HUMAN PROLACTIN. EVIDENCE OBTAINED BY THE BIOASSAY OF HUMAN PLASMA

Abstract

SUMMARY Single plasma samples from 27 control subjects and from 18 women in early lactation have been assayed for lactogenic activity using a semi-quantitative rabbit mammary gland organ culture method. Tests with a variety of anterior pituitary, posterior pituitary, placental and steroid hormones have shown the method to be specific for prolactin and for prolactin-like hormones such as human growth hormone (HGH) and human chorionic somatomammotrophin (HCS). Twelve of the 18 samples from women in early lactation gave positive lactogenic responses, while only one of the control samples did so. Plasma HGH levels were measured by radioimmunoassay. The levels of HGH in the medium, resulting from addition of plasma, were in all cases below the limits of sensitivity of the assay. The conclusion that human prolactin immunologically distinct from HGH is being measured is supported by the failure of antiserum to HGH to affect the in-vitro lactogenic response to plasma. Assay of fractions prepared from plasma by gel filtration suggests a molecular weight of approximately 20000 for the lactogenically active material.