I. The 24-hour profile of prolactin in depression

The 24-hour profile of plasma PRL was studied in 10 patients with unipolar depression and 8 patients with bipolar depression and compared to 18 control profiles obtained in healthy subjects. Alterations in the basal PRL secretion as well as the characteristics of the 24-hour rhythm were found in all patients but differed strikingly according to the type of depressive illness. The basal PRL level was elevated in unipolars, mainly as a result of increased secretion during wakefulness, and lowered in bipolars because of a lack or reduction of sleep-associated elevation. The nocturnal rise of PRL was maintained in unipolars but absent in 75% of the bipolar subjects. The variability of PRL levels around the 24-hour mean appeared to be reduced in both types of affective illness. These abnormalities in the 24-hour profile of PRL could serve as a biological marker of sub-types of depression.