Effect of phosphodiesterase inhibitors on bovine ciliary muscle and outflow facility.

To understand the aqueous outflow mechanism, we compared changes in the outflow facility with the response of ciliary muscle in fresh bovine eyes. The facility was measured in intact ocular globes. Theophylline, caffeine, and isobutylmethylxanthine (IBMX), all phosphodiesterase (PDE) inhibitors, increased outflow facility in a dose-dependent manner. However, neither epinephrine nor isoproterenol increased the outflow facility, regardless of their concentrations up to 10(-3) M. Neither epinephrine nor isoproterenol (0.01-1 microM)) relaxed the tone of bovine ciliary muscle, whereas theophylline and IBMX remarkably relaxed the muscle which had been contracted by carbachol, and also inhibited the nerve-mediated contraction. It is interesting that PDE inhibitors have a much greater influence on changes in outflow facility and ciliary muscle contraction than beta-adrenergic agonists.