Short- and long-term fluctuations in plasma prolactin concentration in normal subjects

Abstract. The physiological changes in plasma prolactin concentration were studied in 447 normal subjects, including 65 men, 75 pre-menopausal women and 307 post-menopausal women. The within-day and day-to-day variation as well as the circadian and circannual rhythm of plasma prolactin levels were determined. Furthermore, the relationship between changes in prolactin and oestradiol-17β levels during the normal menstrual cycle and in the climacteric was studied. Pre-menopausal women had significantly ( P <0.01) higher basal plasma prolactin concentration than men and post-menopausal women. Furthermore, they had significantly ( P < 0.01) higher day-to-day variation than men. This suggests that prolactin in women is secreted in a pulsatile fashion. Only small seasonal variations in both sexes were seen. The levels of plasma prolactin during the ovulatory and the luteal phase in the cycle were significantly ( P < 0.02) higher than that of the follicular phase, and a positive correlation between changes in plasma concentration of oestradiol-17β and prolactin was found. Also in post-menopausal women a relationship between plasma concentration of prolactin and oestradiol-17β was seen. It is concluded that the assessment of prolactin concentration in blood is dependent on the physiological variation recorded during sleep in both sexes. However, only in women day-to-day changes and the changes related to the menstrual cycle and the climacteric are of importance.