Evidence for a Difference in Nitric Oxide Biosynthesis Between Healthy Women and Men

There is indirect evidence for a gender difference in nitric oxide (NO) synthesis from vascular endothelium. The aim of the present study was to determine NO production more directly in healthy women and men by the measurement of N nitrate excreted in urine after the intravenous administration of L-[() N] (2-guanidino) arginine. Twenty-four healthy volunteers (13 men aged 22 to 40 years and 11 women aged 23 to 42 years) participated in this study. No subjects were receiving any medication. Women were studied between the 7th and 14th days of their menstrual cycles. Arterial blood pressure was measured oscillometrically, and 1.13 [micro sign]mol L-[() N]2 arginine was administered intravenously after an overnight fast. Urine was collected for the next 36 hours in separate 12-hour periods. Urinary N/() N nitrate ratio was assessed by dry combustion in an isotope ratio mass spectrometer. Mean 36-hour urinary N nitrate excretion was greater in women than in men (2111 +/- 139 versus 1682 +/- 87 eta mol; P