blood samples were obtained every 10 min for 24 h, and plasma GH was measured with a sensitive chemiluminometric assay. Octreotide infusion suppressed 24-h mean GH by 84 +/- 3% (P = 0.00026), GH pulse amplitude by 90 +/- 3% (P = 0.00031), and trough GH by 54 +/- 5% (P = 0.0012), whereas GH pulse frequency remained unchanged. The response of GH to GH-releasing hormone (GHRH) was not suppressed, and the GH response to GH-releasing peptide-6 (GHRP-6) was unaffected. We conclude that, in women, periodic declines in hypothalamic SRIH secretion are not the driving force of endogenous GH pulses, which are most likely due to episodic release of GHRH and/or the endogenous GHRP-like ligand.     

Pituitary receptors for gonadotropin-releasing hormone in relation to changes in pituitary and plasma luteinizing hormone in ovariectomized-hypothalamo pituitary disconnected ewes. I. Effect of changing frequency of gonadotropin-releasing hormone pulses

Studies were undertaken to determine if changes in the amplitude of luteinizing hormone (LH) pulses that occur in response to changes in the frequency of gonadotropin-releasing hormone (GnRH) pulses are due to an alteration in the number of GnRH receptors. Ewes were ovariectomized (OVX) and the hypothalamus was disconnected from the pituitary (HPD). Ewes were then given pulses of GnRH at a frequency of 1/h or 1/3 h. Two control groups were included: OVX ewes not subjected to HPD, and HPD ewes that were not OVX. At the end of one week of treatment, blood samples were collected to determine the amplitude of LH pulses. The treated ewes were killed just before the next scheduled pulse of GnRH, and the content of LH and number of GnRH receptors were measured in each pituitary. The amplitude of LH pulses was highly correlated with the amount of LH in the pituitary gland (r = 0.71, p less than 0.01), and both LH content and pulse amplitude (mean + SEM) were higher in ewes receiving GnRH once per 3 h (189.7 +/- 39.3 microgram/pituitary, 10.3 +/- 1.1 ng/ml, respectively) than in ewes receiving GnRH once per h (77.8 +/- 11.4 microgram/pituitary, 5.2 +/- 1.3 ng/ml). The pituitary content of LH was highest in the OVX ewes (260.2 +/- 57.4 micrograms/pituitary) and lowest in the nonpulsed HPD ewes (61.7 +/- 51.2 micrograms/pituitary). The number of GnRH receptors was similar in all groups, and was not correlated with any other variable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma GH and somatomedin C responses to single and repeated administrations of human growth hormone releasing factor (hGRF)

Plasma growth hormone (GH) and somatomedin C responses to single and repeated administrations of synthetic human growth hormone releasing factor (hGRF-44) were studied in 29 patients with GH deficiency. hGRF-44 administered by single iv bolus (10 micrograms/kg), repeated iv boluses (50 or 100 micrograms, once a day), repeated iv infusions (2.5 micrograms/min for 90 min, once a day), and/or repeated im injections (100 micrograms, twice a day) for three to six consecutive days. Ten of 16 patients had plasma GH responses to a single iv bolus injection, i.e., their plasma GH increased above 5 ng/ml or twice the basal level. However none of them showed a plasma somatomedin C increase. To repeated iv bolus injections and repeated iv infusions of hGRF-44, 7 of 17 patients showed plasma GH responses, however in none of 7 patients did somatomedin C increase. Plasma somatomedin C did not increase after repeated im administrations of hGRF-44 for 5 days. Plasma somatomedin C increase was observed in two patients, from 0.32 to 0.54 U/ml and from 0.16 to 0.46 U/ml, in response to repeated iv boluses and repeated iv infusions, respectively. These results suggest that hGRF-44 stimulates plasma GH secretion in some patients with GH deficiency, however the increases are not enough to stimulate somatomedin generation.     

Effect of synthetic ovine corticotropin-releasing factor on growth hormone secretion in patients with acromegaly

In a significant proportion of patients with acromegaly, a non-specific increase in plasma growth hormone (GH) has been recognized following administration of thyrotropin-releasing hormone (TRH) or luteinizing hormone-releasing hormone (LH-RH), probably due to the lack of the specificity of the receptor in their tumor cells. In this study, the effects of corticotropin-releasing factor (CRF), a newly isolated hypothalamic hormone, in addition to TRH and LH-RH, on plasma levels of GH and the other anterior pituitary hormones were evaluated in 6 patients with acromegaly. Synthetic ovine CRF (1.0 microgram/kg), TRH (500 micrograms) or LH-RH (100 micrograms) was given as an iv bolus injection, in the morning after an overnight fast. Blood specimens were taken before and after injection at intervals up to 120 min, and plasma GH, adrenocorticotropin (ACTH), thyrotropin, prolactin, luteinizing hormone, follicle-stimulating hormone and cortisol were assayed by radioimmunoassays. A non-specific rise in plasma GH was demonstrated following injection of TRH and LH-RH, in 5 of 6 and 2 of 5 patients, respectively. In all subjects, rapid rises were observed in both plasma ACTH (34.3 +/- 6.2 pg/ml at 0 min to 79.5 +/- 9.5 pg/ml at 30 min, mean +/- SEM) and cortisol level (9.1 +/- 1.3 micrograms/dl at 0 min to 23.4 +/- 1.2 micrograms/dl at 90 min). However, plasma levels of GH and the other anterior pituitary hormones did not change significantly after CRF injection. These results indicate that CRF specifically stimulates ACTH secretion and any non-specific response of GH to CRF appears to be an infrequent phenomenon in this disorder.     

Naloxone evokes large-amplitude GnRH pulses in luteal-phase ewes

Ewes were sampled during the mid-late luteal phase of the oestrous cycle. Hypophysial portal and jugular venous blood samples were collected at 5-10 min intervals for a minimum of 3 h, before i.v. infusions of saline (12 ml/h; N = 6) or naloxone (40 mg/h; N = 6) for 2 h. During the 2-h saline infusion 2/6 sheep exhibited a GnRH/LH pulse; 3/6 saline infused ewes did not show a pulse during the 6-8-h portal blood sampling period. In contrast, large amplitude GnRH/LH pulses were observed during naloxone treatment in 5/6 ewes. The mean (+/- s.e.m.) amplitude of the LH secretory episodes during the naloxone infusion (1.07 +/- 0.11 ng/ml) was significantly (P less than 0.05) greater than that before the infusion in the same sheep (0.54 +/- 0.15 ng/ml). Naloxone significantly (P less than 0.005) increased the mean GnRH pulse amplitude in the 5/6 responding ewes from a pre-infusion value of 0.99 +/- 0.22 pg/min to 4.39 +/- 1.10 pg/min during infusion. This episodic GnRH secretory rate during naloxone treatment was also significantly (P less than 0.05) greater than in the saline-infused sheep (1.53 +/- 0.28 pg/min). Plasma FSH and prolactin concentrations did not change in response to the opiate antagonist. Perturbation of the endogenous opioid peptide system in the ewe by naloxone therefore increases the secretion of hypothalamic GnRH into the hypophysial portal vasculature. The response is characterized by a large-amplitude GnRH pulse which, in turn, causes a large-amplitude pulse of LH to be released by the pituitary gland.     

Effect of FSH on ovarian inhibin secretion in anoestrous ewes

In Exp. 1, 7 Finn-Merino ewes which had one ovary autotransplanted to a site in the neck had jugular and timed ovarian venous blood samples collected at 10-min intervals for 2 h before and 3 h after injection of 5 micrograms NIAMDD-oFSH-S16. In Exp. 2, 8 Finn-Merino ewes with ovarian autotransplants had jugular and timed ovarian venous blood samples collected at 15-min intervals for 2 h before and 12 h after bolus injection of 40 micrograms NIAMDD-oFSH-S16 and infusion of oFSH-S16 at 6 micrograms/min for 4 h. In Exp. 2 the follicular population of the ovary was assessed by real-time ultrasound at the beginning and end of the experimental period. In both experiments the secretion rates of inhibin (1-3 ng/min) and oestradiol (0.5-8 ng/min) were similar to those observed during the luteal phase of the cycle in the breeding season, indicating significant follicular development in these animals. In Exp. 1 there was no change in the secretion of oestradiol or inhibin after the injection of FSH which resulted in a 25% increase (P less than 0.05) in the concentration of FSH in plasma. Inhibin secretion was pulsatile but there was no difference in inhibin pulse frequency before (1.6 +/- 0.2 pulses/h) or after (1.2 +/- 0.5 pulses/h) injection of FSH. In Exp. 2 injection of FSH resulted in an increase (P less than 0.001) in plasma concentrations of FSH in the sample taken 10 min after injection from a baseline of 1.2 +/- 0.2 ng/ml to a peak of 10.6 +/- 1.0 ng/ml (mean +/- s.e.m.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Intranasal administration of His-D-Trp-Ala-Trp-D-Phe-LysNH2 (growth hormone releasing peptide) increased plasma growth hormone and insulin-like growth factor-I levels in normal men

The effects of intranasal and iv administration of His-D-Trp-Ala-Trp-D-Phe-LysNH2 (GHRP) on plasma GH, PRL, LH, FSH, TSH, cortisol, insulin, IGF-I as well as GHRH-like immunoreactivity (LI) levels were examined in 6 healthy male subjects. An iv bolus injection of GHRP(1 micrograms/kg BW) caused a remarkable increase in plasma GH levels with a mean (+/- SE) peak of 54.9 +/- 4.2-micrograms/L. In addition an intranasal administration of GHRP resulted in a significant, dose-related increase in plasma GH with peaks of 39.6 +/- 15.3 micrograms/L at a dose of 30 micrograms/kg BW, 14.1 +/- 5.0 micrograms/L at 15 micrograms/kg BW and 7.5 +/- 5.7 micrograms/L at 5 microgram/kg BW. Plasma PRL and cortisol levels were slightly but significantly increased after iv administration of GHRP, whereas GHRP totally failed to affect plasma TSH, LH, FSH, insulin, blood sugar and GHRH-LI levels. Seven consecutive, intranasal administrations of 15 micrograms/kg BW GHRP every 8h were well tolerated in all subjects examined. During this treatment, GH responsiveness to GHRP was not attenuated by desensitization and plasma IGF-I was increased from 94.5 +/- 5.8 micrograms/L before GHRP to 125.8 +/- 6.0 micrograms/L after repeated GHRP administration. These findings indicate that intranasal administration of GHRP stimulates GH secretion and consequently enhances IGF-I production in normal subjects. If GHRP is demonstrated to be beneficial in the treatment of some patients with GH deficiency, the intranasal route of administration may be more useful than the painful injection because a prolonged period is required for the treatment.     

Acute effects of clonidine and growth-hormone-releasing hormone on growth hormone secretion in patients with hyperthyroidism

Patients with hyperthyroidism have reduced growth hormone (GH) responses to pharmacological stimuli and reduced spontaneous nocturnal GH secretion. The stimulatory effect of clonidine on GH secretion has been suggested to depend on an enhancement of hypothalamic GH-releasing hormone (GHRH) release. The aim of our study was to evaluate the effects of clonidine and GHRH on GH secretion in patients with hyperthyroidism. Eight hyperthyroid females with recent diagnosis of Graves' disease (age range 20-55 years, body mass index range 19.2-26.2 kg/m2) and 6 healthy female volunteers (age range 22-35 years, body mass index range 19-25 kg/m2) underwent two experimental trials at no less than 7-day intervals: (a) an intravenous infusion of clonidine 150 micrograms in 10 ml of saline, or (b) a bolus intravenous injection of human GHRH (1-29)NH2, 100 micrograms in 1 ml of saline. Hyperthyroid patients showed blunted GH peaks after clonidine (7.1 +/- 1.7 micrograms/l) as compared to normal subjects receiving clonidine (28.5 +/- 4.9 micrograms/l, p less than 0.05). GH peaks after GHRH were also significantly lower in hyperthyroid subjects (8.0 +/- 1.7 micrograms/l) as compared to normal subjects receiving GHRH (27.5 +/- 4.4 micrograms/l, p less than 0.05). No significant differences in the GH values either after clonidine or GHRH were observed in the two groups of subjects examined. Our data demonstrate that the GH responses to clonidine as well as to GHRH in patients with hyperthyroidism are inhibited in a similar fashion with respect to normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pyridostigmine enhances even if it does not normalize the growth hormone responses to growth hormone-releasing hormone in patients with Cushing's disease.

Subjects with Cushing's disease have diminished growth hormone (GH) response to growth hormone-releasing hormone (GHRH). The aim of our study was to investigate the underlying mechanism of this diminished GH response in these patients using pyridostigmine (PD), an acetylcholinesterase inhibitor, which is reported to increase GH secretion by reducing somatostatin tone. Eight subjects with untreated Cushing's disease (caused by a pituitary adenoma) and 6 control subjects received GHRH 100 micrograms in 1 ml of saline, as intravenous bolus injection 60 min after (1) placebo (2 tablets, p.o.) or (2) PD (120 mg, p.o.). After GHRH plus placebo, the GH peak (mean +/- SEM) was significantly lower in subjects with Cushing's disease (2.4 +/- 0.5 micrograms/l) compared to control subjects (25.1 +/- 1.8 micrograms/l, p less than 0.05). After GHRH plus PD, the GH peak was significantly enhanced both in subjects with Cushing's disease (7.1 +/- 2.3 micrograms/l, p less than 0.05) and in control subjects (42.3 +/- 4.3 micrograms/l, p less than 0.05). In patients with Cushing's disease, the GH response to GHRH plus PD was lower with respect to the GH response to GHRH alone in normal subjects. We conclude that hypercortisolism may cause a decrease in central cholinergic tone which is in turn hypothesized to be responsible of an enhanced somatostatin release from the hypothalamus. However, other metabolic or central nervous system alterations may act synergistically with hypercortisolism in causing GH inhibition in patients with Cushing's disease.     

Atrial natriuretic factor inhibits the CRH-stimulated secretion of ACTH and cortisol in man.

Corticotrophic secretion of ACTH is stimulated by corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), and suppressed by glucocorticoids. In vitro and preclinical studies suggest that atrial natriuretic factor (ANF) may be a peptidergic inhibitor of pituitary-adrenocortical activity. The aim of this study was to elucidate a possible role of ANF as a modulator of ACTH release in humans. A bolus injection of 100 micrograms human CRH (hCRH) during a 30 min intravenous infusion of 5 micrograms/min human alpha atrial natriuretic factor (h alpha ANF) was administered at 19:00 to six healthy male volunteers. In comparison to saline, a blunted CRH-stimulated secretion of ACTH (mean maximum plasma level +/- SD 45 min after hCRH: saline 46.2 +/- 14.2 pg/ml, h alpha ANF 34.6 +/- 13.8 pg/ml, p-value = 0.007) and a delayed rise (10 min) in cortisol were detected. The maximum plasma cortisol levels remained nearly unchanged between saline and h alpha ANF administration (mean maximum plasma level +/- SD 60 min after hCRH: saline 182 +/- 26 ng/ml, h alpha ANF 166 +/- 54 ng/ml). No effects of h alpha ANF on basal cortisol levels were observed; in contrast, basal ACTH plasma levels were slightly reduced. Basal blood pressure and heart rate remained unaffected. In the control experiment, infusion of 3 IU AVP in the same experimental paradigm increased basal and stimulated ACTH and cortisol levels significantly in comparison to saline. These observations suggest that intravenously administered haANF inhibits the CRH-stimulated release of ACTH in man.     

Comparative effect of galanin and pyridostigmine on the growth hormone response to growth hormone-releasing hormone in normal aged subjects.

The aim of our study was to investigate the effects of aging on the growth hormone (GH) response to growth hormone-releasing hormone (GHRH) alone and in combination with either the neuropeptide galanin or the acetylcholinesterase inhibitor pyridostigmine (PD) in normal subjects. In protocol 1 (GHRH/galanin), 9 old healthy volunteers, ranging in age from 68 to 97 years, and 6 young subjects, ranging in age from 25 to 31 years, received: (a) human GHRH (1-29)NH2, 100 micrograms in 1 ml saline, as an intravenous bolus, and (b) porcine galanin, 500 micrograms in 100 ml saline, as an intravenous infusion from -10 to 30 min combined with GHRH, 100 micrograms i.v. at time 0. In protocol 2 (GHRH/PD), 14 old healthy volunteers, ranging in age from 65 to 91 years, and 11 young subjects, ranging in age from 19 to 34 years, received: (a) GHRH (1-29)NH2, 100 micrograms in 1 ml saline, as an intravenous bolus, and (b) PD, 120 mg administered per os 60 min before GHRH, 100 micrograms as an intravenous bolus. Blood samples for GH were drawn at -75, -60 (time of PD administration), -45, -30, -15, -10 (time of beginning of galanin infusion), 0 (time of GHRH injection), 15, 30, 45, 60, 90, and 120 min. The GH response to GHRH was significantly (< 0.05) enhanced either by galanin or PD pretreatment both in young and old subjects. However, the GH response to GHRH alone or combined with either galanin or PD was significantly greater in the young subjects as compared to the old subjects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of gonadotropin-releasing hormone pulse amplitude, frequency, and treatment duration on the regulation of luteinizing hormone (LH) subunit messenger ribonucleic acids and LH secretion

The effects of GnRH pulse amplitude, frequency, and treatment duration on pituitary alpha and LH beta subunit mRNA concentrations were examined in castrate-testosterone replaced male rats. Experimental groups received iv GnRH pulses (5, 25, or 125 ng) at 7.5-, 30-, or 120-min intervals for 8, 24, or 48 h. Saline pulses were given to control rats. Acute LH secretion was measured in blood drawn before and 20 min after the last GnRH pulse. In saline controls, alpha and LH beta mRNAs (150 +/- 14, 23 +/- 2 pg cDNA bound/100 micrograms pituitary DNA) fell to 129 +/- 14 and 18 +/- 2, respectively, after 48 h. In animals receiving GnRH pulses (7.5-min intervals), the 125-ng dose stimulated a slight increase (P less than 0.01) in alpha mRNA levels after 8 and 24 h and both LH subunit mRNAs were increased by the 25- and 125-ng doses after 48 h. The 30-min pulse interval injections (25- and 125-ng doses) increased LH beta mRNA levels after 8 h, but alpha mRNAs were not elevated until after 24 h. Maximum (3-fold) increases in alpha and LH beta mRNAs were seen in rats receiving 25-ng pulses every 30 min for 48 h. Using 120-min pulses, LH subunit mRNAs were not increased by any GnRH dose through 48 h. Acute LH release was not seen in rats receiving 5 ng GnRH pulses at any pulse interval.(ABSTRACT TRUNCATED AT 250 WORDS)