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Endothelin is a vasoactive peptide that has been shown to play an important role in vascular homeostasis. Recently, endothelin and its receptors have been found in ocular tissues where it appears to have a regulatory function. Endothelin is found in both the aqueous and vitreous humors and its concentration is elevated in glaucoma patients and in animal models of glaucoma. In the current review, the authors present information about the distribution of endothelin and endothelin receptors in the eye and the ocular actions of endothelins. Specifically, endothelin/aqueous humor dynamics, endothelin/nitric oxide interactions, endothelin and ischemia, and endothelin/optic nerve head effects. Observations concerning the potential role of endothelin in glaucoma pathophysiology is presented and discussed relative to its effects on the optic nerve head and in relation to glaucoma theories.

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It has become increasingly clear that astrocytes may play an important role in the genesis of glaucoma. Astrogliosis occurs in response to ocular stress or the presence of noxious stimuli. Agents that appear to stimulate reactive gliosis are becoming increasingly clear. One class of agents that is emerging is the endothelins (ETs; specifically, ET-1). In this review we examine the interactions of ET-1 with astrocytes and provide examples where ET-1 appears to contribute to activation of astrocytes and play a role in the neurodegenerative effects that accompany such reactivation resulting in astrogliosis. These actions are presented in the context of glaucoma although information is also presented with respect to ET-1's role in the central nervous system and brain. While much has been learned with respect to ET-1/astrocyte interactions, there are still a number of questions concerning the potential therapeutic implications of these findings. Hopefully this review will stimulate others to examine this potential.

NCX 125, a compound targeting 2 different mechanisms, is endowed with potent ocular hypotensive effects. This may lead to potential new perspectives in the treatment of patients at risk of glaucoma.

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PURPOSE. The prostaglandin F2alpha (PGF2a) analogue bimatoprost lowers intraocular pressure (IOP) by increasing uveoscleral outflow at doses shown to elicit redness of the eye. With the aim to enhance the IOP-lowering effect of bimatoprost we studied NCX 470, a dual-acting compound combining bimatoprost with nitric oxide (NO) known to mainly act via relaxation of trabecular meshwork and Schlemm's canal.METHODS. New Zealand white rabbits with transient hypertonic saline-induced IOP elevation (tOHT-rabbits), cynomolgus monkeys with laser-induced ocular hypertension (OHT-monkeys), and normotensive dogs (ONT-dogs) were used. The levels of NCX 470, bimatoprost, and bimatoprost acid were determined in aqueous humor (AH), cornea (CR), and iris/ciliary body (ICB) by liquid chromatography-mass spectrometry/mass (LC-MS/MS), while cGMP in AH and ICB was monitored using an enzyme immunoassay (EIA) kit in pigmented Dutch Belted rabbits.RESULTS. NCX 470 (0.14%, 30 lL) lowered IOP in tOHT-rabbits with an E max of À7.2 6 2.8 mm Hg at 90 minutes. Bimatoprost at equimolar dose (0.1%, 30 lL) was noneffective in this model. NCX 470 (0.042%, 30 lL) was more effective than equimolar (0.03%, 30 lL) bimatoprost in ONT-dogs (IOP change, À5.4 6 0.7 and À3.4 6 0.7 mm Hg, respectively, P < 0.05) and in OHT-monkeys (IOP change, À7.7 6 1.4 and À4.8 6 1.7 mm Hg, respectively, P < 0.05) at 18 hours post dosing. NCX 470 (0.042%, 30 lL) or bimatoprost (0.03%, 30 lL) resulted in similar bimatoprost acid exposure in AH, CR, and ICB while cGMP was significantly increased in AH and ICB at 18 and 24 hours after NCX 470 dosing.CONCLUSIONS. NCX 470 lowers IOP more than equimolar bimatoprost in three animal models of glaucoma by activating PGF2a and NO/cGMP signaling pathways.