Abstract

A simple method suitable for the quantitative evaluation of autonomic drugs and blocking compounds has been described. Enucleated eyeballs from mice, rats or guinea pigs were placed in a specially designed chamber and maintained at 37°C in oxygenated Krebs-HCO₃-Ringer solution. The chamber was constructed to fit the standard microscope stage and low power measurement of pupillary diameter was made.

There is in the method sufficient in vitro stability to enable optimal use of this naturally occurring measuring device. Moreover, the usual in vivo complications are avoided: namely, undesired pharmacologic and physiologic events tending to modify pupil diameter and the factor of drug distribution.

1. The ED50's of the miotics dl-muscarine, carbamyl choline, DFP, physostigmine, methacholine, neostigmine, pilocarpine, ACh, TMA, PTMA, 3-OH PTMA ranged from 7.5 x l.0^-7 for muscarine to 5 x 10^-2 for 3-OH PTMA.

2. The mouse eye was 10 times more sensitive than the rat eye. Removal of the cornea in the rat eye increased the sensitivity to ACh ca. 4500 times.

3. Parasympathetic blocking compounds, as exemplified by atropine, could be evaluated by antagonism of miosis induced by a fixed ACh dose.

4. In the decorneated rat eye, l-epinephrine, l-norepinephrine and l-isoproterenol exhibited potency ratios of 100:53:6 in the antagonism of miosis induced by a fixed ACh dose.

5. Histamine proved to be a miotic in the guinea-pig eye; this allowed the evaluation of diphenhydramine potency through antagonism.

6. The high precision of the method allows meaningful analysis of small shifts in dose-response curves contingent upon drug synergism, addition, or antagonism.