CATECHOLAMINE RELEASE FROM THE ISOLATED PERFUSED ADRENAL GLAND

Muscarinic receptor modulation of release of [Met5]enkephalin immunoreactive material and catecholamines from the bovine adrenal gland

Muscarinic receptor modulation of secretion from the adrenal medulla was studied using retrogradely perfused bovine tissue. Atropine, at a dose not affecting 1,1 dimethyl-4-phenylpiperizinium (DMPP)-stimulated release, inhibited the acetylcholine (ACh)-stimulated release of noradrenaline and [Met5]enkephalin-immunoreactive material (ME-IRM). DMPP-stimulated release of catecholamines and ME-IRM was potentiated by the addition of methacholine. Pilocarpine significantly potentiated the release of noradrenaline only. Methacholine, pilocarpine or muscarine, when infused alone, had no stimulatory affect on the basal release of ME-IRM. These findings suggest that the muscarinic receptors in the bovine adrenal medulla function by potentiating the release of ME-IRM and catecholamines induced by nicotinic receptor stimulation.

Release of catecholamines and [Met5]enkephalin immunoreactive material from perfused bovine adrenal glands

Retrogradely perfused bovine adrenal glands were stimulated by acetylcholine (ACh) and 1,1-dimethyl-4-phenyl-piperazinium (DMPP), with or without hexamethonium. Stimulation by either agent resulted in an increased release of both [Met5]enkephalin immunoreactive material (ME-IRM) and catecholamines as measured by radioimmunoassay and high performance liquid chromatography with electrochemical detection, respectively. ACh (5 X 10(-5) M) and DMPP (5 X 10(-5) M) stimulated the release of norepinephrine greater than the release of epinephrine. The action of these agents was antagonized by hexamethonium (5 X 10(-4) M). DMPP produced the same percentage increase in the release of ME-IRM and norepinephrine but produced a greater percentage increase in the release of ME-IRM compared to the release of epinephrine. There was no apparent correlation between the percentage increase in the release of ME-IRM and either norepinephrine or epinephrine after ACh.

Inhibition of catecholamine release from the adrenal medulla by halothane. Site and mechanism of action

In isolated bovine adrenals perfused with Locke solution in a retrograde fashion we investigated the effects of halothane on the catecholamine release evoked by various secretagogues. 1. The catecholamine release induced by activation of the nicotinic receptors on the chromaffin cells with 1,1-dimethyl-4-phenylpiperazinium was almost completely inhibited (by about 90%) by 1.4 X 10(-3) M halothane. 2. It was shown by means of cumulative concentration-response curves of acetylcholine for its stimulating effect on catecholamine release (pD2 = 4.04) that halothane was a non-competitive antagonist (pD'2 = 3.17). 3. Halothane (1.4 X 10(-3) and 4.3 X 10(-3) M) did not decrease the catecholamine secretion in response to pilocarpine or histamine. 4. The 5-hydroxytryptamine-induced catecholamine release was not impaired by 1.4 X 10(-3) M halothane, but was significantly inhibited (by 44%) by 4.3 X 10(-3) M halothane. 5. At 1.4 X 10(-3) M halothane the catecholamine release induced by gamma-aminobutyric acid (GABA) was inhibited by 40%. 4.3 X 10(-3) M halothane completely blocked the secretion induced by GABA. 6. The catecholamine secretion in response to 56 mM KCl or to introduction of CaCl2 after perfusion with Locke solution deficient in CaCl2 was not reduced by halothane (1.4 X 10(-3) and 1.4 X 10(-2) M). 7. Halothane (1.4 X 10(-3) M) did not inhibit the catecholamine release evoked by acetaldehyde or tyramine from glands perfused with Ca2+ -free Locke solution throughout the experiments. It is concluded that the site of action of halothane is the cell membrane of the chromaffin cell. The anaesthetic does not impair the permeability of the membrane to calcium ions. Halothane may cause a conformational change of membrane proteins, particularly of the nicotinic receptor (and at higher concentrations of GABA and 5-hydroxytryptamine receptors); thus, stimulation may be prevented by an inhibition of agonist-receptor interaction.

Secretion from the cortex-free bovine adrenal medulla

1. The isolated bovine adrenal medulla was prepared from whole glands by careful removal of the cortex. The tissue was perfused with physiological salt solution and stimulated with a variety of secretogogues.2. Catecholamines were secreted from the tissue upon stimulation with carbamylcholine, nicotine sulphate, acetylcholine bromide, histamine dihydrochloride, (+)-amphetamine sulphate and potassium chloride.3. Carbachol-induced secretion of catecholamines was reduced in the presence of either hexamethonium bromide or tetracaine hydrochloride, during perfusion with calcium-free perfusion fluid, or during perfusion at low temperature.4. Stimulation of the medulla with carbachol also led to secretion of chromaffin granule protein and acid deoxyribonuclease. The relationships between catecholamines secreted and the amounts of these proteins secreted were similar to the corresponding values for the perfused whole bovine adrenal gland. Perfusate lactate dehydrogenase activity and perfusate haemoglobin content were unchanged after carbachol stimulation.5. It is concluded that there are no differences in the mechanisms for catecholamine secretion from the cortex-free perfused medulla and the perfused whole gland.