5‐Hydroxytryptamine metabolism in rat brain and liver homogenates

Abstract

1. The metabolism of 5-hydroxyindoleacetaldehyde derived from 5-hydroxytryptamine incubated with tissue homogenates was studied as an indicator of aldehyde dehydrogenase and alcohol dehydrogenase activities. 2. In liver and brain from rats, there were indications of the presence of one or more aldehyde dehydrogenases which were stimulated by NAD+ to a greater extent than by NADP+. 3. In liver from rats, there were indications of the presence of one or more alcohol dehydrogenases, which were stimulated by NADH to a greater extent than by NADPH. 4. In brain from rats, there were indications of the presence of one or more alcohol dehydrogenases which were stimulated by NADPH to a greater extent than by NADH.Eccleston, Moir, Reading & Ritchie (1966) reported that 5-hydroxytryptamine (5-HT) was converted to 5-hydroxytryptophol by way of 5-hydroxyindoleacetaldehyde in rat and human brain homogenates. These investigators found that the conversion in brain was effected by an alcohol dehydrogenase which depended on NADPH (Eccleston, Moir, Reading & Ritchie, 1966) rather than NADH as in liver (Kveder, Iskric & Keglevic, 1962; Feldstein & Wong, 1965a, b). It was reported also that the conversion of 5-HT to 5-hydroxyindoleacetic acid (5-HIAA) by way of 5-hydroxyindoleacetaldehyde in rat brain homogenates was more effective in the presence of NADP+ than NAD+ (Eccleston, Moir, Reading & Ritchie, 1966), although another investigator (Deitrich, 1966) found that NAD+ was the more effective. The effects of the coenzymes on 5-HT metabolism in both rat liver and brain homogenates were re-investigated and the results reported herein. MethodsMale rats, Sprague-Dawley descendants, [150][151][152][153][154][155][156][157][158][159][160][161][162][163][164][165]

Behavioral outcomes of monoamine oxidase deficiency: preclinical and clinical evidence

“…Given the predominance of the MAO-ALDH pathway in 5-HT metabolism, urinary levels of 5-HIAA are used as an index for measurement of plasma 5-HT content (with diagnostic value as a biomarker for carcinoid syndrome, a paraneoplastic disorder caused by gastrointestinal apudomas secreting 5-HT). Small amounts of 5-HT (1–5%) are converted into 5-hydroxyindolethanol (5-HIET, also termed 5-hydroxytryptophol) by either ALR or ADH (Feldstein and Williamson, 1968; Beck et al , 1984; Consalvi et al , 1986; Svensson et al , 1999) (Table I). Interestingly, the amount of 5-HIET can be enhanced by compounds that compete with endogenous 5-HT metabolite for ALDH, such as ethanol (Helander et al , 1993).…”