The relaxant effects of alfentanil and remifentanil on noradrenaline-treated rat aorta

Background and objective: In this in vitro study on rat thoracic aorta, the effects of indomethacin (a prostaglandin synthesis inhibitor), propranolol (a beta adrenergic receptor blocker), tetraethylammonium (TEA) (a calcium-actived potassium channel blocker), glibenclamide (an ATP-dependent potassium channel blocker) and naloxone (an opioid receptor antagonist) on the responses induced by alfentanil and rernifentanil were investigated. Methods: Aortas isolated from rats were cut into spiral strips 12 mm in length, 3 mm wide. Strips were mounted in organ baths at 37degreesC continuously gassed with 95% and 5% CO2. The responses of the drugs were recorded isometrically on polygraph. Results: In both groups, strips were precontracted with 10(-6) M noradrenaline (NA). Then alfentanil or remifentanil (10(-8) to 10(-5) M) was administered cumulatively. Both alfentanil and rernifentanil significantly produced relaxation (p < 0.05). Indomethacin, propranolol, TEA, glibenclamide and naloxone did not significantly modify responses of the opioids. The rank order of potencies of these drugs was alfentanil > remifentanil. Conclusion: Prostaglandins, beta adrenergic receptors, potassium channels and opioid receptors have no role in the responses induced by alfentanil and remifentanil.