Declining catecholamine secretion in adrenal medulla on prolonged stimulation with acetylcholine.
Perfused pig adrenal glands and cortex-free ox adrenal medullae were stimulated by continuous infusion of 10(-4) M acetylcholine (ACh). Secretion of adrenaline rose to a maximum in approximately 5 min but, after a further 15 min, declined to 36 +/- 19% (+/- S.D.) of maximum for pig (N = 5) and 27 +/- 10% of maximum for ox (N = 3), in spite of continued infusion of ACh. After 20 min, no further significant decline was detectable. Nevertheless, in ox medullae, oxygen consumption measured after stimulation showed no significant change relative to the pre-stimulation value, indicating that the decline in secretion did not arise from a failure of oxidative energy metabolism. In 4 pig adrenal glands subjected to a 1 hr infusion of ACh, adrenaline secreted in the last 20 min was only 52 +/- 10% of that secreted in the first 20 min but, after a 2 hr rest interval, recovered to 74 +/- 18% (P less than 0.05) in the first 20 min of a second 1 hr stimulation. In the same glands, no reproducible recovery was detectable for noradrenaline and, by the last 20 min of the second 1 hr stimulation, noradrenaline secretion had declined to 36 +/- 20% of the initial value, even though only 15% of the noradrenaline originally in the gland had been secreted. It is concluded that, while decline and recovery of adrenaline secretion may, in part, have arisen from desensitization and resensitization of the ACh receptor; the decline in noradrenaline secretion arose mainly from depletion of a readily secreted pool which was considerably smaller than the total in the gland.
D000109:Acetylcholine / Q000494:pharmacology*; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D066298:In Vitro Techniques; D008297:Male; D010101:Oxygen Consumption; D013268:Stimulation, Chemical; D013552:Swine
D002395:Catecholamines; D000109:Acetylcholine