An oxytocin receptor in anococcygeus muscles isolated from male mice

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Abstract
1 The nature of the neurohypophyseal peptide receptor in the anococcygeus muscles from male mice was investigated. 2 The rank order of potency of naturally occurring peptides was oxytocin > Arg-vasotocin > Arg-vasopressin>Lys-vasopressin, which is similar to that found in the uterus and mammary gland. 3 Selective agonists on the oxytocin (OT) receptors of the uterus and mammary gland (Thr4-OT; Gly7-OT; Thr4-Gly7-OT) were also potent agonists in the mouse anococcygeus. 4 Competitive antagonists of uterine responses to oxytocin (dP-TyrMe-Thr4-OT; dP-TyrMe-OT; dP-Thr4-OT; dp-Orn8-OT) were also competitive antagonists of oxytocin-induced contractions of the mouse anococcygeus. 5 It is concluded that the neurohypophyseal peptide receptor of the male mouse anococcygeus is of the oxytocin type; antagonist pA2 values suggest that this receptor resembles, but may not be identical to, the uterine oxytocin receptor. Possible physiological and pharmacological implications of these observations are discussed.