Effects of chronic hypocalcaemia on plasma renin activity in man

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Abstract
The role of serum Ca in the regulation of renin secretion was studied. The subjects for this study comprised of 2 groups. Group I consisted of 10 patients with primary or secondary hypoparathyroidism. Blood samples for basal PRA (plasma renin activity) were drawn at 0800 h when the patientspatients were recumbent and on a normal Na intake. Then all the patients were given a constant diet containing 10 mEq Na for 4 days and were given 80 mg Furosemid orally every day. On the morning of the 5th day blood samples were drawn after the patients had been upright for 4 h. These patients were treated with vitamin D2 and when normocalcemic states were achieved the same study was repeated. Group 2 (control group) consisted of 10 normal, healthy subjects of both sexes. They were prepared for the experiment in the same way as for Group 1. In the hypocalcemic state mean serum Ca level was 5.6 .+-. 0.3 mg/100 ml. After treatment with vitamin D2, the mean serum Ca level was increased to 9.6 .+-. 0.1 mg/100 ml (P < 0.001). There was no significant difference in the mean serum Na and K levels in either hypocalcemia or normocalcemia. But the mean stimulated PRA (12.12 .+-. 1.13 ng/ml per h) was decreased in hypocalcemia compared to in normocalcemia and in the control group (22.87 .+-. 1.18 and 23.83 .+-. 0.86 ng/ml per h, respectively). The difference of means was significant (P < 0.001). There were no significant differences between basal PRA in hypocalcemic and normocalcemic state as well as in the cntrol group: (P > 0.5 P > 0.2 and P > 0.5, respectively). Serum Ca apparently plays an important role in the regulation of renin secretion.