Sympathicomimetische Wirkungen von Papaverinderivaten

Interaction of papaverine and isoproterenol in the vascular system of the dog and intestinal smooth muscle of the rabbit

It was found that the effect of isoproterenol on the vasculature of the anesthetized dog can be potentiated by previous administration of papaverine. This effect is apparent in spite of concomitant potentiation of inotropic and/or chronotropic effects, which tend to obscure the vasomotor effect. Evidence is presented supporting the hypothesis that papaverine interacts with receptors of the vascular tree, which are usually classified as beta receptors and are responsive to isoproterenol. Evidence is presented showing almost complete inhibition of the chronotropic effects of papaverine by propranolol, and a synergism of papaverine with the chronotropic effects of isoproterenol. Evidence was obtained using the intestinal smooth muscle of the rabbit in support of the hypothesis linking mediation of the beta adrenergic system to papaverine effects.

Effects of papaverine on isolated rabbit papillary muscle

The effect of papaverine on the positive inotropic response to isopreqaline and to calcium was studied on the rabbit isolated papillary muscle; theophylline and the calcium antagonistic D600 were used for comparison. The dose-response curve for isoprenaline was shifted to the left by papaverine (3 times 10- minus 6 to 3 times 10- minus 5 M), in a dose-dependent manner, while that for calcium was not affected by the same concentration. In this respect papaverine was about 30 times more potent than theophylline. In the presence of papaverine isoprenaline induced arrhythmic contractions of the papillary muscle: the incidence of arrhythmic contractions was positively correlated to the concentration of papaverine. Papaverine 10- minus 5 to 10- minus 4 M caused only a positive inotropic response whereas 3 times 10- minus 4 to 10- minus 3 M induced a biphasic response, i.e., after a positive inotropic effect followed a negative one. In the presence of 3 times 10- minus 4 M papaverine isoprenaline failed to cause a positive inotropic response but exclusively induced arrhythmic contractions. Calcium, on the other hand, readily antagonized the negative inotropic effect of papaverine (3 times 10- minus 4 M) and caused a contracture of the papillary muscle. The results indicate that papaverine (3 times 10- minus 6 to 10- minus 5 M) like theophylline (10- minus 4 to 10- minus 3 M) produces its effect by phosphodiesterase inhibition and thereby specifically potentiates the response through beta-adrenoceptor stimulation. In higher concentrations (3 times 10- minus 4 to 10- minus 3 M) it acts as a calcium antagonistic, like D600, and furthermore may interact with calcium moving through myocardial cell membranes to cause a contracture via a mechanism which it shares with theophylline.

The time course of the effects of beta- and alpha-adrenoceptor stimulation by isoprenaline and methoxamine on the contractile force and cAMP level of the isolated rabbit papillary muscle

In the isolated papillary muscle of the rabbit the time course of the effects of selective beta- and alpha-adrenoceptor stimulation by isoprenaline and methoxamine, respectively, on the contractile force and on the level of 3',5'-cyclic AMP (cAMP) was determined. 1. Isoprenaline (3 times 10(-7) M) increased significantly the content of cAMP at 15 sec and elevated it to the maximal level-about twice the control value-at 30 sec after its administration, while the developed tension of the papillary muscle was also increased significantly at 15 sec and reached gradually its maximum at 90 sec. 2. Compared with isoprenaline methoxamine (10(-4) M) increased the developed tension very slowly: the maximal response was reached after 20 min. The level of cAMP, on the other hand, was changed neither before nor during the induction of the positive inotropic effect of methoxamine. 3. The phosphodiesterase inhibitor papaverine (10(-5) M) inhibited the PDE activity of the papillary muscle by about 40% after an incubation of 1 hr, and increased the level of cAMP significantly. The effects of isoprenaline on the contractile forced and on the level of cAMP were considerably enhanced by papaverine: the content of cAMP was increased by isoprenaline (3 times 10(-7) M) to about 3 times the control value and also its positive inotropic effect was significantly greater than in controls without papaverine. On the other hand, the positive inotropic effect of methoxamine (10(-4) M) was not affected by papaverine (10(-5) M). Furthermore, in the papillary muscle treated with papaverine the level of cAMP was significantly reduced by methoxamine: the papaverine-induced increase of cAMP was abolished by methoxamine. 4. The present results are compatible with the hypothesis that cAMP is involved as a mediator in the positive inotropic effect induced by beta-adrenoceptor stimulation, and indicate further that the stimulation of alpha-adrenoceptors evokes its positive inotropic effec through a mechanism other than that elicited by beta-adrenoceptor stimulation, i.e., independent of cAMP.

Non-competitive spasmolytics as antagonists of Ca++-induced smooth muscle contraction

The spasmolytic drugs papaverine, phenpropamine, Cxn 2 (1-methyl-amino-3,3,5-trimethylcyclohexane), khellin, cyclandelate, magnesium chloride, cocaine, 2,4-dinitrophenol and KCN antagonize various types of spasmogens, such as acetylcholine or histamine, non-competitively. They are assumed to act at some level in the excitation-contraction process common to the various spasmogens. Ca++ is essential for the induction of a contraction by the spasmogens. In the non-competitive action of some spasmolytics, Ca++ is postulated to be involved. To detect possible differences in their mechanism of action the various spasmolytics were tested against Ca++ acting as a pseudo-spasmogen on the K+-primed taenia caeci of the guineapig in a Ca++-free medium. Although different mechanisms of action for the various spasmolytics are to be expected, they all behaved similarly with respect to Ca++ in that they all caused a parallel shift in the log dose-response curve of Ca++ to higher concentrations.