Hypothalamic peptide regulation of ACTH secretion from sheep pituitary

The relative abilities of the hypothalamic peptides corticotropin-releasing factor (CRF), arginine vasopressin (AVP), oxytocin (OT), and angiotensin II (ANG II) to stimulate adrenocorticotropic hormone (ACTH) secretion from cultured sheep anterior pituitary cells were studied. Incubation of cells with CRF, AVP, and OT, but not ANG II, was associated with increased ACTH secretion. CRF and AVP were equally effective in stimulating ACTH release at 0.1 nM, but larger doses of each resulted in distinctly different ACTH secretory patterns. The minimally effective dose of OT was 10 nM; greater doses of this peptide resulted in ACTH secretory responses similar to those measured after addition of AVP. Cotreatment with ANG II did not affect the ACTH-secretory response to CRF, AVP, or OT. These data confirm that AVP is a potent stimulus for ACTH secretion from sheep anterior pituitary in vitro and also show that CRF is effective in low concentrations in releasing ACTH. In contrast, the data do not support a regulatory role for ANG II in stimulating ACTH release directly from sheep corticotroph cells.