Effect of vasopressin on liver blood flow in the hypophysectomised rat

Liver blood flow (xenon-133 clearance method) and portal venous flow were measured in hypophysectomised rats following the infusion of vasopressin at a range of infusion varying from 0.0125 to 0.8 microU/g b.w./min over the range 0.0125-0.1 microU/g b.w./min, portal venous flow was reduced, the reduction being linearly related to the logarithm of the dose (r = -0.88). Following the infusion of 0.8 microU/g b.w. of vasopressin, portal venous flow significantly increased above pre-infusion levels (p less than 0.05). Liver blood flow was increased significantly (p less than 0.05) when vasopressin was infused over the range 0.0125-0.2 microU/g b.w. At higher rates of infusion, liver blood flow was progressively reduced, and at 0.8 microU/g b.w./min liver blood flow was less than pre-infusion levels (p less than 0.05). These data suggest that the effects of vasopressin on hepatic haemodynamics is related to the rate of infusion with a reversal of effects at higher rates of infusion. The implications of these findings in relation to the use of vasopressin in the management of portal hypertension and bleeding oesophageal varices is discussed.