Cardiovascular effects of enprofylline and theophylline

The cardiovascular effects of enprofylline (with no adenosine receptor antagonism) and of theophylline (with adenosine receptor antagonism) were compared in six normal subjects in a double-blind trial at steady-state concentrations of theophylline (12.5 +/- 1.6 mg/L) and enprofylline (2.7 +/- 0.3 mg/L). The mean (+/- SD) recumbent heart rate (HR) was higher (P less than 0.04) after enprofylline (70 +/- 14 bpm) than after theophylline (58 +/- 13 bpm) or saline solution (57 +/- 10 bpm). Forearm arterial resistance determined by plethysmography was lowered (P less than 0.01) by theophylline (-37% +/- 14%) and enprofylline (-43% +/- 24%) but not by saline solution (-6% +/- 16%). In the semiupright position, the mean arterial pressure was lower (P less than 0.01) after enprofylline (93 +/- 15 mm Hg) than after theophylline (108 +/- 16 mm Hg). The cardiac index (CI) and left ventricular ejection fraction (LVEF) determined by radionuclide angiocardiography and the left ventricular end-systolic pressure/volume ratio were not different for any regimen. During maximal exercise, HR was higher (P less than 0.01) after both enprofylline (176 bpm) and theophylline (175 bpm) than after saline solution (161 bpm), but the increases in mean arterial pressure (18% to 32%), CI (153% to 167%), and LVEF (34% to 74%) were similar for all three regimens. Both theophylline and enprofylline lowered forearm arterial resistance without an increase in CI, LVEF, or cardiac inotropy, although enprofylline tended to cause a lower blood pressure and higher HR than did theophylline.