Positive inotropic and relaxant effects of papaverine on cat papillary muscle

The effects of papaverine and isoproterenol on the isometric twitch and high KCI-induced contractures were compared in papillary muscles from reserpinized cats. Papaverine (10-⁵m) significantly increased developed tension (T), maximal rate of rise of tension (+dT/dt max) and maximal velocity of relaxation (-dT/dt max) in 52.3 + 6.1, 74.1 + 6.7 and 82.1 + 12.1 % respectively with respect to control values. Time to peak tension (TTP) and contracture tension decreased in 9.1 + 2.0 % and 50.9 + 5.6yo respectively with respect to controls (P < 0.05). lsoproterenol in a dose (8 × 10^-10 m), that produced an increase in +dT/dt max non significantly different to the one elicited by papaverine (65.9 + 9.0 % increased (in % with respect to control values), T in 55.3 + 7.3, -dT/max in 73.8 + 13.1 and decreased TTP in 6.6 + 1.1 and contracture tension in 40.7 + 6.3 (P < 0.05). The effects of isoproterenol on all the parameters studied were not statistically different from the ones of papaverine. It is concluded that in cat papillary muscles, papaverine has a positive inotropic action and an isoproterenol-like relaxant effect.