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  • Title: Excitatory and inhibitory actions of vasopressin on colonic excitation-contraction coupling in dogs.
    Author: Ward SM, Bayguinov OP, Lee HK, Sanders KM.
    Journal: Gastroenterology; 1997 Oct; 113(4):1233-45. PubMed ID: 9322518.
    Abstract:
    BACKGROUND & AIMS: Vasopressin, a circulating hormone and agent used to treat gastrointestinal bleeding, affects gastrointestinal motility. Both excitatory and inhibitory responses that may be caused by species differences or concentration-dependent effects of this hormone have been reported. This study examined the actions of vasopressin on the canine colon and studied the mechanism underlying the excitatory effects of vasopressin. METHODS: Intracellular microelectrodes and isometric force measurements were used to measure vasopressin responses in muscle strips. The patch-clamp technique was used to record arginine vasopressin activation of nonselective cation currents in isolated myocytes. RESULTS: Vasopressin (10(-12) to 10(-9) mol/L) increased electrical slow waves and enhanced phasic contractions. Atropine and tetrodotoxin did not alter the responses to vasopressin. In myocytes, vasopressin activated a nonselective cation conductance at concentrations that enhanced slow waves. Vasopressin (> 5 x 10(-8) mol/L) caused a tetrodotoxin- or NG-nitro-L-arginine methyl ester-insensitive inhibition of slow waves and contractile activity. A V1-receptor antagonist shifted the effects of vasopressin to higher concentrations. Immunohistochemistry showed expression of vasopressin-like immunoreactivity within the colonic wall, suggesting that local concentrations may exceed circulating levels. CONCLUSIONS: These data document the concentration dependence of the biphasic effects of vasopressin and provide a mechanism for the excitatory effects of vasopressin at physiological levels.
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