Farzin Hadizadeh - Department of Medicinal Chemistry, School of Pharmacy and Biotechnology Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
Mohammad Fatehi - Atlantic Centre for Comparative Biomedical Research, Charlottetown, PEI, Canada. (Former Faculty member of Department of Physiology and Pharmacology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran)
Zahra Fatehi-Hassanabad - Atlantic Centre for Comparative Biomedical Research, Charlottetown, PEI, Canada. (Former Faculty member of Department of Physiology and Pharmacology, Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran)
Mojgan Zandieh - Department of Medicinal Chemistry, School of Pharmacy and Biotechnology Research Center, Mashhad University of Medical Sciences, Mashhad, Iran

Objectives In order to provide a pharmacological profile for some newly synthesized dihydropyridines, we investigated their effects on the isolated rat colon segments and the isolated rat atrium contractility. The tested compounds include alkyl ester analogues of nifedipine, in which the ortho-nitrophenyl group at position ۴ is replaced by ۲-alkylthio-۱-benzyl-۵-imidazolyl substituent, and nifedipine as a positive control substance. Materials and Methods Isolated rat colon and atrial tissues were prepared. Rat colon was contracted with ۸۰ mM KCl, and maximum response was recorded (۱۰۰%).  After washing tissue with Krebs solution it was preincubated with different concentrations of test compounds and again KCl was added and percent change in contraction was calculated. Spontaneous contractions and its frequency for colon and atrium before and after addition of test compounds were also recorded and percent change was calculated. Nifedipine (۱۰-۸ -۱۰-۵ M) was used as positive control at all experiments. Results The compounds showed similar effects to that of nifedipine on the isolated rat colon. The potency of these analogues with concentration range ۱۰-۵ to ۱۰-۴ M was compared to potency of nifedipine which was effective at ۱۰-۸ to ۱۰-۵ M (P<۰.۰۱). However, unlike nifedipine, the test compounds exerted significant positive inotropic effect on the isolated rat atrium (P < ۰.۰۱). Our observations suggest that these analogues of nifedipine selectively enhance contractility of heart muscle while causing relaxation of intestinal smooth muscle. Conclusion These compounds may serve as valuable probes to develop novel dihydropyridines with dual smooth muscle relaxant effect and positive inotropic action.

Colon, Dihydropyridines, Heart Atria, Myocardial Contraction, Rat