Hormone replacement reduces elevated in vivo venous tone in hypertensive ovariectomized rats

Abstract

The venous system may play a role in the development and progression of postmenopausal hypertension. In the present study, we investigated the effect of chronic angiotensin II-induced hypertension on the geometric, elastic, and contractile properties of the saphenous vein in sex hormone deficient and replaced female rats. Thirty Sprague-Dawley rats were ovariectomized (n = 10), ovariectomized and angiotensin-infused (n = 10), or ovariectomized plus angiotensin-infused and hormone replaced with estradiol and medroxyprogesterone (n= 10). After 4 weeks, the saphenous veins were removed and cylindrical segments of the vessels were placed into a microangiograph and cannulated at both ends. Intraluminal pressure versus outer diameter curves were registered in Krebs-Ringer solution, in maximal norepinephrine contraction, and in full papaverine relaxation. In vivo venous tone of the saphenous vein in ovariectomized plus angiotensin-infused animals was significantly higher than in ovariectomized animals without angiotensin treatment (27.2 +/- 3.7% versus 5.3 +/- 2.1%, respectively; P <.05). Hormone replacement restored venous tone (9.6 +/- 3.4%; P <.01). In vitro pressure-induced myogenic tone was markedly reduced by chronic angiotensin infusion, which was partially reversed by hormone replacement. Passive incremental distensibility was lowered after angiotensin infusion independently of the sex hormone state. Hormone replacement improved venous contractility (rapid adaptation response), which was seen as decreased in vivo venous tone, but venous distensibility (chronic adaptation) was not improved by hormone replacement in our short-term study. We demonstrate beneficial short-term effects of hormone replacement on the venous system in our model of postmenopausal hypertension. Further studies might be warranted to see whether long-term benefits can be achieved.