Sex differences in cardiovascular control by nitric oxide in normotensive and hypertensive rats

R Nitric oxide probably plays an important role in mechanisms determining sexual dimorphism in the development of cardiovascular diseases, including hypertension. Because stress together with gender are significant cardiovascular risk factors, we studied the role nitric oxide in car-diovascular regulation in male and female nor-motensive and hypertensive rats under normal and stress conditions. Experiments were per-formed in mongrel normotensive and hyperten-sive (two kidney, one clip) rats of both sexes, weighing 200-250g. The study of mean arterial pressure and heart rate was carried out: 1) under control condition; 2) during nitric oxide blo- ckade by NG-nitro-L-arginine-methyl ester (L-NAME, 10 mg/kg, iv) 3) during 60 min immobilization stress and recovery; 4) during 60 min immobi-lization stress + L-NAME and recovery. We found that the severity of hypertension in fe-males was lower than in males. We also ob-served that both normotensive and hyperten-sive females demonstrated more favorable pat-tern of cardiovascular responses to stress. At rest, nitric oxide blockade increased the mean arterial pressure and decreased the heart rate more effectively in female normotensive and hypertensive rats than in male groups. During stress, nitric oxide blockade modified the stress- induced cardiovascular responses more sig-nificantly in female normotensive and hyper-tensive rats compared with male groups. Our data show that both normotensive and hyper-tensive females demonstrated the more effec-tive nitric oxide control of cardiovascular activ-ity under normal and especially stress condi-tions than male groups. This male-female dif-ference may be important mechanism respon-sible for greater in females vs. males of cardio-vascular resistance to stress and development of hypertension.