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 facto r (CRF) stimulate adrenocorticotropic hormone (ACTH) secretion. Increa sed hypothalamic secretion of these peptides at the end of gestation i nitiates 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 fetuse s and lambs (74 days' gestation to 4 weeks postnatal). Hypothalamic co ncentrations of immunoreactive AVP (IR-AVP) and CRF (IR-CRF) significa ntly increased during late fetal and neonatal development (p < 0.01). Pituitary AVP concentration did not change. Western blot and gel exclu sion chromatography revealed both processed and precursor forms of IR- CRF and IR-AVP in the hypothalamus. We conclude that ovine fetal and n eonatal hypothalami contain both processed and unprocessed forms of IR -CRF and IR-AVP and that, overall, concentrations of the immunoreactiv e peptides increase over the course of development.