Hypoproteinemia and recovery from edema in dogs

We studied the effects of hypoproteinemia following 12 days of repeated plasmapheresis and low-protein diet on sodium balance, fluid volumes, and renal hemodynamics in six conscious dogs on 50 mmol sodium intake. Measurements during hypoproteinemia were obtained during a 5-day recovery period starting 20 h after the final plasmapheresis session, with continued low-protein diet. During the plasmapheresis period sodium was retained. Sodium balance became negative on the first recovery day when plasma protein was 29 +/- 1 g/l (control 60 +/- 2 g/l, P less than 0.01), and plasma colloid osmotic pressure (COP) was 9 +/- 1 mmHg (control 22 +/- 1 mmHg, P less than 0.01). Subcutaneous fluid COP was lowered from 14 +/- 1 to 4 +/- 1 mmHg (P less than 0.01). Blood volume, plasma renin activity, and aldosterone were unchanged. Glomerular filtration rate and effective renal plasma flow were slightly reduced (NS), and filtration fraction was unchanged. After a second plasmapheresis period in three of the dogs, plasma protein fell to 26 +/- 1 g/l and COP to 7 +/- 1 mmHg. Now sodium was retained on the first day after stopping plasmapheresis, and renin and aldosterone were high. The next day, when plasma protein was again 29 +/- 1 g/l and COP 8 +/- 1 mmHg, these three dogs were able to completely excrete an infusion of 130 mmol sodium. These data suggest that the level of plasma COP below which dogs on a medium-sodium intake would retain sodium averages 8 mmHg, which is considerably lower than generally thought.