Transmembrane signals mediating adrenocorticotropin release from mouse anterior pituitary cells

The effect of arginine vasopressin (AVP) and corticotropin releasing factor (CRF) an adrenocorticotropin (ACTH) secretion, phosphatidylinositol breakdown and cAMP accumulation was examined in primary cultures of mouse anterior pituitary cells. AVP and CRF added alone stimulated ACTH secretion in a dose-dependent manner. At 10(-8) M concentration of peptide, AVP and CRF stimulated ACTH secretion 2.8- and 4.6-fold, respectively. AVP and CRF added in combination at equal doses gave an additive effect. CRF enhanced cAMP accumulation, but AVP had no effect on basal or CRF-induced cAMP accumulation. Both forskolin (10(-5) M) and 8-bromo-cAMP (10(-3) M) increased ACTH secretion in these cells by 2.8- and 1.7-fold, respectively. AVP induced the breakdown of phosphoinositides, and CRF alone, or in combination with AVP did not modify this effect. Phorbol 12-myristate 13-acetate (10(-7) M), dioctanoylglycerol (10(-4) M) and phospholipase C (100 mU/ml) also stimulated ACTH secretion in these cells by 4.2-, 2.4-, and 3.7-fold, respectively. Depletion of intracellular and extracellular Ca2+ decreased ACTH secretion, but had no significant effect on CRF-induced cAMP accumulation. However, AVP-induced phosphoinositide breakdown was dependent on extracellular Ca2+. These results indicate that CRF stimulates ACTH secretion via the cAMP-dependent pathway and AVP via the phosphoinositide breakdown-phospholipase C pathway. In the presence of AVP and CRF, both pathways appear to operate independently to produce an additive effect on ACTH secretion.