Effect of low-dose vasopressin infusion on vital organ blood flow in the conscious normal septic sheep

The effect of low-dose vasopressin (AVP) on vital regional circulations may be clinically relevant but has not been fully described. We sought to determine the effect of low-dose AVP on systemic haemodynamics, coronary, mesenteric and renal circulations in the conscious normal and septic mammal. We studied seven Merino sheep using a prospective randomized cross-over double-blind placebo-controlled animal design. We inserted flow probes around aorta, coronary, mesenteric and renal arteries and, three weeks later, we infused low-dose AVP (0.02 IU/min) or placebo in the normal and septic state induced by intravenous E.coli. In normal sheep, AVP (0.02 IU/min) induced a 17% decrease in mesenteric blood flow (393.0±134.9 vs 472.1±163.8 ml/min, P<0.05) and a 14% decrease in mesenteric conductance (P<0.05). In septic sheep, AVP decreased heart rate and cardiac output by 28% and 22%, respectively (P<0.05). It also decreased mesenteric blood flow and mesenteric conductance by 23% (flow: 468.5±159.7 vs 611.3±136.3 ml/min, P<0.05; conductance: 6.3±2.7 vs 8.2±2.7 ml/min/mmHg; P<0.05). Renal blood flow was unchanged but urine output and creatinine clearance increased (P <0.05). We conclude that low-dose AVP infusion has similar effects in the normal and septic mammalian circulation: bradycardia, decreased cardiac output, decreased mesenteric blood flow and conductance and increased urine output and creatinine clearance. This information is important to clinicians considering its administration in humans.