DIURNAL VARIATIONS OF RENAL FUNCTION IN MAN

Abstract

The diurnal variations of urine flow, tubular reabsorption of water, glomerular filtration rate (GFR) and renal plasma flow (RPF) were studied in 18 male adult patients who exhibited no evidence of cardiovascular-renal disease. The U/P (urine/plasma concentration ratio) for inulin was used as a measure of tubular reabsorption of water, the renal clearance of inulin (CIN) and of endogenous "creatinine" (CCR) were used as measures of GFR and the clearance of p-aminohippurate (CPAH) as a measure of RPF. Inulin and PAH were admd. intraven. through a plastic catheter at rates varying between 0.3 and 0.6 cc./min. The mean night to day ratios for urine flow was 0.83 [plus or minus]0.38, for the inulin U/P ratio 1.4 [plus or minus]0.41, for CIN 0.96 [plus or minus]0.07, for CCR 0.97 [plus or minus]0.06 and for CPAH 0.98 [plus or minus]0.06, indicating a significant decrease in urine flow, a considerable increase in tubular reabsorption of water, and a relatively constant GFR and RPF through the night as a whole. However, when the sleeping hrs. were broken up into 4-hr. periods, a slight but significant fall in GFR occurred between the 12 midnight to 4 A.M. period. The renal extraction of PAH in 2 subjects after a 24-hr. infusion of this substance was 0.903 and 0.93, indicating the validity of CPAH as a measure of RPF after prolonged infusion. Good agreement between CCR and CIN was obtained throughout 24 hrs. The average CCR/CIN ratio was 0.95 [plus or minus] 0.07. The mean peak values for GFR and RPF for these subjects, who were in bed throughout the period of observation, on a regular hospital diet and allowed fluid, ad lib., were 119 [plus or minus]23 and 597 [plus or minus] 124 cc./min. per 1.73 sq.m., respectively.