Capacitance effects and blood reservoir function in the splanchnic vascular bed during non-hypotensive haemorrhage and blood volume expansion in anaesthetized cats.

1. These experiments were designed to measure how much blood is mobilized from or pooled in the liver, spleen and gastro-intestinal tract to compensate for a haemorrhage or infusion of blood.2. Hepatic volume, splenic weight and intestinal volume were recorded in cats anaesthetized with sodium pentobarbitone. Whole blood was removed or infused at rates of 0.5-0.6 ml. kg(-1).min(-1) until 10 ml./kg (19% blood volume) had been removed or 18 ml./kg (34% blood volume) had been infused. These blood volume changes produced only small changes in arterial and portal pressures except after removal of 8 ml./kg (15% blood volume) when arterial pressure began to decrease rapidly.3. With small haemorrhages of up to 4% blood volume, the liver contributed 16%, the gastro-intestinal tract 23% and the spleen a negligible proportion of the blood volume removed. With haemorrhages of 15% blood volume, the liver contributed 21%, the gastro-intestinal tract 22% and the spleen 19% of the volume removed; a total splanchnic contribution of 62%.4. During infusions of 5-18 ml./kg (10-34% blood volume), the liver pooled 20%, the gastro-intestinal tract 40% and the spleen 6% of the volume infused; a total splanchnic contribution of 66%.5. It is concluded that the splanchnic bed mobilizes or pools up to 65% of the volume of blood removed from or infused into the cats. The mechanisms responsible for this blood reservoir function are discussed. While several factors may be involved, it seems likely that a reflex regulation involving atrial receptors and the sympathetic innervation of the splanchnic capacitance vessels is of predominant importance.