Effects of the oestrous cycle and gender on acute vasodilatory responses of isolated pressurized rat mesenteric arteries to 17 beta-oestradiol.

The influence of the oestrous cycle and gender on responses of isolated pressurized mesenteric arteries to acute 17 beta-oestradiol was investigated. All vessels, pre-contracted with 60 mM KCl or 10 microM U46619 (9,11 dideoxy-11alpha, 9alpha-epoxy methano-prostaglandin), exhibited concentration-dependent vasodilatory responses to 17 beta-oestradiol (3 - 30 microM). The largest responses were seen in vessels from female rats in pro-oestrous (38.9+/-5.4% U46619 max and 63.1+/-4.0% KCl max for 30 microM oestradiol), the smallest from animals in di-oestrous (20.1+/-3.7% U46619 and 50.1+/-4.5% KCL - both P:<0.05 cf pro-oestrous (all n=8)). Responses of vessels from male rats were similar to those from pro-oestrous rats (41.5+/-9.1% U46619 (n=10) and 54.9+/-2.9% KCl (n =8)). All responsees were unaffected by inhibition of nitric oxide synthase (NOS). Female rats in pro-oestrous had the highest plasma concentrations of 17 beta-oestradiol and testosterone (40.76+/-4.73 pg ml(-1) and 0.29+/-0.05 ng ml(-1) respectively (n=8)) while those in di-oestrous had the lowest (15.24+/-3.94 pg ml(-1) for oestradiol and 0.08+/-0.03 ng ml(-1) for testosterone (n=8)). In male rats the concentration of oestrogen was 10.29+/-1.21 pg ml(-1) (n=7) while that of testosterone was 3.15+/-0.36 ng ml(-1) (n=7). Incubation of arteries isolated from male rats and from female rats in pro-oestrous and di-oestrous with testosterone (1 microM, 3 h) significantly enhanced the subsequent vasodilatory responses to acute 17 beta-oestradiol. Following incubation, the responses to 17 beta-oestradiol were similar in all groups. These observations suggest that gender and the oestrous cycle may influence the vascular responses to acute 17 beta-oestradiol administration.