[Effect of endothelin-1 on ocular circulation].

Endothelin (ET)-1, a potent vasoconstrictor which was discovered recently, might be involved in the regulation of ocular circulation. In this paper, we studied the effects of ET-1 on capillary blood flow of the optic nerve head and choroid in rabbits, using a hydrogen gas clearance flowmeter. Intravitreal injection of 0.1 ml of ET-1 at 10(-5) M and 10(-6) M caused a significant decrease in blood flow, which in the optic nerve head continued more than 3 hours, but in the choroid recovered at 3 hours after the injection (maximum decrease occurred at 75 minutes and at 30-60 minutes, respectively). Intraocular pressure was reduced as the time passed. Intravenous administration of 10(-10) mol/kg of ET-1 induced a reduction in blood flow, which in the optic nerve head continued more than 3 hours, but in the choroid recovered at 90 minutes after the administration. Intraocular pressure was reduced during 3 hours' observation. The decrease in blood flow in the optic nerve head was inhibited by previous administration of calcium antagonist (nicardipine), so the calcium channel was thought to be involved in this reaction.