Effects of Changes in Serum Calcium on Blood Pressure in Conscious Dogs

Studies were undertaken to explore the role of changes in serum calcium on blood pressure and the blood pressure response to antihypertensive drugs which block the renin-angiotensin axis. In 47 control experiments the baseline mean arterial pressure was 103.9 ± 1.29 mm Hg. After significant reduction of serum calcium in 26 experiments by thyroparathyroidectomy (TPTX; n = 18) or ethylenediaminetetraacetic acid (EDTA) infusion (n = 8) the mean arterial pressure was lower at 101.8 ± 2.94 mm Hg (p < 0.05). In 12 paired experiments TPTX reduced the mean arterial pressure from 107.8 ± 2.3 to8.5 9 ± 3.3 mm Hg (p < 0.01). In 10 experiments with different doses of EDTA infusion there was a linear correlation between serum calcium and mean arterial pressure (r = 0.91 p < 0.001). Plasma renin activity in normocalcemic animals was 1.52 ± 0.29 ng/ml/h and increased to 3.76 ± 0.85 ng/ml/h in hypocalcemic animals (p < 0.05). In 30 experiments in which angiotensin blockade was used in normocalcemic animals, the blood pressure decreased by -9.6 ± 1.8 mm Hg. in 22 hypocalcemic dogs the blood pressure decreased by –15.3 ± 1.93 mm Hg after angiotensin blockade with the same doses of the drugs (p < 0.05). In 5 paired experiments saralasin reduced blood pressure -2.2 ± 5.09 mm Hg (n. s.) under control normocalcemic conditions, but after being rendered hypocalcemic (TPTX) saralasin reduced blood pressure from 97.4 ± 7.02 to 83.6 ± 5.73 mm Hg (p < 0.01). Finally, there was a correlation between serum calcium and decrease in mean arterial pressure in response to saralasin (r = 0.766, p < 0.01) and in response to captopril (r = 0.6042, p < 0.05). In these investigations reduction of serum calcium decreased blood pressure, increased plasma renin activity, and potentiated the vasodepressor effects of saralasin and captopril. Elevations of calcium blunted the effects of these drugs.