Influence of Gender on Control of Arterial Tone in Experimental Hypertension

Endothelial dysfunction has been found to be less severe in female than in male spontaneously hypertensive rats (SHR), which could contribute to the gender differences observed in the extent and rate of progression of hypertension in SHR. However, the influence of gender on the roles of different endothelium-derived mediators in the arterial responses in hypertension have not been evaluated in detail. Therefore, contractile and relaxation responses of mesenteric arterial rings in vitro were studied in female and male SHR, with normotensive female and male Wistar-Kyoto rats (WKY) serving as controls. In norepinephrine (NE)-precontracted arterial rings, endothelium-dependent relaxations to ACh as well as endothelium-independent dilations to sodium nitroprusside were more pronounced in female than in male SHR, whereas relaxations to the beta-adrenoceptor agonist isoproterenol remained equally impaired in female and male SHR. The cyclooxygenase inhibitor diclofenac, which reduces the synthesis of dilating and constricting prostanoids, markedly enhanced the relaxations to ACh in male SHR but not in the other groups. The nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester attenuated the relaxations to ACh more effectively in female SHR and WKY than in the male groups. However, when endothelium-dependent hyperpolarization was prevented by precontracting the preparations with KCl, no significant differences were found in relaxations to ACh among the study groups. In conclusion, release of cyclooxygenase-derived constricting factors appeared to be more pronounced in male than in female SHR. In addition, the relative role of NO in endothelium-dependent arterial relaxation seemed to be higher in female than in male SHR, and relaxation induced by an NO donor also was more pronounced in female than in male SHR.