Morphine and morphine/naloxone modification of glucose, glucagon and insulin levels in fasted and fed rats.

In rats weighing 200-250 g catheters were placed in the internal jugular vein and carotid artery. After 1 week of accommodation the training for the experimental situation, morphine (10 mg kg-1) was injected intravenously alone or in combination with naloxone (0.04 mg ml-1, 0.8 ml h-1). Otherwise no form of anaesthesia was used during the experiments. In control fed and fasted rats, there were no significant differences in blood glucose. In fed rats, morphine increased blood glucose as compared to control rats (p < 0.001). This was not seen in the fasted rats. The morphine induced increase in blood glucose in the fed rats was abolished by naloxone (p < 0.001). Glucagon was significantly higher in fasted than in fed control rats (p < 0.01). It was significantly increased after morphine in fed (p < 0.05), but not in fasted rats. The morphine induced increase in glucagon in fed rats was abolished by naloxone (p < 0.01). Insulin was significantly higher in fed than in fasted control rats (p < 0.05). Morphine increased insulin levels significantly in fed and fasted rats (p < 0.001), p < 0.01). The morphine induced increase in insulin in the fed rats was abolished by naloxone treatment. It is concluded that morphine stimulates glucose and glucagon release in fed but not fasted rats, and that these increases are caused by opioid action. Insulin increases after morphine were proved to be opioid-mediated only in the fed state.