cAMP-dependent ACTH secretagogues facilitate corticotropin releasing activity of angiotensin II on rat anterior pituitary cells in vitro

Both arginine vasopressin (AVP) and angiotensin II (AII) potentiate the corticotropin-releasing activity of CRF41 via a potentiation of CRF41-induced cAMP production. In perfused rat anterior pituitary cells, AII (10(-8) mol) showed a transitory 2-fold increase in its ACTH-releasing activity, when tested after application extract of rat stalk median eminence. In order to determine whether this facilitating effect on AII corticotropin-releasing activity occurred through cAMP-dependent mechanisms, the ACTH-releasing activity of AII was tested after stimulation with CRF41, AVP or forskolin, three secretagogues with known effects on cAMP production. When given 16 min after CRF41, 10 micrograms/l, AII (10(-8) mol) showed a significant increase (210%) in its ACTH-releasing activity, which returned to the normal level when AII-stimulation was repeated at 32 min (121%) and 48 min (100%). Similarly, forskolin, 3 X 10(-6) mol, produced a significant transitory increase (208%) in the subsequent AII-induced ACTH release whereas AVP, 10 micrograms/l and 100 micrograms/l, had no effect on the following ACTH response to AII. These results suggest that the AII-induced ACTH secretion--which is cAMP independent--nevertheless may be modulated by previously stimulation of the cAMP pathway