Estrous cycle- and acute stress-related changes of rat ovarian immunoreactive corticotropin-releasing factor

Corticotropin-releasing factor (CRF), the major regulator of the stress response within the central nervous system, is also present at peripheral sites, including the gonads, and the gene encoding its own receptor can be finely induced in selective ovarian compartments in both control and stressful conditions during the gonadal life cycle. The present study, therefore, investigated the influence of both gonadal function and estrous cycle on the immunoreactive CRF (irCRF) contents in the immature and adult rat ovary. In addition, the effect of an acute (5 min) or chronic intermittent (twice a day for 4 days) cold swimming stress on ovarian irCRF contents was evaluated. High-performance liquid chromatography (HPLC), gel-chromatography (Sephadex G-75, 45 x 1 cm) and a direct radioimmunoassay were performed to measure irCRF ovarian contents. The HPLC elution profile of irCRF in ovarian tissues of adult rats was superimposable on that of synthetic rat/human CRF and gel-chromatograms performed according to the phase of the estrous cycle revealed higher irCRF contents at proestrus. Total irCRF ovarian content was undetectable both in control and acute stressed immature rats, while adult rats showed the highest values at proestrus (p < 0.0001). The acute stress exposure induced a significant increase (p < 0.0001) of irCRF ovarian contents only at proestrus, without affecting irCRF at the other phases of the estrous cycle. Finally, no significant changes were found in ovarian irCRF after chronic intermittent stress. The proestrus-related changes of ovarian irCRF, confirming the adult ovary as an extrahypothalamic source of CRF, may constitute a neuropeptidergic signal involved in the gonadal reproductive cycle. Furthermore, the stress-related changes of ovarian irCRF indicated that the gonad may be locally sensitive to acute stressful stimuli.