• Twenty-four-hour rhythms of serum prolactin (PRL) levels were studied in seven depressive patients. Blood was collected through an indwelling catheter and the PRL level was determined by homologous double antibody radioimmunoassay. Findings showed a different pattern of secretion of prolactin among depressives as compared to the normal 24-hour rhythm of the hormone. A statistically significant elevation of PRL levels during the evening, several hours before sleep, was found. Morning PRL levels were slightly higher and the average increase of PRL level from one determination to the consecutive one was higher among the depressives. It is assumed that there may be a connection between the diurnal rhythmicity of mood, characteristic of vital depression, and the different 24-hour rhythmicity of PRL level.
Halbreich U, Grunhaus L, Ben-David M. Twenty-four-Hour Rhythm of Prolactin in Depressive Patients. Arch Gen Psychiatry. 1979;36(11):1183-1186. doi:10.1001/archpsyc.1979.01780110037004