Lung lipoprotein lipase: inhibition by barbiturates

The action of barbiturates on the enzymatic activity of lung lipoprotein lipase has been studied in vitro and in vivo. Mouse lung preparations can be separated into two fractions containing lipoprotein lipase activity and designated as soluble and membrane-bound. In vitro, both enzyme fractions were inhibited in a graded manner by the barbiturates when present in concentrations of 1-4 mg/ml. Experiments to determine the mechanism for the inhibition of lipoprotein lipase suggest that it may be related to non-specific binding of the drug to the enzyme since other drugs e.g., phenylbutazone and a coumarin derivative which bind non-specifically to serum albumin showed similar inhibitory activity. When rat lungs were perfused in situ with heparin, 49% of the total lipoprotein lipase activity was released into the perfusate. However, when pentobarbital was perfused prior to heparin, no lipoprotein lipase activity was observed in the perfusate. The possible clinical implications resulting from inhibition of pulmonary lipoprotein lipase by barbiturates are discussed in this paper.