title: A comparative study of the relaxing effect of nitroprusside and verapamil on human umbilical vessels.
abstract: Relaxing effects of nitroprusside and verapamil on the resting or K-stimulated tension and 45Ca uptake in human umbilical vessels were investigated. Both nitroprusside and verapamil reduced the resting and K-stimulated tensions in a dose-dependent manner. Nitroprusside was much more effective than verapamil in reducing resting tension. However, verapamil caused a greater relaxation of the K-induced contraction than nitroprusside. In a Ca2+-free medium, K+ still caused a small and sustained contraction. Nitroprusside abolished the contraction in the Ca2+-free medium, which verapamil failed to inhibit. Neither nitroprusside nor verapamil affected the resting 45Ca uptake measured by a lanthanum method. The K-induced increase in 45Ca uptake was inhibited by verapamil, but not by nitroprusside. The results suggest that nitroprusside unlike verapamil does not act as a Ca2+ influx inhibitor resulting in the relaxation of human umbilical vessels.
mesh_terms: D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D005292:Ferricyanides / Q000494:pharmacology*; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation / Q000187:drug effects*; D009599:Nitroprusside / Q000494:pharmacology*; D010276:Parasympatholytics / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D014469:Umbilical Arteries / Q000187:drug effects / Q000502:physiology*; D014471:Umbilical Veins / Q000187:drug effects / Q000502:physiology*; D014700:Verapamil / Q000494:pharmacology*
chemical_list: D005292:Ferricyanides; D010276:Parasympatholytics; D009599:Nitroprusside; D014700:Verapamil; D011188:Potassium; D002118:Calcium