PITUITARY-ADRENAL RESPONSE TO STRESS IN RATS WITH HYPOTHALAMIC ISLANDS

To pursue the question of hypothalamic autonomy, 'non-stress' and stress levels of corticosterone (Cpd B) were determined fluorometrically in plasma obtained before and after stress from adult female rats with hypothalamic (HI), basal hypothalamic (BHI) and pituitary (PI) islands. Sham-operated and intact rats served as controls. Twenty-four hours after partial brain removal, blood samples were obtained rapidly (< 3 min) for determination of 'non-stress' levels of Cpd B. Stress plasma samples were obtained 15 min following onset of 3-min ether or immobilization stress. Whereas BHI, sham-operated and intact rats had comparable 'non-stress' Cpd B levels and showed significant stress responses, HI rats had higher 'non-stress' Cpd B levels and did not show stress responses. PI rats did not respond to stress but had 'non-stress' Cpd B levels comparable to those of controls. These results suggest that the isolated hypothalamo-pituitary unit responds to stress if 'non-stress' Cpd B levels are not elevated. The inability of PI rats to respond to stress implies that the hypothalamus and/or median eminence are essential to the stress response. © 1969.