Effect of muscarinic antagonists on micturition pressure measured by cystometry in normal, conscious rats

Abstract

Objectives. To establish an in vivo model to screen new muscarinic antagonists for the treatment of overactive urinary bladder and to calculate the respective ID 50 values. Methods. The conscious rat cystometry model was modified to determine a complete dose-response curve in each animal. Spontaneous micturition was induced by infusion of room-temperature saline into rat bladders at a constant rate of 12 mL/hr. Cumulative doses of muscarinic antagonists administered in the femoral vein caused dose-dependent inhibition of the urinary bladder contraction measured as the micturition pressure. In addition, the in vitro pK B values for atropine, PNU-200577 (DD01), tolterodine, oxybutynin, and terodiline were determined in carbachol-contracted rat bladder strips. Results. The rank order of the in vivo ID 50 values were atropine (14 ± 4 nmol/kg), PNU-200577 (22 ± 12 nmol/kg), tolterodine (94 ± 20 nmol/kg), oxybutynin (175 ± 89 nmol/kg), darifenacin (236 ± 144 nmol/kg), desethyloxybutynin (313 ± 209 nmol/kg), propiverine (4561 ± 2079 nmol/kg), and terodiline (18,339 ± 5348 nmol/kg). Tolterodine and PNU-200577 caused a parallel shift of the in vitro concentration-response curve to the right and did not alter the maximal contraction. The ID 50 values correlated significantly with the in vitro rat pK B and human bladder pA 2 values. Conclusions. The present results suggest that the rat cystometry model can be used in in vivo screening for new muscarinic antagonists.