Sex differences in ischemia/reperfusion-induced acute kidney injury are dependent on the renal sympathetic nervous system

Resistance to ischemic acute kidney injury has been shown to be higher in female rats than in male rats. We found that renal venous norepinephrine overflow after reperfusion played important roles in the development of ischemic acute kidney injury. In the present study, we investigated whether sex differences in the pathogenesis of ischemic acute kidney injury were derived from the renal sympathetic nervous system using male and female Sprague-Dawley rats. Ischemia/reperfusion-induced acute kidney injury was achieved by clamping the left renal artery and vein for 45 min followed by reperfusion, 2 weeks after contralateral nephrectomy. Renal function was impaired after reperfusion in both male and female rats; however, renal dysfunction and histological damage were more severe in male rats than in female rats. Renal venous plasma norepinephrine levels after reperfusion were markedly elevated in male rats, but were not in female rats. These sex differences were eliminated by ovariectomy or treatment with tamoxifen, an estrogen receptor antagonist, in female rats. Furthermore, an intravenous injection of hexamethonium (25 mg/kg), a ganglionic blocker, 5 min before ischemia suppressed the elevation in renal venous plasma norepinephrine levels after reperfusion, and attenuated renal dysfunction and histological damage in male rats, and ovariectomized and tamoxifen-treated female rats, but not in intact females. Thus, the present findings confirmed sex differences in the pathogenesis of ischemic acute kidney injury, and showed that the attenuation of ischemia/reperfusion-induced acute kidney injury observed in intact female rats may be dependent on depressing the renal sympathetic nervous system with endogenous estrogen.