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 < 0.01), and plasma colloid osmotic pressure (COP) was 9 ± 1 mmHg (control 22 ± 1 mmHg, P < 0.01). Subcutaneous fluid COP was lowered from 14 ± 1 to 4 ± 1 mmHg (P < 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.