Korean J Physiol Pharmacol.  2005 Aug;9(4):223-230.

Naltrexone Inhibits Catecholamine Secretion Evoked by Nicotinic Receptor Stimulation in the Perfused Rat Adrenal Medulla

• Yu BS
• Min SY
• Seo YS
• Choi CH
• Lee EH
• Lim DY

Abstract

The purpose of the present study was to examine the effect of naltrexone, an opioid antagonist, on secretion of catecholamines (CA) evoked by cholinergic nicotinic stimulation and membrane-depolarization from the isolated perfused rat adrenal gland and to establish the mechanism of its action. Naltrexone (3x10 (-6) M) perfused into an adrenal vein for 60 min produced time-dependent inhibition in CA secretory responses evoked by ACh (5.32x10 (-3) M), high K+ (5.6x10 (-2) M), DMPP (10 (-4) M) and McN-A-343 (10 (-4) M). Naltrexone itself did also fail to affect basal CA output. In adrenal glands loaded with naltrexone (3x10 (-6) M), the CA secretory responses evoked by Bay-K-8644, an activator of L-type Ca2+ channels and cyclopiazonic acid, an inhibitor of cytoplasmic Ca2+-ATPase, were also inhibited. However, in the presence of met-enkephalin (5x10 (-6) M), a well-known opioid agonist, the CA secretory responses evoked by ACh, high K+, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were also significantly inhibited. Collectively, these experimental results demonstrate that naltrexone inhibits greatly CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors as well as that by membrane depolarization. It seems that this inhibitory effect of naltrexone does not involve opioid receptors, but might be mediated by blocking both the calcium influx into the rat adrenal medullary chromaffin cells and the uptake of Ca2+ into the cytoplasmic calcium store, which are at least partly relevant to the direct interaction with the nicotinic receptor itself.

Keyword

Naltrexone; Opioid receptors; Secretion of catecholamines; Adrenal gland; Nicotinic receptors

MeSH Terms

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
Adrenal Glands
Adrenal Medulla*
Animals
Calcium
Catecholamines
Chromaffin Cells
Cytoplasm
Dimethylphenylpiperazinium Iodide
Enkephalin, Methionine
Membranes
Naltrexone*
Rats*
Receptors, Nicotinic*
Receptors, Opioid
Veins
(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride
3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester
Calcium
Catecholamines
Dimethylphenylpiperazinium Iodide
Enkephalin, Methionine
Naltrexone
Receptors, Nicotinic
Receptors, Opioid