SYNTHESIS AND TRANSPORT OF LIPOPROTEIN-LIPASE IN PERFUSED GUINEA-PIG HEARTS

Total lipoprotein lipase (LPL) activity did not differ significantly between hearts from fed or fasted guinea pigs. Incorporation of [S-35]methionine into immunoprecipitable LPL was also the same. The rates at which perfused hearts from fed or fasted guinea pigs released LPL activity into the medium were, however, different (2 vs. 4 mU.g-1.min-1). These rates remained constant over 60 min of perfusion. Addition of heparin to the medium resulted in a peak of LPL activity during the first 2 min, followed by a shoulder of relatively high activity, which gradually declined to a constant rate from 30 min. The peak and shoulders were less with hearts from fed animals than with hearts from fasted animals, but the constant rates were similar. Cycloheximide added at the start of the perfusion had no effect on the peak or on the early part of the shoulder, but the LPL activity released from 30 min continuously decreased so that at 60 min it was less than half of that in controls. Studies in which the enzyme was pulse labeled by perfusion 15 min with medium containing [S-35]methionine and then chased up to 75 min with unlabeled medium showed no differences in how LPL is transported and metabolized in hearts from fed vs. fasted guinea pigs. Thus the data suggest that factors outside the heart influence the disposition of heart LPL in vivo.