In vivo effects of different antispasmodic drugs on the rat bladder contractions induced by topically applied KCl.
The model originally proposed by Postius and Szelenyi for in vivo screening of spasmolytic compounds on the rat urinary bladder, has been modified and tested to verify its predictivity. The topically applied KCl induced reproducible contractions of the bladder that were dose dependently inhibited by i.v. administration of calcium antagonists like nifedipine, nicardipine, and verapamil. The other spasmolytics tested (oxybutynin, terodiline, flavoxate, and papaverine), showed a non-dose-related inhibition of the contractions. The in vivo potency of the calcium antagonists was related to their in vitro activity on the agonist-induced contractions of rat bladder strips, whereas the activity of the other spasmolytics appeared higher than that predicted on the basis of their in vitro efficacy. Nicardipine showed a dose-dependent inhibition of KCl-induced contractions also after oral administration, whereas oxybutynin and papaverine behaved as after i.v. administration. The described model represents, therefore, a good, quantitative, and reproducible tool of screening at the bladder level only for antispasmodic drugs endowed with strong calcium antagonistic activity.