Ovariectomy eliminates sex differences in rat tail artery response to adrenergic nerve stimulation

The influence of gonadal hormones on vasoconstrictor responses to adrenergic nerve stimulation was investigated by comparing tail arteries from intact and gonadectomized male and female Fisher 344 rats. Arterial ring segments from females were significantly less responsive to transmural nerve stimulation (1-8 Hz) than arteries from age-matched males. Significant male-female differences persisted after correcting the contractile responses for sex-related differences in arterial mass, optimal resting tension, and maximal contractile force. Arteries were taken from cycling, intact females in either proestrus, estrus, metestrus, or diestrus, but no significant differences were found among the four stages for vasoconstrictor responses to either adrenergic nerve stimulation or exogenous norepinephrine. These data suggest adrenergic function in the artery is not affected by hormonal variations during the estrous cycle. After bilateral ovariectomy, however, contractile responses of female arteries to adrenergic nerve stimulation were increased to levels similar to those observed in male arteries. Orchidectomy of males, in contrast, had no effect on neural-evoked contraction. Low concentrations of norepinephrine also produced greater contractile responses in male compared with female arteries; however, this sex-related difference was eliminated by orchidectomy but not ovariectomy. Taken together, the results indicate that circulating gonadal hormones contribute to gender differences observed in rat tail artery. Vasoconstrictor responses to exogenous norepinephrine appear to be enhanced by testicular hormones. In contrast, vasoconstriction induced by adrenergic nerve stimulation appears to be influenced by chronic exposure to circulating ovarian hormones, resulting in a smaller vascular response in female arteries.