Papaverine decreases the efflux of 42K in guinea-pig atrial heart muscle

Papaverine-induced positive inotropism with failure to increase cyclic AMP in rat atria

Phosphodiesterase inhibition by papaverine is likely to play a minor role in the rat atrial inotropic response because non-significant changes in cyclic AMP were obtained. Isoprenaline however raised the nucleotide levels three-fold and up to seventeen-fold when papaverine was added in a similar preparation. A prominent effect of papaverine was to lengthen relaxation instead of shortening it as did isoprenaline. The results suggest different sites of action, although overlapping effects cannot be excluded.

Effects of papaverine on calcium efflux and contractility in superfused rat left atria

The effects of papaverine upon force of contraction, maximal rate of contraction, maximal rate of relaxation and 45Ca efflux were studied in isolated superfused rat left atria electrically driven at 1 Hz. Papaverine (3 X 10(-5) mol/l, increased developed tension (from 5.35 +/- 1.17 mN to 7.18 +/- 1.51 mN) by 1.8 +/- 0.41 mN (+33%, p less than 0.01) and maximal rate of contraction (+T) by 34.5 +/- 13% (p less than 0.05). In all experimental conditions tested, papaverine increased the rate of 45Ca efflux. The amount by which papaverine increased 45Ca efflux was 175 +/- 41 nmoles . g wet wt-1 and 304 +/- 76 nmoles . g wet wt-1, in the presence and in the absence of caffeine, respectively. The plot of changes in 45Ca efflux versus changes in developed tension fitted to a straight line (r = +0.56, n = 17, p less than 0.05), with a slope and intercept of 42 nmoles Ca . mN-1 . g wet wt-1 and -0.47 mN respectively, suggesting an association between the changes induced by papaverine in force development and increased 45Ca efflux.

A negative inotropic effect of acetylcholine in the presence of several phosphodiesterase inhibitors

The phosphodiesterase inhibitors papaverine, theophylline and 3-isobutyl-1-methylxanthine (IBMX) reveal a negative inotropic effect of acetylcholine in cat ventricular heart muscle. This effect in unrelated to beta-adrenoceptor stimulation and possibly mediated by the accumulation of cyclic GMP.