Plasma concentrations of adrenocorticotropin-related peptides after corticotropin-releasing hormone and vasopressin injections in sheep

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Abstract
Ovine corticotropin-releasing hormone (1 .mu.g/kg body weight) and arginine vasopressin (1 .mu.g/kg) were injected iv in sleep, both separately and in combination. Plasma were sampled just before and 5, 15 and 30 min after the injection. ACTH-related peptides were isolated by Sephadex G-50 column chromatography and measured by RIA. Cortisol and aldosterone were determined on the same plasma samples. Three molecular forms of immunoreactive ACTH (IR-ACTH) were isolated: big (> 20 000 mol wt), ''intermediate'' (= 8000 mol wt) and ''little'' (= 4500 mol wt). Following CRH injections, the three molecular forms of ACTH were enhanced, particularly the ''little'' form, whereas ''intermediate'' IR-ACTH was highly and specifically responsive to AVP. After a simultaneous injection of CRH and AVP, additive increases occurred for ''intermediate'' and ''little'' IR-ACTH. The release of different molecular forms of IR-ACTH after stimulation by CRH or AVP of corticotrope cells suggests that ACTH-related peptides could be stored in different intracellular pools or secreted by different pituitary cells.