Adrenaline in the CNS and the action of antihypertensive drugs

Quantification of the heterocyclic aromatic amine DNA adduct N-(deoxyguanosin-8-yl)-2-amino-3-methylimidazo[4,5-f]quinoline in livers of rats using capillary liquid chromatography/microelectrospray mass spectrometry: a dose-response study

Capillary liquid chromatography/microelectrospray-mass spectrometry (capillary LC/muESI-MS) was used to quantify DNA adducts of the heterocyclic aromatic amine 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in livers of male Fischer-344 rats. Animals received a single oral dose of either 0.05, 0.50, 1.0, or 10 mg/kg IQ and were sacrificed 24 h following treatment. The major lesion identified at all doses was N-(deoxyguanosine-8-yl)-2-amino-3-methylimidazo[4,5-f]quinoline (dG-C8-IQ). The capillary LC/muESI-MS method provided the means for quantifying 17.5 fmol of dG-C8-IQ (2.0 adducts in 10(8) nucleosides) (S/N 10) in 300 microg of liver DNA with an intra- and interday precision of 3.5 and 6.6% (RSD), respectively. dG-C8-IQ was quantified with a mean intra- and interday accuracy of 105 +/- 26 and 106 +/- 28 (SD) based on back-calculated adduct masses from five standard curves analyzed over a four-week period. This is the first report on development of a capillary LC/muESI-MS method to quantify dG-C8-IQ adducts in liver DNA of rats following dosing with IQ at different levels. Furthermore, the ability to accurately and precisely quantify dG-C8-IQ at a level of 2.0 adducts in 10(8) nucleosides in vivo makes this method well suited for use in future studies relating carcinogen exposure to risk in humans.

Antimutagenic activity of cacao: inhibitory effect of cacao liquor polyphenols on the mutagenic action of heterocyclic amines

We investigated the effect of polyphenols derived from cacao liquor on the mutagenic action of heterocyclic amines (HCAs) in vitro and ex vivo. In the Ames test, the cacao liquor polyphenols showed antimutagenic effects in bacteria treated with HCA in the presence of an S-9 mixture; however, they showed less efficacy than quercetin. On the other hand, the cacao liquor polyphenols showed potent antimutagenic activity in bacteria treated with activated forms of HCA, compared with quercetin. We also evaluated the effect of these compounds on enzymatic activation of HCA. They weakly suppressed the production of activated HCA. In the host-mediated assay in mice, a method used to estimate the potential carcinogenicity of chemicals ex vivo, oral administration of the cacao liquor polyphenols, reduced the number of colonies of revertant bacteria recovered from the liver. These data suggest that the cacao liquor polyphenols have an antimutagenic effect not only in vitro, but also ex vivo.

Role of adrenergic neuronal activity in the yawning induced by tacrine and NIK-247 in rats

The present experiments were performed to investigate the potential role of central adrenergic neurons in regulating occurrence of yawning in rats. Intraperitoneal injection of tacrine (THA) or 9-amino-2,3,5,6,7,8-hexahydro-1H-cyclopenta(b)-quinoline monohydrate HCl (NIK-247), cholinesterase inhibitors, induced yawning, which was markedly increased by pretreatment with the beta-adrenoceptor antagonist, pindolol. The yawning evoked by tacrine or NIK-247 given alone or in combination with pindolol was inhibited by pretreatment with scopolamine but not by mecamylamine or spiperone. Treatment with tacrine or NIK-247 increased acetylcholine content of the striatum, but this effect was not enhanced by pindolol, which per se did not affect basal acetylcholine content. Moreover, pretreatment with the central adrenaline synthesis inhibitors, (+-)-2,3-dichloro-alpha-methylbenzylamine HCl (LY-78335) and 2-cyclooctyl-2-hydroxyethylamine HCl (UK-1187A), increased tacrine-induced yawning. Subcutaneous injection of talipexole (B-HT 920), a dopamine D2 receptor agonist, evoked yawning, which was also increased by pindolol, LY-78335, and UK-1187A. These receptors antagonists and synthesis inhibitors per se did not cause yawning responses. The results suggest that the beta-adrenoceptor blockade and the inhibition of adrenaline synthesis facilitate the occurrence of yawning induced by cholinergic and dopaminergic agonists, and thus the central adrenergic neuronal systems may be implicated in the regulation of yawning responses.

Real-time monitoring of endogenous noradrenaline release in rat brain slices using fast cyclic voltammetry: 1. Characterisation of evoked noradrenaline efflux and uptake from nerve terminals in the bed nucleus of stria terminalis, pars ventralis

Fast cyclic voltammetry (FCV) at carbon fibre microelectrodes was used to monitor endogenous noradrenaline (NA) efflux in superfused slices of bed nucleus of stria terminalis pars ventralis (BSTV) in 'real time'. NA efflux was evoked by local electrical stimulation at bipolar tungsten stimulating electrodes. Confirmation of the identity of the released species as NA was made on the basis of anatomical, electrochemical and pharmacological proofs. Firstly, the signal matched the NA innervation density; efflux of monoamine was greater in BSTV than in the pars dorsalis of the nucleus. Secondly, the voltammogram of the released species was indistinguishable from those of the catecholamines NA and dopamine (DA) but dissimilar to that of the indoleamine serotonin (5-hydroxytryptamine, 5-HT). Thirdly, amine efflux was influenced in a predictable fashion by the drugs tested. Tetrodotoxin (10(-6) M) or omission of Ca2+ from the superfusate reversibly reduced amine efflux by 90.2 and 88.0% respectively. Ro 4-1284 (10(-6) M) decreased amine efflux by 75.8%. Desipramine (5 x 10(-8) M), the selective NA uptake blocker, significantly increased amine efflux and uptake half-life (to 214.3 and 389.5% of control respectively). Fluvoxamine (5 x 10(-7) M) and GBR 12909 (3 x 10(-7) M), blockers of 5-HT and DA uptake respectively, had no effect on amine efflux, although fluvoxamine caused a modest (91.0%) increase in the uptake half-life. Pargyline (2 x 10(-6) M) affected neither efflux nor uptake. The combined anatomical, electrochemical and pharmacological data confirm that the monoamine detected in BSTV by local electrical stimulation was NA. Stimulated NA efflux was stable and reproducible over at least 2.5 h (longest period tested). This study demonstrates the ability of FCV to selectively monitor endogenous NA efflux and uptake in 'real time' and with high spatial resolution.

Age-dependent increase in neuropeptide Y gene expression in rat adrenal gland and specific brain areas

Age-dependent changes in the expression of neuropeptide Y (NPY) peptides and prepro-NPY mRNA (NPY mRNA) were studied in rat adrenal gland and brain areas by means of radioimmunoassay, immunohistochemistry, and northern blot analysis. In the adrenal gland, NPY immunoreactivity (NPY-I) increased by 80-fold, mainly in the chromaffin cells, during aging (from 7 to 33 weeks old). The increase in NPY-I was accompanied by a concomitant increase in the content of NPY mRNA (800 bases in size, by 16-fold) and putative NPY pre-mRNA, a result suggesting that this increase results from that in NPY gene expression, probably at the level of transcription. In contrast, in some brain areas, such as striatum and medulla oblongata plus pons, NPY-I decreased in an age-dependent manner, whereas NPY mRNA abundances in these areas increased by twofold with age (from 7 to 33 weeks old). The opposite changes between NPY and NPY mRNA content in specific brain areas suggested the accelerated turnover/degradation of NPY peptide in the brain areas. Furthermore, beta-actin mRNA abundance did not change in rat adrenal gland and brain areas during aging. Thus, the characteristic age-related increase in NPY gene expression in rat adrenal gland and some brain areas seems to be important for physiological regulation of some neuronal functions, such as blood pressure, in aged animals.

Rapid decrease in neuropeptide Y gene expression in rat adrenal gland induced by the alpha 2-adrenoceptor agonist, clonidine

1 The mechanism of regulation of the neuropeptide Y (NPY) gene by pharmacological treatment with the alpha 2-adrenenoceptor agonist, clonidine, was investigated by quantitative Northern blot analysis of the effects of this drug on the NPY mRNA levels in rat adrenal gland and medulla oblongata/pons. 2 In the adrenal gland, clonidine-treatment (50 microgram kg-1, s.c., once daily) resulted in decrease in the amount of NPY mRNA to 44 +/- 10% of the control level in 24 h and then its increase to 162 +/- 16% of the control level after 5 days. Concomitant changes in putative NPY pre-mRNA species (7.0 and 3.3 kb) were observed, probably due to changes at the level of NPY gene transcription. 3 The short-term (24 h) effect of clonidine was blocked by yohimbine (5 mg kg-1, i.p., once daily). Yohimbine alone tended to increase the NPY mRNA level after 24h. 4 The recovery/increase in the NPY mRNA level in the adrenal gland after 5 days treatment with clonidine was similar to its increase after treatment with reserpine (0.5 mg kg-1, i.p., once daily). 5 NPY gene expression in the medulla oblongata/pons was not changed by short- or long-term treatment with clonidine. 6 These results suggest that clonidine suppresses NPY gene expression in the adrenal gland, probably at the level of transcription, by activation of the alpha 2-adrenoceptor.

Effect of pH on the oxidation pathway of alpha-methyldopa catalysed by tyrosinase

This paper deals with the quantitative description of the effect of pH on the oxidation pathway of alpha-methyldopa. Tyrosinase catalyses the oxidation by molecular oxygen of alpha-methyldopa to o-alpha-methyldopaquinone, which evolves non-enzymically through a branched pathway with cyclization or hydroxylation reactions. The intermediates of the hydroxylation branch have been identified, and the corresponding rate constants have been determined. These compounds, which have been detected in melanosomes and in tumour cells, have great cytotoxic power and could have physiological significance in acidic media.