Formation of respiratory 14CO2 from variously labeled forms of tryptophan-14C in intact and adrenalectomized rats

High-voltage electrophoretic separation of tryptophan metabolites of the kynurenine pathway

An analytical separation method for tryptophan and its seven metabolites of the kynurenine pathway by high-voltage paper electrophoresis is presented. Anthranilic acid, 3-hydroxyanthranilic acid, kynurenic acid, kynurenine, nicotinic acid, quinolinic acid, xanthurenic acid and unmetabolized tryptophan are measured in urine. Using radioactive labelling and scintillation counting as a quantification method, the relative standard deviation varied from 3.5% to 14.4%, corresponding to kynurenine and nicotinic acid, respectively. The recovery of labelled tryptophan added to urine was 95%. An advantage of the electrophoretic method is the minor tailing of spots and, hence, a good resolution of the components. For the monovalent anions of the kynurenine pathway metabolites, a linear correlation (r = 0.9996) was found between the experimental relative electrophoretic mobility and the quantity M-2/3, where M is the molecular mass of the anion.

The metabolism of L-tryptophan by liver cells prepared from adrenalectomized and streptozotocin-diabetic rats

1. The metabolism of L-tryptophan by liver cells prepared from fed normal, adrenalectomized and streptozotocin-diabetic rats was studied. 2. At physiological concentrations (0.1 mM), the rate of oxidation of tryptophan by tryptophan 2,3-dioxygenase was 3-fold greater in liver cells from diabetic rats than in those from fed rats. In liver cells from diabetic rats, oxidation of tryptophan to CO2 and metabolites of the glutarate pathway was increased 7-fold. Quinolinate synthesis was decreased by 50%. These findings are consistent with an increase in picolinate carboxylase activity. 3. Rates of metabolism of 0.1 mM-tryptophan by hepatocytes from fed and adrenalectomized rats were similar. 4. In all three types of cell preparation, fluxes through tryptophan 2,3-dioxygenase with 2.5 mM-tryptophan were 7-fold greater than those obtained with 0.1 mM-tryptophan. Tryptophan 2,3-dioxygenase and kynureninase fluxes in hepatocytes from fed and adrenalectomized rats were comparable, whereas those in liver cells from diabetic rats were increased 2.5-fold and 3.3-fold respectively. Picolinate carboxylase activities of liver cells from diabetic rats were 15-fold greater than those of cells from fed rats, but rates of quinolinate synthesis were unchanged. 5. It is concluded that: (i) adrenal corticosteroids are not required for the maintenance of basal activities of the kynurenine pathway, whereas (ii) chronic insulin deficiency produces changes in both the rate of oxidation and metabolic fate of tryptophan carbon.

Putrescine metabolism and the study of diamine oxidase activity in vivo

The catabolism of 14C-putrescine (1,4-tetramethylene-diamine) to labeled CO2 in small laboratory animals has been studied extensively in order to establish the influence of nutritional, endocrine and other factors on this process. Special attention has been paid to treatments that are known to affect the activity of diamine oxidase (DAO, histaminase, EC, 1.4.3.6), a copper-containing enzyme characteristically inhibited by semicarbazide. Thus, copper-deficient rats metabolize putrescine more slowly than their controls. Antimalarial drugs that inhibit histamine N-methyltransferase also inhibit putrescine catabolism in vivo and DAO activity in vitro. Adrenalectomized rats metabolize the diamine at a reduced rate, a result consistent with the previously demonstrated decrease of DAO in the tissues of several species of animal. There is no effect on the rate of catabolism of putrescine when thyroid state is altered. Heparin (up to 15,000 U/kg), which releases DAO from the small (0.1 mg/kg), intestine, and aminoguanidine (0.1 mg/kg), which inhibits the enzyme powerfully, both cause decreased rates of catabolism of the diamine in rats. The putrescine-catabolizing ability returns with a half-time of recovery of 15-18 h, corresponding to the estimates of SHAFF and BEAVEN [36] for recovery of intestinal DAO activity following administration of heparin or cycloheximide. Together with out other results this suggests that what is being measured by putrescine catabolism depends to a significant extent on the activity of DAO in vitro.

Inhibition of diamine oxidase by antimalarial drugs

The antimalarial drugs amodiaquine, quinacrine and chloroquine inhibit the catabolism of putrescine by the rat. Amodiaquine, the most potent of the three, does so in a dose-dependent fashion. This is attributed to the action in vivo of the drugs on diamine oxidase, an enzyme that is inhibited by them in vitro.

n-Pentylamine: effect on motor activity of mice

Motor and autonomic effects of n-pentylamine in mice have been evaluated in relation to aminergic mechanisms by combining administration of the amine with drugs having well known effects on such mechanisms. Some evidence has been found to indicate the importance of dopaminergic pathways in the actions of pentylamine; these actions are modifiable by central blockade of muscarinic receptors with atropine. Serotonin-regulated pathways do not seem important for the effects of pentylamine that have been studied.

Putrescine catabolism in rats given heparin or aminoguanidine

Rats treated acutely with aminoguanidine, a potent inhibitor of diamine oxidase, or with heparin display reduced ability to metabolize 14C-putrescine to radioactive carbon dioxide. After either drug rats recover 50% of the ability to catabolize putrescine in 15--18 h. This is in close agreement with the half-time for recovery of diamine exidase activity, and indicates that putrecine-catabolizing ability of the rat reflects in a physiologically significant way the function of diamine oxidase in vivo.

The kynurenine load test, an adjunct to the tryptophan load test

The kynurenine load test was introduced to distinguish, in vivo, between abnormal tryptophan metabolism caused by induction of tryptophan oxygenase or by impaired kynureninase function. This test was carried out by giving a loading dose of 700 mumol L-kynurenine sulphate followed by determination of urinary metabolites of the tryptophan-nicotinic acid ribonucleotide pathway. The results of the kynurenine load test in a group of healthy post-menopausal female subjects show a consistant increase in urinary excretion of some metabolites of the tryptophan-nicotinic acid ribonucleotide pathway (kynurenine, 3-hydroxy-kynurenine, and 3-hydroxyanthranilic acid) of a magnitude comparable to the increase seen after a loading dose of 9800 mumol L-tryptophan (the tryptophan load test).

Enzyme histochemistry as a link between biochemistry and morphology

The presented paper describes the role of enzyme histochemistry in cell biological investigations. In the first chapter a general discussion has been given about enzyme histochemistry as a connecting link between biochemistry and morphology. The methods available for determination of enzymes in a particular cell or cell compartment have been reviewed. In this respect the characteristics of enzyme histochemistry have been discussed. Furthermore, attention has been paid to the possibilities and limitations of enzyme histochemistry. In chapter two a comparison has been made between histochemically judged and biochemically determined enzyme activities. Some fundamental differences between the biochemical and the histochemical approach in cell biological investigations are dealt with. To correlate histochemically and biochemically determined enzyme activities, a description has been given of the application of histochemical methods on isolated fractions and sucrose-ficoll gradients of these fractions. Several experimental results are described concerning the question whether a relation exists between histochemically and biochemically determined activities of respectively alkaline phosphatase, glucose-6-phosphatase, 5'-nucleotidase and 3ss-hydroxysteroid dehydrogenase. From these results the conclusion could be drawn that in general a good correlation exists between histochemically judged activity per volume (area X thickness) and biochemically determined activity per gram tissue. In chapter three the role of enzymes as markers of cellular particles and as parameters of metabolic pathways is described. Histochemical methods are available for most marker enzymes. Only activities of key enzymes can be regarded as parameters of metabolic pathways. The distribution in sucrose-ficoll gradients of enzymes, regarded as markers of mitochondria, lysosomes, endoplasmic reticulum and plasma membranes has been given. The changes occur ing under different experimental conditions for a number of marker enzymes in rat liver are described. Attention has been given to the contibution of enzyme histochemistry in the study of the heterogeneity of mitochondria, the dual localization of some (lysosomal) enzymes, the complexity of the microsomal fraction, the function of the Golgi apparatus and the heterogeneity and function of plasma membranes. Based on these results and on literature findings the possible role of some marker enzymes in cell metabolism has been discussed. In chapter four problems coherent with species and sex differences in enzyme activities are described. The interpretation of histochemical and biochemical results in view of these differences is discussed. Enzymes characteristic for a given cell type -3ss-hydroxysteroid dehydrogenase in steroid producing cells, ATP-ase in liver plasma membrane surrounding the bile canaliculi - do show less variations between species and sexes than enzymes not directly involved in specialized functions...

Liver and brain tryptophan metabolism following hydrocortisone administration to rats and gerbils

1 Liver tryptophan pyrrolase activity is low in the mongolian gerbil (Meriones unguiculatus) and is not induced by hydrocortisone (5 mg/kg). In contrast, there is measurable activity in the rat liver and this is induced by hydrocortisone. In vivo measurements confirmed the absence of induction in gerbils but suggested that they were able to metabolize tryptophan. However no detectable pyrrolase activity was found in any other tissues either before or after hydrocortisone. 2 In agreement with previous observations hydrocortisone decreased rat brain 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) 6 h after administration. Brain tryptophan concentrations were also decreased at this time. In contrast, hydrocortisone did not alter gerbil brain 5-HT, 5-HIAA or trytophan. alpha-Methyltryptophan activated hepatic tryptophan pyrrolase and decreased brain 5-HT and 5-HIAA in both animals. 3 Results suggest that the decrease in rat brain 5-HT and 5-HIAA following hydrocortisone may be associated with the rise in liver tryptophan pyrrolase and that the brain amine changes are mediated through the decrease in brain tryptophan concentration.

Distribution and metabolism of 14C-tryptophan in normal and endotoxin-poisoned mice

dl-Tryptophan (benzene ring-(14)C) and its metabolites persist longer and in greater quantity in tissues of endotoxin-poisoned mice than in tissues of normal mice. Correspondingly less label is excreted in urine and feces and expired as (14)CO(2) in the poisoned animals. The distribution of label (1.1 x 10(6) dpm per microgram of tryptophan) was relatively constant whether it was administered alone or in combination with 20 mg of unlabeled l-tryptophan. Tryptophan must be metabolized through the tryptophan oxygenase pathway to be converted to carbon dioxide, but attempts to quantitatively correlate depressed tryptophan oxygenase activity with depressed carbon dioxide production were unsuccessful. It appears that neither tryptophan oxygenase nor substrate availability exclusively determine the quantity of tryptophan converted to (14)CO(2) except under highly selected conditions. The validity of an earlier suggestion that expired (14)CO(2) could be used to monitor in vivo tryptophan oxygenase activity is not supported by our data.

Iron- and riboflavin-dependent metabolism of a monamine in the rat in vivo

n-Pentylamine enters into intermediary metabolism by the action of monoamine oxidase. [1-(14)C] Pentylamine injected into rats is rapidly converted to (14)CO(2). The rate of catabolism decreases progressively in the course of nutritional iron deficiency, reaching about 60 percent of control values in 3 weeks. Feeding with iron yields control levels within 6 days. The catabolism of amyl alcohol, which shares a common pathway with n-pentylamine by way of valeric aldehyde, is not significantly affected by the deficiency. The results demonstrate that the maintenance of normal monoamine oxidase activity in vivo depends upon an adequate supply of dietary iron.