Determination of plasma insulinlike activity, using the hypophysectomized-adrenalectomized rat.

Abstract

An in vivo method of assaying 0.2–2.0 mU/ml plasma insulin using 4–6 hypophysectomized- adrenalectomized rats is described. Taking the decreases of blood sugar during a 1-hr period following intraperitoneal injection of test samples as responses, a rectilinear regression line was constructed against log dose of standard insulin solutions. The validity of this assay was confirmed by statistical analysis. Although insulinlike activity could not be demonstrated in the plasma obtained from fasting men or dogs, the plasma from the Superior pancreaticoduodenal vein of dogs showed various degrees of insulinlike activity under different experimental conditions, the fasting level being in the range of 0.2–0.4 mU/ml. Disappearance of this activity following treatment with cysteine strongly suggests the insulinlike nature of this activity. After intravenous injection of I131-insulin in dogs, the time course of blood I131-insulin level and insulinlike activity, pursued by determining TCA-precipitable radioactivity an...