AN ASSAY OF PROLACTIN BASED ON A DIRECT EFFECT OF THIS HORMONE ON CELLS OF THE CORPUS LUTEUM

ABSTRACT An attempt was made to develop a quantitative method of assay for prolactin. This seemed possible since experimental results with hypophysectomized, HCG- and PMS-treated immature female rats, with or without a hypophyseal transplant, showed considerable differences in the number of corpus luteum cell nuclei (CLCN) counted per surface unit of these two groups, while there were low variations within each group. In subsequent experiments it was shown that subcutaneous injections of increasing concentrations of a hypophyseal homogenate or purified prolactin from the 5th–11th day after hypophysectomy, progressively decreased the number of CLCN per 0.0972 mm2 in hypophysectomized immature female rats which were treated with high doses of HCG and PMS from 1st–11th day after hypophysectomy. After some experience reproducible counts were obtained. Correlation between dose and response proved to be satisfactory (correlation-coefficient = 0.94). Regression equation X = 1.36813 − 0.00652 Y, in which Y stands for the number of CLCN/0.0972 mm2 and X for the log. dose of sheep prolactin in IU. Response variations in the course of time were low. The practicability of this test is discussed against the background of literature on other prolactin assay methods.