Modification of pituitary-adrenal axis responses to hemorrhage by handling techniques in conscious swine

Responses of the pituitary-adrenal axis to hemorrhagic hypotension were compared in chronically instrumented swine that were allowed to move freely in a holding cage (n = 11) and swine trained to accept physical restraint in a Pavlov sling (n = 14). Seven to ten days after surgical preparation, each animal was hemorrhaged (37.5 ml/kg over 60 min) while confined to its environment. Before hemorrhage, control values for ACTH, cortisol, heart rate, and mean arterial pressure were at near-basal levels in both groups, and during hemorrhage both groups showed similar decrements in blood pressure. Hemorrhage in the sling animals, however, led to increases in plasma ACTH and cortisol concentration much greater than those seen in caged animals. Log-linear plots of ACTH against mean arterial pressure revealed similar response characteristics in the two groups but significant rightward shift of the response curve in sling-restrained animals. Our results indicate that sling restraint, even in highly trained animals, potentiates pituitary-adrenal responses to hemorrhage by some as yet unknown mechanism.