Uptake and utilization of long chain and medium chain fatty acids by the perfused rat kidney

Biochemical

aspects

of kidney

xix

function

FATTY ACID UPTAKEAND SYNTHESISBY THE KIDNEY Institute

M. Hohenegger and H. Schuh for Gen. and Exp. Pathology, Univ. Wahringerstrasse 13, A 1090 Wien.

of Vienna,

In the state of starvation larger amounts of fatty acids (FA) are taken up by the rat and dog kidney than can be utilized (Dzurik, perfonall communication). This is particularly the case with free FA, triglyceride FA and total FA; cholesterol bound FA and phospholipids do not show any consistent behaviour. Under normal feeding and after infusionofglucose the amount of FA released equals the amount taken up under starvation. This means that triglyceride content of the kidney would This led us to determine triglyceride content of the depend onthenutritional state. rat kidney tissue under normal feeding conditions and under starvation lasting for 12 and 24 hours respectively. Thepercentage triglyceride content of the kidney cortex (wet weight) in the fed state was found to be 0.6 + 0.22%. After starvation for 12 and 24 hours this is increased to 0.9 f 0.23% and 1.19 f 0.28% respectively. The triglyceride content of the outer and inner medulla (0.54 f 0.1% and 0.57 f 0.12% respectively) does not change significantly after starvation. A lipoproteinlipase-like activity (more than 80% inhibition by 0.6 M NaCl) can be detected in kidney cortex tissue. This is independent of the nutritional state of the animal. In vivo measurements of lipid synthesis by employing the 3H20-method reveals about 90% lower rate of synthesis in kidney cortex, outer and inner medulla as compared with that of the liver,

UPTAKEAND UTILIZATION OF LONGCHAIN AND MEDIUMCHAIN FATTY ACIDS BY THE PERFUSEDRAT KIDNEY V.A. Medical

Mary Ellen Trimble Center, Syracuse, N.Y.,

13210,

USA.

Studies were done to determine.the capacity of the perfused rat kidney to transport and meabolize the long chain fatty acid (FA), palmitate, and to compare these results to previous studies with the medium chain FA, octanoate. Kidneys were perfused with Krebs bicarbonate buffer containing 1% defatted albumin, 0.2-2.0 mM palmitate and 0.125 uCi [U-14C] palmitate. Perfusate 14C label was identified as FA using the Dole extraction and chemical FA were determined by titration. Renal uptake of FA was linear from 0.2-1.1 mMperfusate palmitate. Above 1.1 mM (1.2-2.0 mM), a maximum uptake of 3.0 f 0.2 pmoles/g/20 min. was approached (N = 11). Due to extensive binding to albumin (>99%), filtration of the 14C label is minimal and uptake must occur primarily from the peritubular side. In.an attempt to determine whether this “apparent Tml’ was due to a limitation of metabolism, kidneys were first perfused with an inhibitor of FA oxidation, 0.4 mMa-bromopalmitate (aBP) (N = 5) or no aBP (N = 5) for 30 min. and then perfused for 60 min. with palmitate only. Inhibition of FA oxidation was confirmed by a decrease in water solublemetabolites of 14C palmitate oxidation in renal tissue and decreased fractional Na+ reabsorption. No apparent decrease in palmitate uptake was noted in a8P-treated kidneys compared to We have previously determined that maximum peritubular octanoate uptake controls. is approximately 2.1 umoles/g/20 min. With either 2.0 mMperfusate octanoate or palmitate, total FA uptake was approximately 3.4 vmoles/g/ZO min. In the case of palmitate, complete oxjdation of this amount of FA could account for the Q02 observed in the perfused kidney. It is not yet clear whether the apparent T, reflects the existence of a specialized transport system, a limitation of metabolism, or both. However,. under conditions of these experiments, partial inhibition of FA oxidation did not appear to cause a decrease in FA uptake. (Supported by the Veterans Administration).