IN-VIVO CAMP LEVEL IN RABBIT IRIS-CILIARY BODY AFTER TOPICAL EPINEPHRINE TREATMENT

Purpose. The present study estimates the in vivo cyclic AMP (cAMP) lev el in the rabbit iris-ciliary body after topical treatment with epinep hrine. Methods. Epinephrine 1% was applied unilaterally to pigmented r abbits. At selected time points between 10 min and 6 hr, a 2.5-mm diam eter iris-ciliary body, in the treated eye, was irradiated with 2 J di ode laser (2 W for 1 sec). Instant heat generated by the irradiation d eactivated the cellular enzymes used in the synthesis and degradation of cAMP. Rabbits were sacrificed immediately, and samples of the iris- ciliary body were isolated from the irradiated area, the non-irradiate d area, and from the contralateral, untreated eye. Levels of cAMP in t hese samples and in the aqueous humor were determined by radioimmunoas say. Further experiments were performed in rabbits pretreated with an alpha(2)-adrenergic antagonist, yohimbine, and a beta-adrenergic antag onist, timolol, 30 min before the epinephrine treatment. Unilateral la ser photocoagulation of the iris-ciliary body was performed at 10 min and 1 hr after the epinephrine treatment. Results. The cAMP level in t he photocoagulated iris-ciliary body did not change in parallel to the change in the aqueous humor. An increase of aqueous humor cAMP was ob served for 6 hr. However, a reduction of cAMP level in the photocoagul ated iris-ciliary body was observed at 1 hr after the epinephrine trea tment. In yohimbine-pretreated rabbits, the reduction of cAMP level in the photocoagulated iris-ciliary body was absent. Pretreatment with t imolol had no effect. Conclusions. These observations suggest that, at 1 hr after the epinephrine treatment, the cellular signal via the alp ha(2)-adrenergic receptors in the iris-ciliary body, which reduces the intracellular cAMP level, is stronger than that via the beta-adrenerg ic receptors.