The effect of fentanyl, sufentanil, and alfentanil on cerebral arterioles in piglets.

The effect of fentanyl, sufentanil, and alfentanil on cerebral arterioles was determined in 17 halothane-anesthetized newborn piglets. A closed cranial window was inserted over the parietal cortex, and changes in the luminal diameter of pial arterioles were measured by intravital microscopy as increasing concentrations of opioid (10(-9)-10(-5) M) were suffused over the cortical surface. Each opioid caused a dose-dependent decrease in arteriolar diameter that was attenuated by coadministration of naloxone (10(-5) M). Fentanyl was more potent than either alfentanil or sufentanil. Naloxone alone had no effect at concentrations < or = 10(-5) M, suggesting that endogenous opioids contribute little to resting cerebrovascular tone. These results indicate that fentanyl, sufentanil, and alfentanil produce cerebral vasoconstriction by action at an opioid receptor and that their vasoconstrictive potency appears to differ from their analgesic potency.