Hormonal Regulation of Human Adipose Tissue Lipoprotein Lipase

Abstract

The intravenous injection of heparin releases a variety of lipolytic activities into the plasma that are active against a variety of substrates including triglycerides (TG), monoglycerides, and phospholipids (Biale and Shafrir, 1969; Vogel et al., 1971). Lipoprotein lipase (LPL), the rate-limiting enzyme in the removal of TG from plasma lipoproteins (LP) (Robinson, 1963, 1970), is present in many tissues (Robinson, 1970; La Rosa et al., 1972; Pykalisto et al., 1974); therefore, its activity is estimated indirectly as postheparin lipolytic activity (PHLA) (Robinson, 1970; Korn, 1959). Recent evidence suggests that postheparin triglyceride lipase activity (PHTGLA) is composed of several enzymes including a hepatic triglyceride lipase (TGL) that contributes significantly to PHLA (La Rosa et al., 1972; Krauss et al., 1974; Ehnholm et al., 1974a, 1974). Hepatic TGL can be differentiated from LPL by immunochemical methods (Huttunen et al., 1975) and affinity chromatography on Sepharose (Ehnholm et al., 1974b) and does not require C-apolipoproteins for activation (Ehnholm et al., 1974a). LPL, which is present in many tissues, may also be heterogeneous in requiring different apolipoprotein activators (Ganesan et al., 1975). The importance of either one or several TGLs in the removal of TG from plasma LP in man is suggested by the association of marked hypertriglyceridemia with decreased PHLA (Havel and Gordon, 1960) and low adipose tissue LPL (Harlan et al., 1962) in familial LPL deficiency. However, the exact mode of action and the regulation of these TGLs has not been established.