RESUMEN
We wish to report an early (10 to 30 min) 6 to 7 mm Hg increase in IOP above predrug levels following topical norepinephrine (NE) (5mumol) administration in conscious normal rabbits. This early elevation in IOP was significantly more pronounced in bilateral superior cervical ganglionectomized (BG) rabbits. The time course for peak IOP elevation slightly preceded the accompanying peak mydriatic effect in all groups. IOP returned to baseline levels in about 60 min in the BG rabbits, but the mydriasis persisted. Pretreatment with topical indomethacin significantly reversed the early hypertonic NE effect on IOP in the BG animals implying the involvement of prostaglandin synthesis. The IOP continued to fall significantly after 60 min in the BG group with indomethacin pretreatment. This latter result suggests a predominant long-lasting NE effect. The indomethacin pretreatment had no effect on pupil size of any group, but phenoxybenzamine (PBA) reduced the mydriatic effect, implying a direct or a predominant role of NE on iris muscle.