Role of AVP in maintenance of circulatory homeostasis during hemorrhagic shock

Hemorrhagic hypotension produces significantly increased plasma arginine vasopressin (AVP) concentrations. We have utilized a specific antagonist (AVP-A) of the pressor effects of endogenous AVP to investigate the role of this neurohypophyseal hormone on the pathogenesis of hemorrhagic shock. Infusion of the AVP-A (2 μg/kg bolus + 2 μg.kg^-1.h^-1 infusion) into sham-shocked animals produced no significant changes in any of the observed experimental variables. Cats subjected to hemorrhagic shock given AVP-A had final superior mesenteric artery flow (SMAF) values significantly (P < 0.05) higher than shock cats given vehicle (7.7 ± 1.1 vs. 4.5 ± 0.8 ml.kg^-1.min^-1, respectively). Increases in postreinfusion plasma cathepsin D activities were significantly blunted in hemorrhaged animals treated with AVP-A (10.4 ± 2.0 vs. 24.8 5.5 U/mg protein; P < 0.05) Plasma proteolysis as well as the plasma accumulation of myocardial depressant factor (MDF) were also significantly modulated by AVP-A treatment in hemorrhaged animals. MDF activities were 75 ± 6 and 53 ± 4 U/ml (P < 0.02) for shock cats given vehicle or AVP-A, respectively. However, these beneficial actions were not reflected in any significant improvement in postreinfusion mean arterial blood pressure (MABP). These findings suggest that endogenous AVP functions not only as a potent splanchnic vasoconstrictor but also as a key humoral factor in the maintenance of postreinfusion MABP, a profile that is different from the role of angiotensin II, the other major splanchnic vasoconstrictor, in shock.