Effect of 6-hydroxydopamine treatment on TSH secretion in basal and cold-stimulated conditions in the rat.
6-Hydroxydopamine (6-OHDA) (two doses of 200 micrograms each, administered intraventricularly at a 48 h interval) caused a marked decrease of hypothalamic noradrenaline content and blocked the TSH rise elicited by cold exposure. Clonidine (0.4 mg/kg i.p.), a noradrenaline receptor agonist, was able to reverse the 6-OHDA of cold-induced TSH surge. The plasma TSH levels after cold stress in rats treated with 6-OHDA + clonidine were significantly higher than in vehicle + clonidine-injected animals, thus suggesting the presence of noradrenaline receptor supersensitivity in 6-OHDA-pretreated rats. 6-OHDA did not modify the basal concentrations of TSH but the administration of clonidine to 6-OHDA-injected animals caused a significant increase in thyrotropin secretion when compared with the vehicle + clonidine group.
D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D003080:Cold Temperature / Q000009:adverse effects*; D006892:Hydroxydopamines / Q000494:pharmacology*; D007031:Hypothalamus / Q000187:drug effects*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D013972:Thyrotropin / Q000097:blood / Q000378:metabolism*
D006892:Hydroxydopamines; D013972:Thyrotropin; D003000:Clonidine; D009638:Norepinephrine