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.

In-vivo effect of prostaglandin F-2 alpha treatment on secretory granules in the corpus luteum of the late pregnant cow.

Electron microscopy evaluation indicated that the large luteal cells from control (saline-injected) cows were morphologically similar: 42-72% of the large luteal cells, in which the nucleus was present in the tissue section, contained secretory granules (100-300 nm diameter). From cell to cell, clustering of granules was observed in various regions of the cell cytoplasm, ranging from locations next to the nucleus to those next to the cell membrane where exocytosis was noted. The large mitochondria containing dense inclusions (500-1800 nm diameter) were uniformly distributed throughout the cytoplasm of 98% of the large luteal cells. The morphology of large luteal cells at 2.5 and 5 min after PGF-2 alpha treatment (25 mg) was similar to that of saline controls. However, at 15 and 30 min after PGF-2 alpha the secretory granules were observed primarily at the cell periphery and at 15 min only 22% of the large luteal cells contained secretory granules. Exocytosis involving fusion of the granule and cell membrane was more evident at this time. At 60 min after PGF-2 alpha few large luteal cells (0.5%) were observed with small granules. We suggest that the secretory granules represent those organelles responsible for packaging secretory proteins for transport out of the cell, and PGF-2 alpha is an effector that will initiate cell depletion of these granules and their contents.

Ovulation triggers oxytocin gene expression in the bovine ovary.

The gene for the nonapeptide neurohormone oxytocin is highly expressed in the bovine corpus luteum. Measurements of oxytocin-specific mRNA through the oestrous cycle of non-pregnant cows show that transcription is maximal accompanying ovulation and decreases rapidly thereafter. In contrast, immunohistochemistry shows neurophysin peptide levels to be greatest at mid-cycle. Low levels of oxytocin mRNA are detected in follicles and in the luteolytic half of the cycle. This mRNA is virtually absent in the corpus luteum of pregnant cattle. No cyclicity is evident in hypothalamic oxytocin mRNA levels.