Urinary concentration does not exclusively rely on plasma vasopressin. A study between genders Gender and diurnal urine regulation

AIM: We investigated the influence of gender on the diurnal regulation of urine production with special focus on vasopressin, oxytocin and prostaglandin E2. METHODS: Fifteen young women in mid-follicular phase and 22 young men (20-33 years) were included. All participants underwent a 24-h circadian inpatient study under standardized conditions for measurements of plasma vasopressin, oxytocin, sodium and osmolality. Urine was fractionally collected for measurements of electrolytes, aquaporin-2 and prostaglandin E2. RESULTS: Plasma vasopressin expressed a diurnal rhythm with a night-time increase in both genders (P < 0.001). The ratio between mean daytime and mean night-time was 1.57 [95% CI: 1.33-1.84] P < 0.001 in men and 1.35 [95% CI: 1.11-1.64] P = 0.002 in women. P-vasopressin was higher in males during the night (P < 0.05). There was no difference in diuresis (P = 0.43), urine osmolality (P = 0.12) or aquaporin-2 excretion (P = 0.80) between genders. We found a trend towards a higher reabsorption of free water in males (P = 0.07). The excretion of prostaglandin E2 was higher in males (P < 0.001). There was no diurnal rhythm in p-oxytocin (P = 0.37) and no correlation to diuresis, urine osmolality or aquaporin-2 excretions. CONCLUSION: Similar urinary flows and osmolalities are associated with levels of plasma vasopressin and renal PGE2, which are higher in males than in females. Oxytocin does not seem to play a role in the diurnal urine formation, whereas prostaglandin E2 could represent a mediator of the gender difference, not only as a mediator of the vasopressin response, but also as an independent factor. These findings need further elucidation.