Plasma prolactin (Prl) and follicle stimulating hormone (FSH) concentrations were determined in 196 normal post-menopausal women, aged 45–54 years, receiving different doses of oestrogens in combination with gestagen (28 day cycle) in a placebo-controlled trial. In experiment I, 15 women received trisequens forte for 3 years, 19 women the same hormone combination for 2 years followed by 1 year's placebo treatment, and 15 women received placebo for 3 years. In experiment II, 30 women received trisequens forte, 22 women trisequens, 23 women trisequens mite, 20 women trisequens without oestriol, and 42 women placebo for 1 year. In both studies plasma concentrations of Prl and FSH were measured with 3 to 6 months interval.
The mean plasma Prl concentration increased about 25% (P < 0.01) in all hormone treated groups in both experiments within 1 year's treatment. However, only 26/139 (19%) of the hormone treated women had elevated Prl levels (> 20 μg/l) after 1 year of treatment. The elevated mean plasma Prl levels were maintained throughout the second and the third year of treatment with a trend to further increase. Initially, 6/196 (3.1%) of the post-menopausal women had plasma Prl concentrations of 21–40 μg/l. After 3 years of hormone therapy, 5/15 (33%) had plasma Prl concentrations of 21–60 μg/l. A significant and clearly dose-related fall in the plasma FSH concentration occurred in the hormone treated groups. The decrease varied between 40% and 75% and was seen within the first 3 months of treatment. No significant changes occurred in the mean plasma concentrations of FSH and Prl in the placebo groups.
It is concluded that hormone substitution with cyclical oestrogen/gestagen induces a rise in plasma Prl concentration, which is not related to the dose of oestrogens; and a fall in plasma FSH concentration, which is doserelated. Furthermore, it is suggested that oestriol has no significant Prl stimulating effect.