Effects of haemorrhage and volume expansion on portal–systemic collateral vascular resistance in conscious portal hypertensive rats

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Abstract
In order to study the acute effects of blood volume changes on the vascular resistance of portal-systemic collaterals (collateral vascular 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. 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 .times. 103 to 11.1 .+-. 2.0 .times. 103 kPal-1 s. 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 .times. 103 to 4.9 .+-. 0.4 .times. 103 kPal-1 s. This study shows that in rats with portal hypertension, portal-systemic collateral vascular resistance is modified by alterations in blood volume.