Potassium ion as a regulator of adrenal angiotensin II receptors

The importance of potassium as a regulator of angiotensin II receptors of two target tissues has been investigated by combining high-K+ diet in rats with a converting enzyme inhibitor (Captopril; SQ 14,225) or angiotensin II. K+ loading alone produced the characteristic increase in Ka and decrease in number of smooth muscle receptors and decrease in Ka and increase in number of adrenal receptors. The combination of Captopril and high-K+ diet blocked the development of most of these effects. In smooth muscle, the number of angiotensin II receptors was 40% higher (n = 5) and Ka was 94% lower (n = 5); in the adrenal the Ka was 29% higher (n = 4) than with K+ loading alone. However, development of the increment in number of adrenal receptors occurred in spite of Captopril treatment. In addition, angiotensin II infusion concomitantly with high-K+ diet resulted in a further increment in the number of adrenal receptors. These studies represent the first example of an ion as a regulator of a peptide hormone receptor and emphasize that different mechanisms of regulation are involved in adrenal and smooth muscle.