Erythrocyte concentrations and transmembrane fluxes of sodium and potassium and biochemical measurements during the menstrual cycle in normal women.

The erythrocyte concentrations and the transmembrane fluxes of sodium and potassium were investigated in 20 normal women during the two stages of the menstrual cycle. Half of the women were using oral contraceptives and the other half were not. In women with a normal menstrual cycle the erythrocyte sodium concentration and the ouabain-insensitive total potassium efflux were lower in the luteal than in the follicular phase. Intracellular potassium concentration, ouabain-sensitive rubidium 86 uptake and the furosemide-sensitive sodium and potassium efflux did not differ significantly between the two periods of the cycle. No cycle-related variation in sodium or potassium intracellular concentration was observed in women using oral contraceptives. In these women, however, the ouabain-sensitive 86Rb uptake was increased in the second part of the menstrual cycle. In each woman with a normal menstrual cycle the plasma progesterone, renin activity, angiotensin II, plasma aldosterone concentration, and urinary aldosterone excretion increased during the luteal phase. The increment in the plasma renin activity, plasma angiotensin II, and plasma and urinary aldosterone indicate a stimulation of the renin-aldosterone axis in this menstrual period. During the same phase, serum cholesterol was decreased significantly. When the women using oral contraceptives were compared to those not using them, the renin-aldosterone axis was already stimulated during the first part of the cycle; no further stimulation occurred during the second part.