SEXUAL DIMORPHISM IN VASOPRESSIN-INDUCED CONTRACTION OF RAT AORTA

Previously, we reported that, in the rat, pressor responsiveness to vasopressin (VP) is higher in males than in females during most phases of the estrous cycle. To explore the role of the vasculture in this phenomenon, we examined vascular reactivity to VP in thoracic aortas of male rats and female rats during each phase of the estrous cycle. Aortic rings were prepared from age-matched male and female Sprague-Dawley rats and mounted for isometric tension recording. Maximal response of female aortas to VP (4,246 +/- 163 mg/mg ring dry wt) was more than twice (P < 0.001) that of male aortas (1,877 +/- 215 mg/mg ring wt). Sensitivity of female aortas to VP was substantially higher (P < 0.001) than that of male aortas (EC50: 10.9 +/- 0.7 vs. 19.0 +/- 1.6 nM, respectively). Maximal rate of tension development (dT/dt(max)) during contraction with VP was nearly twofold higher (P < 0.01) in female aortas (536 +/- 23 mg/min) than in male aortas (300 +/- 19 mg/min). Maximal response, sensitivity, and dT/dt(max) of female aortas did not vary significantly during the estrous cycle. Maximal response of female aortas to phenylephrine (PE; 1,251 +/- 93 mg/mg ring wt) was half that (P < 0.001) of male aortas (2,546 +/- 194 mg/mg ring wt); sensitivity to PE did not differ respectively). Significant quantitative differences may exist in the contractile mechanisms of male and female rat aortas, which may result from differences in the endothelium as well as vascular smooth muscle at the receptor and/or the postreceptor levels and may be modulated by the gonadal steroids.