The effect of ACTH on calcium distribution in the perfused cat adrenal gland.

1. Experiments were carried out to study the effects of adrenocorticotrophin (ACTH) on calcium distribution in the isolated cat adrenal gland perfused with Locke solution.2. The addition of ACTH to Locke solution caused a small, but significant, increase in the radiocalcium ((45)Ca) space and content of the adrenal cortex.3. The average (45)Ca washout curve obtained after exposure to ACTH was significantly displaced above the average washout curve for the control glands during the first 20 min of washout. During the time that the two curves were significantly different, maximum corticosteroid secretion was attained.4. The rate of (45)Ca efflux was slowed after ACTH was added to the perfusion medium.5. The total calcium content of the cortex was not altered by ACTH.6. Perfusion with calcium-free Locke caused a rapid decrease in the calcium content of the cortex to about 20% of the control value. Dinitrophenol was required to deplete completely the cortical calcium content during perfusion with the calcium-deprived medium.7. The results are consistent with the suggestion that a translocation of calcium occurs during stimulation of the cortex by ACTH. The source of the calcium ions needed to support the secretory response to ACTH is probably not the extracellular fluid; but ACTH may shift calcium from a rapidly exchanging to a more slowly exchanging cellular pool.