Effect of intraventricular administration of anti-somatostatin gamma-globulin on the lethal dose-50 of strychnine and pentobarbital in rats

Effects of intraventricular injection of sheep anti-somatostatin gamma-globulin (anti-SSG) on strychnine-induced seizures, strychnine LD50, and pentobarbital LD50 were examined in male rats under light ether anesthesia. Ten microliters of anti-SSG given 2 h earlier significantly decreased the duration of strychnine-induced seizures as compared with that in the control rats pretreated with normal sheep gamma-globulin (NSG). This effect of anti-SSG seemed to be specific, as there was no difference in seizure duration between sheep anti-LHRH gamma-globulin (anti-LHRHG)- and NSG-pretreated rats. Survival rates in anti-SSG-pretreated rats after injection of strychnine and pentobarbital were significantly larger (P less than 0.01 and P less than 0.05, respectively) than those in the control rats receiving NSG. The administration of anti-SSG resulted in 26.7% and 22.9% increases in the LD50 of strychnine and pentobarbital, respectively. These results indicate that endogenous somatostatin in the cerebrospinal fluids and/or the periventricular tissue nodulates the response of the central nervous system to strychnine and pentobarbital in rats.

Effects of thyrotropin-releasing hormone on sleep and sleep-related growth hormone release in normal subjects

Effects of TRH on sleep and sleep-related growth hormone (GH) release were examined in four normal volunteers. A bolus of 500 microgram of synthetic TRH was injected iv at the onset of sleep, followed by continuous iv infusion of 1000 microgram of TRH dissolved in saline for 3 h on two nights. Saline alone was infused on two control nights in each of these subjects. Polygraphic sleep records showed that TRH transiently interrupted sleep on both nights in all of the four subjects. The arousal phenomenon was observed from 80 to 151 min after the start of TRH administration until 20 to 212 min after the end of TRH infusion. The mean (+/-SE) percentage of awakening on the nights of TRH administration was significantly larger than on the control nights (36.4 +/- 1.9% vs. 1.3 +/- 0.8%, P less than 0.001). Plasma GH increased in close relationship to the initial appearance of slow wave sleep (SWS) within 40 min after sleep onset on both control nights in all four subjects. On nights of TRH administration, however, plasma GH levels during the initial 80 min of sleep were significantly lower (P less than 0.005) than on control nights, whereas SWS was demonstrated before the interruption of sleep. On nights when sleep was interrupted by forced wakefulness 1 h after sleep onset, plasma GH rose to levels comparable to those on control nights during early sleep periods in all subjects examined. These results suggest that TRH inhibits sleep and sleep-related GH release in normal subjects.

Growth hormone release by gamma-aminobutyric acid (GABA) and gamma-amino-beta-hydroxybutyric acid (GABOB) in the rat

Effects of gamma-aminobutyric acid (GABA) and gamma-amino-beta-hydroxybutyric acid (GABOB) on growth hormone (GH) release were investigated in the urethaneanesthetized male rat. An intraventricular injection of GABA and L-GABOB but not D-GABOB caused a significant increase in plasma GH. An intravenous injection of L-GABOB, at the dose which had no significant effect on basal plasma GH, remarkably enhanced plasma GH response to pentobarbital. These results suggest that GABA and L-GABOB stimulate GH release possibly via the central nervous system in the rat.

Sleep-related growth hormone release following 2-bromo-alpha-ergocriptine treatment in acromegalic patients

Plasma growth hormone (GH) concentrations were measured over 24 h in seven acromegalic patients before and during treatment with 2-bromo-alpha-ergocriptine (CB-154). Before treatment basal plasma GH levels were consistently elevated but no significant change was observed between the mean plasma GH levels during sleep and during waking in five of the seven patients examined. The daily administration of CB-154 (5 to 10 mg, orally) for 14 days resulted in a significant fall in the 24 h mean plasma GH levels in six of the seven patients. In all of the six patients who responded to CB-154 treatment, the mean plasma GH concentrations during sleep were significantly greater than during waking. Daytime sleep was associated with a significant rise in plasma GH in both of the two patients examined. It is concluded that CB-154 treatment resulted in a significant decrease in plasma GH levels with sleep-related increase in some acromegalics although the mechanism responsible for this sleep-related GH rise remains to be further investigated.

Effect of hypothalamic surgery on prolactin release induced by 5-hydroxytryptophan (5-HTP) in rats

Intravenous injections of varying doses of 5-HTP (1, 3 and 5 mg/100 g body wt), a precursor of serotonin, caused a significant and dose-related increase in plasma prolactin concentrations in urethane-anesthetized rats. Increases in plasma prolactin concentrations caused by 5-HTP (1 mg/100 g body wt iv) were abolished by the concomitant administration of L-DOPA (2 mg/100 g body wt iv). Plasma prolactin levels were also significantly elevated following the injection of 5-HTP in rats with complete hypothalamic deafferentation, whereas 5-HTP had no significant effect on plasma prolactin levels in rats with extensive hypothalamic ablation. These results suggest that 5-HTP causes prolactin secretion by stimulating the serotoninergic mechanism in the hypothalamus.

Suppression by thyrotropin-releasing hormone (TRH) of growth hormone release induced by arginine and insulin-induced hypoglycemia in man

Plasma growth hormone (GH) levels were significantly increased following L-arginine (30 g) infusion or insulin (0.1 U/kg body wt)-induced hypoglycemia in normal men. When synthetic thyrotropin-releasing hormone (TRH) (1 mg) was infused intravenously for 150 min, beginning 30 min before arginine or insulin administration, GH responses to arginine and insulin were significantly blunted with a mean (+/- SE) percentage inhibition of 80.1 +/- 8.8% and 30.6 +/- 10.3%, respectively. These results suggest a possible inhibitory effect of TRH on GH secretion in man.

Effects of hyperthyroidism and hypothyroidism on rat growth hormone release induced by thyrotropin-releasing hormone

The effect of synthetic thyrotropin-releasing hormone (TRH) on the release of growth hormone (GH) and thyroid-stimulating hormone (TSH) was investigated in euthyroid, hypothyroid, and hyperthyroid rats under urethane anesthesia. In euthyroid control rats, intravenous injection of TRH (200 ng/100 g BW) resulted in a significant increase in both plasma GH and TSH. In rats made hypothyroid by treatment with propylthiouracil or by thyroidectomy, basal GH and TSH levels were significantly elevated with exaggerated responses to TRH. In contrast, plasma GH and TSH responses to TRH were both significantly inhibited in rats made hyperthyroid by L-thyroxine (T4) treatment. These results suggest that altered thyroid status influences GH release as well as TSH secretion induced by TRH in rats.

Suppression by cyproheptadine of human growth hormone and cortisol secretion during sleep

The effect of cyproheptadine on plasma growth hormone and cortisol levels was studied in seven male volunteers with polygraphic sleep monitoring. Sleep-related growth hormone release was completely inhibited in three of the seven normal subjects by the intravenous infusion of cyproheptadine (5 mg) which was started at the onset of sleep. In the other four, growth hormone release during sleep was significantly decreased or delayed by cyproheptadine when the drug infusion was started at 7:00 p.m., 1-2 h before the onset of sleep. The usual increase in plasma cortisol in the early morning was completely suppressed in all five subjects given cyproheptadine infusions from 4:00 to 7:00 a.m. The intravenous infusion of cyproheptadine increased slow wave sleep, although the time from sleep onset to the first occurrence of slow wave sleep was not affected. In contrast, rapid eye movement sleep was significantly decreased by cyproheptadine. These results suggest that cyproheptadine inhibits growth hormone and ACTH secretion during sleep in man, possibly by antagonizing serotoninergic mechanisms although other actions of the drug are not ruled out.

Stimulating and inhibiting effects of thyrotropin-releasing hormone on growth hormone release in rats

The effect of thyrotropin-releasing hormone (TRH) on the mechanism regulating growth hormone (GH) secretion was investigated in urethane-anesthetized male rats. The iv injection of TRH (0.2 and 3 mug/100 g BW) caused a significant and dose-related increase in plasma GH. Greater GH responses to TRH were not obtained with doses of TRH larger than 5 mug/100 g BW. TRH injection also raised plasma GH in rats subjected to hypothalamic ablation, in which the maximum increments of plasma GH after TRH injection were greater than in control rats. Plasma GH responses to the iv injection of chlorpromazine (200 mug/100 g BW) were significantly augmented by the concomitant iv injection of TRH in a dose of 3 mug/100 g BW. However, a large dose of TRH (25 mug/100 g BW) injected with chlorpromazine caused a significantly smaller increase in plasma GH than did smaller doses of TRH (0.2 and 3 mug/100 g BW). TRH injection into the lateral ventricle (0.02 and 0.2 mug/100 g BW) inhibited significantly the GH release induced by chlorpromazine, whereas TRH (0.2 mug/100 g BW) alone caused only a slight increase in plasma GH. These results suggest that TRH may not only stimulate GH release by a direct action on the pituitary, but may also modify GH secretion by acting through the central nervous system.

Plasma prolactin responses to thyrotropin-releasing hormone in patients with breast cancer

Plasma human prolactin levels were measured by homologous radioimmunoassay in patients with primary breast cancer and in normal women of similar age. In normal controls mean (+/- SEM) basal plasma prolactin levels were 11.9 +/- 1.5 ng/ml and intravenous injection of synthetic thyrotropin-releasing hormone (TRH), 500 mug, caused a significant rise in plasma prolactin in all subjects examined with a maximum response of 52.6 +/- 3.3 ng/ml (mean +/- SEM). Markedly high plasma prolactin levels and exaggerated plasma prolactin responses to TRH were demonstrated in some patients with breast cancer. However, mean basal plasma prolactin levels and mean plasma prolactin increments following TRH in patients with breast cancer did not differ significantly from those in normal subjects. Plasma prolactin responses to TRH were slightly blunted during the administration of androgen in patients with breast cancer. These results suggest that some of the patients with primary breast cancer have abnormal prolactin secretion.

Growth hormone release following thyrotrophin-releasing hormone injection into patients with anorexia nervosa

The effect of thyrotrophin-releasing hormone (TRH) or luteinizing hormone-releasing hormone (LH-RH) on plasma levels of growth hormone (GH), prolactin (PRL), thyrotrophin (TSH), and luteinizing hormone (LHY, were studied in patients with anorexia nervosa. The basal plasma GH levels were elevated in 6 of 11 patients studied. Intravenous injection of synthetic TRH T500 mug) significantly raised the plasma GH levels in 9 of 11 patients. The peak values of plasma GH after TRH ranged from 6.0 to 31.5 ng/ml. Plasma GH concentrations also increased following the administration of synthetic LH-RH (100 mug) 1 of 7 patients. The intravenous injection of saline solution caused no significant change in plasma GH in these patients. The plasma LH responses to LH-RH were significantly blunted in all patients, whereas the plasma PRL and TSH responses to TRH were almost normal in the patients examined. These results suggest that the hypothalamo-pituitary function regulating GH and LH secretion is altered in patients with anorexia nervosa.

Suppressive effect of L-dopa on human prolactin release during sleep

Immunoreactive plasma human prolactin (HPr) and human growth hormone (HGH) concentrations were measured in six normal young men with polygraphic sleep monitoring during normal sleep and during sleep in which l-dihydroxyphenylalanine (l-DOPA) was infused intravenously at a rate of 0.8 to 1.0 mg/min. The intravenous infusion of l-DOPA significantly suppressed the episodic release of HPr during sleep and the occurrence of rapid eye movement (REM) sleep. However, HGH release during sleep was not remarkably influenced by l-DOPA. These results suggest that central catecholaminergic neural mechanisms are related to both sleep-related HPr release and REM sleep, but do not play an important role in sleep-related HGH release.

Effect of sulpiride on plasma prolactin in rats

I.v. injection of sulpiride (S; 0.5-20 mug/100 g b.w.) caused a significant and dose-related increase in plasma prolactin (Prl) levels in urethane-anesthetized rats, with peak values occuring 10 min after the injection. L-dopa administration (2 mg/100 g b.w., i.v.) significantly blunted plasma Prl response to S(1 mug/100 g b.w., i.v.). S injection (1 mug/rat) into a lateral ventricle also raised plasma Prl significantly. Hypothalamic destruction resulted in a prominent increase of basal plasma Prl, which increased further following the injection of S. These results suggest that S stimulates Prl secretion by its possible direct action on the anterior pituitary.

Stimulation of human prolactin secretion by sulpiride

Intramuscular injection of 100 mg of sulpiride significantly raised plasma human prolactin (hPRL) levels in all of 7 normal subjects examined. The mean (+SE) peak value was 78.0 +/- 16.6 ng/ml, which was observed 30 min after the injection. Daily administration of sulpiride (50 mg tid po) raised plasma hPRL levels in all 7 patients with peptic ulcer, with peak values obtained within 2 weeks. Lactation occurred in 2 of these patients. It is concluded that sulpiride stimulates hPRL secretion in man.

Suppression by thyrotropin-releasing hormone (TRH) of human growth hormone release induced by L-dopa

Oral administration of L-dopa (600 mg) significantly raised plasma human growth hormone (hGH) in 6 of 7 normal subjects examined. This L-dopa induced hGH release was significantly suppressed by the intravenous infusion of 1 mg of thyrotropin-releasing hormone (TRH). TRH administration alone had no significant effect on plasma hGH. In contrast, plasma human prolactin (hPRL) consistently increased following TRH infusion. L-dopa significantly lowered basal plasma hPRL levels and also significantly blunted TRH-induced hPRL release. These results suggest that TRH plays an inhibitory role in the regulation of hGH secretion in normal subjects, whereas it stimulates hPRL release.

Pasma growth hormone responses to thyrotropin-releasing hormone in the urethane-anesthetized rat

Intravenous injection of synthetic thyrotropin-releasing hormone (TRH) resulted in a significant and dose-related increase in plasma growth hormone (GH) in the urethane anesthetized rat. The minimum effective does of TRH was 40 ng per 100 g body wt when administered intravenously. The maximum responses of plasma GH to TRH were observed at 5 min following TRH, whereas those of plasma TSH were obtained at 10 min. Pretreatment with either T3 (50 mug/100 g body wt ip) significantly suppressed both plasma GH and TSH responses to TRH. The GH release induced by TRH was significantly inhibited by somatostatin (5 mug/100 g body wt iv) which was injected 5 min and immediately before the injection of TRH.

Studies on the mechanism controlling growth hormone release induced by chlorpromazine in the anesthetized rat

In intact urethane-anesthetized rats, plasma growth hormone (GH) levels were low but increased significantly following intravenous injection of chlorpromazine. Plasma GH levels were significantly elevated in rats with hypothalamic cuts such as complete deafferentiation, anterior cut and antero-lateral cut, whereas plasma GH levels in rats with posterior cut or postero-lateral cut were not significantly different from those in rats with sham-operation. Intravenous injection of chlorpromazine caused an increase of plasma GH in rats with any type of hypothalamic cut. However, the maximum increments of plasma GH following chlorpromazine were larger in rats with antero-lateral cut and smaller in rats with posterior cut than in rats with sham-operation. These results suggest that extrahypothalamic inhibiting and stimulating neurons influence the regulatory mechanism of rat GH secretion through anterior and posterior routes to the hypothalamus respectively.

Growth hormone and prolactin release after injection of thyrotropin-releasing hormone in patients with depression

The effects of thyrotropin-releasing hormone (TRH) on the release of growth hormone (GH), prolactin (PRL) and thyrotropin (TSH) were investigated in patients with depression. Intravenous injection of synthetic TRH (500 mug) caused a significant increase in plasma GH (peak value: 7.7 minus 35.0 ng/ml) in 8 of 13 patients with mental depression. After clinical recovery these patients had no response of plasma GH to TRH. TRH administration did not raise plasma GH in normal subjects examined. Plasma PRL responses to TRH were significantly enchanced (P smaller than 0.05) in depressed patients compared with control subjects. Plasma TSH responses to TRH were significantly blunted in patients with depression (P smaller than 0.05). These results suggest disorders in the hypothalamo-pituitary function in depression.

Effects of drugs influencing brain catecholamines on GH release in rats with hypothalamic surgery

The effect of pretreatment with alpha-methyl-p-tyrosine (alpha-MT) on the basal levels of plasma growth hormone (GH) and the responses to chlorpromazine (CPZ) were investigated in urethane-anesthetized rats with either complete hypothalamic deafferentation (c.d.), hypothalamic ablation (H.A.) or sham operation (Sham). Basal GH levels were high in C.D. rats, intermediate in H.A. rats, and low in Sham rats without any pretreatment. Pretreatment with alpha-MT caused a significant increase in basal GH levels in both C.D. and Sham rats, but not in H.A. rats. GH release following the intravenous injection of CPZ, which was observed in C.D. and Sham rats without alpha-MT pretreatment, was blunted by treatment with alpha-MT. In H.A. rats CPZ failed to stimulate the secretion of GH regardless of alpha-MT pretreatment. Neither the injection of L-DOPA nor DL-DOPS affected basal GH levels in non-alpha-MT pretreated C.D. rats. However, plasma GH levels significantly decreased following the injection of L-DOPA, but not DL-DOPS, in C.D. rats pretreated with alpha-MT. These findings suggest that the injection of CPZ causes an enhancement of GH release by inhibiting the catecholaminergic (dopaminergic) mechanism, which is active within the basal medial hypothalamus (BMH) and plays an inhibitory role in GH secretion. They also suggest that the extrahypothalamic inhibitory neural pathway, which is connected to the BMH and is interrupted by hypothalamic deafferentation, is not catecholaminergic.