RENAL SODIUM RETENTION DOES NOT OCCUR DURING THE LUTEAL PHASE OF THE MENSTRUAL-CYCLE IN NORMAL WOMEN

Objective To determine whether weight gain due to renal sodium and water retention occurs in the luteal phase of the normal menstrual cycle. Design Prospective observational study. Setting Research laboratory installed with modified spa bath. Subjects Ten normal healthy women. Intervention Each subject underwent two experiments, one in each phase of the menstrual cycle, involving 3 h head-out water immersion and a pre- and post immersion control hour. 25 ml blood samples were obtained every hour before, during and after water immersion. Main outcome measures Renal and hormonal responses to water immersion during the luteal and proliferative phases of the cycle. Results There was no change in weight, creatinine clearance, basal sodium excretion or plasma atrial natriuretic peptide between the two phases of the cycle. There was a significant rise in basal progesterone, plasma aldosterone and plasma renin activity in the luteal phase of the ovulatory cycles. Renal and hormonal responses to immersion including sodium and calcium excretion, elevation of atrial natriuretic peptide (ANP) and suppression of plasma aldosterone and plasma renin activity were identical in the two phases of the menstrual cycle. Conclusion We found no evidence to support the hypothesis that renal sodium and water retention occurs in the luteal phase of the normal menstrual cycle.