Effects of Ether-Laparotomy and Water Immersion-Restraint Stress on CRH Concentration in the Hypothalamus, Extrahypothalamic Tissues and Peripheral Blood

The effect of sustained stress on the plasma CRH level was studied in rats subjected to the stress of laparotomy conducted under ether anesthesia or water immersion-restraint. The role of AVP in ACTH secretion during such stress was also investigated. Concentrations of CRH and AVP in the hypothalamus, extrahypothalamic tissues and peripheral blood were measured by radioimmunoassays. Persistent secretion of ACTH was observed from 10 or 30min to 120min after the onset of each stress. Plasma CRH levels rose significantly 10min after the onset of ether-laparotomy stress and remained significantly elevated at 120min compared with controls. In the animals subjected to water immersion-restraint stress, plasma CRH tended to increase during the time course of the stress, reaching levels that were at least two times higher than the control. CRH concentrations in the median eminence (ME) during both types of stress decreased significantly at 120min. In the ether-laparotomy stressed rats, CRH in the neurointermediate lobe (NIL) decreased significantly at 120min, similar to the ME. Although a significant change in the adrenal CRH content was observed in the ether-laparotomy stressed rats, the involvement of adrenal CRH in ACTH secretion is unlikely as the absolute change in CRH was very small. These findings suggest that continuous CRH increase reflects a persistent secretion of CRH from the hypothalamic median eminence to the hypophysial portal vessels. It is possible that CRH secretion from the posterior pituitary gland is at least partly responsible for the persistent plasma ACTH increase in ether-laparotomy stress. Concentrations of AVP in the tissue and plasma showed no significant change during the sustained phase of each stress; the role of AVP in persistent ACTH secretion may therefore be small.