Inhibition of pentobarbital-induced release of growth hormone by thyrotropin releasing hormone

Antagonism by Taurine of Morphine Induced Growth Hormone Secretion

The intraperitoneal (IP) or intraventricular (IVT) administration of small amounts of taurine did not modify pentobarbital-induced sleep or pituitary hormone release. However, the drastic increment in plasma GH values induced by morphine administration was completely blocked by the IVT injection of the amino acid. Whether taurine plays a physiological role in the control ofGH secretion is highly speculative.

Stimulation of growth hormone secretion by human pancreatic growth-hormone-releasing factor and thyrotrophin-releasing hormone in anaesthetized chickens

Sodium pentobarbitone anaesthesia depressed the concentration of growth hormone (GH) in the plasma of young (6 weeks of age) and old (22-30 weeks of age) domestic fowl. In both cases the concentration was reduced (P less than 0.05) within 10 min and had declined (P less than 0.001) to stable low levels (less than 5 ng/ml) within 50 min. The intravenous administration of synthetic human pancreatic growth-hormone-releasing factor (hpGRF) (10 micrograms/kg) (2 X 10(-9) mol/kg) increased (P less than 0.01) the GH concentration in both the young and old birds. This effect was observed irrespective of whether the birds were conscious or anaesthetized. The magnitude of the response in conscious young birds (164 ng/ml) was, however, greater (P less than 0.01) than that in anaesthetized chicks (64 ng/ml). The response in anaesthetized adult fowl (18.8 ng/ml) was also less (P less than 0.05) than that in their conscious counterparts (42.8 ng/ml). The GH response in conscious and anaesthetized 6-week-old birds to hpGRF was greater (P less than 0.01) than that in the corresponding adult birds. Thyrotrophin-releasing hormone (TRH) (10 micrograms/kg (2.8 X 10(-8) mol/kg); iv) also provoked (P less than 0.01) GH secretion in conscious and anaesthetized young birds and in anaesthetized (but not conscious) adults. Anaesthesia blunted (P less than 0.01) the GH response to TRH in the immature cockerels, although the response was greater (P less than 0.05) than that in anesthetized adults.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of TRH on the release of TSH, PRL and GH in man under basal conditions and following methysergide

Pretreatment with methysergide, a blocker of serotoninergic receptors, significantly reduced the TSH response to TRH in six male volunteers. The TRH-induced PRL release was also slightly decreased, while plasma GH levels were not significantly modified by TRH either during the control period or after methysergide. These results indicate that alterations of central nervous system monoaminergic pathways may modify the hypophysiotropic effects of TRH.

Inhibition of dopamine-induced release of growth hormone by thyrotropin-releasing hormone

The effects of thyrotropin-releasing hormone (TRH) and dopamine (DA) on serum growth hormone (GH) levels were examined in the adolescent male baboon. Intravenously administered DA (40 microgram/kg-min-1 for 20 min) raised serum GH and glucose and lowered serum insulin concentrations but caused no increase in blood pressure. Concomitant intravenous infusion of TRH at 2 doses (96 ng/kg-min-1 and 40 microgram/kg-min-1 for 20 min) blocked the DA-induced increase in serum GH. The relatively low effective doses of TRH used to suppress the DA-induced GH increase suggest an interaction with catecholamines at the hypothalamic and/or pituitary to influence GH release.

Antagonism of pentobarbital-induced hormonal changes by TRH in rats

In adult male rats, injection of TRH into a lateral ventricle of the brain 5 min prior to pentobarbital (PB) administration caused a significant dose-related inhibition of prolactin (PRL) release, in doses ranging from 500 to 5 ng. Among 8 TRH analogues devoid of thyrotropin-releasing activity, 6 were found to significantly suppress PB-induced PRL secretion at an intraventricular dose level of 10 microgram, and the 3 most effective in this respect were also able to counteract growth hormone (GH) release elicited by PB. The derivative [1,3'-DCM2]TRH was still potent enough to block PB-induced PRL secretion at an intraventricular dosage of 50 ng. The peptide ACTH 4--10 was ineffective, whereas another ACTH derivative H-Met(O2)-Glu-His-Phe-D-Lys-Phe-OH (Org 2766) reduced PRL release. TRH did not affect the increase of plasma PRL induced by acute stress. alpha-Methyl-p-tyrosine (alpha-MT) failed to influence the inhibiting effect of TRH on GH secretion but significantly reduced that on PRL release. p-Chlorophenylalanine (PCPA) completely blocked the antagonistic effect of TRH on all PB-induced hormonal changes, suggesting that serotoninergic mechanisms may be involved in the extra-pituitary effect of TRH.

Effects of thyrotropin-releasing hormone on prolactin, growth hormone and corticosterone secretions in adult male rats treated with pentobarbital or morphine

Thyrotropin-releasing hormone (TRH) injected either IP (10 mg/kg) or intraventricularly (10 mug/rat) antagonized the pentobarbital-induced secretion of prolactin (PRL). This effect was not blocked by propranolol. In thyroidectomized animals the effect was not apparent; tri-iodothyronine (T3) injection was however ineffective. The injections of luteinizing hormone-releasing hormone (LH-RH) and of melanocyte stimulating hormone release-inhibiting factor (MIF) were also ineffective. Of six TRH analogues, only those containing histidine antagonized pentobarbital-induced PRL release, but none modified plasma levels of growth hormone (GH) or corticosterone (B). Brain levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were not modified by TRH. Morphine-induced secretion of PRL and GH was also significantly antagonized by TRH. Since pentobarbital and morphine-induced hormonal changes are probably exerted through a central nervous system depressant action, these data indicate that TRH can influence brain activity through an extrapituitary mechanism.