The lipolytic activity of rat kidney cortex and medulla

Slices of rat kidney medulla and cortex were incubated for 30 min in a triglyceride medium with and without heparin; the slices were then removed and the lipolytic activity of the medium measured over the following 30 min. Heparin markedly increased the activity in the medium when medullary slices were used; it had a much smaller effect with cortical preparations. Protamine sulphate and 1 m sodium chloride inhibited the activity released by medullary slices. Homogenates of rat kidney medulla hydrolyzed activated triglyceride to a greater extent than nonactivated substrate. The activity of medullary homogenates was enhanced by heparin and inhibited by protamine and strong salt solutions. Cortical homogenates hydrolyzed activated substrate to only a slightly greater extent than nonactivated substrate, and the activity of these homogenates was not affected by heparin or by protamine sulphate. The results suggest that lipoprotein lipase is present in rat kidney medulla and that a lipase differing from this enzyme in a number of respects is present in rat kidney cortex.