EFFECTS OF NIFEDIPINE AND CROMAKALIM ON ISOLATED RAT BLADDER TISSUE AND AORTA STRIP

Relaxing effects of nifedipine and cromakalim on rat aorta strip, bladder ring and bladder strip were compared on receptor and KCl mediated contraction. The IC₅₀ of nifedipine to inhibit NE induced contraction (by stimulation of α₁-adrenoceptor in aorta strip) was found to be 2.76±0.79 nmol·L^-1. For the same action the IC₅₀ of cromakalim (a potassium channel opener) was 48±25 nmol·L^-1. However, to inhibit 27.5 mmol·L^-1 KCl induced contraction, the IC₅₀ for nifedipine and cromakalim were 1.83±1.3 nmol·L^-1 and 64±19 nmol·L^-1, respectively. On bladder ring, to inhibit carbachol mediated contraction (by cholinergic M-receptor stimulation), the IC₅₀ for nifedipine and cromakalim were found to be 15±13 nmol·L^-1 and 13±80 nmol·L^-1, respectively. To inhibit KCl induced contraction, the IC₅₀s were 2.05±1.26 nmol·L^-1 and 38±26 nmol·L^-1. On bladder strip, nifedipine and cromakalim antagonized carbachol mediated contraction with IC₅₀s of 12±12 nmol·L^-1 and 32.0±2.4 nmol·L^-1. Both compounds reduced the contraction force mediated by KCl with IC₅₀ of 1.57±0.7 nmol·L^-1 and 71±25 nmol·L^-1, respectively.Our study showed that cromakalim was better to relax receptor mediated contraction of bladder ring. While, nifedipine was more potent to antagonize NE induced aorta strip contraction. Nifedipine also showed greater effect on KCl induced responses in all three tissue preperations.