Antagonism of conditioned salivation in conscious dogs by antihypertensive drugs.
Methyldopate (methyldopa (ethyl ester)), carbidopa, clonidine, and ST-91 were evaluated for their effects on conditioned salivation in unanesthetized dogs. Clonidine produced dose-dependent inhibition of salivation 20 min after an intravenous injection. At equivalent and larger doses, ST-91, a clonidine analog which does not penetrate the blood-brain barrier, was ineffective  in inhibiting conditioned salivation, suggesting that central rather than peripheral mechanisms are involved in clonidine-induced inhibition of salivation. Methyldopate also produced a dose-dependent inhibition of salivation in dogs. The mechanism involved in methyldopa-induced inhibition of salivation may involve both central and peripheral mechanisms because carbidopa, an inhibitor (like methyldopa) of peripheral aromatic decarboxylase (EC 4.1.1.28), significantly inhibited salivation.
D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D001285:Atropine / Q000494:pharmacology; D002230:Carbidopa / Q000494:pharmacology; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D003214:Conditioning, Classical / Q000187:drug effects*; D004285:Dogs; D004347:Drug Interactions; D005260:Female; D008297:Male; D008750:Methyldopa / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology; D012472:Salivation / Q000187:drug effects*
D000959:Antihypertensive Agents; D010862:Pilocarpine; D008750:Methyldopa; D001285:Atropine; D003000:Clonidine; D002230:Carbidopa