Lack of Effect on Human Lipoprotein-Triacylglycerol on the Function of Perfused Rat Kidney

We determined whether addition of human lipoprotein-TG to the perfusate for the isolated rat kidney would increase net Na⁺ reabsorption or maintain renal tissue K⁺ content. Rat kidneys (n = 6) were perfused for 75 min with a perfusate containing 6 g% of substrate-free albumin in Krebs-Ringer bicarbonate and a mixture of human chylomicrons and very low density lipoproteins (human lipoprotein-triacylglycerol (HL-TG)). Control kidneys (n = 6) were perfused in the substrate-limited state, i.e., without any exogenous substrates added to the perfusate. Means (n = 6) for function of control kidneys were GFR = 808 ± 50 μl g^-1 min^-1; %T-Na⁺ = 63.3 ± 1.3%. A significant loss of tissue K⁺ occurred: tissue K⁺ remaining after 75 min of perfusion = 79.1 ± 1.9%. Although kidney tissue contains lipoprotein lipase, HL-TG (n = 6) did not increase %Na⁺ reabsorption (64.3 ± 2.6%) or maintain tissue K⁺ content (80.6 ± 2.0%). Therefore, the TG might have been hydrolyzed and taken up for biosynthesis, the rat kidney lipoprotein lipase might have been inactive, or the rat kidney might not use lipoprotein-TG for biosynthesis or oxidation.