Studies on the relation of γ-hydroxybutyric acid (GHB) to γ-aminobutyric acid (GABA): Evidence that GABA is not the sole source for GHB in rat brain

The effects of γ-aminobutyric acid (GABA)-α-oxoglutarate aminotransferase (GABA-T) inhibitors, l-glutamic acid decarboxylase (GAD) inhibitors, and antipetit mal anticonvulsants on γ-hydroxybutyric acid (GHB) and GABA were studied. Treatment with anticonvulsants and GABA-T inhibitors resulted in an increase in steady-state brain levels of both GHB and GABA. GAD inhibitors produced markedly decreased levels of brain GABA but no change in GHB concentrations. Studies of GHB derived exclusively from GABA showed that GABA-T inhibitors which produced an elevation of steady-state levels of GHB in brain also resulted in a decrease in GABA-derived GHB. Intracere-broventricular (i.c.v.) administration of GABA, putrescine, and 1,4-butanediol all produced significant elevations in brain GHB, but GABA-T inhibitors blocked this effect of GABA and putrescine. These data suggest that there may be another source for GHB in brain in addition to GABA and raise the possibility that 1,4-butanediol may be that source.     

The epileptogenic spectrum of opiate agonists

The present authors gave mu, delta, kappa, epsilon and sigma opiate receptor agonists intracerebroventricularly to rats both singly and in combination while monitoring the electroencephalogram from cortical and depth electrodes. Dose-response curves were plotted with naloxone against the changes produced by each agonist, and the effect of a number of anticonvulsant drugs on agonist-induced seizures was ascertained. Each opiate agonist produced a different seizure pattern with a different naloxone dose-response curve and anticonvulsant profile. The order of convulsive potency was epsilon greater than delta greater than mu greater than sigma much greater than kappa. Petit mal-like seizure activity was unique to the delta agonist, leucine-enkephalin, while only the mu agonist, morphine produced generalized convulsive seizures. These experiments raise the possibility that opiate systems in the brain may be involved in the pathogenesis of a wide spectrum of seizure disorders.     

Ethanol and methadone in man: A possible drug interaction

Possible opiate-ethanol interaction was studied in five selected stable non-alcoholic chronic methadone-maintained patients. Ethanol and methadone levels were determined during oral methadone, ethanol and combined methadone-ethanol tolerance tests. The data do not suggest a significant acute interaction between ethanol and methadone as reflected by the rates of disappearance in the blood.     

Enzymes of salvage and de novo pathways of synthesis of pyrimidine nucleotides in human colorectal adenocarcinomas

The activity of uridine-cytidine kinase (Urd-Cyd kinase), a key enzyme in the salvage of pyrimidine nucleosides, averaged 0.86 ± 0.16 (S.E.M.) nmole uridine phosphates · min^?1(mg protein)^?1 in fifty-three specimens of human colorectal adenocarcinomas. The activity of fluorouracil phosphoribosyltransferase (FUPRTase) in thirty-five carcinoma specimens averaged only 0.19 ± 0.07 nmole fluorouridine phosphates · min^?1 · (mg protein)^?1. The activity of the last enzyme in the de novo pathway of biosynthesis of UMP, i.e. orotidine 5'-monophosphate (OMP) decarboxylase, averaged 0.21 ± 0.04 nmole CO₂ · min^?1 · (mg protein)^?1. The activity of Urd-Cyd kinase was increased ~2.3-fold, and that of OMP decarboxylase by about 91%, while that of FUPRTase was increased by only 27%, as compared to that of normal human colonie mucosa. Of the colorectal carcinomas studied, 72% were moderately differentiated, 21% poorly differentiated, and 7% well differentiated. The mean diameter of the fifty-three carcinomas was 5.5 cm, and pathologic staging led to classification of 15% as Dukes' A, 36% as Dukes' B, 47% as Dukes' C, and 2% as carcinoma in situ. No correlations between the level of the enzyme activities studied and any pathologic characteristics of the carcinomas could be discerned.     

GTP depletion and other erythrocyte abnormalities in inherited pnp deficiency

GTP levels were low and NAD⁺ levels high in purine nucleoside phosphorylase (PNP) deficient erythrocytes, in addition to the raised deoxy-GTP (dGTP) levels previously noted by others. dGTP was also identified in the PNP deficient child's lymphocytes.A further novel finding was the conversion of hypoxanthine to inosine by the PNP deficient red cells, as compared to inosine monophosphate (IMP) in controls. This has been attributed to IMP formation with subsequent breakdown, and raises interesting questions regarding the controls which normally maintain erythrocyte nucleotide pools.These findings may also explain the gross purine overproduction seen in this defect; they may likewise be related to the associated immunodeficiency, anaemia, and other clinical manifestations. The results may also have important implications for the development and clinical use of PNP inhibitors.     

Reciprocal relationship between erythrocyte ATP and deoxy-ATP levels in inherited ADA deficiency

A reciprocal relationship between erythrocyte ATP and deoxy-ATP levels has been noted in an immunodeficient child with adenosine deaminase (ADA) deficiency during therapy with red cell transfusions. The sum of red cell ATP plus deoxy-ATP equalled the normal complement of ATP prior to any form of therapy. dATP, dADP and dAMP levels were found in the same ratio (10:1:0.1) as the adenine nucleotides ATP, ADP and AMP. Red cell ATP levels were low, not high or normal as found by others in ADA deficiency, but no deoxyadenosine nucleotides could be found in peripheral blood mononuclear cells.Erythrocyte ATP depletion has recently been identified as a serious consequence of anti-leukaemic therapy with ADA inhibitors; it may thus be an important but hitherto unrecognised contributing factor in the clinical expression of inherited ADA deficiency.     

The distribution of inorganic lead in guinea pig brain and neural barrier tissues in control and lead-poisoned animals.

The central neural distribution of radiolabeled lead nitrate (²¹⁰Pb) and total lead concentrations were investigated in adult pigs after intravenous injection of the tracer. Control animals were fed ad libitum, whereas lead encephalopathy was induced by feeding other animals 165 mg lead carbonate daily for 6 days. Lead was not detected in choroid plexus (CP). (Average concentration in control animals <1.2 μg/g; <1.5 μg/g in poisoned animals.) Brain lead concentrations averaged 0.095 ± 0.016 μg/g wet weight in control nimals and 0.427 ± 0.067 μg/g in poisoned animals. CP concentrated the pulsed radiolabel more than 70 times as avidly as brain, and in meninges and ependyma the concentration of ²¹⁰Pb also exceeded markedly that occurring in brain. The high initial uptake of radiolead by CP indicates that this organ may act as a “sink”, tending to reduce lead entry into CSF and brain. Pretreatment with ouabain iv (1.6 – 1.7 × 10^?9 mol/kg) reduced significantly ²¹⁰Pb accumulation by CP and by brain 5 and 60 min after label injection in control animals but not in lead-poisoned animals. These results suggest that active transport of cations by the barrier tissues may influence the central neural distribution of lead.     

Differential effects of chronic ethanol feeding on cytochrome P-448- and P-450-mediated drug metabolism in the rat

The effects of chronic ethanol feeding on cytochrome P-448- and P-450-mediated drug metabolism have been studied both in vivo and in vitro in the rat, using caffeine, phenacetin, antipyrine and aminopyrine as test substrates. N-Demethylation of aminopyrine (P-450 mediated) was increased both in vivo and in vitro in rats after chronic ethanol feeding (P < 0.05) whereas in vivoN-demethylation of caffeine and O-dealkylation of phenacetin (P-448 mediated) were unchanged in the same animals. N-rmDemethylation of antipyrine was increased by both phenobarbital and 3-methylcholanthrene pretreatment and by chronic ethanol feeding (P < 0.05), possibly due to cytochrome P-450 induction. Furthermore, the Michaelis affinity constants. K_m, for hepatic microsomal aminopyrine N-demethylase and antipyrine N-demethylase were lower in chronic ethanol-fed animals (P < 0.05), suggesting a qualitative change in the enzymes resulting in greater substrate affinity. These findings suggest a differential effect of chronic ethanol feeding on the induction of cytochrome P-450- and cytochrome P-448-mediated drug metabolism, with a greater effect on the former microsomal system.     

Alcohol and aggression in a group interaction

Forty-four volunteer male subjects participated in groups of four along with two experimental confederates in a group interaction after consuming either 1.32 mg/kg of 95% USP alcohol or placebo. According to a balanced-placebo design, subjects were told they were either consuming alcohol or placebo. The task of one confederate was to initiate conversation and distract subjects from monitoring their state of intoxication while the second confederate's role was to antagonize subjects at a prescribed time. Sessions were videotaped and rated for frequency of positive and negative interactions and subjects completed rating scales evaluating each other. The results failed to show an expectancy effect on any measures; however, there was an alcohol effect seen in an increase in negative interactions as well as positive interactions and a significant expectancy X alcohol interaction for negative ratings of the provocative confederate. In those groups where the manipulation matched the expectation, alcohol-told alcohol and placebo-told placebo the confederate was seen more negatively than in the mixed groups. An attributional explanation for the results is offered and the generality of the alcohol-expectancy phenomenon questioned.     

S-methylation of captopril. Demonstration of captopril thiol methyltransferase activity in human erythrocytes and enzyme distribution in rat tissues

The presence of a methyltransferase enzyme in human red blood cells (RBCs) capable of S-methylation of captopril is described. The apparent Michaelis-Menten (Km) constant for captopril was 0.5 mM and the maximum velocity (Vmax) was 0.391 pmoles S-methylcaptopril (mg protein)-1 min-1. There is some evidence presented to show that S-methylcaptopril inhibited its own formation with a ki value of 5.81 mM. Captopril thiol methyltransferase activity was also examined in rat tissues and was found to be present in all tissue studied. Subcellular localisation studies in rat liver suggest that the enzyme was microsomal in origin. The order of activity was liver greater than heart greater than spleen greater than lung greater than kidney much greater than RBC (rat). This tissue distribution was quite different from previous studies using other thiol substrates and is consistent with more than one form of thiol methyltransferase enzyme in tissues.