Forskolin Stimulates Adenylate Cyclase Activity, Cyclic AMP Accumulation, and Adrenocorticotropin Secretion from Mouse Anterior Pituitary Tumor Cells

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Abstract
The effects of forskolin, an adenylate cyclase activator, were investigated on adrenocorticotropin (ACTH) secretion from AtT‐20/D16‐16 mouse pituitary tumor cells. Forskolin increased adenylate cyclase activity in these cells in the absence of added guanyl nu‐cleotide, an effect blocked by somatostatin. Cyclic AMP synthesis and ACTH secretion increased in a concentration‐dependent manner, not only in the clonal cells, but in primary cultures of rat anterior pituitary as well. Somatostatin inhibited cyclic AMP synthesis and ACTH secretion in response to forskolin. When forskolin was coapplied with corticotropin releasing factor, cyclic AMP synthesis was potentiated and ACTH secretion additive. The calcium channel blocker, nifedipine, inhibited forskolin, and 8‐bromocyclic AMP stimulated ACTH secretion. These data suggest that ACTH secretion may be regulated at the molecular level by changes in cyclic AMP formation, which in turn regulate a calcium gating mechanism.