title: Effects of intravenous magnesium infusion on in vivo release of acetylcholine and catecholamine in rat adrenal medulla.
abstract: We applied microdialysis technique to the left adrenal medulla of anesthetized rats and examined the effects of intravenous Mg(2+) infusion on presynaptic acetylcholine (ACh) release and postsynaptic catecholamine release induced by electrical stimulation of splanchnic nerves. The dialysis probes were perfused with Ringer's solution containing neostigmine. Low-dose MgSO4 (25 μmol/kg/min for 30 min i.v.) increased mean plasma Mg(2+) concentration to 2.5mM; the administration suppressed norepinephrine (NE) release by approximately 30% and epinephrine (Epi) release by approximately 20%, but did not affect ACh release. High-dose MgSO4 (50 μmol/kg/min for 30 min i.v.) increased mean plasma Mg(2+) concentration to 3.8mM; the administration suppressed ACh release by approximately 25%, NE release by approximately 60% and Epi release by approximately 45%. Administration of Na2SO4 (50 μmol/kg/min for 30 min i.v.) did not change the release of ACh, NE or Epi. Local administration of nifedipine (200 μM) suppressed NE release by approximately 40% and Epi release by approximately 30%, but did not affect ACh release. In the presence of nifedipine, low-dose MgSO4 did not suppress the release of ACh, or further suppress NE or Epi compared to nifedipine alone, but high-dose MgSO4 suppressed ACh release by approximately 25% and further suppressed NE release by approximately 60% and Epi release by approximately 50% compared to nifedipine alone. In conclusion, intravenous administration of Mg(2+) inhibits both presynaptic ACh release and postsynaptic catecholamine release in the adrenal medulla, but L-type Ca(2+) channel-controlled catecholamine release may be more sensitive to Mg(2+) than non-L-type Ca(2+) channel-controlled ACh release.
authors.affiliation: Department of Cardiac Physiology, National Cerebral and Cardiovascular Center Research Institute, 5-7-1 Fujishiro-dai, Suita, Osaka 565-8565 Japan; Department of Anesthesiology, Shiga University of Medical Science, Seta Tsukinowa-cho, Otsu, Shiga 520-2192, Japan.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Komaki
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Akiyama
authors.forename: Toji
authors.initials: T
authors.lastname: Yamazaki
authors.forename: Hirotoshi
authors.initials: H
authors.lastname: Kitagawa
authors.forename: Syuichi
authors.initials: S
authors.lastname: Nosaka
authors.forename: Mikiyasu
authors.initials: M
authors.lastname: Shirai
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000313:Adrenal Medulla / Q000187:drug effects* / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D007262:Infusions, Intravenous; D008278:Magnesium Sulfate / Q000008:administration & dosage*; D008297:Male; D017551:Microdialysis / Q000379:methods; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002395:Catecholamines; D008278:Magnesium Sulfate; D000109:Acetylcholine
keywords: Acetylcholine; Anesthetized rats; Epinephrine; Magnesium; Microdialysis technique; Norepinephrine