Intracameral administration of neurotensin induces miosis in the rabbit

The present investigation was designed to evaluate the effect of selected peptides on pupillary diameter and intraocular pressure (IOP) in rabbits. Intracameral (IC) administration of neurotensin (NT) in doses of 5–100 μg produced a significant, long lasting and dose-dependent decrease in pupillary diameter without affecting IOP. NT-induced miosis appears to be relatively specific because a variety of peptides including Gn-RH, somatostatin, met-enkephalin, bombesin, leu-enkephalin or NT 1–6, (a biologically inactive N-terminal fragment of NT), produced no effect on pupillary diameter; only substance P produced miosis similar to NT when tested in a dose equimolar to 30 μg of NT. In addition, peripheral (intravenous) administration of NT (100 μg/kg) was equally ineffective. Inhibition of prostaglandin synthesis with indomethacin, did not prevent subsequent NT-induced miosis. Finally, IC administration of an effective dose of NT (30 μg) did not alter the protein concentration in the aqueous humor. These results indicate that NT-induced miosis is not mediated by endogenous prostaglandins and that this effect of NT does not appear to involve disruption of the blood-aqueous barrier, suggesting that NT may play a role in regulation of pupillary diameter