Insulinlike Activity of Serum from Normal and Hypophysectomized Monkeys

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Abstract
Changes in the rate of the net gas exchange of rat adipose tissue have been used to measure the insulinlike activity of sera from normal and hypophysectomized monkeys. The activity of normal serum when assayed undiluted corresponds on the average to that given by 97 μU insulin/ml of incubation medium, while the corresponding value for the serum of hyphophysectomized animals is 44 μU/ml. If the serum is diluted 1:3 for assay, then the average values for normal and hypophysectomized sera are 198 and 54 μU of insulin/ml, respectively. Thus, sera from hypophysectomized animals not only tend to show an insulinlike activity lower than that of sera from normal animals, but also fail to display the marked increase in values seen upon dilution of normal sera. The results are discussed in relation to the presence in normal sera of an insulin antagonist, the elaboration of which is dependent upon an intact pituitary.