ROLE OF ENDOTHELIUM IN SEXUAL DIMORPHISM IN VASOPRESSIN-INDUCED CONTRACTION OF RAT AORTA

In rat thoracic aorta, contractile responses to arginine vasopressin (AVP) are twofold higher in females than in males. To determine the role of the endothelium in this phenomenon, the effects of endothelium removal and inhibition of nitric oxide (NO) synthase and cyclooxygenase were examined in thoracic aortas prepared from male and female Sprague-Dawley rats and mounted for isometric tension recording. Maximal contractile response to AVP was substantially higher in female (4,232 +/- 316 mg/mg ring dry wt) than in male aortas (1,365 +/- 239; P < 0.01). Removal of the endothelium markedly potentiated maximal response to AVP in male aortas (4,100 +/- 422 mg/mg ring wt; P < 0.01); endothelium removal increased sensitivity but not maximal response in female aortas. Inhibition of NO synthase with N(G)-monomethyl-L-arginine (L-NMMA, 250 muM) doubled maximal contraction to AVP in male aortas (3,175 +/- 193 mg/mg ring wt; P < 0.01); L-NMMA increased sensitivity but not maximal response in female aortas. Inhibition of cyclooxygenase with indomethacin (10 muM) did not alter maximal response to AVP in male aortas but significantly attenuated responses of female aortas (2,816 +/- 306 mg/mg ring wt; P < 0.01). In contrast, maximal contractile response to phenylephrine hydrochloride (PE) was 40% higher in males than in females (P < 0.01); L-NMMA increased both the sensitivity and maximal response to PE to a greater extent in female (3,061 +/- 121 vs. 4,971 +/- 135 mg/mg ring wt, P < 0.01) than in male aortas (4,317 +/- 227 vs. 4,899 +/- 104 mg/mg ring wt; P < 0.01). Thus male-female differences in reactivity of the rat aorta are vasoconstrictor specific and are primarily due to sexual differences in the modulatory actions of basal and/or agonist-stimulated NO and constrictor prostanoid release. These sexual differences in the vascular actions of AVP and PE may involve gonadal steroid modulation of the release and/or vascular actions of NO and prostanoids.