Plasma post-heparin lipolytic activity in hyperchylomicronemia (fat-induced lipemia)

Abstract

1. 1. Low levels of plasma post-heparin lipolytic activity, assayed in vitro, were observed in three siblings with hyperchylomicronemia, a heritable disorder characterized by markedly increased levels of serum triglyceride transported as chylomicrons ( S f > 5000). Although no evidence of inhibitors was observed in pre- or post-heparin plasma from these hyperchylomicronemic siblings, in vitro studies with esterase and lipase inhibitors demonstrated that plasma post-heparin lipolytic activity in these siblings was relatively less inhibited by NaCl, sodium deoxycholate, Triton, or sodium dodecyl sulfate than was the post-heparin lipolytic activity in plasma from subjects with other types of hyperglyceridemia or from subjects with normal serum triglyceride concentrations. 2. 2. The lipolytic activity in post-heparin plasma was measured using individual triglycerides containing C 4 through C 18 fatty acids as substrates. The plasma tributyrinase activity was normal in the siblings with hyperchylomicronemia, whereas the rates of lipolysis for triglycerides containing C 8 through C 18 fatty acids were low. Lipolytic activity in the plasma of these hyperchylomicronemic siblings had a relative substrate specificity (the ratio of the rate of lipolysis of an individual triglyceride to that of tricaprin) for triglycerides containing longer-chain fatty acids similar to that for subjects with other types of hyperglyceridemia. The K m value of the lipolytic activity in post-heparin plasma differed several-fold between the siblings with hyperchylomicronemia and the other subjects studied. 3. 3. It is suggested that subjects with hyperchylomicronemia have a genetically determined structural abnormality of the lipolytic enzyme or enzymes resulting in a lessened hydrolysis of triglycerides containing longer-chain fatty acids.