Effects of oral contraceptives containing different progestogens on sodium-lithium countertransport in normal females

Abstract

In view of the lack of unanimity on the effect of long-term intake of combined oral contraceptives (OC) on external sodium-dependent lithium efflux, otherwise known as sodium-lithium countertransport (SLC), we undertook a double-blind study to investigate the possible interaction between SLC and OC in healthy women with regular menstrual cycles. In a group of 17 volunteers, aged 27.0 ± 1.1 years (mean ± s.e.m.) and weighing 61.4 ± 2.0 kg, ingestion of 30 μg ethinyloestradiol + 150 μg desogestrel for 3 months caused an increase in SLC activity from a baseline value of 0.254 ± 0.017 mmol/lcell.h to 0.274 ± 0.017 mmol/lcell.h (P = 0.05). The activity of the transport system after 6 months treatment remained higher than at baseline (0.280 ± 0.016 mmol/lcell.h, P < 0.025) but was comparable to that at 3 months. blood pressure and weight remained unaltered during the study period. in a comparable group of 16 volunteers of age 26.1 ± 1.3 years and weight 63.5 ± 2.1 kg, control slc activity (0.218 ± 0.012 mmol/lcell.h) was comparable to that after 3 months (0.215 ± 0.011 mmol/lcell.h) and 6 months (0.216 ± 0.011 mmol/lcell.h) intake of 35 μg ethinyloestradiol + 2 mg cyproterone acetate. body weight and blood pressure remained similarly unchanged. these results not only confirm that long-term intake of oc may cause increased slc activity, but also suggest that the type of the progesterone in the medication used could be an important determinant of such interaction.