24-HOUR PROLACTIN PROFILES IN NIGHT WORKERS

In addition to sleep processes, it has been suggested that an intrinsi c circadian rhythmicity is involved in the temporal organization of pr olactin (PRL) secretion. Eight night workers were studied to determine whether the PRL rhythm is adapted to their rest-activity schedule and whether this provides evidence in favor of an endogenous clock-driven component. Ten day-active subjects, sleeping once during the night an d once after an 8-h delay in their sleep period, were used as a contro l group. Plasma PRL, body temperature, and plasma melatonin were measu red at 10-min intervals. Twenty-four-hour PRL profiles did not differ between night workers sleeping as usual during the daytime and day-act ive subjects submitted to an abrupt sleep shift to daytime. For the tw o groups of subjects a transient PRL peak, similar in size and time of occurrence, was observed during the night. Melatonin, a strong marker of the primary circadian oscillator, displayed a phase shift that dif fered widely among night workers. Body temperature, on the other hand, was found to be more regularly adapted despite the persistence of a s mall decrease or leveling off during the night. Although no relationsh ip was found between the melatonin increase and the nocturnal PRL peak , a concomitance with this transient temperature decrease could be dem onstrated. The persistence of this PRL peak in night workers raises th e question of its significance.