Dual action of morphine on cold-stimulated thyrotropin secretion in male rats.
The effect of morphine infused into 4 hypothalamic locations and the periaqueductal gray (PAG) on cold-stimulated thyrotropin (TSH) secretion was studied in male rats. Morphine decreased TSH cold-response when infused into the 3rd ventricle (1-20 micrograms/rat) or the median eminence (5 and 10 micrograms/rat). Infusions bilaterally into the anterior hypothalamus (1-10 micrograms/side) or PAG (1 and 10 micrograms/rat) were ineffective, while those given into the posterior hypothalamus (1 and 5 micrograms/side, but not 10 micrograms/side) significantly enhanced TSH cold-response. Naloxone pretreatment (2 or 5 mg/kg, s.c.) reversed the decreasing effect of morphine in the 3rd ventricle (1 microgram/rat) and the increasing effect of morphine in the posterior hypothalamus (1 microgram/side). We conclude that morphine has a dual hypothalamic action on cold-stimulated TSH secretion: an inhibition periventricularly, and a stimulation in the posterior hypothalamus.
D000818:Animals; D003080:Cold Temperature; D007031:Hypothalamus / Q000187:drug effects; D007276:Injections, Intraventricular; D007279:Injections, Subcutaneous; D008297:Male; D008473:Median Eminence / Q000187:drug effects; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013972:Thyrotropin / Q000378:metabolism*
D009270:Naloxone; D009020:Morphine; D013972:Thyrotropin