Abstract
The mechanism of release of catecholamine was studied using bovine adrenal medullary slices or granules.
1. Acetylcholine or excess potassium caused an increase in the rate of catecholamine release from the slices. Omission of calcium from the incubation medium also stimulated the release of catecholamine.
2. The stimulatory effect of acetylcholine or excess potassium was lost when calcium was omitted from the medium, and markedly inhibited by the addition of cocaine.
3. Addition of reserpine or tyramine stimulated the release of catecholamine from the slices. The effect of reserpine was diminished in calcium free medium, but that of tyramine was not affected in calcium free medium. Cocaine had a weak inhibitory effect on the release of catecholamine caused by reserpine but no effect on the response to tyramine.
4. Calcium ion itself stimulated the released of catecholamine from the granules, but its effect was prevented by magnesium.
From the above results it is suggested that calcium ion plays a cardinal role in the process of catecholamine release from the adrenal medulla and it acts as a link between the excitation of the membrane and the secretory response.
