The release of acetylcholine and of catecholamine from the cat's adrenal gland

The cat's adrenal gland was perfused in situ with Krebs solution containing eserine; the amount of acetylcholine and of catecholamine released was measured. Splanchnic nerve stimulation (5 Hz for 2 min) increased the release of acetylcholine and catecholamine; the molar ratio of evoked release of catecholamine to acetylcholine was 122 +/- 8. It is suggested that this amplification is achieved because a chromaffin cell granule contains more mediator than does the acetylcholine quantum that releases it. The release per impulse of catecholamine during splanchnic nerve stimulation at 30 Hz was less than that released by stimulation at 1 or 5 Hz. This depression is attributed to a presynaptic failure, because the release of acetylcholine was similarly frequency dependent. The release of catecholamine was linearly related to the release of acetylcholine over the range tested, indicating that the input-output relationship at the splanchnic-adrenal medullary junction is linear. During continuous stimulation of the splanchnic nerve (5 Hz), catecholamine release declined to a level that was 32 +/- 2% of the initial output. This fatigue is attributed primarily to a postsynaptic depression, because the release of acetylcholine was maintained at 71 +/- 6% of its initial level. The presence of eserine in the perfusate was necessary for the release of acetylcholine to be detected, but in the presence of eserine catecholamine release was 90 +/- 10% that in the drug's absence. It is concluded that released acetylcholine is hydrolysed at some distance from its site of release and action. Glands perfused with raised K+ released acetylcholine and catecholamine.(ABSTRACT TRUNCATED AT 250 WORDS)