The role of calcium in the mechanism of corticotropin releasing factor mediated ACTH release

Abstract

To investigate the role of calcium (Ca +2 in CRF stimulated ACTH release, we studied the effect of the following conditions on CRF (10 nM) mediated ACTH release in primary pituitary monolayer culture: (1) different concentrations of Ca +2 (2) EGTA (3) lanthanum (La +3) and nifedipine, blockers of calcium cell influx and (4) penfluridol, trifluoperazine, and pimozide, inhibitors of calmodulin activation. Higher concentrations of Ca +2 in the culture medium led to greater amounts of CRF induced ACTH release. EGTA at 3 mM decreased the amount of CRF stimulated ACTH release by 60% but did not alter the spontaneous release of ACTH. At 0.5 mM and 1.0 mM La +3, ACTH release induced by CRF was inhibited by 23% and 35% respectively ( p<0.01). Nifedipine (both 10 −5 and 10 −4 M) inhibited CRF stimulated ACTH release but only to a maximum of 30%. This inhibition was completely overcome by the addition of 12 mM calcium. Penfluridol, pimozide, and trifluoperazine blocked the release of ACTH induced by CRF by 63%, 26%, and 0% respectively. In conclusion, extracellular Ca +2, Ca +2 influx, and calmodulin play a role in the mechanism of CRF stimulated ACTH in vitro.