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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 filtration rate (GFR) to that of arterial blood pressure (BP) suggests that systemic hemodynamic factors contribute to this variation. In the present study, this was investigated using continuous BP monitoring and pulse wave analysis. The study was performed in eight healthy subjects and in seven patients with nephrotic syndrome who had normal or reversed rhythms of GFR.


METHODS
Circadian variations of renal function (continuous infusion of inulin/paraaminohippuric acid), noninvasive finger arterial pressure (Portapres), and vasoactive hormone levels were monitored during 27 hours. With stepwise backward regression analysis, the contributions of the measured variables to the circadian variation of GFR were investigated.


RESULTS
Both groups showed a reduction of BP at night. In the controls, this was related to a drop in cardiac output, while in the patients, total peripheral resistance decreased at night. None of the hemodynamic variables explained the circadian GFR variation in both groups. In the controls, only 6% of the effective renal plasma flow (ERPF) rhythm was associated with variations in cardiac output (P = 0.03). In the patients, atrial natriuretic peptide 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 does not result directly from changes in BP or cardiac output. An inverted GFR rhythm in patients with nephrotic syndrome may originate from hormonal mechanisms rather than directly from the hemodynamic effects of edema mobilization.