Physicochemical analysis of phasic menstrual cycle effects on acid-base balance

Area of Science:

• Exercise Physiology
• Reproductive Endocrinology
• Acid-Base Physiology

Background:

• The human menstrual cycle involves hormonal fluctuations, particularly progesterone, which can influence ventilation.
• Ventilatory changes can impact acid-base balance, specifically plasma hydrogen ion concentration ([H(+)]).
• Understanding these effects is crucial for interpreting physiological responses to exercise.

Purpose of the Study:

• To investigate the determinants of plasma hydrogen ion concentration ([H(+)]) at rest and during exercise.
• To compare these determinants between the follicular phase (FP) and luteal phase (LP) of the menstrual cycle.
• To assess the influence of menstrual cycle phase on acid-base regulation during physical activity.

Main Methods:

• Healthy, active women were divided into FP (n=14) and LP (n=14) groups.
• Arterialized blood samples were analyzed at rest and during cycling exercise at 70% and 110% of ventilatory threshold (T(Vent)).
• Measurements included plasma [H(+)], arterial carbon dioxide tension (Pa(CO(2))), total weak acid ([A(Tot)]), and strong-ion difference ([SID]).

Main Results:

• Exercise significantly increased plasma [H(+)] in both groups, with higher levels at 110% T(Vent) compared to rest and 70% T(Vent).
• No significant differences in plasma [H(+)] were found between FP and LP groups at rest or during exercise.
• At rest, LP showed lower [A(Tot)] and Pa(CO(2)) than FP, but this was offset by a reduced [SID].

Conclusions:

• Acid-base regulation mechanisms demonstrate phase-related differences during the menstrual cycle.
• These regulatory differences ensure plasma [H(+)] remains relatively constant despite potential progesterone-induced ventilatory changes.
• The study highlights the body's ability to maintain acid-base homeostasis across different physiological states.