Ocular responses to leukotriene C4 and D4 in the cat

The effects of leukotriene C4 (LTC4) and D4 (LTD4) on the iridial smooth muscles, intraocular pressure, blood-aqueous barrier and regional blood flow in the eye have been studied in cats. The test compounds were injected into the anterior chamber. Both LTC4 and LTD4 caused a dose-dependent constriction of the pupil, the agents being about equipotent. The effect on the iridial sphincter muscle was not dependent on nerve conduction, cyclo-oxygenase products or muscarinic receptors. Maximal constriction was achieved with 0.1-1 microgram of the test compounds. The smallest dose to induce a decrease in pupil diameter was 0.01 microgram. After intracameral injection of 4 micrograms the miotic response was markedly delayed. This indicates that in high concentrations LTC4 and LTD4 probably also stimulate the iridial dilator muscle. The blood flow in the anterior uvea decreased after intracameral injection of 4 micrograms LTC4/LTD4. Smaller doses had no clear effect. There was no effect on the blood-aqueous barrier as judged from the aqueous humor protein concentration. The intraocular pressure decreased slightly after injection of the test compounds.