Topical Epinephrine Effects on True Outflow Resistance and Pseudofacility in Vervet Monkeys Studied by a New Anterior Chamber Perfusion Technique

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Abstract

Outflow facility was measured in 20 anesthetized vervet monkeys by two techniques; both involved the recording of the rate of inflow of fluid from a reservoir connected to the anterior chamber. In the first technique the pressure in the anterior chamber was periodically raised and lowered, while the extraocular venous pressure was not changed. In the second technique the intraocular pressure was kept constant and the extraocular venous pressure periodically raised and lowered by changing the positive pressure against which the animal was breathing. The trunk of the monkey was in a pressure suit, and the venous pressure was recorded from the sagittal sinus. The change in inflow rate from the reservoir divided by the pressure change that caused it gives a facility. With technique 1 the facility is the sum of true outflow facility and pseudofacility, and with technique 2 it approaches true facility. One eye of the monkeys had been treated with 2 drops of 2 per cent l-epinephrine bitartrate one hour before the experiment. Both eyes were studied simultaneously and the two techniques applied in the order No. 1, No. 2, No. 1. Pseudofacility was estimated as the difference between the results of techniques 1 and 2; epinephrine effects were estimated by comparing the two eyes. In 11 untreated eyes pseudofacility was 0.087 ± 0.034 (S.E.M.) and true facility 0.311 ± 0.054 (S.E.M.) microliter · minute¹ per ynillirneter Hg. The effect of epinephrine on true outflow resistance in 20 monkeys was best described as a reduction in resistance by 0.49 ± 0.20 (S.E.M.) millimeter Hg per microliter · minute^-1 independent of the resistance in the control eye which was 3.38 ± 0.37 (S.E.M.). The effect of epinephrine on pseudofacility in 8 eyes was 0.074 ± 0.020 (S.E.M.) microliter · minute^-1 per millimeter Hg and seemed to be rather independent of starting pseudofacility. Thus, the early effect of epinephrine on outfloio facility is a double one. The effect on pseudofacility will be more important when true facility is low, than on true outflow resistance, when true facility is high.