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Besides its antimuscarinic effects, propiverine may possess an additional mode of action. We compared the effects of propiverine, three of its metabolites (M-5, M-6, M-14) and atropine in human, pig and mouse urinary bladder preparations in order to elucidate the nature of a possible additional mode of action. Like the parent compound, M-5, M-6 and M-14 reduced to variable degrees the contractions elicited by electric field stimulation (EFS) of isolated, urothelium-denuded detrusor strips. In mouse the atropine-resistant and therefore the nonadrenergic, noncholinergic component of contractile response to EFS was reduced by M-5, M-14 and propiverine, but was hardly affected by M-6. Atropine, propiverine and M-6 significantly shifted the cumulative concentration–response curves for carbachol (CCh) to higher concentrations. Atropine and M-6 did not affect the maximum tension induced by CCh. Propiverine, M-5 and M-14 reduced the maximum CCh effect, suggesting at least one additional mode of action. This pattern of response was observed in all the three species, albeit with some differences in sensitivity to the various agents. In freshly isolated human detrusor smooth muscle cells, propiverine and M-14 inhibited the nifedipine-sensitive L-type calcium current (ICa) in a concentration-dependent manner. In contrast, the effects of M-5 and M-6 on ICa were insignificant in the concentration range examined. The investigated responses to propiverine and its metabolites suggest that impairment of maximum CCh-induced contractions is due to strong effect on ICa and that this may be associated with the presence of the aliphatic side chain. Keywords: Propiverine and metabolites, electric field stimulation, concentration–response curves for carbachol, human, porcine and mouse detrusor, L-type calcium current Introduction Activation of muscarinic (M) receptors plays a major role in the control of urinary bladder contractility (Andersson, 1993). Although M2 receptors are the predominant subtype found in detrusor muscle (Yamanishi et al., 2001), M3 receptors appear to mediate urinary bladder contractile responses in many species (Yamanishi et al., 2000; Chess-Williams et al., 2001; Choppin & Eglen, 2001; Fetscher et al., 2002). Detrusor contraction in response to muscarinic receptor (M receptor) stimulation requires Ca2+ entry via nifedipine-sensitive L-type calcium channels (Schneider et al., 2004a; Wegener et al., 2004). Antimuscarinic drugs are used for the treatment of the overactive bladder syndrome (OAB; Sellers et al., 2001; Andersson et al., 2002; Andersson & Yoshida 2003; Ouslander, 2004). In addition to its antimuscarinic effect, propiverine appears to have additional spasmolytic effects (Andersson et al., 1999; Wuest et al., 2002). Thus, propiverine inhibits contractile responses elicited by electric field stimulation (EFS) as well as acetylcholine (ACh)-induced contractions in human detrusor strips (Wada et al., 1995). The drug potently reduces KCl-induced contractions in guinea-pig (Haruno, 1991; Tokuno et al., 1993), as well as KCl- and CaCl2-induced contractions in human bladder strips (Wada et al., 1995). In rabbit, propiverine also impairs intracellular Ca2+ homeostasis in addition to its antagonistic muscarinic effects (Madersbacher & Murtz, 2001). Propiverine is rapidly absorbed after oral administration and is subject to extensive first-pass metabolism, giving rise to several active metabolites, for example, M-5, M-6 and M-14 (for chemical structures, see Figure 1). At 24 h after oral application, these compounds can be recovered among other derivatives from the human urine (in percent of the original dose): propiverine, 2–3%; M-5, 20%; M-6, 5%; M-14, 1% (Haustein & Huller, 1988). Siepmann et al. (1998) reported that after 5 days of treatment with multiple dosing of propiverine the following maximum serum concentrations were detected (median; range): propiverine (155 (96–240) ng ml−1) corresponding to 0.38 (0.24–0.59) μM, and its N-oxide M-5 (645 (385–955) ng ml−1) corresponding to 1.68 (1.00–2.49) μM. The metabolites M-6 and M-14 were not detected in serum but in urine only. Figure 1 Chemical structures of propiverine and its metabolites M-5, M-6 and M-14. The pharmacological activities of these metabolites have not yet been studied in detail (Andersson et al., 1999). In order to estimate their contribution to the therapeutic action, we have chosen the three main metabolites in man (M-5, M-6 and M-14) for investigation of their effects on detrusor muscle and used atropine and the congener propiverine for comparative purposes. Pig detrusor was studied because of its similarity to human detrusor. Mouse detrusor was studied because of its high nonadrenergic–noncholinergic (NANC) component of contraction (Wuest et al., 2002). Furthermore, we investigated the effects of these compounds on contractions in human, pig and mouse urinary bladder preparations and on the L-type calcium current (ICa) in human and porcine detrusor smooth muscle cells (DMSC) to estimate additional mechanisms of propiverine and possibly also of its metabolites. |
