Active and passive control of hepatic blood volume responses to hemorrhage at normal and raised hepatic venous pressure in cats.

Hepatic blood volume decreases in response to a rapid hemorrhage (15.3 mL/min) were measured in cats anesthetized with pentobarbital or ketamine-chloralose, by use of in vivo plethysmography alone or in combination with various surgical procedures and vascular circuits. The hepatic blood volume contracts during hemorrhage to compensate for a constant proportion (26 +/- 6%) of the blood loss regardless of the extent of the actual blood loss. Following denervation of the liver and alpha adrenoreceptor blockade (3 mg phentolamine, intraportal) the liver compensation was unaltered. After denervation, nephrectomy, hypophysectomy, and adrenalectomy the liver was still able to compensate for 20 +/- 7.4% of the hemorrhage. Decreases in liver volume were linearly related to decreases in total hepatic blood flow that ensued whether the decreased blood flow was induced by hemorrhage or by clamping of the arteries supplying the splanchnic organs (superior mesenteric artery, celiac artery). The hepatic volume response to hemorrhage could be predicted accurately (97 +/- 6.6%) simply from the linear passive relationship between flow and volume for a particular animal. However when hepatic venous pressure was experimentally elevated, the volume response to passive flow decrease was markedly reduced whereas the response to hemorrhage and noradrenaline infusion was unimpaired suggesting that active control factors were required to produce normal hepatic volume responses to hemorrhage at raised venous pressure. Phentolamine reduced the response at raised venous pressure but was without effect at normal venous pressure in the same animal, indicating that the hepatic nerves and (or) adrenal catecholamines are of paramount importance in control of the response at raised venous pressure when the passive flow influence is much reduced.