Sleep-Related, Nyctohemeral and Briefly Episodic Variation in Human Plasma Prolactin Concentrations

A recently developed, sensitive, specific homologous radioimmunoassay for human prolactin (hPRL) made possible our study of hPRL variation in plasma across sleep-wake cycles and in daytime naps. Samples were drawn at 20-min intervals from 5 normal young adults (4 ♂, 1 ♀), studied over at least three 24-hr periods each, and in 12 daytime naps. Study periods consisted of 1–3 baseline sleep-wake cycles per subject (total 8/5 subjects), 1-2 sleep-wake cycles per subject in which the wake cycle contained a single 2-hr daytime nap period (total 8 sleep-“nap” cycles/5 subjects) and a single daytime nap added onto the end of a 24-hr sleep-wake cycle (total 4/4 subjects). Sleep was polygraphically monitored. Round the clock hPRL concentrations exhibit briefly episodic, rather aperiodic, circhoral variation that rarely approaches undetectability or reported t½ values of labeled exogenous PRL. The briefly episodic pattern does not repeat itself at 24-hr periods or in sleep each night, and is not synchronous with hGH...