Effect of premedication on the changes of neuropeptide Y (NPY) in anesthesia

Premedication is one of the popular techniques in anesthesia, not only for the decrease of side effects but also for the increase of actions. Clinically, we found that plasma neuropeptide Y-like immunoreactivity (NPY-IR) was lowered in patients who had received premedication. In rats, plasma NPY-IR was not modified by the intravenous injection of diazepam. Pethidine reduced the plasma NPY-IR level which could be reversed by naloxone. Direct inhibition of plasma NPY-IR through an activation of opioid receptors can thus be considered. To the cold-stress stimulation, plasma NPY-IR was markedly raised. Diazepam reduced this stimulation-induced increase of plasma NPY-IR in a dose-dependent manner. Similar derivative of benzodiazepine produced an inhibition in a way following the potency as that to produce anxiolytic action. Also, this inhibition was reversed by PK11195, an antagonist of peripheral benzodiazepine receptors. Moreover, pain-stimulated increase of plasma NPY-IR in rats was also reduced by pethidine. This action was totally reversed in the presence of naloxone, indicating the participation of opioid receptors in the process. The obtained results suggest that premedication of diazepam and/or pethidine has the ability to decrease plasma NPY-IR in animals.