Mesotocin increases the sensitivity of the hen oviduct uterus to arginine vasotocin.

The present study was performed to elucidate whether mesotocin (MT), one of avian neurohypophysial hormones, relates to the action of arginine vasotocin (AVT) on oviposition of hens. The ratio of AVT-induced oviposition was increased when 1 microg/hen of MT was injected together with AVT. An intravenous injection of 1 microg/hen of MT caused an increase in the binding affinity of the uterine AVT receptor and a decrease in the binding capacity. Blood MT concentrations measured by RIA increased approximately 1 min before oviposition during the period of the bearing-down behavior, but the AVT concentration did not change at this time. The blood AVT concentration dramatically increased within 1 min just after oviposition. The results suggest that MT may have an effect of enhancing the inducing oviposition by AVT through the increase in the sensitivity of the uterus to AVT at oviposition in hens.