Measurement of 3-methoxy-4-hydroxyphenylglycol (MHPG) in mouse brain by h.p.l.c. with electrochemical detection, as an index of noradrenaline utilisation and presynaptic alpha 2-adrenoceptor function.
1. A novel method for measurement of 3-methoxy-4-hydroxyphenylglycol (MHPG) in mouse brain by use of high performance liquid chromatography (h.p.l.c.) with electrochemical detection is described. This technique incorporates an ethyl acetate purification procedure and uses 3-hydroxy-4-methoxyphenylglycol (iso-MHPG) as the internal standard. 2. Inhibition of monoamine oxidase by injection of tranylcypromine (5 and 10 mg kg-1) or pargyline (50 and 100 mg kg-1) markedly decreased brain MHPG concentrations. After injection of the tyrosine hydroxylase inhibitor, alpha-methyl-p-tyrosine (200 mg kg-1), there were time-dependent linear decreases in the concentrations of noradrenaline and MHPG in mouse brain. In addition, a very good correlation (r = 0.95, n = 30; P less than 0.001) was found between the concentrations of noradrenaline and MHPG present in the brains of the same mice after alpha-methyl-p-tyrosine treatment. 3. Mouse brain MHPG concentrations were dose-dependently reduced after administration of the alpha 2-adrenoceptor agonist, clonidine (1-3000 micrograms kg-1), and elevated by the antagonists, idazoxan (1 and 5 mg kg-1), and yohimbine (1 and 5 mg kg-1). Intracerebroventricular injection of the alpha 1-adrenoceptor agonist, phenylephrine (5-50 micrograms) dose-dependently increased MHPG levels. The alpha 1-adrenoceptor antagonist, prazosin, had no effect at the moderate dose of 1 mg kg-1, but increased MHPG concentrations at 5 mg kg-1. The beta-adrenoceptor agonist, clenbuterol (10-1000 micrograms kg-1) and the antagonist, pindolol (1 and 5 mg kg-1), were both without effect. 4. The decrease in brain MHPG concentrations induced by clonidine (100 micrograms kg-1) was prevented by prior injection of 1 mg kg-1 of idazoxan or yohimbine, but not by prazosin or pindolol. 5. MHPG levels were decreased after administration of the noradrenaline reuptake inhibitor desipramine (5 and 10 mg kg-1) and the non-selective monoamine reuptake inhibitors, sibutramine HCl (BTS 54 524; 1 and 3 mg kg-1) and amitryptyline (5 mg kg-1). However, the selective 5-hydroxytryptamine reuptake inhibitor, zimeldine (5 and 10 mg kg-1), was without effect. Dexamphetamine (1 and 5 mg kg-1) and methamphetamine (1 and 5 mg kg-1) both decreased brain MHPG concentrations in a dose-related fashion. 6. Overall the data show that MHPG can be used as a functional index of both presynaptic alpha 2-adrenoceptor activity and noradrenaline turnover and utilisation.
Heal
D J
DJ
Research Department, Boots Company PLC, Nottingham.
Prow
M R
MR
Buckett
W R
WR
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D002851:Chromatography, High Pressure Liquid; D003000:Clonidine / Q000494:pharmacology; D003913:Dextroamphetamine / Q000494:pharmacology; D004563:Electrochemistry; D006018:Glycols / Q000378:metabolism*; D066298:In Vitro Techniques; D007202:Indicators and Reagents; D008694:Methamphetamine / Q000494:pharmacology; D008734:Methoxyhydroxyphenylglycol / Q000378:metabolism*; D008781:Methyltyrosines / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D019805:alpha-Methyltyrosine
D006018:Glycols; D007202:Indicators and Reagents; D008781:Methyltyrosines; D008996:Monoamine Oxidase Inhibitors; D011942:Receptors, Adrenergic, alpha; C021209:isoMHPG; D008694:Methamphetamine; D008734:Methoxyhydroxyphenylglycol; D019805:alpha-Methyltyrosine; D003000:Clonidine; D003913:Dextroamphetamine; D009638:Norepinephrine