The prejunctional inhibitory effect of alpha-methylnoradrenaline in the rat vas deferens is not mediated via alpha 2-adrenoceptors.
In field-stimulated rat vas deferens, clonidine (10(-9)-10(-7) M) and alpha-methylnoradrenaline (10(-7)-3 x 10(-5) M) concentration-dependently inhibited twitch response to electrical field stimulation. The inhibitory effects of clonidine and alpha-methylnoradrenaline were similarly reduced by phenoxybenzamine (10(-6) M). However, idazoxan (3 x 10(-7) M) antagonized clonidine but not alpha-methylnoradrenaline-induced responses. The inhibitory effect of alpha-methylnoradrenaline was also not antagonized by phentolamine (3 x 10(-7) M), SK&F 104856 (2-vinyl-7-chloro-3,4,5,6-tetrahydro-4-methylthienol[4,3,2 ef][3]benzazepine) 3 x 10(-6) M) or yohimbine 3 x 10(-7) M). These antagonists however, attenuated the twitch-inhibiting effect of clonidine. The -logKB values were 8.02 +/- 0.05, 6.91 +/- 0.10, and 7.58 +/- 0.07 for phentolamine, SK&F 104856 and yohimbine respectively. In-vivo treatment of rats with N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (6 mg kg-1), to inactivate prejunctional alpha 2-adrenoceptors, attenuated clonidine, but not alpha-methylnoradrenaline-induced responses. It was concluded that adrenoceptors are not involved in the prejunctional inhibitory effects of alpha-methylnoradrenaline in the rat vas deferens.
Oriowo
M A
MA
Department of Pharmacology and Toxicology, Faculty of Medicine, Kuwait University, Safat, Kuwait.
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D003000:Clonidine / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D019329:Idazoxan; D007093:Imidazoles / Q000494:pharmacology; D007537:Isometric Contraction / Q000187:drug effects; D008297:Male; D009469:Neuromuscular Junction / Q000187:drug effects; D008771:Nordefrin / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism; D014649:Vas Deferens / Q000187:drug effects* / Q000378:metabolism; D014662:Vasoconstrictor Agents / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D001552:Benzazepines; D004146:Dioxanes; D007093:Imidazoles; D011804:Quinolines; D018341:Receptors, Adrenergic, alpha-2; D014662:Vasoconstrictor Agents; D010643:Phenoxybenzamine; C071739:SK&F 104856; D015016:Yohimbine; C000470:EEDQ; D003000:Clonidine; D008771:Nordefrin; D019329:Idazoxan; D010646:Phentolamine