The effects of estrogen and progesterone on corticotropin-releasing hormone and arginine vasopressin messenger ribonucleic acid levels in the paraventricular nucleus and supraoptic nucleus of the rhesus monkey

Ovarian steroids increase hypothalamic-pituitary-adrenal (HPA) axis activit y and sensitize the hypothalamic-pituitary-ovarian (HPO) axis to stress-ind uced inhibition. The present study investigated the effect of ovarian stero ids on CRH and arginine vasopressin (AVP) messenger RNA (mRNA) levels in th e rhesus monkey hypothalamus, as both neuropeptides have been shown to stim ulate the HPA axis and inhibit the HPO axis in this species. This was accom plished by measuring CRH and AW mRNA in the paraventricular nucleus (PVN) a nd supraoptic nucleus (SON) by in situ hybridization histochemistry. Menstr ual cycles were simulated in ovariectomized (OVX) rhesus monkeys by sequent ial addition and removal of SILASTIC brand (Dow Coming Corp.) tubing contai ning either 17 beta-estradiol (E-2) or progesterone (P-4). On the morning o f day II of the simulated follicular phase (E-2 alone) or day 21 of the lut eal phase (E-2 + P-4), animals were anesthetized, and the brains were perfu sed with paraformaldehyde via the carotid artery. Coronal sections (30 mu m ) were cut, and mRNA for CRH and AVP in the paraventricular nucleus (PVN) a nd supraoptic nucleus (SON) were semiquantified by in situ hybridization. C RH mRNA in the PVN of E-2-replaced OVX animals (n = 7) was 2-fold greater t han that in untreated OVX controls (n = 4), whereas CRH mRNA after E-2 + P- 4 (n = 4) was no different from that in controls (optical density +/- SEM, 0.38 +/- 0.06, 0.13 +/- 0.08, and 0.14 +/- 0.09 for OVX + E-2, OVX + E-2 P-4, and OVX, respectively; P = 0.02). CRH in the SON was undetectable. In contrast to CRH, AVP mRNA in the PVN and the SON was similar in the three t reatment groups. We conclude that E-2 and E-2 + P-4 replacement to OVX monk eys exert different effects on CRH and AVP gene expression, as estrogen sti mulation of CRH mRNA in the PVN was abrogated by progesterone, whereas no e ffect of ovarian steroids on AVP mRNA in either the PVN or SON was observed . We postulate that ovarian steroid regulation of CRH synthesis and release may in part explain the central nervous system mechanisms by which ovarian steroids affect the HPA and HPO axes during basal and stress conditions.