Brain and plasma tetrahydroisoquinolines in rats: effects of chronic ethanol intake and diet.

Brain concentrations of salsolinol (SAL), a simple tetrahydroisoquinoline (sTIQ) condensation product of dopamine (DA) and acetaldehyde, are reported to increase in chow-fed rats drinking ethanol/H2O ad libitum. However, our analyses showed that rat chow contains traces of SAL and, as previously reported, appreciable 3,4-dihydroxyphenylalanine (DOPA), a sTIQ precursor. To examine the effect of consumption of ethanol in a DOPA- and SAL-free diet on endogenous sTIQs, we analyzed two brain regions and blood plasma of rats undergoing prolonged intake (3 weeks and 23 weeks) of liquid diet containing 6.6% ethanol or isocaloric carbohydrate. SAL and three other DA-related sTIQs were quantitated using capillary gas chromatography/mass spectrometry in the selected ion mode with deuterated standards. In accord with studies on ethanol/chow-fed rats, sTIQ concentrations in hypothalamus were elevated after 3 weeks of ethanol, although after 23 weeks, hypothalamic sTIQs were either unchanged or reduced (O-methylated SAL). Furthermore, sTIQ concentrations in corpus striatum and, with one exception, plasma were not altered by ethanol ingestion for either duration. (However, 23 weeks of ethanol intake significantly reduced the striatal concentrations of DA and its acid metabolite, presumably reflecting neurotoxicity.) Reasoning that DOPA in diet might underlie the reported ethanol-dependent increases in striatal sTIQs, we found that L-DOPA supplementation (500 micrograms/rat/day) of EtOH/liquid diet-fed rats for 13 weeks tended to increase striatal SAL. Overall, the data indicate that elevations in endogenous sTIQ concentrations due to prolonged ethanol intake depend on the brain region, duration of intake, and even associated dietary constituents. In that regard, the higher striatal SAL concentrations in rats drinking ethanol ad libitum could have been facilitated by DOPA and perhaps SAL consumed in lab chow.

Estimation of blood acetaldehyde during ethanol metabolism: a sensitive HPLC/fluorescence microassay with negligible artifactual interference.

A novel high performance liquid chromatographic (HPLC) procedure has been developed for the quantitation of acetaldehyde in 50 microliter samples of primate whole blood during ethanol metabolism. This microassay has a minimum detectable concentration of about 0.1 microM, displays an intra-assay precision under 10%, and is linear over a reasonable concentration range. Of importance is that negligible acetaldehyde is generated artifactually from ethanol during blood analysis. The assay is based on the reaction of acetaldehyde with 1,3-cyclohexanedione and ammonium ion to form a water-soluble fluorogenic adduct, which is separated by reversed phase HPLC and quantitated fluorometrically. Propionaldehyde, added as an internal standard, forms an analogous separable adduct. Blood acetaldehyde concentrations in Rhesus monkeys were between 1-2 microM 150 min after acute administration of ethanol (1.5 g/kg). Traces of endogenous components which are chromatographically identical with cyclohexanedione adducts of acetaldehyde and formaldehyde also were apparent in blood from monkeys and humans not given ethanol.