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

GHRH treatment: studies in an animal model

This study examined the effects of chronic deletion of circulating growth hormone-releasing (GHRH) and/or somatostatin (SRIF) on normal growing male rats, as well as the effects of exogenous GHRH (1-29)NH2 and/or SMS 201-995 administration on the growth of rats with hypothalamic ablation. Passive immunization with anti-rat GHRH goat gamma-globulin (GHRH-Ab) for 3 weeks caused a marked decrease in the levels of pituitary GH mRNA and severe growth failure. Treatment with anti-SRIF goat gamma-globulin (SRIF-Ab) for 3 weeks produced a more modest decrease in GH mRNA levels in the pituitary and a slight but significant inhibition of normal somatic growth. Hypothalamic ablation produced a marked decrease in the level of mRNA in the pituitary. Chronic continuous administration of GHRH (1-29)NH2 stimulated pituitary GH synthesis, elevated serum levels of insulin-like growth factor I and increased body weight gain in rats with hypothalamic ablation treated with replacement doses of cortisone, testosterone and L-thyroxine. Combined treatment with GHRH (1-29)NH2 and SMS 201-995 appeared to promote the effect of GHRH on pituitary GH release and somatic growth in these animals. The results suggest that continuous administration of GHRH will be useful in the treatment of children with growth retardation resulting from hypothalamic disorders. In children with combined GHRH and somatostatin deficiencies, the addition of somatostatin to a GHRH treatment regimen may produce better results.

Central nervous system effect of calcitonin: stimulation of prolactin release in rats

Effect of [Asu 1,7]eel calcitonin (CT) on prolactin (PRL) release was examined in male rats under urethane anesthesia. Intravenous injection of 4-20 micrograms [Asu1,7]eel CT did not modify plasma PRL levels. Injections of 0.5-2.5 micrograms [Asu1,7]eel CT into the lateral ventricle produce a significant and dose-related increase of plasma PRL within 10 min of injection. When intraventricularly injected in an equimolar dose (0.74 nmol/10 microliters), eel CT11-32, eel CT15-32, [Asu1,7]eel CT1-16 and [Asu1,7]eel CT1-9 showed 44.8, 25.7, 19.9 and 10.1% the potencies of [Asu1,7]eel CT, respectively, in stimulating activity of PRL release. The rise of plasma PRL after [Asu1,7]eel CT injection were significantly less or abolished not only in hypothalamic-lesioned rats but also in rats with complete deafferentation. Pretreatment with alpha-methyl-p-tyrosine (250 mg/kg, 12 h before) but not with p-chlorophenylalanine (300 mg/kg, 72 and 24 h before) resulted in a suppression of [Asu1,7]eel CT-induced PRL release. These results suggest the following: first, PRL release is stimulated by centrally injected [Asu1,7]eel CT, the action site of which may exist in the extrahypothalamic area; second, brain catecholamines may be involved in the mechanism of [Asu1,7]eel CT-evoked PRL release; third, the C-terminal portion of the peptide may play an important role in stimulating PRL release.

Effect of ethanol on endogenous rhythms of growth hormone secretion

Studies in man on the effect of ethanol on growth hormones (GH) release have been inconclusive. In order to investigate the effect of ethanol on spontaneous episodic secretion of GH, rats were implanted with chronic carotid catheters to permit frequent sampling in unanesthetized rats. Secretion during the 3 hr before (0--180 min) and after (181--360 min) ethanol or saline was assessed by means of samples drawn every 15 min. Secretion patterns after saline or ethanol 0.5 and 2 g/kg were indistinguishable, but ethanol in doses of 3 and 4 g/kg abolished rat GH (rGH) secretion in a majority of animals. Mean rGH after saline injection for the period 181--360 min was 62 +/- 9 ng/ml. When ethanol was given, mean rGH values for this time period were 0.5 g/kg, 63 +/- 6 ng/ml; 2.0 g/kg, 47 +/- 7 ng/ml; 3 g/kg, 28 +/- 3 ng/ml; and 4 g/kg, 23 +/- 2 ng/ml. Differences were not statistically significant between saline and 0.5 or 2 g/kg ethanol, but were significant (p less than 0.01) for 3 or 4 g/kg ethanol. Thus, a single dose of ethanol can abolish spontaneous rGH secretion, but it must be a high dose. The effect of chronic ethanol administration remains to be investigated.