Cardiorespiratory responses to intestinal injection of carbon monoxide

Experiments were conducted to investigate whether direct, intestinal injection of carbon monoxide (CO) can be used as a reliable method of exposing rats to CO. Laboratory rats were anesthetized with urethane. A laparotomy was performed and the small intestine isolated. The pylorus and ileocaecal valve were ligated and air or 100% CO (75 ml/kg) was injected directly into the small intestine. Heart rate and respiratory rate were monitored by impedance pneumography. COHb and blood lactate concentrations were determined spectrophotometrically. CO was rapidly absorbed from the intestinal tract and COHb levels reached 70.9 +/- 1.3% one hr after treatment. After 45 min, heart rate decreased in the CO-injected animals to 86% of pre-injection value. Blood pressure decreased rapidly to levels significantly lower than controls 5 min after treatment. Respiratory rate decreased to levels significantly lower than controls 55 min after treatment. CO treatment resulted in a 4-fold increase in blood lactate concentration. The results indicate that 100% CO injected directly into the small intestine is absorbed rapidly and the resulting elevated COHb levels cause a rapid decrease in blood pressure, a decrease in heart and respiratory rates, and an increase in the blood's lactic acid concentration.