Magnesium ions and oxytocin sensitivity of the male mouse anococcygeus.
The sensitivity of the mouse anococcygeus to contraction by oxytocin was shown to be Mg2+-dependent. Decreasing [Mg2+]0 from the optimal concentration of 1 to 0 mM caused a 20-fold parallel rightward displacement of the oxytocin dose-response curve. Contractions to oxytocin-related peptides (Arg-vasotocin, Arg-vasopressin and Lys-vasopressin) were also Mg2+-dependent, but those to other drugs (carbachol, methoxamine and thyrotrophin releasing hormone) were not. The onset of the potentiating effect of Mg2+ was rapid, full potentiation occurring within 70 s. 1-Deaminopenicillamine 8-ornithine-vasotocin produced competitive antagonism of responses to oxytocin, but was more potent in the absence (pA2 = 8.01) than in the presence of Mg2+ (1 mM; pA2 = 7.52). Thus, physiological concentrations of [Mg2+]0 enhanced oxytocin agonist potency but decreased oxytocin antagonist potency; possible mechanisms are discussed.
Gibson
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D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D066298:In Vitro Techniques; D008236:Lypressin / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008729:Methoxamine / Q000494:pharmacology; D051379:Mice; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010121:Oxytocin / Q000494:pharmacology*; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D014668:Vasotocin / Q000494:pharmacology
D001127:Arginine Vasopressin; D010121:Oxytocin; D008236:Lypressin; D013973:Thyrotropin-Releasing Hormone; D002217:Carbachol; D008729:Methoxamine; D008274:Magnesium; D014668:Vasotocin