High-calcium diet reduces blood pressure, blood volume and preserves vasorelaxation in oral contraceptive-treated female rats.

Cardiovascular complications are the major clinical challenges among users of synthetic steroids in oral contraceptive (OC) formulations. Interventions that reduce blood volume and improve vasorelaxation have been shown to reduce hypertension and the associated risk factors. The aim of the present study was to investigate the influence of increasing dietary calcium from 0.9 to 3.0% on the development of OC-induced high blood pressure and associated changes in female Sprague-Dawley rats treated with a combination of OC steroids (1 microg ethinyl estradiol and 10 microg norgestrel; p.o.) daily for 10 weeks. Results showed that OC administration led to significant increases in blood pressure, blood volume and cardiac weight. Conversely, OC caused significant reductions in body weight, urinary excretion of water, plasma levels of calcium, 17beta-estradiol and progesterone. Increased dietary calcium attenuated the elevation in blood pressure induced by OC and abrogated the associated changes in blood volume, cardiac weight, plasma calcium and urinary excretion of water. The endothelium-dependent relaxation responses to acetylcholine and endothelium-independent relaxation responses to sodium nitroprusside in noradrenaline-precontracted aortic rings were not significantly different among the groups. The results indicate that increased calcium intake abrogated the development of high blood pressure and associated increased blood volume and cardiac weight during OC treatment. The beneficial effect of increased dietary calcium during OC use may be explained by improved diuretic and preserved vasorelaxant responses. 2009 Elsevier Inc. All rights reserved.