Importance of noradrenaline found in a functional pool in maintaining spontaneous locomotor activity in rats.

1. Spontaneous locomotor activity (activity) in male Wistar rats was compared with the concentrations of brain noradrenaline (NA), dopamine (DA) and metaraminol.2. alpha-Methyl-m-tyrosine (alphaMMT) (400 mg/kg) reduced the concentrations of DA as well as NA but activity remained high in the presence of metaraminol formed from the alphaMMT. When tetrabenazine (TBZ) was given after alphaMMT pretreatment there was a fall in the levels of activity and in the concentrations of NA, DA and metaraminol.3. alpha-Methyl-p-tyrosine (alphaMT) produced a fall in activity which was correlated with falls in the concentrations of NA and DA. 5-Hydroxytryptamine (5-HT) did not appear to be affected.4. After depletion of NA and DA by alphaMT and TBZ, administration of L-dopa produced a return in activity which was significantly correlated with the concentration of NA but not DA. When alphaMMT was given to a similar group of pretreated animals there was no recovery of activity despite high concentrations of DA and metaraminol.5. The dopamine beta hydroxylase inhibitor, diethyldithiocarbamate (DDC), suppressed activity as well as the concentrations of NA and DA at high doses (750 mg/kg) but smaller doses (400 mg/kg) plus L-dopa gave high DA concentrations without activity.6. It is concluded that NA and not DA is associated with activity but that it is only part of the total NA which is in the biosynthetic storage granule affected by drugs like alphaMT and TBZ, which controls activity. Drugs that do not affect this pool may lower NA concentrations but not reduce activity.7. The replacement of NA by metaraminol in this functional pool does not restore activity.

Studies on the interrelationship between the syntheses of noradrenaline and metaraminol.

1. Experiments were conducted to determine the influence of the rate of noradrenaline synthesis on the conversion of alpha-methyl-m-tyrosine to metaraminol.2. Male Wistar rats, 175-200 g, were placed into four groups and treated with (1) alpha-methyl-p-tyrosine methyl ester, 250 mg/kg; (2) DL-alpha-methyl-m-tyrosine, 400 mg/kg; (3) alpha-methyl-p-tyrosine methyl ester, 250 mg/kg plus DL-alpha-methyl-m-tyrosine, 400 mg/kg; or (4) an equivalent volume of injection vehicle. All solutions were injected intraperitoneally.3. Immediately after treatment half of the rats were transferred to 4 degrees C with the remaining animals being kept at 27 degrees C.4. The rats were killed 4, 8 and 12 h after injection, the brains, hearts, spleens and adrenals removed and analysed for adrenaline, noradrenaline, metaraminol and alpha-methyl-m-tyramine.5. In virtually all cases, both during rest (27 degrees C) and sympathetic stress (4 degrees C), treatment of the rats with alpha-methyl-p-tyrosine methyl ester increased the amount of metaraminol formed from alpha-methyl-m-tyrosine. The only organ not containing increased quantities of metaraminol in the presence of alpha-methyl-p-tyrosine methyl ester was the adrenals, taken from the rats kept at 27 degrees C. Adrenals removed from the cold-exposed rats contained more metaraminol when alpha-methyl-p-tyrosine methyl ester was combined with alpha-methyl-m-tyrosine than when alpha-methyl-m-tyrosine was used alone.6. These results demonstrate that the inhibition of noradrenaline synthesis, by treatment with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine methyl ester, increased the conversion of alpha-methyl-m-tyrosine to metaraminol. It is concluded that inhibiting the formation of dopa allowed increased amounts of alpha-methyl-m-tyrosine to enter the biosynthetic pathway. These results support the false sympathetic transmitter concept advanced for metaraminol.

High-performance liquid chromatographic determination of metaraminol bitartrate in the presence of parabens.

A high-performance liquid chromatographic (HPLC) procedure was developed for the determination of metaraminol bitartrate in the presence of methylparaben and propylparaben. Reversed-phase ion-pair chromatography was employed using dioctyl sodium sulfosuccinate as the counterion. The current official USP procedure for the determination of metaraminol requires dilution, extraction, and measurement of UV absorption. The HPLC procedure is rapid and precise and correlates well with the USP XX procedure. It can be used for metaraminol injectables as well as the raw material.

Development of analytical methods for the detection of metaraminol in the horse.

Aramine (metaraminol bitartrate) has been found in the possession of horse trainers and veterinarians who have been investigated for possible inappropriate drug administration to racing horses. Metaraminol (3-hydroxyphenylisopropanolamine) is a sympathomimetic amine that directly and indirectly affects adrenergic receptors, with alpha effects being predominant. Because it has the potential to affect the performance of a racing horse, its use is prohibited. In the present study, methods for the detection of metaraminol were developed. Metaraminol was found to be extracted with poor recovery (< 50%) from aqueous solutions by routine basic extraction or cation exchange/reversed-phase solid-phase extraction techniques. However, an extractive acetylation method gave good (> 90%) recovery of metaraminol from aqueous samples. Sequential urine samples collected from horses administered metaraminol intramuscularly at 0.02, 0.10, and 0.23 mg/kg were extracted by the developed extractive acetylation procedure and analyzed by gas chromatography-mass spectrometry (GC-MS) in full-scan and selected ion monitoring modes. Norphenylephrine was used as an internal standard for quantitative analysis. The maximum concentration of metaraminol occurred between 1 and 2 h postadministration. Metaraminol was detected in the 0.23 mg/kg administration urine for 24 h postadministration. Metaraminol was detected for the 0.10 and 0.02 mg/kg doses for approximately 8 h postadministration. No apparent biotransformation products were observed in a reaction mixture of metaraminol and horse liver microsomal reaction mixture. Comparison of gas chromatograms of the extracts of the postadministration urine samples with those of the pre-administration samples failed to reveal any exogenous compound other than metaraminol.

Primary amine drug selective electrodes with special crown ethers as neutral carriers.

Ionophores selectively sensitive to primary amines have been synthesized which display low potentiometric selectivity coefficients for K+, Na+ and NH4+ ions, secondary and tertiary amines as well as quaternary ammonium ions. These ionophores include macrocyclic polyethers with dinaphthyl subunits and azocrown ether with nitrogen donor atoms. The feasibility of these ionophores for preparing primary amine drug selective electrodes was investigated in detail. Practically usable PVC membrane electrodes sensitive to primary amine drugs, such as mexiletine, dopamine, metaraminol and tryptamine, and aliphatic primary amines have been prepared with these ionophores as neutral carriers. Direct potentiometric methods for assaying these drugs have been proposed by using the prepared electrodes. The proposed primary amine drug selective electrodes are remarkably superior to those based on ion-associates. Compared with the electrodes based on common ethers, the interference by K+, Na+ and NH4+ ions is substantially reduced. A digital simulation of the electrochemical process concerning the membrane transport was performed and some interesting conclusions have been drawn.

[Determination of three adrenergic drugs using capillary electrophoresis with amperometric detection].

A method for the determination of three adrenergic drugs, including phenylephrine hydrochloride (PHE), metaraminol bitartrate (MR) and isoprenaline hydrochloride (IP), was developed using capillary electrophoresis with amperometric detection. The detection potential of working electrode was 0.950 V versus the reference electrode of Ag/AgCl. At the applied voltage of 18 kV, the three analytes were completely separated within 18 min in 50 mmol/L borate buffer (pH 10.00) with the injection time of 10 s. Good linear relationships were obtained for all the three analytes in the range of 2-100 micromol/L. The detection limits for PHE, MR and IP were 0.8, 0.8 and 1.0 micromol/L, respectively. The proposed method was applied to the analysis of some injection drugs, and the results were satisfactory.

Fluorometric determination of metaraminol bitartrate injection.

A fluorescence assay for metaraminol bitartrate injection has been developed which uses o-phthalaldehyde as a fluorogenic reagent, and dose not require prior isolation of metaraminol. It is 50 times more sensitive than the USP assay. Six analyses of 2 vials of the same lot of metaraminol bitartrate injection gave 96 +/- 0.4% of label declaration.

[Central action of beta-phenylethylamine derivatives (9). Effects of intracerebral administration of metaraminol on brain monoamine in mice (author's transl)].

Effects of intracerebral (i.c.) administration of metaraminol (MA) on brain monoamine in mice were studied. The results were as follows: MA, dopamine (DA), noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were separated with phosphate buffer using a phosphorylated cellulose column (1X11 cm, 9 ml, Lot No. 2809). When MA was i.c. injected into mice, fluorescence of MA at 275/305 nm decreased in proportion to the time course and remained even at 12 hr after injection. Thirty min after MA in doses of either 40 or 80 microgram, a significant decrease of DA as compared with that of saline-treated group occurred and MA, in doses of 40, 80 and 160 microgram produced a significant decrease of NA and 5-HT. Thirty min after 160 microgram of MA, there was no significant difference in DA. Three hr after MA, DA levels significantly decreased, and 168 hr after were restored to the levels of the saline-treated group. Thirty min after MA, NA and 5-HT signficantly decreased compared with those of the saline-treated group and recovery took place 48 hr and 168 hr after respectively. It was concluded that MA depletes not only NA but also DA and 5-HT in the mouse brain.