Abstract
Rat hearts were perfused retrogradely using a modified technique that allows the separate collection of coronary (Qrv) and interstitial (Qi) effluents. Evidence is presented that Qrv contains products from the coronary vasculature and that Qi contains products arising from cardiac myocytes. Heparin perfusion of rat hearts led to a release of lipolytic activity in Qrv and Qi which was characterized as lipoprotein lipase (LPL). The relative amounts of LPL released in Qrv and Qi were dependent on the feeding condition of the rat. A high LPL activity was recovered from Qrv of fasted rats, and Qi was high in LPL during feeding. On perfusion of hearts with [3H]cholesterol-labeled chylomicrons, the tissue uptake of cholesterol was highest in the fasted state, whereas release of radioactivity in Qi was predominant in the fed state. This radioactivity in Qi appeared to be associated with chylomicron degradation products (remnants and surface fragments). Our experiments indicate that cholesterol uptake during chylomicron breakdown is inhibited in the fed state, and the relationship between myocyte LPL activity and interstitial formation of chylomicron degradation products suggests a role for the myocyte LPL in lipoprotein metabolism.
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