An oviposition-inducing peptide: Isolation, localization, and function of avian galanin in the quail oviduct

It is well established that avian oviposition is regulated, at least partly, by a neurohypophysial hormone, arginine vasotocin, and ovarian hormones, prostaglandins, are regulated through mechanisms of the induction of uterine contractions. Although abundant nerves are terminated in the musculature in the uterine and vaginal oviduct regions, limited information is available on the neuronal control mechanism of avian oviposition. To identify the oviduct factor that plays an important role in the induction of oviposition as a neurotransmitter or a neuromodulator, a study was conducted to isolate the bioactive substance involved in the vaginal and uterine contractions from mature oviducts of the Japanese quail. Acetic acid extracts of 200 quail oviducts were forced through disposable C-18 reversed-phase cartridges, and then the retained material was subjected to the reversed- phase and cation-exchange HPLC purifications. A purified bioactive substance showed a single peak on the reversed phase HPLC and was further subjected to amine acid sequence analysis and molecular weight presumption. The substance was identified as avian galanin, which was previously isolated from chicken intestine. The synthetic peptide enhanced contractions of both the vagina and the uterus in a manner similar to the native peptide, and the threshold concentrations were 10^-9-10^-8 M in the vagina and 10^-10-10^-9 M in the uterus. An intraperitoneal injection of the synthetic peptide significantly evoked quail oviposition during 5 min after injection. Immunohistochemical analysis with the anti-galanin serum revealed that abundant immunoreactive fibers were distributed in muscle layers of the vagina and the uterus. The immunoreaction examined in these regions was completely inhibited by preincubation of the antibody with synthetic peptide. These results suggest that avian galanin in the oviduct evokes oviposition through mechanisms of the induction of uterine and vaginal contractions. This peptide may contribute as a neurotransmitter or a neuromodulator to avian oviposition.