Endogenous catecholamine concentrations in rat iris-ciliary body.

Endogenous catecholamine concentrations in the rat iris-ciliary body (ICB) were determined using the technique of microwave irradiation, whereby enzymes are inactivated within milliseconds, and high performance liquid chromatography. Rats were sacrificed by microwave irradiation at 9.5 kW at 2450 MHz for 0.9 seconds. The eyes were enucleated, the ICBs isolated, and 10 ICBs from 10 eyes were treated as one sample. Endogenous norepinephrine levels in the rat ICB were 19.5 +/- 2.3 nmol per gram tissue protein (mean +/- SE, 7 samples), while endogenous dopamine levels were 3.2 +/- 0.2 nmol. Epinephrine could not be detected. A single instillation of 5 microliters of 0.05% apraclonidine, an alpha-2 agonist, in one eye of an animal raised the NE level in the ICB of the treated eye by 8% compared to that in the untreated fellow eye (P < 0.05).