Relaxin: an ovarian hormone in an avian species (Gallus domesticus)

The objective of this study was to characterize the biochemical, immunological, and biological activity of avian relaxin and to immunolocalize relaxin-like peptides in the ovary of the hen (Gallus domesticus). A relaxin-like peptide was partially purified from ovaries of actively laying hens by size-exclusion chromatography and further purified by ion-exchange chromatography on CM-cellulose. Those fractions containing relaxin immunoreactivity were identified with the use of a homologous porcine relaxin radioimmunoassay on selected column effluent and pooled, and a sample was subjected to SDS-gel electrophoresis. The SDS-gel-separated proteins were electrotransferred onto a nitrocellulose membrane and immunostained with an antiserum to porcine relaxin which showed the presence of a single band of approximately 6000 daltons. The dose-response curve generated by avian relaxin-like peptide in the homologous porcine relaxin radioimmunoassay was parallel to that produced by the porcine relaxin standard. Like porcine relaxin, avian relaxin-like peptide eluted from the Sephadex G-50 in an elution volume for a molecule of approximately 6000 daltons, was retained on CM-cellulose, and was bioactive in in vitro inhibition of spontaneous contractions of estrogen-primed mouse uterus (a relaxin bioassay). Using an antiserum specific to porcine relaxin, avian relaxin-like peptide was immunolocalized to the granulosa cells of postovulatory follicle from ovary of a hen less than 24 hr postoviposition. No immunostaining was detected in the cells of the largest preovulatory follicles or when the antiserum was preabsorbed with porcine relaxin prior to staining. The finding of this study indicates that the avian postovulatory follicle, like the corpus luteum of other vertebrate species (sharks and mammals), contains a relaxin-like peptide.