The renin-angiotensin system in association with hyperreninaemic hypoaldosteronism in neoplasia induced hypercalcaemia.

The renin-angiotensin system was examined in Fischer rats at 7, 11 and 14 days after Leydig cell tumour transplantation, and in age matched controls. Mean arterial blood pressure (MAP), active plasma renin and serum calcium were higher (P less than 0.01) in the tumour transplant rats than in the controls at 11 days after transplantation. There was a positive correlation of both active renin and MAP with serum calcium at this time. Although inactive renin levels were elevated in the tumour transplanted rats, the ratio of inactive to active renin was decreased in comparison to controls. Plasma norepinephrine, active renin and plasma angiotensin II were higher in tumour rats at 14 days. Nevertheless, basal levels of aldosterone and MAP as well as aldosterone responses to graded infusion of angiotensin II, ACTH and KCl were decreased in the tumour rats at 14 days. Moderate hypercalcaemia (day 7 and 11), induced by Leydig cell transplantation in the Fischer rat, is associated, therefore with elevated blood pressure which appears to be related, in part, to activation of the renin-angiotensin system. However, severe hypercalcaemia (day 14) was associated with hypotensive hyperreninaemic hypoaldosteronism state.