Effects of the oestrous cycle and gender on acute vasodilatory responses of isolated pressurized rat mesenteric arteries to 17 β ‐oestradiol

The influence of the oestrous cycle and gender on responses of isolated pressurized mesenteric arteries to acute 17 β ‐oestradiol was investigated. All vessels, pre‐contracted with 60 m M KCl or 10 μ M U46619 (9,11 dideoxy‐11α, 9α‐epoxy methano‐prostaglandin), exhibited concentration‐dependent vasodilatory responses to 17 β ‐oestradiol (3–30 μ M ). 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 μ M 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 β ‐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 μ M , 3 h) significantly enhanced the subsequent vasodilatory responses to acute 17 β ‐oestradiol. Following incubation, the responses to 17 β ‐oestradiol were similar in all groups. These observations suggest that gender and the oestrous cycle may influence the vascular responses to acute 17 β ‐oestradiol administration.British Journal of Pharmacology (2001) 132 , 1055–1062; doi: 10.1038/sj.bjp.0703908