Abstract

It has been generally assumed that reactivity (or responsiveness) of mammalian microcirculatory blood vessels to vasoactive hormones is not influenced by sex. In view of the paucity of knowledge in this area, the present in vivo studies were initiated to determine the quantitative dose-response relationships (by means of a high magnification image-splitting television microscope recording system) of catecholamines, selected sympathomimetics, neurohypophyseal hormones (NHPH), serotonin and angiotensin on mesenteric arterioles of unpretreated male and female rats and male rats pretreated with single low doses of 17 beta-estradiol (2 and 10 mug/100 g s.c.). The results indicate: 1) dose-response curves for the constrictor catecholamines (epinephrine and norepinephrine) and NHPH (vasopressin, oxytocin, vasotocin) in female rats are significantly shifted in parallel manner to the left of those obtained in male rats; 2) pretreatment of male rats with estrogen results in an enhancement of the constrictor actions of catecholamines, NHPH and phenylephrine; 3) the maximal arteriolar contractile responses (i.e., lumen narrowings) to norepinephrine and phenylphrine were enhanced by pretreatment with estrogen; and 4) dose-response curves for arteriolar constrictions induced by dopamine, serotonin or angiotensin were not affected by sex or estrogen pretreatment. The sex-linked differences, observed in this study, thus appear to be specific for NHPH and certain alpha adrenergic agonists. Overall, these findings reinforce the concept that sex hormones may play a role in control of peripheral blood flow and reactivity of arteriolar smooth muscle.