Plasma concentrations of adrenocorticotropin related peptides in lambs injected with ovine corticotropin-releasing factor or vasopressin

: Synthetic ovine corticotropin-releasing factor (oCRF) and arginine vasopressin (AVP) were intravenously injected each alone or in combination (each peptide: 1 microgram/kg body weight) in lambs on days 1, 3, 7 and 20 after birth. Plasma samples were collected just before and 10 and 30 min after injection. Plasma concentrations of cortisol and aldosterone were measured. Adrenocorticotropin (ACTH)-related peptides were isolated by Sephadex G50 column chromatography and measured by radioimmunoassay. Three different peaks with an ACTH immunoreactivity were found in lamb plasma: a "big" ACTH molecular form (Mr = 30,000), an "intermediate" (Mr = 8000) and a "little" (Mr = 4500). In 1 and 3 days-old lambs, both CRF and AVP increased preferentially "intermediate" ACTH. In 7 and 20 days-old lambs, an increase in "little" ACTH occurred after CRF whereas "intermediate" ACTH rose after AVP. The rise in plasma levels of different molecular forms of ACTH after stimulation by CRF or AVP could suggest that the biological pathway of ACTH synthesis, storage and release may occur in different intracellular pools or rather in different pituitary cells. Intermediate ACTH stimulated adrenal secretion of cortisol as soon as the first day of postnatal life and increased plasma aldosterone concentration in 7 and 20 day-old lambs. At these stages aldosterone level did not change after a rise in "little" ACTH.