Dopamine-induced contractile responses of the rat anococcygeus muscle.
In the rat anococcygeus muscle both dopamine and noradrenaline induced concentration-dependent contractile responses. The alpha 1-antagonist prazosin inhibited both dopamine and noradrenaline responses, whereas the alpha 2-antagonist yohimbine influenced noradrenaline-mediated responses only. The concentration-effect curves for dopamine were shifted to the right in presence of cocaine or after treatment with reserpine and alpha-methyl-p-tyrosine. When the tissues were previously exposed to 6-hydroxydopamine, the tyramine-induced contractile effect was abolished. Dopamine-induced concentration-effect curves were markedly shifted to the right. Treatment with 6-hydroxydopamine and reserpine did not modify the concentration-effect curves to noradrenaline. Our results indicate that dopamine has a dual effect: a partial effect due to an indirect sympathomimetic action and a partial effect due to the interaction with postjunctional receptors.
Laboratory of Pharmacology, College of Pharmacy, University of São Paulo, Ribeirão Preto, Brazil.
A M
AM
Oliveira
L M
LM
Bendhack
D000818:Animals; D004298:Dopamine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D008781:Methyltyrosines / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D016627:Oxidopamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012110:Reserpine / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D015016:Yohimbine / Q000494:pharmacology; D019805:alpha-Methyltyrosine
D008781:Methyltyrosines; D015016:Yohimbine; D019805:alpha-Methyltyrosine; D012110:Reserpine; D016627:Oxidopamine; D014446:Tyrosine 3-Monooxygenase; D004298:Dopamine; D009638:Norepinephrine; D011224:Prazosin