Effects of general anesthesia with ketamine in combination with the neuroleptic sedatives xylazine or azaperone on plasma metabolites and hormones in pigs

Physiological research with swine often includes sedation or general anesthesia (GA), which may influence the basal physiological responses of experimental animals and may have the potential to confound or interfere with the effects of experimental factors of interest. Using 6 adult female pigs, we investigated whether selected plasma metabolites and hormones are influenced by GA induced with ketamine (K) and 2 neuroleptic sedatives, namely azaperone (A) and xylazine (X). Fasted pigs rotationally received either no drug, a single intravenous administration of A or X, or A or X combined with ketamine (AK or XK, respectively), and plasma concentrations of glucose, lactate, non-esterified fatty acids (NEFA), triglycerides (TG), glucagon, insulin, and cortisol were determined for a 5-h period following administration. Azaperone and X induced deep sedation, whereas AK and XK induced GA. Overall, the average plasma glucose concentrations were increased by A and X, with the latter exerting a stronger effect that was also associated with hypoinsulinemia (P < 0.05). Time-dependent effects indicated a more rapid increase in glucose concentration due to X or XK than AK. Plasma NEFA concentrations were elevated by A and AK and to a lesser extent by X and XK (P < 0.05). Plasma lactate and TG levels were elevated by A and AK and remained unaffected by X or XK. Plasma cortisol concentrations were elevated (P < 0.05) by X and XK and even more so with a single administration of A (P < 0.05), while the combined effect of A with ketamine resulted in the highest cortisol concentrations (P < 0.05). Our data suggest that the effects of azaperone are mediated by cortisol but less so for xylazine, which also indicates that azaperone elicits a stronger stress response in pigs. Xylazine probably induces long-lasting, fasting-state hyperglycemia through the stimulation of hepatic glucose production associated with hypoinsulinemia. A discriminant analysis based on the variation in all of the measured metabolites and hormones, collectively, indicated that ketamine induced no additional effect on the overall physiological response patterns than that of the individual sedatives. In conclusion, the neuroleptic sedatives azaperone, and to a lesser extent, xylazine, acutely affect the metabolism of pigs, so primary metabolic readouts obtained under these drugs may be confounded.