Influência de diferentes doses de cipionato de estradiol nas alterações hidroeletrolíticas de ratas ovariectomizadas

Abstract

The distribution of estrogen receptors in brain structures that are envolved in the hidroelectrolyte balance such as the lamina terminalis (LT), subfornical organ (SFO) and dorsal raphe nucleus (DRN) demonstrated that estradiol can modulate important responses in body fluids. In the literature experimental data support that estrogen can increase the triptofan-hydroxilase type 2 , the main enzyme for the serotonin synthesis. The primary question here is whether or not differences in the baseline or stimulated intake are a function of different levels of circulating gonadal hormones in female ovariectomized rats. Female Wistar intact rats (~230 g) were previously aclimated in metabolic cages during 5 days and ad libitum access to water and hypertonic saline (1.8%) bottles and food. Room temperature was maintained at 22±2 ºC with 12:12 h light-dark cycle (lights off at 19:00). Rats were anesthetized with intraperitoneal injections of a mixture of ketamine (75 mg/kg) and xylazine (5 mg/kg) and then bilaterally ovariohysterectomized. There were four experimental groups: OVX (replaced with corn oil), 2,5 µg/kg (E2 2,5), 10,0 µg/kg (E2 10,0) and 40,0 µg/kg (E2 40,0), daily during seven days, s.c. After 24 h of the surgery the hormonal replacement initiated (estradiol cypionate, EC, Pfizer, Animal Health). We did three experimental protocols: baseline evaluations, sodium depletion and fluid replacement. The estrogen replacement exibitted a dose dependent effect in the following parameters under basal conditions: daily body weight, daily urinary volume and daily food intake. After sodium depletion there were no difference in the urinary volume after 2 and 24 hours of the experiment. But after fluid reposition we observed a dose dependent effect in the ingestive behaviour of water and hypertonic saline intake in sodium depleted and control animals. Our data support that estradiol can alter the natriorexigenic and dipsogenic responses especially after sodium depletion depending of the estrogenic status.