Effects of cyclic 3',5'-AMP and related compounds on catecholamine-induced contraction of isolated guinea-pig vas deferens.

Not only cyclic 3'. 5'-AMP but also related compounds containing adeno sine moiety potentiated the contractile response of the isolated guinea-pig vas deferens to catecholamines, especially to dl-isoproterenol. The potentiating activity of cyclic 3', 5'-AMP was one-tenth that of adenosine or 5'-AMP. From these findings, it is suggested that not only adenosine moiety but also the steric conformation of adenine mononucleotides play an important role in potentiating the contractile response to catecholamines, and that the potentiation phenomenon occurs on the cell membrane. On the other hand, theophylline reduced the contractile response especially to dl isoproterenol and counteracted the potentiation phenomenon caused by cyclic 3', 5' AMP or adenosine. Possible mechanisms of action are discussed. Cyclic 3', 5'-AMP is considered to be the secondary messenger of the (l-adrenergic action and the smooth muscle-relaxing actions of catecholamines, mediated by the ad renergic fl-receptor, are associated with an increase in the level of cyclic 3', 5'-AMP (1-3). On the contrary, exogenously applied cyclic 3', 5'-AMP hardly resembles the effects of catecholamines as it penetrates cell membrane only with difficulty and is easily hydro lized by phosphodiesterase (4-6). Recently, it has been reported by several workers (7-9) that the smooth muscle con traction in response to catecholamines, mediated by the adrenergic s-receptor, was poten tiated by exogenously applied cyclic 3', 5'-AMP. Considering the evidence that cyclic 3', 5'-AMP penetrates cell membrane with difficulty and that the adrenergic "-receptor effects of catecholamines result in a lowering of the intracellular level of cyclic 3', 5'-AMP (10-13), it is thought that the potentiative action of cyclic 3', 5'-AMP is non-specific. The present study was carried out on the effects of exogenously applied cyclic 3', 5' AMP and related compounds on the catecholamine-induced contraction of the isolated guinea-pig vas deferens which may have both exciting ce-receptor and depressing fl-re ceptor (14-16). MATERIALS AND METHODS Guinea-pigs, weighing 300-350 g, were sacrificed by a blow on the head. Vasa de ferentia were dissected and suspended in a 10 ml organ bath containing Tyrode solution aerated with a mixture of 95 ; 0, and 5 % CO, at 30'C. This was allowed to stand one hr for equilibration before the tissue was exposed to drugs. Contractions produced by agonists were recorded for 50 sec with a isotonic frontal writing lever on a smoked drum. Pretreated drugs were added one min before the addition of agonists. RESULTS 1. Effects of cyclic 3', 5'-AMP and its related compounds on the catecholamine-induced contraction of guinea-pig Vas deferens The contraction of the isolated guinea-pig vas deferens (data not included) produced by cyclic 3', 5'-AMP was not observed even at a concentration of 3 x 10-3 M. The con tractile response of the isolated guinea-pig vas deferens to catecholamines, especially to dl-isoproterenol was, however, remarkably potentiated by pretreatment with cyclic 3, 5'-AMP at a concentration of 10' M (Fig. 1). FIG. 1. Effects of cyclic 3',5'-AMP, adenosine and theophylline on catecholamine induced contraction of isolated guinea-pig vas deferens. Dose-response curves for catecholamines were obtained by the single dose technique. Pretreated drugs were added one min before addition of agonists. Abscissa : molar concentration of dl-NA (noradrenaline), 1-Adr (adrenaline) and dl-IS (isoproterenol). Ordi nate : contraction height (%) relative to the maximal contraction produced by acetylcholine. *-*:control, • -0 : cyclic 3',5'-AMP (C-AMP) 10' M, CC : adenosine 10-'M, 0 -O : theophylline 3 x 10-' M. A similar potentiation phenomenon was also observed when pretreated with adeno sine (Fig. 1). The potentiating activity of adenosine was observed to be ten times as strong as that of cyclic 3', 5'-AMP (Fig. 2, Table 1). On the other hand, theophylline at a higher concentration of 3 x 10' M depressed the contractile response to catecholamines, especially to dl-isoproterenol (Figs. 1, 2). Among other purine or pyrimidine compounds, only compounds containing adeno sine moiety such as 2'-AMP, 3'-AMP and 5'-AMP showed a similar potentiation pheno