Differential fluid regulation during and after soft tissue trauma and hemorrhagic shock in males and proestrus females.

Gender differences in immune and organ functions have been described in different rodent models of trauma- and pressure-controlled hemorrhagic shock. We hypothesized that gender influences the regulation of plasma and tissue fluids in rats under such conditions. To study this we used male and weight matched proestrus female Sprague-Dawley rats, which were assigned to three groups (n = 7/group): sham, maximal bleedout (trauma and 45 min of blood pressure at 35 mmHg without resuscitation), or 5 h after completion of trauma-hemorrhage and resuscitation. Trauma-hemorrhage involved midline laparotomy and approx. 90 min of hemorrhagic shock (35 mmHg), followed by fluid resuscitation (4x the shed blood volume with Ringers lactate). (51)Cr-EDTA, (125)I-albumin distribution, and wet weight/dry weight were used to calculate plasma volume and extracellular fluid volume and cellular water content. Proestrus female rats showed significantly higher plasma volumes compared with weight-matched males. The volume of blood withdrawn in the first 15 min of hemorrhagic shock was significantly less in proestrus females compared with males; however, there was no significant difference in the total shed blood volume. Moreover, proestrus females showed less interstitial edema formation compared with male rats at 5 h after resuscitation. We conclude that differences in the regulation of plasma and tissue volumes exist between males and proestrus females during and after trauma-hemorrhage. The increased circulating blood volume could contribute the improved immune and organ functions in proestrus females under those conditions.