Cholinergic regulation of thyrotropin secretion in male rats.
The cold-stimulated thyrotropin (TSH) secretion in male rats was suppressed by muscarinic agonists, i.e. Oxa-22, McN-A-343 (an M1 agonist), oxotremorine (an M2 agonist) and methacholine (a quaternary compound). The inhibitory effect of Oxa-22 was antagonized by atropine, butylscopolamine and glycopyrrolate as well as by pirenzepine, an M1 antagonist and AF-DX 116, a new M2 antagonist. Various muscarinic antagonists were not active when given alone. Cytisine, a peripheral nicotinic agonist, was not active but nicotine significantly suppressed the cold-stimulated TSH secretion. Its effect was counteracted by mecamylamine but not by hexamethonium. The thyrotropin releasing hormone (TRH)-induced TSH secretion was not inhibited by Oxa-22, nicotine or methacholine. These results show that irrespective of the receptor subtype (muscarinic1 or muscarinic2, nicotinic), cholinergic activation inhibits the cold-stimulated TSH secretion. The results also suggest that this inhibitory effect is at the hypothalamic rather than the anterior pituitary level. The muscarinic action seems to occur outside the blood-brain barrier but the nicotinic action occurs inside this barrier.
Männistö
P T
PT
Department of Pharmacology and Toxicology, University of Helsinki, Finland.
Suomela
A
A
Rauhala
P
P
Tuominen
R K
RK
Suolinna
T
T
D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / Q000494:pharmacology; D000818:Animals; D006571:Heterocyclic Compounds / Q000494:pharmacology; D008297:Male; D008688:Methacholine Compounds / Q000494:pharmacology; D009538:Nicotine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010095:Oxotremorine / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000187:drug effects; D013876:Thiophenes; D013972:Thyrotropin / Q000378:metabolism*; D013973:Thyrotropin-Releasing Hormone / Q000502:physiology
D006571:Heterocyclic Compounds; D008688:Methacholine Compounds; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D013876:Thiophenes; D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride; C011508:2-methyl-5-trimethylammoniummethyl-1,3-oxathiolane; D010095:Oxotremorine; D013973:Thyrotropin-Releasing Hormone; D009538:Nicotine; D013972:Thyrotropin