Comparative studies of the effects of 5-hydroxytryptamine and noradrenaline on the rat anococcygeus muscle.
The effects of 5-hydroxytryptamine (5HT) and noradrenaline (NA) have been studied on rat anococcygeus muscle. 1. 5HT and NA produced a dose-dependent contraction of rat anococcygeus muscle. Cyproheptadine (1.0 X 10(-6) M), a specific 5HT receptor blocker, failed to inhibit the responses to either 5HT or NA. 2. However, phentolamine, a specific alpha receptor antagonist competitively blocked the responses to 5HT and NA. 3. The responses to 5HT were inhibited in the reserpinized (5 mg/kg i.p. 24 h) and 6-hydroxydopamine (6-OHDA) pre-treated preparations. 6-OHDA produced a leftward shift of the dose-response curve of NA. Reserpine pre-treatment potentiated lower doses of NA and the threshold dose of NA was significantly decreased. 4. Nialamide (2.2 x 10(-6) M), the mono-amine oxidase inhibitor produced a significant leftward shift of the dose-response curve of both 5HT and NA. Pyrogallol (2.3 x 10(-5) M), the catechol-o-methyl transferase inhibitor also potentiated the responses to both 5HT and NA, but the potentiation was significant at lower doses of 5HT and NA. 5. Our data suggest that 5HT- and NA-induced contractions in rat anococcygeus muscle are mediated through common alpha adrenoceptors. 5HT actions are probably indirect, mediated through the release of NA.
D000818:Animals; D003533:Cyproheptadine / Q000494:pharmacology; D004347:Drug Interactions; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009526:Nialamide / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*
D006892:Hydroxydopamines; D003533:Cyproheptadine; D012701:Serotonin; D012110:Reserpine; D009526:Nialamide; D009638:Norepinephrine