THE INHIBITORY ACTION OF OESTRADIOL‐17‐β AND PROGESTERONE ON VENOUS SMOOTH MUSCLE

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Abstract
1 The in vitro action of oestradiol-17-β (0.1, 1.0 and 10.0 μg/ml) and progesterone (0.1, 1.0 and 10.0 μg/ml) on the spontaneous activity of the portal veins in female rats at different stages of gestation was studied. 2 Progesterone caused the spontaneous mechanical activity in the rat portal vein to decrease in amplitude and increase in frequency. This action was dose-dependent and the sensitivity of the tissue decreased throughout pregnancy. 3 Oestradiol-17-β had a biphasic effect on spontaneous mechanical activity in the rat portal vein. At 0.1 μg/ml the vessel was stimulated while a similar effect to progesterone occurred with higher concentrations. The tissue was more sensitive to oestradiol at 7 days of gestation than at either the 10-14 or 17-21 day periods of gestation. 4 These effects of oestradiol and progesterone were still seen after blockade of the β-adrenoceptors. 5 Hydrocortisone (10 μg/ml) had no inhibitory effect on the spontaneous mechanical activity of the vein. 6 The veins from the 17-21 days pregnant animals showed a smaller amplitude of contraction than comparable non-pregnant females.

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