Variations in Plasma Aldosterone and Plasma Renin Activity Throughout the Menstrual Cycle, With Special Reference to the Pre-Ovulatory Period

ABSTRACT The day to day variations in plasma aldosterone and plasma renin activity throughout the menstrual cycle have been investigated in healthy young women. A sensitive and specific radioimmunoassay for the measurement of plasma aldosterone is described. The actual hormone parameters have been correlated with fluctuations in plasma oestradiol and progesterone, and LH has been measured for the determination of time of ovulation. Plasma renin activity and plasma aldosterone gradually increased two to four times from the early follicular to the mid-luteal phase, in accordance with earlier observations. In one woman using a beta adrenergic blocking agent plasma renin activity rose only slightly, whereas a normal rise in plasma aldosterone was noted. Another woman became pregnant during the cycle investigated. In this subject neither plasma renin activity nor plasma aldosterone decreased at the end of the cycle. Plasma aldosterone was almost doubled on the pre-ovulatory day, as compared with the early follicular phase, whereas no significant change in plasma renin activity or plasma renin substrate was found. The cause of this pre-ovulatory increase in plasma aldosterone is not known.