Arginine vasopressin is a much more potent stimulus to ACTH release from ovine anterior pituitary cells than ovine corticotropin-releasing factor. 1. In vitro studies.
Cultured rat and ovine anterior pituitary cells were treated with a range of doses (0.01-1,000 nM) of arginine vasopressin (AVP) and ovine corticotropin-releasing factor (CRF), alone or in combination, and medium and cell content of immunoreactive (ir-)ACTH determined. In rat cells, a dose-response curve to CRF was obtained, with a threshold dose of 0.1 nM; AVP was much less effective alone, but augmented CRF responses when administered with CRF. In ovine pituitary cells AVP markedly stimulated ACTH release in a dose-dependent fashion, and with a threshold of 0.1 nM; in contrast, CRF increased ACTH release over basal only at doses greater than 100 nM. In combination, subthreshold doses of AVP potentiated rat pituitary cell responses to CRF; addition of 1 nM of AVP to varying doses of CRF was more effective in terms of ACTH release than addition of 1 nM of CRF to increasing doses of AVP. In contrast, in ovine cells the addition of 1 nM CRF to increasing doses of AVP elicited a larger ACTH response than the addition of 1 nM AVP to increasing doses of CRF. Dexamethasone pretreatment (5 nM) for 48 h significantly decreased CRF potentiation of AVP-stimulated ACTH release in ovine cells. These studies confirm that CRF is a more potent stimulus of ACTH release than AVP in the rat, and establish that in contrast AVP is a much more potent stimulus of ACTH secretion than CRF in isolated ovine pituitary cells.