An investigation into the possible physiological roles of vascular alpha 1- and alpha 2-adrenoreceptors.
1 We have investigated the influence of chemical sympathectomy or bilateral adrenal demedullation on vasopressor responses produced by the alpha 1-adrenoreceptor agonist, phenylephrine, and the alpha 2-adrenoreceptor agonist, M-7, in pithed rats to see whether either procedure induced selective supersensitivity to either of these compounds. 5-HT, a tryptaminergic vasopressor agent, was also used to discriminate between nonspecific change in vascular responsiveness and those mediated via alpha-adrenoreceptors. 2 Adrenal demedullation caused a slight reduction in the sensitivity to all agonists. Chemical sympathectomy significantly reduced the vasopressor responses to all doses of phenylephrine, but responses to 5-HT were unchanged. In contrast there was a tendency for responses to M-7 to be greater in sympathectomized rats than in untreated rats. 3 It is concluded that circulating adrenal medullary catecholamines do not physiologically modulate vascular alpha-adrenoreceptor function. The differential effect of chemical sympathectomy on the vasopressor responses to phenylephrine and M-7 might be explained in terms of a small increase in the ratio of vascular alpha 2 : alpha 1-adrenoreceptors, that receive a noradrenergic innervation.
D000313:Adrenal Medulla / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects; D006892:Hydroxydopamines / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009284:Naphthols / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D011941:Receptors, Adrenergic / Q000502:physiology*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D013563:Sympathectomy, Chemical
D006892:Hydroxydopamines; D009284:Naphthols; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D012701:Serotonin; C009957:5,6-dihydroxy-2-dimethylaminotetralin