Twenty-four hour profiles of circulating
prolactin have been documented in eight boys with simple
delayed puberty, eleven with gynaecomastia, three of whom were retested following its spontaneous resolution, and two normal adult men. Mean 24 h
prolactin levels in four boys with
delayed puberty and ten with gynaecomastia exceeded the mean levels for the two adult men. A sleep-associated rise in
prolactin levels occurred at all stages of puberty irrespective of the presence or absence of gynaecomastia, and in some subjects peaks also occurred during the daytime. Boys with gynaecomastia had higher 24 h means levels of
prolactin (P less than 0.05), higher daytime levels (P less than 0.05) and higher sleep-associated levels (P less than 0.05) than did control subjects. These were not related to the degree or duration of the gynaecomastia, but 24 h mean levels of
prolactin and
oestradiol were positively correlated. In one subject who had had transient galactorrhoea, high levels of circulating
prolactin, oestrone and
oestradiol fell following spontaneous resolution of the gynaecomastia. We believe that oestrogen:
androgen imbalance during the daytime is the major cause of pubertal gynaecomastia, with hyperprolacinaemia (which may cause galactorrhoea) sometimes occurring as a response to relative hyperoestrogenaemia.