Rabbits given a single subcutaneous injection of an alkaline extract of hog, bovine, or human anterior pituitary glands developed marked hyperlipemia within 12 to 24 hours. The injections in some instances were followed by sickening and death of the animal, though no anatomical changes responsible for these consequences could be determined. No such sequelae were observed in animals given much larger injections of comparable extracts made from other tissues.

An inhibitor to lipoprotein lipase appeared regularly in the serum of the injected animals in association with the hyperlipemia. The injection of heparin into such animals failed to result in the elaboration of clearing factor, and serum from these animals inhibited in vitro the hydrolysis of lipid emulsions by active lipoprotein lipase obtained from normal rabbits or human beings. The inhibitor was produced only in vitro by the pituitary extracts. It did not antagonize the anticoagulant action of heparin, and is probably a lipoprotein.

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