Behavioral and hormonal influence on blood volume restitution after hemorrhage in swine

Hemorrhage of 14 ml.kg-1.5 min-1 was done in two groups of chronically prepared, splenectomized Yorkshire pigs that were conditioned behaviorally to lie in a Panepinto sling. In group 1 the conditioning included early use of active restraint. It was done before the preparative surgery and on postoperative day 3 before the experiment on day 4. In group 2 the use of active restraint was minimized during conditioning that was extended to postoperative days 4 and 5 before the experiment on day 6. Before hemorrhage, core temperature and plasma catecholamines, cortisol, adrenocorticotropin, vasopressin, and renin were greater in group 1 than in group 2; but blood volume, hematocrit, and body weight were identical. Peak hormonal concentrations were greater or more sustained during the 1st h after hemorrhage in group 1 than in group 2. Restitution of blood volume was greater in group 1 than in group 2 at 4 and 7 h. Greater total peripheral resistance at 2 h after hemorrhage and greater restitution of plasma protein by 7 h in group 1 contributed to its accelerated volume restoration. Comparison of arterial pressure and of right atrial volume (conductance catheter) between groups suggested that a greater response of arterial or right atrial stretch receptors in group 1 could not account for the results. We suggest that the method and duration of behavioral conditioning and the time for recovery from surgery are important determinants of the hemodynamic and hormonal responses to hemorrhage and their subsequent influence on the restitution of blood volume.