EFFECT OF SURGERY ON THE PITUITARY-ADRENAL RESPONSE TO REPEATED HEMORRHAGE

We studied the effect of surgery on hemorrhage-induced facilitation in the pituitary-adrenal system using repeated hemorrhage in chronically prepared dogs. Animals underwent splenectomy and adrenal venous and f emoral arterial catheterization. Two (day 2) or five (day 5) days late r, animals were anesthetized with pentobarbital, respired, and subject ed to two periods of hypovolemia (20% hemorrhage with reinfusion of sh ed blood at 30 min; H1 and H2) separated by 90 min. Arterial and adren al venous blood was sampled, and adrenocorticotropic hormone (ACTH), a rginine vasopressin (AVP), angiotensin II (ANG II), cortisol, and cort isol secretion were measured. On day 2, cortisol secretion increased s imilarly after H1 and H2, despite a smaller response of ACTH to H2. On day 5, neither ACTH nor cortisol secretion changed after H1, but both increased significantly after H2. The adrenal sensitivity to ACTH inc reased after H2 on day 2 and was similar after H2 on both days. AVP an d ANG II increased similarly after H1 and H2 on each day but had large r responses on day 2. These results suggest 1) either surgery or initi al hemorrhage can lead to enhanced pituitary-adrenal responses to subs equent hemorrhage, 2) this effect may have both central and adrenal co mponents, 3) negative feedback may inhibit enhanced responses of ACTH in this model, 4) changes in adrenal sensitivity to ACTH may not depen d on an initial pituitary-adrenal response and may not be blocked by i ncreased circulating corticosteroids, and 5) differences in circulatin g AVP or ANG II do not account for facilitation in pituitary-adrenal r esponses.