Endogenous acetylcholine concentrations in rat iris-ciliary body.

The technique of microwave irradiation, whereby enzymes are inactivated within milliseconds, was employed to accurately determine the in vivo acetylcholine (ACh) concentration in the iris-ciliary body (ICB). Rats were sacrificed by microwave irradiation at 9.5 kW at 2,450 MHz for 0.9 seconds. The eyes were enucleated, the ICBs isolated and 10 ICBs from 10 eyes were treated as one sample. ACh levels were determined using high performance liquid chromatography in an immobilized-enzyme reactor. Endogenous ACh levels in the rat ICB were 58.8 +/- 5.0 nmoles (8.58 +/- 0.73 micrograms) per gram tissue protein (mean +/- SE, 9 samples). A single instillation of 5 microliters of 0.05% atropine in one eye of an animal lowered the ACh level in the ICB of the eye (P < 0.02).