Effect of melatonin on vascular responses of porcine ciliary arteries.
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.
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*
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