Dopamine decreases mesenteric blood flow in the anaesthetised dog through the stimulation of postsynaptic alpha 2-adrenoceptors.
The decrease in mesenteric blood flow produced by dopamine administered intra-arterially in the anaesthetised dog was investigated by means of drugs selective for alpha 1- and alpha 2-adrenoceptors. The selective alpha 1-adrenoceptor agonist phenylephrine (0.3-100 microgram) given by intra-arterial injection (i.a.) into the superior mesenteric artery of the anaesthetized dog produced a decrease in mesenteric blood flow which was preferentially blocked by the alpha 1-adrenoceptor antagonist prazosin (30-300 microgram/kg i.v.). On the other hand, i.a. injections of the selective alpha 2-adrenoceptor agonist M7 (1-100 microgram) or of dopamine (1-300 microgram) produced a decrease in mesenteric blood flow which was blocked by the alpha 2-adrenoceptor antagonist yohimbine (100-300 microgram/kg i.v.) but was not significantly reduced by prazosin (300 microgram/kg i.v.). These results demonstrate that the mesenteric vascular bed of the dog contains both alpha 1- and alpha 2-adrenoceptors located postsynaptically and mediating vasoconstriction. The decrease in mesenteric blood flow produced by i.a. injections of dopamine is mediated predominantly via postsynaptic alpha 2-adrenoceptors.
D000316:Adrenergic alpha-Agonists; D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D003042:Cocaine / Q000494:pharmacology; D004285:Dogs; D004298:Dopamine / Q000494:pharmacology*; D011224:Prazosin / Q000494:pharmacology; D013152:Splanchnic Circulation / Q000187:drug effects*; D014439:Tyramine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D015016:Yohimbine; D003042:Cocaine; D004298:Dopamine; D014439:Tyramine; D011224:Prazosin