The effect of human apolipoprotein E (apoE), either alone or in combination with apoC, on the lipolysis of a radiolabeled triglyceride emulsion was studied with hepatic lipase in solution and immobilized on heparin-Sepharose. The soluble hepatic lipase was inhibited, whereas the heparin-immobilized lipase was stimulated by apoE. This stimulation was attenuated by combining apoE with either apoC-II or C-III. The heparin-immobilized lipase demonstrated much less lipolysis of the zwitterionic phosphatidylcholine-stabilized triglyceride emulsion than did the soluble enzyme. This difference was less when the emulsion was stabilized by a nonionic detergent. apoE inhibited lipase activity when assayed under conditions (0.4 M NaCl) of bound enzyme and unbound substrate. Increasing the emulsion apoE content beyond optimum inhibited lipolysis by the immobilized enzyme. Kinetic analysis of phosphatidylcholine-stabilized triglyceride emulsions revealed a significant decrease in immobilized enzyme Km and an increase in Vmax when the emulsion was supplemented with apoE. Distributing the immobilized lipase in clustered aggregates produced more lipolysis than when the same enzyme content was uniformly bound.

A technique is described to remove the entire liver in a single stage with preservation of intestinal absorptive function. An inverted V-shape polyethylene cannula, either heparin bonded or silicon coated, was inserted into the portal vein and inferior vena cava to maintain venous return from the splanchnic and lower caval regions of the anhepatic rat. Blood glucose fell at a rate of 7 to 11 mg per hr per total plasma volume (4% body weight), usually resulting in hypoglycemia within the initial 2 hr. Euglycemia could be maintained in the first 3 hr after hepatectomy with hourly intravenous infusions of 2.5 to 5 mg per 100 gm body weight of glucose. Larger infusions of glucose (10 to 12.5 mg per hr per 100 gm body weight) were necessary for normal levels at later times. A 0.5 gm per 100 gm rat weight intestinal glucose bolus restored euglycemia for at least a 2-hr interval. Intestinal absorption of cholesterol and oleic acid was demonstrated in the anhepatic rat, although the latter was not so efficiently absorbed as in the control. The plasma cholesterol decreased with time in the anhepatic rat. Prompt increases were observed in plasma free fatty acid and glycerol concentrations after hepatectomy. Progressive increases in both direct and indirect plasma bilirubin levels were noted after hepatectomy. With appropriate maintenance of blood sugar, survival of 36 hr was observed. This procedure for single stage total hepatectomy in the rat can be performed in less than 30 min. The model is particularly useful for studies of the influence of the liver on postabsorptive metabolism.

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