William G. Dewhurst

A method for measurement of tranylcypromine in rat brain regions using gas chromatography with electron capture detection.

Abstract A gas chromatography method, using electron capture detection, is described for measurement of the monoamine oxidase inhibitor tranylcypromine (TCP) in rat brain regions. The analytical method involves extraction of the drug from tissue homogenate with a liquid ion exchange resin and back extraction into acid. TCP is then acetylated and derivatized with pentafluoropropionic anhydride or trifluoroacetic anhydride for gas chromatographic analysis. Conditions for analysis on both packed and capillary columns are described. The method has been used to quantify TCP in rat brain regions after three different dosage/time schedules of TCP administration. The presence of N-acetyl-TCP has been demonstrated in brain tissue from rats treated with TCP.

Screening for amines of psychiatric interest in urine using gas chromatography with electron-capture detection

Abstract 1. 1. An electron-capture gas chromatographic procedure for the simultaneous quantitation of urinary levels of amines of psychiatric interest has been developed. 2. 2. The amines were isolated from urine using a liquid ion exchanger, then acetylated and perfluoroacylated for analysis. This procedure improved extraction efficiency and analytical sensitivity. 3. 3. The developed procedure was rapid, simple, specific and sensitive. 4. 4. Urinary levels of 5-hydroxytryptamine, 3-methoxytyramine, normetanephrine, 2-phenylethylamine, tryptamine, m - and p -tyramine in control subjects were determined using this analytical procedure and agreed with literature values.

Effects of age and of chronic antidepressant treatment on [3H]tryptamine and [3H]dihydroalprenolol binding to rat cortical membranes.

Summary1.The effects of age and of chronic antidepressant treatment on [3H]tryptamine and [3H]dihydroalprenolol binding site density were measured in brain cortical membranes from male Sprague-Dawley rats.2.The density but not the affinity of [3H]tryptamine binding sites was increased in 18-month-old rats relative to 3-month-old rats. Neither the density nor the affinity of [3H]dihydroalprenolol binding sites was affected by age.3.Chronic administration (28 days s.c. via Alzet osmotic minipumps) of tricyclic antidepressant drugs (daily doses: imipramine·HCl, 30 mg kg−1; desipramine·HCl, 10 mg kg−1; clomipramine·HCl, 10 mg kg−1) resulted in decreases in [3H]dihydroalprenolol binding site density but no changes in [3H]tryptamine binding site density; no changes in affinity of either site were observed.4.Chronic administration (s.c. via Alzet osmotic minipumps) of monoamine oxidase inhibitor antidepressant drugs (daily doses: tranylcypromine·HCl, 0.5 and 1.0 mg kg−1; phenelzine sulfate, 5 and 10 mg kg−1, each for 28 days; clorgyline·HCl, 1.0 mg kg−1; (−)-deprenyl·HCl, 1.0 mg kg−1, each for 14 days) resulted in decreases in [3H]tryptamine binding site density, without any effects on the affinity of this site. In addition, each of these monoamine oxidase inhibitors except (−)-deprenyl resulted in a decrease in [3H]dihydroalprenolol binding site density. No affinity changes were observed.5.These data indicate that the [3H]tryptamine binding site exhibits physiological changes with aging and is differentially sensitive to the actions of tricyclic antidepressants and monoamine oxidase inhibitor antidepressants, respectively.

Long-lasting elevation of alanine in brain produced by the antidepressant phenelzine

Time- and dose-response studies were conducted to determine the effects of the antidepressant and antipanic drug phenelzine (a monoamine oxidase inhibitor) on whole brain levels of the aliphatic amino acid alanine. At a dose of phenelzine of 15 mg/kg IP, there was a significant increase in brain levels of alanine up to 16 hr after drug administration. Dose studies at 4 hr indicated that the alanine elevation after phenelzine was a dose-dependent effect.

Regional concentrations of cerebral amines: effects of tranylcypromine and phenelzine.

The effects of tranylcypromine (TCP) HCl (4 mg/kg and 20 mg/kg i.p.) and phenelzine (PLZ) sulfate (10 mg/kg and 50 mg/kg) on levels of dopamine (DA), noradrenaline (NA), 5-hydroxytryptamine (5-HT), 3-methoxytyramine (3-MT) and normetanephrine (NM) in mesencephalon-pons, diencephalon, corpus striatum and hippocampus of rat brain were investigated. Effects of TCP on concentrations of DA and NA varied, depending on the brain area investigated and the dosage used. PLZ either had no effect or increased the concentration of DA and NA in the areas studied. Both drugs increased the concentrations of 3-MT and NM in areas where those metabolites could be measured. Both MAO inhibitors resulted in significant increases in 5-HT in all areas studied.

Tryptamine receptors: fact, myth or misunderstanding?

Tryptamine is an endogenous brain amine which is implicated in neural regulation and proposed to play a significant role in the aetiology of some neuropsychiatric illnesses. Recent reports indicate the possible existence of specific tryptamine binding sites. It has been postulated that these binding sites may be functional tryptamine receptors in the central nervous system. The status of current developments in this area is critically reviewed. Current problems are outlined and discussed in terms of the specificity of the [3H]-tryptamine binding site and its functional assessment with experiments involving both drug treatment and electrolytic and neurotoxin-induced brain lesions. Current data indicate that the [3H]-tryptamine binding site is selective and not attributable to residual monoamine oxidase binding.

Rat brain concentrations of 5-hydroxytryptamine following acute and chronic administration of MAO-inhibiting antidepressants

Groups of male Sprague-Dawley rats were injected once daily with phenelzine (15 mg/kg) or tranylcypromine (10 mg/kg) and killed 6 h after drug administration on days 1, 2, 8 and 19. Brains were analyzed for MAO activity by a radiochemical procedure and for 5-HT concentrations by an electron-capture gas chromatographic procedure. Both drugs affected 5-HT concentrations in a similar manner--a significant increase of 5-HT over control levels by day 1, with levels still increasing between days 8 and 19, having attained concentrations approximately 5 times control values by day 19.

Displacement of serotonin from binding sites in rat cortex: The effects of biogenic “trace” amines

The concentrations for 50 percent inhibition of binding (IC50s) to specific in vitro serotonin binding sites (5-HT1 and 5-HT2) of rat cerebral cortex were determined for the trace amines 2-phenylethylamine, m- and p-tyramine, tryptamine, and (+)- and (-)- alpha-methyltryptamine. Tryptamine gave an IC50 of 66.7 +/- 4.8 nM (n = 7) at the 5-HT1 site and an IC50 of 3.85 +/- 0.16 microM (n = 7) for the 5-HT2 binding site. The IC50 values for all the other compounds were in the micromolar range and were different at the two binding sites except for p-tyramine (IC50, 5-HT1 = IC50, 5-HT2 = 17 microM. The trace amines may have different functional roles as evidenced by their different degrees of displacement of serotonin at 5-HT1 and 5-HT2 binding sites in the brain.

TRACE AMINES: THE EARLY YEARS

In preparing this historical introduction I must first make comment on the term “trace” amines. It came into existence at a meeting of the ACNP in Puerto Rico in 1975. However, I really find the phrase very awkward. To categorize amines (or any other biologically active chemical) by quantity seems almost meaningless without conditions being specified. If I wanted to consult a doctor I would find it much more helpful to know whether he was an obstetrician or proctologist rather than whether he was fat or thin. Hopefully, and eventually, we will find a classification based on function and perhaps during the course of this conference some useful generalizations might emerge. Until then I think we have to be content with chemical designations as the most precise.

Analysis of urinary excretion patterns of bioactive amines and their metabolites in normal control subjects

Abstract 1. Urinary excretion (24 h) of 2-phenylethylamine (PEA), m - and p -tyramine ( m - and p -TA), tryptamine (T), 5-hydroxytryptamine (5-HT), 3-methoxytyramine (3-MTA), normetanephrine (NME), 3-methoxy-4-hydroxyphenylethylene glycol (MHPG), kynurenine (KYN), indole-3-acetic acid (IAA) and 5-hydroxyindole-3-acetic acid (5-HIAA) in control human subjects was investigated. 2. The results (per g creatinine) were analyzed statistically by multiple regression analysis. 3. Multiple regression analyses using MHPG, 5-HIAA, 5-HT, PEA and 3-MTA as the dependent variables showed some high multiple correlation coefficients, with the most notable being the relationship of PEA to p -TA, T and MHPG and the relationship of 3-MTA to KYN and age.