Arg-Vasotocin Directly Activates Isotocin Receptors and Induces COX2 Expression in Ovoviviparous Guppies.

Oxytocin (OT) is a crucial regulator of reproductive behaviors, including parturition in mammals. Arg-vasopressin (AVP) is a nonapeptide homologous to Arg-vasotocin (AVT) in teleosts that has comparable affinity for the OT receptor. In the present study, ovoviviparous guppies () were used to study the effect of AVT on delivery mediated by the activation of prostaglandin (PG) biosynthesis isotocin (IT) receptors (ITRs). One copy each of and and two copies of were identified in guppies. The results of the affinity assay showed that various concentrations of AVT and IT (10, 10, and 10 mol/L) significantly activated (P < 0.05). experiments revealed significant upregulation (P < 0.05) of cyclooxygenase 2 (), which is the rate-limiting enzyme involved in PG biosynthesis, and by AVT and IT. Furthermore, dual hybridization detected positive signals for and at the same site, implying that ITR1 may regulate gene expression. Measurement of prostaglandin F (PGF) concentrations showed that AVT induced PGF synthesis (P < 0.05) and that the effect of IT was not significant. Finally, intraperitoneal administration of PGF significantly induced premature parturition of guppies. This study is the first to identify and characterize AVT and ITRs in guppies. The findings suggest that AVT promotes PG biosynthesis ITR and that PGF induces delivery behavior in ovoviviparous guppies.