title: Effect of melatonin on vascular responses of porcine ciliary arteries.
abstract: OBJECTIVE
  To investigate the effect of melatonin on isolated porcine ciliary arteries.
  
  
  METHODS
  Isolated porcine ciliary arteries were suspended in myograph chambers filled with modified Krebs-Ringer solution (37 degrees C; 95% O2/5% CO2) for isometric tension recording.
  
  
  RESULTS
  In quiescent porcine ciliary arteries with endothelium, melatonin (10(-11)--10(-5) M) evoked no change in vascular tone. The highest concentration of melatonin (10(-4 ) M) evoked a small but significant contraction. In vessels precontracted with U-46619 (10(-7) M), increasing concentrations of melatonin (10(-11)--10(-5) M) did not evoke a response. In precontracted arteries with endothelium, contractile response of vascular smooth muscle to increasing concentrations of serotonin (10(-10)--10(-5) M) and noradrenaline (10(-10)--10(-5) M) was reduced after preincubation with melatonin (10(-4) M). Melatonin (10(-4) M) did not alter the response to endothelin-1 (10(-10)--10( -7) M) and U-46619 (10(-10)--10(-6 ) M) in precontracted arteries with endothelium.
  
  
  CONCLUSIONS
  These findings demonstrate that melatonin attenuates the effect of serotonin and noradrenaline and is itself a mild vasoconstrictor in porcine ciliary arteries. The role of melatonin in human ocular circulation remains to be established.
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000818:Animals; D019842:Ciliary Arteries / Q000187:drug effects* / Q000502:physiology; D019332:Endothelin-1 / Q000494:pharmacology; D066298:In Vitro Techniques; D008550:Melatonin / Q000494:pharmacology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D013552:Swine; D014661:Vasoconstriction; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D019332:Endothelin-1; D014662:Vasoconstrictor Agents; D012701:Serotonin; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D008550:Melatonin; D009638:Norepinephrine