Circulating levels of nitric oxide in fertile women in relation to the menstrual cycle.

Objective: To investigate nitric oxide (NO) production in the two phases of normal menstrual cycle.

Design: Prospective clinical study.

Setting: Normal human volunteers in an academic research environment.

Patient(s): Fifteen normally cycling women.

Intervention(s): Follicle growth monitoring by ultrasound, serum, and plasma sampling in the midfollicular phase, at ovulation, and in the midsecretory phase.

Main Outcome Measure(s): Plasma concentration of NO stable oxidation products and serum concentrations of E2 and P.

Result(s): Plasma concentration of NO metabolites resulted higher in the follicular phase with respect to the secretory phase and peaked at midcycle.

Conclusion(s): The results strongly support the existence of an E2 control of NO production and release. The significant reduction in NO metabolites observed in the secretory phase suggests a possible opposing action of P on either NO production or release.