Influence of Estrous Cycle ond Sexual Hormones in Ventilatory Control during Hypercapnia

Abstract

Our study aimed to evaluate the ventilation (VE), tidal volume (VT), respiratory frequency (fR), oxygen consumption (VO2) ventilatory equivalent (VE/VO2) and body temperature (Tb) of rats at different stages of estrous cycle (proestrus, estrus, metaestrus and diestrus) and ovariectomized rats (OVX) with hormone replacement to estrogen (OVX + E2) and estrogen + progesterone (OVX + EP). Additionally, we compared the ventilatory and metabolic responses during normocapnia and hypercapnia in intact rats and orchidectomized (ORX) with intact estrous (phase that plasma concentrations of E2 and P are lower) and ovariectomized (OVX) rats during normocapnia and hypercapnia (7% CO2). VE, VT, fR, VO2 and VE/VO2 were not different among animals in different stages of the estrous cycle in normocapnia and hypercapnia, Tb was higher in female rats in estrus. Hormone replacement in females did not change the ventilatory and metabolic parameters. However, females OVX, OVX+E2 and OVX+EP showed lower ventilatory responses to hypercapnia compared to intact females in estrus phase. Intact animals (both males and females in estrus) showed a significantly higher VE and VE/VO2 in hypercapnia than castrated animals. We also observed that females in estrus had a higher ventilatory response to CO2 compared to intact male rats. Thus, our data demonstrated that the different phases of the estrous cycle did not change ventilation in normocapnia and hypercapnia. In addition, gonadectomy reduces the ventilatory response to CO2 and that rats in estrus phase have a higher ventilatory responses to hypercapnia than males. Supported by FAPESP and CNPq.