Asunto(s)

RESUMEN

OBJECTIVE: The objective of this study was to evaluate the impact of indices of central nervous system (CNS) serotonin function on cardiovascular reactivity to mental stress. METHODS: Lumbar puncture was performed on 54 healthy volunteers to obtain cerebrospinal fluid (CSF) for determination of 5-hydroxyindoleacetic acid (5HIAA) levels. Genotypes were determined with respect to a functional polymorphism of the serotonin transporter gene promoter region (5HTTLPR). Subjects then underwent mental stress testing. RESULTS: Persons with one or two long (l) 5HTTLPR alleles had CSF levels of the major serotonin metabolite, 5HIAA, that were 50% higher than those of persons with the s/s 5HTTLPR genotype. Persons with one or two l alleles or higher CSF 5HIAA levels also exhibited greater blood pressure and heart rate responses to a mental stress protocol. CONCLUSIONS: These findings suggest the 5HTTLPR polymorphism affects CNS serotonin function, and they are consistent with the general hypothesis that CNS serotonin function is involved in the regulation of potentially health-damaging biobehavioral characteristics. In particular, the l allele could contribute, through its association with increased cardiovascular reactivity to stress, to increased risk of cardiovascular disease.

Asunto(s)

RESUMEN

Delirium affects more than 2 million patients in the United States each year. The onset of delirium often occurs after hospitalization and in many cases is due to medications or procedures performed during the hospitalization. Unfortunately, delirium remains unrecognized in the majority of patients for several reasons. This review addresses the diagnostic criteria for delirium, the neurochemistry that is believed to be causative, risk factors, measures that may be taken to reduce the onset of delirium, and treatment options.

RESUMEN

The effect of an acute intraperitoneal dose of ethanol (1 g/kg), glucose (7.2 g/kg), or the combination of the two on the metabolite pattern of the biosynthetic pathway of L-serine has been determined in rabbit liver in vivo as has the effect of 10 mM ethanol on the glucose-, fructose-, or pyruvate-stimulated accumulation of L-serine in rabbit hepatocytes in vitro. In vivo, the 50% increase in L-serine and 80% increase in L-phosphoserine content of liver following glucose injection was completely prevented by ethanol. In fact, the L-phosphoserine content fell to only 6% of the control value. In spite of these and other significant changes in the metabolite pattern of the pathway of L-serine biosynthesis (D-3-phosphoglycerate dehydrogenase, L-phosphoserine aminotransferase (PSAT), and L-phosphoserine phosphatase), the mass action ratio of the combined reactions of the first two steps remained close to their equilibrium position. As a consequence it is estimated that the tissue content of phosphohydroxypyruvate fell to less than 2% of the control value, to approximately 0.3% of its Km for the PSAT reaction. The conclusion that acute ethanol blocks L-serine biosynthesis (presumably by redox effects) was supported by the prevention or inhibition of L-serine accumulation in hepatocytes metabolizing glucose, fructose, or pyruvate. Because L-serine is an important source of one-carbon fragments, the inhibition of its biosynthesis may be another mechanism by which ethanol interferes with folate and one-carbon metabolism.

Asunto(s)

RESUMEN

L-Serine alone is not gluconeogenic in isolated rabbit hepatocytes, whereas in rat liver this amino acid has been reported to yield as much glucose as does L-lactate itself. The current study has been an investigation into the explanation of the difference between the two species. Hepatocytes were isolated from 48-h-starved, 750- to 1000-g male rabbits, and the viability of each preparation was judged by ATP levels (2.4 +/- 0.2 mumol/g wet wt) at the beginning and end of the incubation as well as gluconeogenesis from 10 mM L-lactate (0.83 +/- 0.08 mumol/min/g wet wt). L-Serine alone produced virtually no glucose or pyruvate accumulation above baseline. Hydroxypyruvate, however, did appear in the incubation mixture. When L-serine and pyruvate were combined to test the functional activity of L-serine:pyruvate aminotransferase (EC 2.6.1.51), however, gluconeogenesis remained at the rate produced by pyruvate alone (0.61 +/- 0.04 mumol/min/g wet wt). On the other hand, the combination of L-serine and L-lactate produced rates of glucose accumulation 35% above that of L-lactate alone. The combination of L-lactate plus hydroxypyruvate produced nearly maximal rates (1.39 +/- 0.08 mumol/min/g wet wt), approaching those achieved by a physiologic ratio (10:1) of L-lactate and pyruvate. Hydroxypyruvate itself was only moderately gluconeogenic (0.44 +/- 0.04 mumol/min/g wet wt). That a reduction of the cytoplasmic free [NAD+]/[NADH] ratio by L-lactate was not its only contribution to L-serine utilization was suggested by the fact that ethanol completely eliminated gluconeogenesis from virtually all precursors (or combinations) tested, with the exception of hydroxypyruvate. It has been concluded from the data that, probably in contrast to the rat, the major pathway for the entrance of L-serine into gluconeogenesis in rabbit hepatocytes is through the pathway initiated by L-serine: pyruvate aminotransferase and that L-lactate is an important participant (i) by generating cytoplasmic reducing equivalents (NADH), (ii) by supplying pyruvate for the transaminating reaction itself, and, perhaps, (iii) by preventing hydroxypyruvate from being reduced by L-lactate dehydrogenase (EC 1.1.1.27) to L-glycerate.

Asunto(s)

RESUMEN

The substrate specificity of choline kinase (ATP:choline phosphotransferase, EC 2.7.1.32) from brewer's yeast has been examined using multiple analogs of choline, most of which have been reported to be a substrate of one or another choline-using system from other sources. In contrast to many such systems, choline kinase from brewer's yeast has been found to have relatively stringent and straight-forward structural requirements for its substrates. It is hypothesized that there are at least four points of interaction of the substrate with the enzyme--one for the hydroxyalkyl side chain and one for each of the three substituents on the quaternary nitrogen. Of the latter, one site seems relatively more sterically hindered than the other two. Short, single or double alkyl substitutions on the quaternary nitrogen are possible without a large loss of substrate capacity of the analog. Thus N,N-dimethyl-N-propylethanolamine had a relative Vmax of 116% and a relative Vmax 96% that of choline and a Km of 68 +/- 15 microM [nearly four times that of choline itself (18 microM)]. However, N-butyl-N,N-dimethylethanolamine and N,N,N-triethylethanolamine were very poor substrates. Analogs with substituents on the quaternary nitrogen of longer chain length were without activity as were aromatic derivatives. None of the bisquaternary compounds of the general structure HOCH2CH2N+(CH3)2-(CH2)n-N+(CH3)2CH2CH2OH (n = 2-10) showed any substrate capacity, as well. Restrictions on the hydroxyethyl side chain were also severe. One additional methylene group in this chain greatly reduced substrate capacity of the analog and two additional ones eliminated it entirely, as did almost any substituent on the beta carbon. A single (but not a double) substituent on the alpha carbon was moderately tolerated, however. Thus alpha-methylcholine and N-methyl-2-hydroxymethylpiperidine were substrates (although the latter one was a poor one) but beta-methylcholine and N-methyl-3-hydroxypiperidine were not. Such information may be of use toward designing cholinergic probes targeting specific enzyme or metabolic functions.

Asunto(s)