Sympathetic stimulating effects of sufentanil in the cat are mediated centrally

The hemodynamic and adrenal secretory response to sufentanil (25 micrograms/kg i.v.) was evaluated during halothane anesthesia in 3 groups of cats: group I, n = 5, control; group II, n = 4, naloxone pretreatment (3 mg/kg i.v.); and group III, n = 5, acute spinal transection at T3-4. Administration of sufentanil in intact cats (group I), caused a significant increase in mean arterial blood pressure and adrenal vein plasma levels of norepinephrine, epinephrine, dopamine, and Met-enkephalin. These effects were abolished in naloxone-pretreated cats (group II). Following spinal transection (group III), sufentanil evoked a significant increase in blood pressure and heart rate, but no change in adrenal hormone levels. Intraventricular injections of sufentanil suggest that these sympathetic stimulating effects are mediated at central sites in proximity to the lateral and third ventricle.