Role of physical factors in the acute changes in renal function elicited by antihypertensive drugs.

Abstract

An analysis of the correlations between acute changes in blood pressure and renal function elicited by antihypertensive drugs in hypertensive subjects is presented. The drugs used in the study were chlorisondamine, guanethidine, clonidine, phentolamine, hydralazine, a pyrogen and a new hydrazinopyridazine derivative (BQ 22-708). On average mean blood pressure (mBP) decreased by 16%, glomerular filtration rate (GFR) by 11%, urine volume (V) by 8% and sodium clearance (CNa) by 17%. The PAH clearance (CPAH) increased by 3%. Changes in CPAH were not related to changes in mBP. GFR correlated directly with mBP, CPAH and the product mBP × CPAH. The changes in all subgroups in the fractional excretion of water and sodium correlated with the changes in mBP. They correlated further with CPAH in the pyrogen and hydralazine subgroups. There was no consistent relationship between V or CNa and the estimated peritubular capillary oncotic pressure. In 2 subgroups, CNa was not related to plasma aldosterone. The fractional urea excretion was also dependent on blood pressure. The data indicate that, after single doses of antihypertensive agents, changes in renal function largely depend on physical factors. The fall in blood pressure depresses GFR and enhances tubular reabsorption of water, sodium and urea. Renal vasodilation opposes these effects and, if of sufficient magnitude, actually reverses them. There is no evidence for an additional role of humoral or nervous factors.