Preclinical neuropharmacology of naratriptan

The basic CNS neuropharmacology of naratriptan is reviewed here. Naratriptan is a second-generation triptan antimigraine drug, developed at a time when CNS activity was thought not to be relevant to its therapeutic effect in migraine. It was, however, developed to be a more lipid-soluble, more readily absorbed and less readily metabolized variant on preexisting triptans and these variations conferred on it a higher CNS profile. Naratriptan is a 5-HT(1B/1D) receptor agonist with a highly selective action on migraine pain and nausea, without significant effect on other pain or even other trigeminal pain. Probable sites of therapeutic action of naratriptan include any or all of: the cranial vasculature; the peripheral terminations of trigeminovascular sensory nerves; the first-order synapses of the trigeminovascular sensory system; the descending pain control system; and the nuclei of the thalamus. Naratriptan may prevent painful dilatation of intracranial vessels or reverse such painful dilatation. Naratriptan can prevent the release of sensory peptides and inhibit painful neurogenic vasodilatation of intracranial blood vessels. At the first order synapse of the trigeminal sensory system, naratriptan can selectively suppress neurotransmission from sensory fibers from dural and vascular tissue, while sparing transmission from other trigeminal fibers, probably through inhibition of neuropeptide transmitter release. In the periaqueductal gray matter and in the nucleus raphe magnus, naratriptan selectively activates inhibitory neurons which project to the trigeminal nucleus and spinal cord and which exert inhibitory influences on trigeminovascular sensory input. Naratriptan has also a therapeutic effect on the nausea of migraine, possibly exerting its action at the level of the nucleus tractus solitarius via the same mechanisms by which it inhibits trigeminovascular nociceptive input. The incidence of naratriptan-induced adverse effects in the CNS is low and it is not an analgesic for pain other than that of vascular headache. In patients receiving selective serotonin uptake inhibitors (SSRIs) naratriptan may cause serotonin syndrome-like behavioral side effects. The mechanism of action involved in the production of behavioral and other CNS side effects of naratriptan is unknown.

Quantitative determination of melatonin in human plasma and cerebrospinal fluid with high-performance liquid chromatography and fluorescence detection

A validated new and precise reversed-phase high-performance liquid chromatographic method for the determination of melatonin in human plasma and cerebrospinal fluid, with 5-fluorotryptamine as internal standard, is described. Liquid-liquid extraction with dichloromethane was performed under alkaline conditions. After evaporation of the organic solvent, the extract was dissolved in eluent and chromatographed on a base-deactivated octadecyl column, using an eluent composed of 650 mL potassium dihydrogenphosphate solution (0.07 mol/L water), adjusted to a pH of 3.0 with a 43% phosphoric acid solution, mixed with 350 mL methanol. Fluorescence detection at an excitation wavelength of 224 nm and an emission wavelength of 348 nm was used for quantitation. Melatonin and 5-fluorotryptamine chromatographed with retention times of 5.3 and 9. 3 min, respectively. Mean recoveries of 96% (n = 10) and 95% (n = 5) were found for melatonin in plasma and cerebrospinal fluid respectively. 5-Fluorotryptamine was found to have a mean recovery of 90% (n = 10) and 82% (n = 5) in plasma and cerebrospinal fluid, respectively. The repeatability coefficients of variation for both melatonin and 5-fluorotryptamine in plasma were 4-5% [five different samples (r = 5) on two consecutive days (n = 2)], with reproducibility coefficients of 1.6-7% (n = 2, r = 5) and 0.9-4% (n = 2, r = 5) for melatonin and internal standard, respectively. In cerebrospinal fluid the repeatability coefficient of variation of the extraction procedure was 5% (n = 1, r = 5) for melatonin and 7% (n = 1, r = 5) for 5-fluorotryptamine. The correlation coefficients of the calibration curves were 0.9998 (n = 2) in plasma at a concentration range of 0.108-25.9 ng/mL and 0.9994 (n = 2) at a concentration range of 0.108-25.9 ng/mL in cerebrospinal fluid. The limit of detection was determined at 8 pg/mL which enables to measure melatonin concentrations at physiological concentrations reached during daytime.

Precursors and metabolites of phenylethylamine, m and p-tyramine and tryptamine in human lumbar and cisternal cerebrospinal fluid

Phenylacetic acid, p-hydroxyphenylacetic acid, m-hydroxyphenylacetic acid, phenylalanine, indoleacetic acid, 5-hydroxyindoleacetic acid and tryptophan were measured in lumbar and cisternal cerebrospinal fluid (CSF) taken during pneumoencephalography. The data suggest that the concentration of the acid metabolites of the trace amines tryptamine, phenylethylamine, p-tyramine and m-tyramine in lumbar CSF are influenced by the system that transports these acids out of CSF. In cisternal CSF this mechanism does not operate and more information can be obtained on the metabolism of the parent amines in the CNS. Our data indicate that (1) m-tyramine is relatively unimportant quantitatively (2) the rate of metabolism of phenylethylamine in human brain is similar to that of 5-hydroxytryptamine (3) the most important variable controlling the synthesis of phenylethylamine is the activity of aromatic amino acid decarboxylase (4) p-tyramine is synthesised at about half the rate of phenylethylamine and is thus quantitatively important in metabolic terms.

CNS tryptamine metabolism in hepatic coma

Lumbar CSF indoleacetic acid (IAA) was higher in patients with cirrhosis of the liver than in controls. It was also higher in CSF of patients in coma than in those with hepatic cirrhosis but not in coma. There was a strong correlation (r = 0.89, p less than 0.01) between the grade of hepatic coma and CSF IAA. These data indicate that there is an association between elevated CNS tryptamine metabolism and hepatic coma. How far changes in the metabolism of tryptamine and other trace amines are relevant to the induction of hepatic coma or are simply a reflection of advanced liver dysfunction is unclear.

Hallucinogenic N-methylated indolealkylamines in the cerebrospinal fluid of psychiatric and control populations

The incidence and quantities of dimethyltryptamine and O-methylbufotenine were studied in the cerebrospinal fluid of patients suffering acute schizophrenic illnesses and in surgical and neurological control groups. Some schizophrenic patients have higher levels of both amines than do controls, though the differences in distribution did not reach statistical significance in the sample studied. The gas-chromatographic technique used is sensitive at the low picogram level.

Adsorption of tryptophan metabolites from physiological fluids on XAD-2 and determination by single ion monitoring

Endogenous tryptamine, 5-hydroxytryptamine, indoleacetic acid, 5-hydroxyindoleacetic and tryptophan have been recovered from urine and cerebro-spinal fluid by adsorption on XAD-2 resin (0.3 g). After adsorption of the sample on the resin, desorption with methanol provides a single fraction that contains all of these metabolites. The mass spectra of their pentafluoropropionyl derivatives show prominent ions at m/e 276 and 438 which are characteristic of indoles and 5-hydroxyindoles, respectively, a feature that allows the concurrent determination of all the components of each group by functional group analysis. A method has been developed to carry out single ion monitoring with the peak matching system of an Hitachi RMU-6H mass spectrometer. Identifications are based on the respective Kovats Indices and single ion monitoring of two characteristic ions per compound: tryptophan (m/e 276 and 347); tryptamine (m/e 276 and 289); indoleacetic acid (m/e 276 and 335); 5-hydroxytryptamine (m/e 438 and 451); 5-hydroxyindoleacetic acid (m/e 438 and 497). The method described illustrates the feasibility of assaying biogenic indoleamines and acidic metabolites, as well as their precursor amino acid on a single fraction in contrast to other standard fractionation methods. This is possible even if the mass spectrometer is not equipped with an alternating voltage accelerator provided that it has a peak matcher, although the lack of an alternating voltage accelerator requires two separate injections of the same sample, for quantification and identification; one for the indole profile and another for the 5-hydroxyindole profile. Both profiles can be verified by individual monitoring of the other confirmatory ions. With this method the use of a multiple ion detector would allow a simultaneous determination of all of these metabolites in one gas chromatograph mass spectrometer run.