Whole body response of the peripheral circulation following hemorrhage in the rat

Changes in mean circulatory filling pressure (MCFP) after hemorrhage reflect the whole-body response of the peripheral circulation to restore the driving force for venous return. In this study, changes in MCFP were measured for 15 min following a rapid 8 ml/kg hemorrhage. Three groups of rats were studied: 1) conscious, untreated; 2) conscious, ganglion blocked; and 3) pentobarbital anesthetized. In all three groups, hemorrhage decreased MCFP approximately 2.6 mmHg immediately after hemorrhage. In the conscious untreated rat, MCFP recovered 1.3 mmHg in 15 min; 83% of this recovery was complete within 2 min, and over 50% was complete by 30 s posthemorrhage. With ganglionic blockade, recovery was slowed to about 70% of that in the conscious, untreated animal during the first 5 min after hemorrhage. MCFP recovery was substantially depressed by pentobarbital, averaging only 42% of that in the untreated animal 5 min after hemorrhage. The results demonstrate that peripheral changes can quickly restore nearly 50% of the MCFP decrease occurring immediately after mild hemorrhage and that about one-third of this response is mediated by the sympathetic nervous system. Pentobarbital anesthesia greatly inhibits recovery, although its repressive mechanism is not known.