Direct vasomotor effects of theophylline and enprofylline on human coronary artery in-vitro: comparison with feline coronary and cerebral arteries.

The vasomotor effects of theophylline and enprofylline were investigated on circular segments of human coronary artery taken 6 h after death. Isolated arterial segments were examined using a sensitive myograph and isometric contractions were recorded with Grass transducers. The results were compared with those obtained in feline coronary and cerebral arteries. Theophylline and enprofylline induced pronounced relaxation of all types of precontracted arteries. In feline cerebral arteries the potency for eliciting relaxation was slightly higher for theophylline compared with enprofylline, while there was no difference in potency for the methylxanthines in coronary arteries. Prostaglandin F2 alpha frequently induced rhythmic contractions in human, but not in feline coronary arteries. Theophylline increased the amplitude of the rhythmic contractions while this was not seen following administration of enprofylline. Whether this mode of activity by theophylline contributes to its arrhythmogenic properties in-situ requires clarification.