Ontogeny and molecular weight of immunoreactive arginine vasopressin and corticotropin-releasing factor in the ovine fetal hypothalamus.

In sheep, arginine vasopressin (AVP) and corticotropin-releasing factor (CRF) stimulate adrenocorticotropic hormone (ACTH) secretion. Increased hypothalamic secretion of these peptides at the end of gestation initiates parturition in this species. We hypothesized that CRF and/or AVP content in the fetal hypothalamus increases late in gestation and that this content was comprised of multiple molecular weight forms of these peptides. Hypothalami and pituitaries were collected from fetuses and lambs (74 days' gestation to 4 weeks postnatal). Hypothalamic concentrations of immunoreactive AVP (IR-AVP) and CRF (IR-CRF) significantly increased during late fetal and neonatal development (p < 0.01). Pituitary AVP concentration did not change. Western blot and gel exclusion chromatography revealed both processed and precursor forms of IR-CRF and IR-AVP in the hypothalamus. We conclude that ovine fetal and neonatal hypothalami contain both processed and unprocessed forms of IR-CRF and IR-AVP and that, overall, concentrations of the immunoreactive peptides increase over the course of development.