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Kristine A. Erickson, Alison Schroeder; Direct Effects of Muscarinic Agents on the Outflow Pathways in Human Eyes. Invest. Ophthalmol. Vis. Sci. 2000;41(7):1743-1748.
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purpose. Recent studies demonstrating the presence of muscarinic receptors and
contractile-like cells in the trabecular meshwork tissue and/or cell
cultures from human eyes suggest the possibility that there may be a
direct effect of muscarinic agonists on outflow facility. The present
studies were conducted to determine whether muscarinic agonists could
change outflow facility in perfused human ocular anterior segments,
which lack an intact ciliary muscle.
methods. Human eyes were dissected and perfused according to previously
described methods. A steady state baseline facility was established for
90 minutes, after which up to four sequential concentrations ranging
from 10−9 to 10−3 M of pilocarpine,
aceclidine, or carbachol were added to the perfusion medium. In other
studies, 10−6 M atropine was perfused alone followed by
10−7 M carbachol with 10−6 M atropine,
whereas fellow control eyes received carbachol alone. Outflow facility
was measured for 60 minutes after each drug addition. The outflow
facility measurement in each eye after drug administration was compared
with the baseline measurement.
results. Outflow facility increased from baseline facility in eyes treated with
pilocarpine, aceclidine, or carbachol at lower concentrations
(10−9 to 10−6 M) but remained unchanged at
higher concentrations (10−4 to 10−2 M). The
effects of carbachol at 10−7 M were completely blocked by
conclusions. Muscarinic agonists increase outflow facility in human eyes by a direct
stimulation of the outflow tissues in the absence of an intact ciliary
muscle. This effect is biphasic, occurring at concentrations of
10−6 M and lower with no effect at higher
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