title: Calcium antagonism of the inhibitory effects of fentanyl on the contraction of the nictitating membrane in cats.
abstract: The contractile responses elicited from the nictitating membrane of cats by postganglionic sympathetic nerve stimulation were decreased by fentanyl (10-20 micrograms/kg injected in the lingual artery). The inhibitory effect of fentanyl was preferential on responses elicited bu low frequency stimulation. Fentanyl (10-25 micrograms/kg) did not change the contractile response to noradrenaline and tyramine. The inhibitory effect of fentanyl was antagonized by naloxone. Increases in plasma calcium concentration did not alter the contractile responses to sympathetic nerve stimulation but antagonized the inhibitory effect of fentanyl in a dose-dependent manner suggesting a possible competitive antagonism.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D005283:Fentanyl / Q000037:antagonists & inhibitors*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects*; D009541:Nictitating Membrane / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects; D014439:Tyramine / Q000494:pharmacology
chemical_list: D002118:Calcium; D005283:Fentanyl; D009638:Norepinephrine; D014439:Tyramine