Lipolytic activity in rat heart

¹ Cardiovascular Section, Oklahoma Medical Research Institute, and Department of Medicine, University of Oklahoma School of Medicine, Oklahoma City, Oklahoma

In homogenates of rat heart pronounced lipolytic activity was found which had a broad pH optimum between 7.5 and 8.5. In the presence of a high concentration of NaCl or protamine sulfate an activity peak persisted between pH 6.5 and 7. This activity was greatest when hearts from fasting animals were preincubated with epinephrine and subsequently assayed in the presence of albumin. The activity was least in heparin-incubated samples and was inhibited by NaF. When lipase activity was determined in the presence of NaF a pH optimum of 8.5 was found. This lipase required serum protein and ammonium sulfate for optimal activity and could be inhibited by high concentrations of NaCl and by protamine sulfate. The yield of this lipase was similar whether hearts were obtained from fasting or from fed rats. This lipase was considered identical with the lipoprotein lipase described by E. D. Korn. It was found only in small amounts in the medium after incubation, in the presence of heparin, of the whole heart but in greater amounts when minced or sliced heart was used. After differential centrifugation most of the activity of both lipases was found in the mitochondrial fraction and in the soluble fraction.