Effect of subchronic exposure to opioids on the effective dose of intravenous and inhalation anaesthetics.

This study aimed to investigate the effect of subchronic exposure to morphine on the 50% effective dose (EC50) (median effective concentration/EC50) values of intravenous (propofol and ketamine) and inhalation (sevoflurane) anaesthetics in mice. Eight to 12-week-old male mice were administered morphine subcutaneously for 5 days to create a subchronic morphine exposure model. Control mice were injected with saline. The EC50 for righting reflex loss and tail clip reflex of general anaesthetics on the first (D1), third (D3) and seventh days (D7), after establishing a subchronic morphine exposure model, were determined. Sevoflurane: No change in the minimum alveolar concentration for righting reflex loss or tail clip reflex loss was observed between the treated and the control values (P>0.05). Propofol: the EC50 for righting reflex loss of D7 was significantly lower than the control and D1 (P<0.05). The EC50 for tail clip reflex loss of D3 and D7 decreased compared with the control (P<0.05). Ketamine: the EC50 for righting reflex loss of D3 and D7 was significantly higher than that of the controls. The EC50 for tail clip reflex loss at D1, D3 and D7 increased compared with the control (P<0.05). In summary, after subchronic exposure to morphine, the minimum alveolar concentration value of sevoflurane did not change significantly; the EC50 of propofol decreased, whereas the EC50 of ketamine increased. The changes induced by subchronic exposure to morphine can alter the response to anaesthetics, and the effects vary with the modes of action of anaesthetics.