Circadian rhythms in systemic hemodynamics and renal function in healthy subjects and patients with nephrotic syndrome

Background. The resemblance of the circadian rhythm of glomerular filtratio n rate (GFR) to that of arterial blood pressure (BP) suggests that systemic hemodynamic factors contribute to this variation. In the present study, th is was investigated using continuous BP monitoring and pulse wave analysis. The study was performed in eight healthy subjects and in seven patients wi th nephrotic syndrome who had normal or reversed rhythms of GFR. Methods. Circadian variations of renal function (continuous infusion of inu lin/paraaminohippuric acid), noninvasive finger arterial pressure (Portapre s), and vasoactive hormone levels were monitored during 27 hours. With step wise backward regression analysis, the contributions of the measured variab les to the circadian variation of GFR were investigated. Results. Both groups showed a reduction of BP at night. In the controls, th is was related to a drop in cardiac output, while in the patients, total pe ripheral resistance decreased at night. None of the hemodynamic variables e xplained the circadian GFR variation in both groups, In the controls, only 6% of the effective renal plasma flow (ERPF) rhythm was associated with var iations in cardiac output (P = 0.03). In the patients, atrial natriuretic p eptide and plasma renin activity were responsible for 36% of the variation in GFR (P < 0.01). Conclusions. These results indicate that the circadian variation of GFR doe s not result directly from changes in BP or cardiac output. An inverted GFR rhythm in patients with nephrotic syndrome may originate from hormonal mec hanisms rather than directly from the hemodynamic effects of edema mobiliza tion.