Serum requirement for release of heparin-induced lipase from perfused rat heart

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Abstract
The release of a lipolytic enzyme from the isolated perfused rat heart was studied. The perfusion medium was a Krebs-Henseleit bicarbonate buffer, pH 7.4, with or without heparin and/or serum. The lipolytic activity of perfusates was determined by incubating the perfusate in a phosphate buffer, pH 7.4, at 37 C for 1 or 2 hr using coconut oil emulsion, rat chylomicrons, or cottonseed oil emulsion as a substrate in the presence of serum albumin. Both heparin and serum were required for optimal enzyme release; the optimal concentrations of heparin and serum were 50 µg/ml and 10% by volume, respectively. Addition of serum to the assay system could not replace its effect in the perfusion medium. The appearance of the enzyme in the perfusion medium was rapid; 55% of the total lipolytic activity was released within 2 min. The lipolytic activity of this enzyme was inhibited by protamine, NaCl, NaF, and taurocholate.