Cardiovascular effects of two different xanthines in healthy subjects. Studies at rest, during exercise and in combination with a beta-agonist, terbutaline.

The haemodynamic response to two xanthines, enprofylline and theophylline, was studied in 6 healthy male volunteers at rest, during exercise and in combination with the beta 2-agonist, terbutaline. At rest the haemodynamic effects of both xanthines were small and were qualitatively different from each other. While theophylline exerted a "pressor" response, enprofylline seemed to have arterial dilating ability. During exercise both xanthines as compared to placebo were associated with a higher heart rate and in general with increased systolic blood pressure. In combination with terbutaline enprofylline and theophylline both increased systolic blood pressure more than placebo, i.e. they augmented the positive inotropic effect of terbutaline. The systolic blood pressure was higher after theophylline than enprofylline despite their equipotent bronchodilator activity. This may reflect different inotropic effects of the xanthines as well as a difference in their influence on the response to adenosine.