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PubMed1983

Variation in the release of thyroxine, triiodothyronine and growth hormone in response to thyrotrophin releasing hormone during development of the domestic fowl.

In newly hatched chicks, TRH administration was followed by increased circulating concentrations of growth hormone (GH), thyroxine (T4) and 3,3',5-triiodothyronine (T3). Little change in the circulating concentration of 3,3',5'-triiodothyronine (rT3) was however observed. The effect of TRH on the circulating concentration of GH was not found in chick embryos at 17 or 19 days of incubation but was observed during pipping. The T4 response was maximal in newly hatched chicks and present in 17 and 19 days embryos. The magnitude of the T3 responses increased with age while that of T4 decreased.

Age Factors↗
PubMed1983

Mechanism of serotonin effects on prolactin and growth hormone secretion in domestic fowl.

Brain serotonin levels were increased in immature chickens by ip injection of pargyline (75 mg/kg) and clorgyline (5 mg/kg) and by L-tryptophan (100 mg/kg) and imipramine (10 mg/kg) treatment. These treatments increased the circulating prolactin level and reduced the concentration of plasma growth hormone (GH). Treatment with para-chlorophenylalanine (PCPA, 100 mg/kg) reduced the brain serotonin content and the level of plasma prolactin. Treatment with these drugs in vivo similarly affected the basal level of prolactin release from pituitary glands in vitro, although it did not affect the basal level of GH release. The in vitro responsiveness of the pituitary gland to hypothalamic stimuli eliciting prolactin secretion was increased by in vivo pargyline and combined tryptophan: imipramine treatment but reduced by PCPA administration. The in vitro GH response to hypothalamic stimulation was reduced after the in vivo injection of pargyline, clorgyline and tryptophan: imipramine. The hypothalami from clorgyline and tryptophan: imipramine treated birds induced a greater stimulation of in vitro prolactin secretion from control pituitary glands than hypothalami from controls birds, whereas the GH releasing activity was reduced. These results suggest that serotonin stimulates prolactin secretion in chickens by increasing pituitary responsiveness to hypothalamic releasing factors and by increasing the prolactin releasing activity of the hypothalamus. Serotonin appears to suppress GH secretion by reducing pituitary sensitivity to releasing factors and by reducing hypothalamic GH releasing activity.

Animals↗
PubMed1984

Serotonin and acetylcholine affect the release of prolactin and growth hormone from pituitary glands of domestic fowl in vitro in the presence of hypothalamic tissue.

Anterior pituitary glands from broiler fowl were incubated alone or with hypothalamic tissue in medium containing either serotonin or serotoninergic drugs, acetylcholine or cholinergic drugs, and the release of prolactin (Prl) and growth hormone (GH) measured by homologous radioimmunoassays. The neurotransmitters and drugs affected the release of hormones from the pituitary gland only when hypothalamic tissue was also present. Serotonin and its agonist quipazine stimulated the release of Prl and inhibited release of GH in a concentration-related manner. The antagonist methysergide blocked the effects of serotonin and quipazine on Prl. Acetylcholine and its agonist pilocarpine also stimulated release of Prl and inhibited release of GH in a concentration-related manner. Atropine blocked these responses. The results show that serotonin and acetylcholine affect pituitary hormone secretion by acting on the hypothalamus. They may stimulate the secretion of a Prl releasing hormone and somatostatin.

Acetylcholine↗