There is evidence for a bidirectional communication between HPA and HPG axis involving different structures, however the involved mechanisms are poorly known.Stress situations may alter the reproductive function, and gonadal steroids may modify the stress response.The aim of this study was verify if estrogen (E 2 ) and progesterone (P 4 ) can alter the basal activity of hypothalamic-pituitaryadrenal axis, analyzed by corticosterone (CORT) and P 4 secretions and by mineralocorticoid and glicocorticoid receptors (MR and GR, respectively) expression at HPA axis central feedback sites.Adult female Wistar rats were kept in 12h light-dark cycle and had free access to food and water.The estrous cycle was monitored by vaginal smears and the luteinizing hormone dosage was done to confirm proestrus.Six samples of blood were collected by jugular cannula, during the afternoon (13-18h), of the following groups: ovariectomized (OVX), proestrus controls, treated with E 2 or P 4 antagonists (tamoxifen or RU486, respectively), or with both, and treated with antagonists" vehicle.The plasm was stored for hormonal dosages by radioimmunoassay.After the last blood sample, animals were anesthetized, perfused, and the brains were removed and processed for immunofluorescence to analyze MR and GR expression at ventral hippocampus" CA 1 and subiculum, and GR expression at paraventricular nucleus (PVN).The results showed that: LH secretion confirmed the proestrus; CORT basal secretion was not altered by injections neither by ovariectomy; there was a CORT and a P 4 secretion peak at 14h in all experimental groups, E 2 and P 4 antagonists did not modify the CORT total secretion, however RU486 increased (at 13 and 15h) and tamoxifen reduced (at 15h) CORT levels, another P 4 secretion peak in the late afternoon (17-18h) was blocked by ovariectomy and tamoxifen, but enhanced by RU486, the P 4 second peak did not occur in rats treated with both tamoxifen and RU486, there were no changes in the number of neurons expressing GR and MR at ventral hippocampus" CA 1 and subiculum neither of GR expressing neurons at PVN.In conclusion, our results indicate that: E 2 and P 4 can have antagonistic effects over basal CORT secretion; stimulatory and inhibitory, respectively; the P 4 secretion peaks have different origins, the first (14h) is adrenal"s and the second (17-18h) is ovarian: E 2 stimulates ovarian P 4 secretion in the proestrus afternoon; E 2 and P 4 do not alter the number of neurons that express MR and GR at HPA axis feedback sites, but one can not exclude the possibility that they alter the activity of these neurons. Introdução