Renal Hemodynamic Responses to Stress in Normotensive and Hypertensive Subjects

Abstract

Renal responses to stress were studied in 28 normotensive and 51 hypertensive patients. Renal clearances of inulin and PAH, filtration fraction, arterial blood pressure, and renal vascular resistance were determined in each patient immediately before, during, and after exercise (sit-ups), or the cold pressor test. In the control periods immediately before stress the majority of patients with essential hypertension displayed reduced values for inulin clearance (C_in) and clearance of paraaminohippurate (C_pah) and increased values for filtration fraction and renal vascular resistance, when compared with normotensive groups. These abnormalities were more severe in malignant hypertension than in benign essential hypertension. The pattern of response to stress was similar in normotensive and untreated hypertensive patients: reduction in C_in and C_pah, and increases in filtration fraction, blood pressure, and renal vascular resistance. These responses were more marked with exercise than with the cold pressor test. These responses to stress were also quantitatively similar in normotensive and untreated hypertensive subjects, except for renal vascular resistance, which was increased more in the hypertensive groups. Hyperreactivity in terms of vascular resistance, however, is not necessarily indicative of vascular smooth muscle hyperreactivity. The renal responses to exercise or the cold pressor test were reduced or abolished in hypertensive subjects by sympathectomy, and were diminished, in the majority of patients, by therapy with reserpine. Neither sympathectomy nor reserpine affected control (prestress) values for renal clearances or renal vascular resistance, however. The majority of patients with malignant hypertension, though showing severely reduced values for C_in and C_pah, and marked elevations in renal vascular resistance initially, showed minimal renal responses to exercise or the cold pressor test.