Effects of calcium loading in DOCA-salt hypertensive rats

The effects of oral calcium loading on blood pressure (BP) of DOCA (deoxycorticosterone acetate)-salt hypertensive rats (D-S rats) were investigated. Calcium loading was performed by adding 1% CaCl2 (calcium chloride) to the drinking water. Calcium loading attenuated the development of high BP in D-S rats, and at the end of a two week experiment, BP was 141 +/- 3 (calcium treated) vs. 174 +/- 7 mmHg (non-calcium treated) (p less than 0.01). However, calcium loading did not cause any changes in BP in normotensive rats. Further, in established D-S rats [after four weeks of DOCA and 1% NaCl (sodium chloride) treatment], calcium loading for 4 weeks also reduced BP [144 +/- 6 (calcium treated) vs. 181 +/- 4 mmHg (non-calcium treated), p less than 0.01, at the end of experiment]. With calcium treatment, there were no significant changes in sodium-water balance, plasma levels of epinephrine and norepinephrine, plasma renin activity, plasma aldosterone concentration and serum electrolytes both in developing and established D-S rats. The depressor mechanism of calcium loading was studied by observing vascular responsiveness to norepinephrine both in whole body and in hind limb preparations. Vascular reactivity in both developing and established D-S rats was significantly attenuated by calcium treatment. These results suggest that the antihypertensive effects of calcium treatment in D-S rats are mainly caused by attenuation of vascular reactivity.