Neuroprotective effects of eliprodil in retinal excitotoxicity and ischemia.

PURPOSE: To evaluate whether eliprodil (SL82.0715), a NR2B-selective N-methyl-D-aspartate (NMDA) antagonist, is protective of retina subjected to an excitotoxic or ischemic insult. METHODS: To evaluate protection against retinal excitotoxicity, eliprodil was administered intraperitoneally before and after the injection of NMDA (5 microl, 20 nmol) into the vitreous of rats. Integrity of the retina was assessed by counting cells in the retinal ganglion cell layer (GCL) and measuring choline acetyltransferase (ChAT) activity. In a subsequent experiment, total retinal ischemia, as measured by a cessation of electroretinographic (ERG) activity, was induced in anesthetized rabbits by elevating intraocular pressure above systolic blood pressure for 65 minutes. After ischemia, recovery of ERG activity was assessed at 24 and 48 hours in animals treated with vehicle or eliprodil (1.0-10.0 mg/kg). RESULTS: Intravitreal NMDA injection resulted in a dose-related decrease in cells of the GCL and in ChAT activity. Eliprodil administered intraperitoneally at 10 mg/kg completely prevented the loss of ChAT and the loss of cells in the GCL. Twenty-four hours after retinal ischemia, A and B waves of vehicle-treated animals were suppressed by 60% to 70%. Eliprodil administered intraperitoneally at 10 mg/kg ameliorated the A- and B-wave depression throughout the 48-hour experiment. CONCLUSIONS: Eliprodil is neuroprotective of retinae subjected to either an excitotoxic or ischemic challenge and may be useful for treating a variety of retinal and optic nerve head disorders.

Affinities of muscarinic drugs for [3H]N-methylscopolamine (NMS) and [3H]oxotremorine (OXO) binding to a mixture of M1-M4 muscarinic receptors: use of NMS/OXO-M ratios to group compounds into potential agonist, partial agonist, and antagonist classes.

The relative affinities of various muscarinic drugs in the antagonist ([3H]N-methyl scopolamine ([3H]NMS)) and agonist ([3H]Oxotremorine-m ([3H]OXO-M)) binding assays using a mixture of tissues containing M1-M4 receptor subtypes have been determined. [3H]NMS bound with high affinity (Kd = 25 +/- 5.9 pM; n = 3) and to a high density Bmax = 11.8 +/- 0.025 nmol/g wet weight) of muscarinic receptors. [3H]OXO-M appeared to bind to two binding sites with differing affinities (Kd1 = 2.5 +/- 0.1 nM; Kd2 = 9.0 +/- 4.9 microM; n = 4) and to a different population of binding sites (Bmax1 = 5.0 +/- 0.26 nmol/g wet weight; Bmax2 = 130 +/- 60 nmol/g wet weight). Well known antagonists exhibited high affinity for [3H]NMS binding but a lower affinity for [3H]OXO-M binding. The opposite was true for acetylcholine and other known agonists. However, pilocarpine and McN-A-343 had similar affinities for sites labeled by both radioligands. Using the ratios of antagonist-to-agonist binding affinities, it was possible to group compounds into apparently distinct full agonist (ratios of 180-665; e.g. carbachol, muscarine, OXO-M, OXO-S and arecoline), partial agonist (ratios of 14-132; e.g. McN-A-343, pilocarpine, aceclidine, bethanechol, OXA-22 and acetylcholine) and antagonist (ratios of 0.22-1.9; e.g. atropine, NMS, pirenzepine, methoctramine, 4-DAMP and p-fluorohexahydrosialo-difenidol) classes. These data suggest that the NMS/OXO-M affinity ratios using a mixture of M1-M4 muscarinic receptors may be a useful way to screen and group a large number of compounds into apparent agonist, partial agonist, and antagonist classes of cholinergic agents.

Inlfuence of high-viscosity vehicles on miotic effect of pilocarpine.

Gel formulations containing 2% pilocarpine hydrochloride were prepared from ethylene maleic anhydride, carbomer, hydroxyethylcellulose, polyacrylamide, ethylhydroxyethylcellulose, hydroxypropylcellulose, and poly(methylvinyl ether--maleic anhydride). The viscosity characteristics of each formulation were evaluated from rheograms developed at 37 degrees using a cone and plate viscometer. Single-point viscosities were determined at room temperature using a single-point rotational viscometer. Plastic viscosity parameters correlated to miosis durations in the rabbit following ophthalmic dosing of 50 microliters. Carbomer formulations varying in concentration between 0.9 and 5.0% (w/w) showed a discontinuous relationship when either yield value or plastic viscosity was plotted against miosis durations. At carbomer concentrations above 3%, miosis durations increased 1.5-fold. Above and below this range, plastic parameters did not correlate to miosis duration. It was reasoned that the increased duration was a consequence of the gel's increased yield value such that appreciable in vivo thinning of the gel does not take place with eyelid and/or eyeball movements. As a result, the residence time of the drug in the eye would be expected to increase, thus promoting an increased duration.