Circadian periodicity of serum prolactin concentration in man

Abstract

Immunoreactive human serum prolactin of pituitary origin has been measured by a radioimmunoassay developed for ovine prolactin. Blood samples were collected at four-hour intervals during a 24-hour period from 12 non-pregnant women, three pregnant women, and seven adult men. A circadian periodicity was found in serum prolactin concentration, with peak values during the night, between 1 a.m. and 5 a.m. for the nonpregnant women, and at 5 a.m. for the adult men. Mean serum levels of prolactin were 1•5 times higher in nonpregnant women than in men. In women investigated during the last month of their pregnancy the mean serum prolactin levels were 2•3 times higher than in the non-pregnant women, but there was no circadian periodicity. © 1972, British Medical Journal Publishing Group. All rights reserved.