Hypophysial-portal plasma levels, median eminence content, and immunohistochemical staining of corticotropin-releasing factor, arginine vasopressin, and oxytocin after pharmacological adrenalectomy

Abstract

Changes in immunostaining, median eminence content, and secretion into the hypophysial-portal circulation of immunoreactive CRF (irCRF), arginine vasopressin (irAVP), and oxytocin (irOT) were directly evaluated after pharmacological adrenalectomy (PHADX). Mean circulating levels of ACTH rose from 270 +/- 57 (+/- SE) to 1560 +/- 283 pg/ml after 72 h of treatment with metyrapone and aminoglutethimide. Initially, hypophysial-portal plasma irCRF levels decreased to 52.6% (12 h) and 21.7% (24 h) of control levels (230 +/- 41 pg/ml). Accompanying changes in the patterns of CRF immunostaining in the paraventricular nuclei (PVN) or in median eminence irCRF content at 24 h did not parallel alterations in portal plasma irCRF levels at this time. By 72 h posttreatment, portal irCRF levels were elevated 2.2-fold, while the number of detectable CRF-positive perikarya in the PVN increased 3.0-fold. The mean hypophysial-portal plasma irAVP concentration was unchanged from the control value (1312 +/- 287 pg/ml) at 12 h, but was only 34.9% of the control value at 24 h. Inverse changes in median eminence irAVP content were noted at these times, whereas the number of AVP-immunostained cells exhibited a tendency toward an increase at 24 h, in parallel with significantly increased content. By 72 h post-PHADX, portal irAVP, median eminence irAVP content, irAVP immunostaining intensity, and AVP-immunopositive cell number were elevated. Approximately 64% of CRF-positive perikarya in the parvocellular PVN costained for AVP at this time, whereas no colocalization was evident in untreated rats. These changes were prevented by corticosterone replacement. irOT staining intensity, irOT-positive cell number, median eminence irOT content, and portal plasma irOT concentration remained stable at all times examined. We conclude that: removal of adrenal steroids by PHADX results in a sequence of changes in CRF and AVP within the PVN (as determined by immunocytochemistry) and the median eminence (as determined by peptide content) similar to those observed after surgical adrenalectomy; after steroid removal the secretion of both irCRF and irAVP changes in a biphasic manner characterized by reduced secretion at 24 h and greatly enhanced secretion at 72 h; neither immunostaining nor median eminence content alone proved to be a reliable index or secretory activity during the initial phases of steroid blockade; and the hypophysiotropic OT system of normal male rats appears to be insensitive to adrenal steroid influences.