AJP - Renal Physiology, Vol 244, Issue 3 320-F324, Copyright © 1983 by American Physiological Society
Renal contribution to acid-base regulation during the menstrual cycle
N. Takano and T. Kaneda
Menstruating women exhibit a light but sustained hypocapnia during the
luteal phase. To elucidate whether the hypocapnia results primarily from a
respiratory or renal mechanism, we measured the rate of urinary excretion
of acid at intervals during the menstrual cycle in five subjects. The
acid-base composition of arterial blood in three subjects and end-tidal
PCO2 in the remaining two subjects were also determined. During the
follicular phase, the acid-base composition of blood and the rate of net
acid excretion remained virtually constant. After ovulation, significant
decreases in PaCO2 (3.5 mmHg), [HCO3]p (2 meq/liter), and net acid
excretion (2 meq/h) occurred in the first 4-6 days of the luteal phase (14
days long). Following this, net acid excretion returned to the preovulatory
level. PaCO2 and [HCO3]p, however, remained decreased for 3 more days. At
the end of the luteal phase, restoration of PaCO2 proceeded faster than
that of [HCO3]p. The acid-base changes in blood and urine observed during
the luteal phase were comparable to those occurring during adaptation and
recovery from sustained hypocapnia, suggesting that hypocapnia during the
luteal phase is primarily respiratory in origin.
