Interdependence of exchangeable sodium and plasma renin concentration in determining blood pressure in patients treated by maintenance dialysis.

Plasma renin concentration and exchangeable sodium were measured in 13 patients with terminal renal failure maintained by dialysis therapy. Blood pressure in seven "responsive" patients was controlled by ultrafiltration but was not controlled in six "resistant" patients. Plasma renin concentration was inversely related to exchangeable sodium in the responsive group but was inappropriately high for the level of exchangeable sodium in the resistant group. There was a better correlation between mean blood pressure and the product of plasma renin concentration and exchangeable sodium than with renin concentration alone.These results indicate that a severely diseased kidney can respond to changes in exchangeable sodium by alterations in renin secretion and they also support the concept that the potential pressor effect of renin is modified by exchangeable sodium. The product of the two factors might be used to determine the "effective" plasma renin concentration in respect of blood pressure.