Metabolic Clearance and Secretion Rates of Prolactin in the Rat

Abstract

Rat prolactin 131I, prepared by a standard method for radioimmunoassay, was given intravenously by constant infusion or by a single injection into anesthetized (Na pentobarbital) intact male rats, and ovariectomized, hypophysectomized or intact female rats. Blood samples were collected at frequent intervals and the serum was assayed for immuno-precipitable prolactin and for total radioactivity. The disappearance curve after a single intravenous injection of rat prolactin in a pituitary homogenate, as measured by radioimmunoassay, was the same as that of the labeled prolactin, indicating that the latter was cleared from the blood in a manner identical to that of the endogenous hormone. The metabolic clearance rate (MCR), denned as the volume of blood cleared of prolactin per unit time, was 1.26 ± 0.08 ml/min by the constant infusion method and 1.2 to 1.46 ml/min by the single injection method. The half-life time for the first exponential (first 10 min after iv injection) of injected rat prolactin ranged fr...