OVARIECTOMY ELIMINATES SEX-DIFFERENCES IN RAT TAIL ARTERY RESPONSE TOADRENERGIC-NERVE STIMULATION

The influence of gonadal hormones on vasoconstrictor responses to adre nergic nerve stimulation was investigated by comparing tail arteries f rom intact and gonadectomized male and female Fisher 344 rats. Arteria l ring segments from females were significantly less responsive to tra nsmural nerve stimulation (1-8 Hz) than arteries from age-matched male s. Significant male-female differences persisted after correcting the contractile responses for sex-related differences in arterial mass, op timal resting tension, and maximal contractile force. Arteries were ta ken from cycling, intact females in either proestrus, estrus, metestru s, or diestrus, but no significant differences were found among the fo ur stages for vasoconstrictor responses to either adrenergic nerve sti mulation or exogenous norepinephrine. These data suggest adrenergic fu nction in the artery is not affected by hormonal variations during the estrous cycle. After bilateral ovariectomy, however, contractile resp onses of female arteries to adrenergic nerve stimulation were increase d to levels similar to those observed in male arteries. Orchidectomy o f males, in contrast, had no effect on neural-evoked contraction. Low concentrations of norepinephrine also produced greater contractile res ponses in male compared with female arteries; however, this sex-relate d difference was eliminated by orchidectomy but not ovariectomy. Taken together, the results indicate that circulating gonadal hormones cont ribute to gender differences observed in rat tail artery. Vasoconstric tor responses to exogenous norepinephrine appear to be enhanced by tes ticular hormones. In contrast, vasoconstriction induced by adrenergic nerve stimulation appears to be influenced by chronic exposure to circ ulating ovarian hormones, resulting in a smaller vascular response in female arteries.