A pilot study of erythrocyte lithium-sodium countertransport in women during the menstrual cycle.

Objective: The study investigated lithium-sodium countertransport in erythrocytes of normal female volunteers during different phases of the menstrual cycle or during administration of oral contraceptives.

Methods: Ten normally menstruating, and eight oral contraceptive using, normal female subjects were studied over at least one cycle. Erythrocyte lithium-sodium countertransport was determined using. standard, previously validated methods at different phases of the menstrual cycle. Hematological, electrolyte, blood pressure and other transport measures were also made and these were related to the self-reported incidence of premenstrual symptomatology.

Results: A correlation, (p < 0.02), was found between lithium-sodium countertransport rate and the premenstrual symptom severity score but only in the premenstrual phase. There was no correlation between any of the electrolyte, blood pressure or hematological data and lithium-sodium countertransport rate nor between it and other ion transport measures. Pre-menstrual symptomatology was conspicuously absent from those subjects taking oral contraceptives. Cyclical fluctuations in normally menstruating women, and differences between them and oral contraceptive users, were seen in lithium-sodium countertransport rate although the groups were too small to show statistical significance.

Conclusions: Care was taken to exclude influences due to circadian, dietary and diurnal variations and the present results show somewhat less within-individual variability in erythrocyte lithium-sodium countertransport during the menstrual cycle than do other reports in the literature. Some interesting features were observed which justify a much larger scale study than the present pilot experiment which should involve a larger number of subjects studied over more than one cycle and in particular a more detailed study of the ovulatory phase.