Oxygen Consumption in Rats Before and After Administration of Morphine

Opiates have long been a useful tool in medicine due to their potent analgesic properties.   Although there has been a significant increase in prescribed use of opioids in recent years there has also been a large increase in deaths related to prescription opioids that may involve abnormal control of ventilation.  Opiate effects on ventilation have largely been considered to be due to depression of respiratory chemosensitivity (sensitivity to carbon dioxide and/or acid-base balance), but another effect may include decreased oxygen consumption and therefore decreased production of carbon dioxide.  In this study, we are using a whole body plethysmograph and a respirometer to measure the rate of oxygen consumption levels in juvenile rats 18-23 days) during sleep - before and after administration of morphine at varying dosages (5mg/kg to 45mg/kg). Our initial findings show no decrease in oxygen consumption and surprisingly instead demonstrate increases up to 50% following opioid administration.  These unexpected findings illustrate the need for additional investigation on possible causes of prescription opiate associated deaths.  Increased oxygen consumption (and therefore increased carbon dioxide production) in the presence of drug induced decreased sensitivity to carbon dioxide may interact to lead to dangerous compromises in the control of ventilation in patients taking a broad range of opiates doses in the community.