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POSTNATAL CHANGES OF ACTIVITY OF ACID LIPASE AND NONSPECIFIC NEUTRAL ESTERASE IN RAT LIVER

Hydrolysis of the 4-methylumbelliferyl (4-MU) esters, oleate and nonanoate, was studied in homogenates of liver from suckling and adult rats. In both age groups, the pH optimum for 4-MU oleate hydrolysis was 4.0, whereas 4-MU nonanoate was hydrolyzed maximally at pH 6.5-7.0. Acid lipaee (4-MU oleate, pH 4.0) was resistant to inhibition by the organophosphate, dlethyl-p-nitrophenyl phosphate (E600), while nonspecific neutral esterase (4-MU nonanoate, pH 7.0) was sensitive to inhibition. Acid lipase and nonspecific neutral esterase differed substantially in the patterns of their postnatal development in the liver. Acid lipase activity was high during the suckling period and decreased after the third week of life to adult levels which were 50% of suckling levels. Nonspecific neutral esterase increased markedly with age, and adults attained levels 10 times those of sucklings. These experiments together with our concomitant findings of high acid lipase in the small intestine of suckling rats suggest the important metabolic role of acid lipase during the suckling period when fat intake is high. (Supported in part by NIH grants HD 08536 and HL 18723-01).