Complex role of 5-HT in the regulation of TSH secretion in the male rat.
The role of 5-hydroxytryptamine (5-HT) in the regulations of TSH secretion was studied in male rats using both peripheral and central administration of the drugs. Basal TSH levels were not modified by moderate doses of 5-HT (subcutaneously) or its precursors or antagonists (intraperitoneally) given 1 h before decapitation. The cold-stimulated TSH secretion was decreased by L-tryptophan (L-TRP, 400 mg/kg i.p.), quipazine (10 mg/kg i.p.) and 5-HT (1 or 5 mg/kg s.c. or i.v.) as well as by p-chlorophenylalanine (pCPA, 20 or more mg/kg i.p.) when the drugs were given 1 h before sampling. pCPA (100-400 mg/kg i.p.) was active 24-48 h after the injection but repetitive administration did not affect TSH levels. 5-HT (5 mg/kg s.c.) was effective also in pinealectomized animals. L-TRP and 5-hydroxytryptophan potentiated the TRH-stimulated TSH secretion when given 1 h before killing. 5-HT (10 microgram/rat) infused into the third ventricle enhanced the cold-stimulated TSH secretion when given 30-45 min before sampling. When injected into the medial basal hypothalamus, 50-HT (1-10 microgram/rat) had no effect on basal or stimulated TSH levels. The results suggest: (1) 5-HT does not play any role in the regulation of basal TSH secretion; (2) in the cold-stimulated TSH secretion 5-HT has a stimulatory action evidently inside the blood-brain barrier and also an inhibitory effect obviously outside this barrier.
D006916:5-Hydroxytryptophan / Q000494:pharmacology; D000818:Animals; D003533:Cyproheptadine / Q000494:pharmacology; D004357:Drug Synergism; D010134:Fenclonine / Q000494:pharmacology; D008297:Male; D010870:Pineal Gland / Q000502:physiology; D011814:Quipazine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D013974:Thyroxine / Q000097:blood; D014364:Tryptophan / Q000494:pharmacology
D003533:Cyproheptadine; D012701:Serotonin; D011814:Quipazine; D013973:Thyrotropin-Releasing Hormone; D014364:Tryptophan; D013972:Thyrotropin; D006916:5-Hydroxytryptophan; D013974:Thyroxine; D010134:Fenclonine