PRELIMINARY OBSERVATIONS ON PROLACTIN ACTIVITY IN HUMAN BLOOD*†

Abstract

Prolactin activity of human whole blood was concentrated by means of acid acetone extracts, using the Sulman method for the extraction of chromatophototropic activity. These extracts were assayed by a single-injection local pigeon crop-weight technique. No prolactin activity was found in extracts obtained from the blood of children, of normal young men, and of normal young women in the first half of the menstrual cycle. On the other hand, extracts obtained from the blood (equivalent to 2.5 ml. whole blood) of young women in the second half of the menstrual cycle induced crop-weight responses of the same order of magnitude as induced by 0.05 I.U. of authentic prolactin, and activity greater than this was found in extracts obtained from the blood of lactating postpartum women. These obser-vations constitute physiologic evidence that prolactin activity was measured, since prolactin activity was found only in those circum-stances that would be expected on the basis of the known physiologic activity of the hormone. Further physiologic evidence was provided by the disappearance of prolactin activity in the blood of adult female rats and an oophorectomized woman one to two weeks following hypophysectomy. Technically, the ability to confirm positive local prolactin assay results by positive systemic assay results with the use of pooled extracts further supports the validity of these observations. The complete recovery of small amounts of prolactin by the Sulman extraction technique is another piece of technical evidence supporting the concept that prolactin activity was demonstrated in human blood.