Vascular actions of 17beta-oestradiol in rat aorta and mesenteric artery.

1. It has been proposed that the cardiovascular protective actions of 17beta-oestradiol may involve calcium antagonistic actions. We have examined the effects of 17beta-oestradiol on contractions to noradrenaline and KCl in male rat small mesenteric artery and aorta. 2. In rat mesenteric artery, 17beta-oestradiol (10 microM) significantly reduced the maximum contraction to noradrenaline (67.7 +/- 5.8% of control) and KCl (38.8 +/- 3.1% of control) without affecting potency. 3. In rat aorta, 17beta-oestradiol (10 microM) also significantly reduced contractions to noradrenaline (77.5 +/- 4.8% of control), and the effects were mimicked by droloxifene (10 microM). The effect of oestrogen was not prevented by the protein synthesis inhibitor cycloheximide (10 microM). In experiments carried out in calcium-free solution in which calcium stores were depleted, 17beta-oestradiol (10 microM) significantly reduced the contraction to calcium restoration in rat aorta. 4. In aorta from female rats, 17beta-oestradiol (10 microM) significantly reduced contractions to noradrenaline (73.6 +/- 10.8% of control), but this effect of oestrogen was not prevented by cycloheximide (10 microM). 5. In summary, 17beta-oestradiol diminishes the maximum contractile response to noradrenaline in both rat small mesenteric artery and aorta, an effect which at least in the aorta is mimicked by the oestrogen receptor antagonist/partial agonist droloxifene, and may be due to restriction of calcium entry by a nongenomic action.