Effects of endothelin A and B receptors on aqueous humor dynamics in the rabbit eye

This study attempted to clarify the role of endothelin A and B (ETA and ETB) receptors in modulating aqueous humor dynamics in the rabbit eye. Intraocular pressure (IOP), aqueous flow, total outflow facility, and uveoscleral outflow were measured before, and 24 hours after, intravitreal injection (20 microliters) of a selective ETB agonist, sarafotoxin S6c (SRTX S6c, 10(-5) M), into one eye and its vehicle into the contralateral eye. The measurements were also performed before and after injection of a selective ETA antagonist, 97-139 (10(-2) M) + ET-1 (10(-5) M) into one eye, and vehicle + ET-1 (10(-5) M) into the contralateral eye. In the SRTX S6c-treated eye, total outflow facility increased significantly by 106% compared with that in the vehicle-treated eye 24 hours after injection; aqueous flow and uveoscleral outflow failed to change significantly. The ETA antagonist 97-139 inhibited the decrease in aqueous flow partially, but significantly, but failed to inhibit the increase in total outflow facility caused by ET-1. Therefore, both ETA and ETB play a significant role in modulating aqueous humor dynamics in the rabbit eye. ETA can modulate aqueous humor production, at least in part. ETB can modulate total outflow facility, and the possibility for ETB in modulating aqueous humor formation cannot be ruled out.