Myocardial Phosphodiesterase Activity in Different Mammalian Species

Theophylline (Theo) has been shown to increase myocardial c-AMP in guinea-pig left auricles (Heitmann et al., Arch. Pharmacol. 293, R 96, 1976) but not in atria from reserpine-pretreated rats (Martinez and McNeill, Can. J. Physiol. Pharmacol. 55, 98, 1977). These conflicting results might be due to species differences in phosphodiesterase (PDE) activity. Therefore, we determined PDE activity in different cardiac muscle preparations isolated from guinea pigs and rats. The results (mean PDE activity in pmoles c-AMP hydrolized/ mg protein x min; N = 5−7; substrate concentration 1 μM) are summarized in the Table.