Influence of Reserpine and Guanethidine On Vascular Reactivity and Antihistamine Constrictor Action in the Microcirculation

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Abstract
Experiments were designed to evaluate the peripheral vascular effects on the rat mesocecum of 2 antlhypertensive agents, reserpine and guanethidine, in regard to vascular reactivity and antihistamine constrictor action. The administration of guanethidine, within 5 min., produced an increase in vascular reactivity to topically applied epinephrine and norepinephrine. This agent also produced an increased venular constriction to topically applied serotonin [5-hydroxytryptamine] and antihistamines. A similar sensitization to topical catecholamines and serotonin was recorded 20 min. after the administration of reserpine. However, antihistamine constrictor activity remained essentially that observed in control animals. The chronic administration of guanethidine yielded results somewhat different from that of reserpine, although both types of treatment produced widespread microvascular dilation. Repeated daily systemic injections of reserpine produced an increase in vascular reactivity to topical epinephrine, norepinephrine, antihistamines and topical vasopressin, whereas chronic administration of guanethidine depressed catecholamine constrictor action without any effect on topically applied serotonin, vasopressin, histamine or antihistaminic agents. These catecholamine depletors failed to prevent the previously observed antihistamine constrictor action on the microcirculation. The findings are discussed in relation to histamine levels in the terminal vascular bed.