EFFECTS OF HEMORRHAGE AND VOLUME EXPANSION ON PORTAL SYSTEMIC COLLATERAL VASCULAR-RESISTANCE IN CONSCIOUS PORTAL HYPERTENSIVE RATS

1. In order to study the acute effects of blood volume change on the vascular resistance of portal-systemic collaterals (collateral vascualr resistance), a model of total portal vein occlusion with 100% portal-systemic shunts was developed in the rat. In this model, we determined the haemodynamic effects of haemorrhage (1.8 ml/100 g body weight)or intravenous infusion of a volume expander (1.8 ml/100 g body weight). Cardiac output and regional blood flows were measured by the radioactive microsphere method. 2. Haemorrhage significantly reduced arterial pressure from 108 ± 4 to 92 ± 4 mmHg (mean ± sem), cardiac output from 56 ± 4 to 24 ± 2 ml min-1 100 g-1 body weight, portal pressure from 15.1 ± 1.5 to 10.0 ± 1.4 mmHg and portal tributary blood flow from 19.9 ± 2.3 to 8.3 ± 1.4 ml/min. Consequently, collateral vascular resistance significantly increased from 6.6 ± 0.9 x 103 to 11.1 ± 2.0 x 103 kPa l-1 s. 3. Volume expansion reduced arterial pressure from 98 ± 3 to 90 ± 3 mmHg, and significantly increased cardiac output from 43 ± 3 to 55 ± 3 ml min-1 100 g-1 body weight, portal pressure from 13.9 ± 0.7 to 16.5 ± 0.8 mmHg and portal tributary blood flow from 16.4 ± 1.3 to 28.2 ± 3.2 ml/min. Consequently, collateral vascular resistance significantly, decreased from 7.0 ± 0.5 x 103 to 4.9 ± 0.4 x 103 kPa l-1 s. 4. This study shows that in rats with portal hypertension, portal-systemic collateral vascular resistance is modified by alterations in blood volume.