Effects of adrenergic agents on transepithelial electrical measurements across the isolated iris-ciliary body

Transmembrane electrical measurements were performed on the isolated rabbit iris-ciliary body to study direct effects of adrenergic drugs on the ciliary epithelium. Alpha-adrenergic agonists (epinephrine, norepinephrine, or phenylephrine) lowered the short-circuit current (SCC) in a dose-dependent fashion relative to which chamber side the drug was added: simultaneous addition to both chambers > blood side only > aqueous side only. Pretreatment (5 × 10^-5 m) with the non-selective β-adrenergic antagonist timolol had no effect while the non-selective α-adrenergic antagonist, phentolamine, completely prevented the α agonist-induced decrease in SCC. The α-adrenergic response was mediated by the α₁ subtype since prazosin, but not yohimbine, blocked the induced reduction in SCC. The β-adrenergic agonist isoproterenol caused a dose-dependent decrease in the SCC. The decrease was similar when the drug was added to only the blood side or to both sides of the chamber. Addition to only the aqueous chamber had no effect. Pretreatment with β-adrenergic antagonists blocked the isoproterenol response: non-selective = selective β₂ > selective β₁. The isoproterenol-induced decrease in SCC was also blocked by non-selective α-adrenergic antagonists. The response was mediated by the α₁ subtype since prazosin, but not yohimbine, blocked the isoproterenol response. This suggests that isoproterenol interacted with the α₁-adrenergic sensitive pathway in the rabbit ciliary process.