Objective: Administration of oral contraceptive (OC) steroids is associated with an increased risk of developing hypertension, although the mechanisms underlying this effect are not well established. This study therefore sought to investigate the effect of L-type calcium channel blocker, nifedipine on OC-induced hypertension.
Methods: Female Sprague-Dawley rats received OC (norgestrel/ethinyloestradiol) and/or nifedipine orally for 10 weeks. . Blood pressure and heart rate were thereafter recorded under anaesthesia from the femoral artery with a Grass Polygraph 7D model, whereas plasma and urinary Na+ and K+ concentrations were measured using a flame photometer. The stable oxidation products of nitric oxide, urinary nitrite/nitrate (NO) were measured in urine by means of the brucine method.
Results: OC administration led to significant (p<0.05) increases in blood pressure and plasma Na+, and decreases in body weight, food and water consumption, excretion of Na+ and NO. Concomitant treatment with nifedipine significantly (p<0.05) abrogated the alterations induced by OC administration.
Conclusion: This study provides evidence that the development of OC-induced hypertension is prevented by calcium channel blockade via improved renal handling of sodium and nitric oxide. The finding confirms the involvement of calcium channels in OC hypertension.