The effects of calcium and vitamin D on blood pressure in conscious sheep

The metabolic and haemodynamic effects of elevating plasma calcium levels were examined in both normal and ACTH-hypertensive sheep. Six weeks of dietary Ca++ supplementation did not alter plasma calcium levels, blood pressure or heart rate. Five days of CaCl2 infusion (2 mmol/h) or intravenous vitamin D injections elevated plasma ionised and total Ca++ levels and heart rate but mean arterial pressure was unchanged. As in other species, elevation of plasma Ca++ levels over 4 hours by infusion of CaCl2 at 2, 5, and 10 mmol/h increased mean arterial pressure and decreased heart rate. The course of ACTH-induced hypertension was not altered in animals supplemented with CaCl2 in their drinking water for 6 weeks nor by intravenous injection of vitamin D for 5 days. This study does not support a major role for altered plasma ionised or total Ca++ levels in the genesis of ACTH-dependent hypertension in the sheep.