EFFECT OF THE NORETHISTERONE MINI-PILL ON THE PLASMA-LEVELS OF BIOLOGICALLY AND IMMUNOLOGICALLY ACTIVE LUTEINIZING-HORMONE IN WOMEN

The relationship between biologically and immunologically active luteinizing hormone (LH) in plasma was investigated daily throughout a menstrual cycle in 29 women before and during the 2nd mo. of the oral administration of norethisterone (Mini-Pe, Astra-Syntex) in a daily dose of 0.3 mg. The biological activity was determined by an in vitro bioassay and the immunological activity by a radioimmunoassay method. A characteristic midcycle surge of LH was observed with both assay methods in all 29 control cycles. Of the 29 treatment cycles studied with both assay methods, 10 cycles exhibited a similar LH pattern, although the levels of both activities were significantly depressed (P < 0.001) during all phases of the cycle. The biological to immunological (B/I) ratios of plasma LH between the treatment and control cycles were not significantly different. Of the remaining 19 treatment cycles, in which no midcycle LH peak was evidenced, the levels of both activities in the treatment periods were significantly lower (P < 0.05) than in the follicular phase and significantly higher than in the luteal phase (P < 0.05) of the control cycles. The overall B/I ratios were significantly lower in the treatment periods than in the control cycles (P < 0.001). However, the influence of this difference on the general pattern of immunological activity in comparison with that of biological activity was relatively small. The irregular patterns of immunological hLH activity which are observed after treatment with low doses of norethisterone are similar to those of the biological activity.