Effect of increased dietary calcium on hemorheological, lipid and lipid peroxidation in oral contraceptive-treated female rats.

Oral contraceptive (OC) steroids use has been associated with variable effects on blood lipid and rheological properties, and abnormal plasma lipid and hemorheological profiles has been shown to be in almost all conditions associated with accelerated atherosclerotic cardiovascular disorders. This study aimed at investigating the effect of increased calcium intake on plasma levels of lipids, malondialdehyde (lipid peroxidation index), free radical defense system and hemorheological variables in OC-treated female Sprague-Dawley rats. OC-treated and OC + Calcium-treated groups received a combination of ethinyl estradiol and norgestrel for 10 weeks by oral gavage. OC + Calcium-treated rats fed on 2.5% calcium diet while other groups fed on 0.9% calcium diet in addition to drinking water ad libitum. Results showed that LDL-cholesterol, total cholesterol/HDL-cholesterol ratio, LDL-cholesterol/HDL-cholesterol ratio, plasma viscosity, hematocrit and plasma fibrinogen were significantly higher while plasma HDL-cholesterol, 17beta-estradiol, testosterone and calcium levels were significantly lower in OC-treated rats when compared with the control rats. The altered plasma lipid and calcium levels were prevented by increased calcium intake, whereas the OC-induced changes in hematocrit, plasma viscosity, fibrinogen, 17beta-estradiol and testosterone were not affected by increased dietary calcium. Plasma lipid peroxidation index, ascorbic acid and albumin levels were comparable in all the groups. The present study demonstrated that OC-induced altered blood lipid and rheological properties were not associated with increased lipid peroxidation. The results also suggest that calcium enriched diet may improve lipid profile but not hemorheological parameters, by a mechanism that is independent of circulating 17beta-estradiol and testosterone in OC-treated rats.