Sex differences in extracellular and intracellular calcium-mediated vascular reactivity to vasopressin in rat aorta

In rat thoracic aorta, contractile responses to arginine vasopressin are two-fold higher in females than in males. To determine the roles of extracellular and intracellular Ca2+ in this sexual dimorphism in vascular function, vascular reactivity and Ca2+ channel function were examined in thoracic aortae of male and female rats. Tn the presence of diltiazem (10 mu M), maximal contraction to vasopressin was reduced to a greater extent in male (65 +/- 2%) than in female aortae (38 +/- 1%). Maximal contractile responses to KCl and Bay K 8644 were similar in male and female aortae. Sensitivity to KCI was slightly but significantly higher in male than in female aorta; in contrast, sensitivity to Bay K 8644 was nearly three-fold higher in males than in females. Removal of the endothelium enhanced sensitivity to KCI similarly in male and female aortae. Tn the presence of simvastatin (60 mu M; an inhibitor of intracellular Ca2+ release), reactivity to vasopressin was reduced substantially in female (42 +/- 1%) but unaltered in male aortae. Removal of the endothelium enhanced the inhibitory effect of simvastatin in both female (73 +/- 2%) and male aortae (41 +/- 2%). These findings demonstrate that male aortae depend more upon extracellular Ca2+ influx, whereas female aortae depend more upon intracellular Ca2+ release for vasopressin-induced contraction. (C) 1998 Elsevier Science B.V. All rights reserved.