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Neutrophil circulation and release from bone marrow during hypothermia

The effect of hypothermia on neutrophil circulation and release from bone marrow has been studied. Pigs were anesthetized and maintained at 37 degrees C or surface cooled to 29 degrees C over 60 min. As the core temperature was reduced to 29 degrees C, the number of circulating neutrophils (X 10(9) per liter) fell from 6.0 +/- 0.6 to 2.3 +/- 0.3 by 60 min. No significant change in the number of circulating mature or immature neutrophils was observed over the 4 h of observation at 29 degrees C. Neutrophil demargination after administration of intravenous catecholamines was similar at 37 and 29 degrees C. Steroid stimulation of bone marrow to release neutrophils was markedly impaired at 29 degrees C. Circulating mature neutrophils in normothermic pigs increased from 5.6 +/- 1.2 to 10.4 +/- 1.2 by 120 min after administration of intravenous hydrocortisone sodium succinate. Circulating immature neutrophils increased from 1.7 +/- 0.3 to 5.3 +/- 0.4. At 29 degrees C, no significant changes in the number of circulating mature or immature neutrophils occurred. Endotoxin also failed to stimulate neutrophil release from the bone marrow. Furthermore, a marked neutropenia occurred in hypothermic pigs after intravenous endotoxin, which persisted for the 3 h of observation. Neutrophil circulation and release from bone marrow are compromised by hypothermia, which may increase the risk for bacterial infection.