Effects of IBMX on the ERG of the isolated perfused cat eye.

Full-field electroretinograms (ERGs) were recorded from isolated cat eyes perfused through the ophthalmociliary artery with isobutylmethylxanthine (IBMX), an inhibitor of cyclic guanosine monophosphate (cyclic GMP) phosphodiesterase. Low doses of IBMX (0.1-0.3 mM) produced decreased rod ERG amplitudes at low stimulus luminances and increased rod ERG amplitudes at high stimulus luminances. A high dose of IBMX (1.0 mM) initially produced the same effect as the low doses and then led to decreased rod ERG amplitudes at all stimulus luminances. Perfusion with IBMX also resulted in elevations in the semi-saturation luminance (sigma), delayed rod a-wave latencies, delayed rod a-wave and b-wave implicit times, and reduced rod a-wave slopes. Eyes perfused with IBMX (1.0 mM) were also found to have elevated levels of retinal cyclic GMP. These effects of IBMX on the rod ERG are considered in the context of previously described ERGs in selected cases of human retinal degeneration.