Possible role of lipoprotein lipase in the regulation of endogenous triacylglycerols in the rat heart.

1. Adrenaline has a biphasic effect on intracellular lipoprotein lipase activity and on endogenous triacylglycerol content in heparin-perfused heart. 2. A high concentration of adrenaline (1 microM in the perfusion buffer) activated endogenous lipoprotein lipase activity and, at the same time, decreased intracellular triacylglycerol stores. 3. In contrast, a low concentration (0.005 microM-adrenaline) inhibited intracellular lipoprotein lipase activity. Under these conditions, cardiac triacylglycerol content was elevated above control values. 4. Perfusing the heart with high and low concentrations of 3-isobutyl-1-methylxanthine elicited a biphasic effect on endogenous lipoprotein lipase activity and triacylglycerol content similar to that seen with adrenaline treatment. 5. The effect of adrenaline on intracellular lipoprotein lipase activity appears to be mediated by cyclic AMP through protein kinase. 6. A possible role for intracellular lipoprotein lipase in the regulation of endogenous triacylglycerol in rat heart is proposed.