Properties of γ-glutamyltranspeptidase,and glutathione levels in rat mammary gland

Summary -Glutamyltranspeptidase activity and glutathione levels were studied in rat mammary gland during the lactogenic cycle; both increased during mid-lactation. The enzyme's specific activity with several amino acids showed that glutamine and methionine were the best substrates. Maleate decreased the transpeptidation reaction and increased the hydrolytic activity. These results suggest that -glutamyltranspeptidase from the mammary gland is similar to the enzyme described in other tissues in relation to these properties and the physiological role proposed in amino acids transport.     

Effect of dexamethasone on Fc γ receptor expression in foetal and neonatal rat gut

Summary When injected into 12-day-old suckling rats, dexamethasone caused a precocious disappearance of Fc receptors from enterocytes of the proximal small intestine. However, dexamethasone appeared to be necessary for the maintenance or production of such receptors in foetal rat gut cultured in vitro.Supported by an award from the Science and Engineering Research Council.     

Effect of tea consumption on the levels ofα-ketoglutarate and pyruvate dehydrogenase in rat brain

Summary Administration of tea to rats fed on a normal diet results in a marked drop in brain levels of total thiamine as well as of -ketoglutarate and pyruvate dehydrogenase activities. The patterns of decrease in both enzyme activities are similar to that of total thiamine content; they drop to about 65% of the control at 14–20 weeks after continuous consumption of tea.Supported by a grant from the International Foundation for Science (IFS), Sweden.     

Development of γ-glutamylcysteine synthetase and oxoprolinase in rat kidney

Summary -Glutamylcysteine synthetase is present in barely detectable amounts in foetal kidney. Its activity starts to increase in postnatal life. In contrast, oxoproline is already found in significant quantities in the foetal tissue. Both enzymes show marked elevation in activities during the weaning period.Acknowledgment. The work was supported by a research grant awarded by the Committee on Research and Conference Grants, University of Hong Kong.     

Effect of 3,5,3′-tri-iodothyronine on cellular growth and oxygen consumption in neonatal rat brain

Summary The effect of thyroid deficiency and treatment with tri-iodothyronine (T₃) on oxygen consumption by neonatal (6-day-old and 15-day-old) rat brain was examined using glutamate, -hydroxybutyrate, succinate and ascorbate+TMPD as substrates. The respiration rates decreased significantly in 15-day-old hypothyroid pups. Treatment of normal and of hypothyroid pups with T₃ resulted in a significant increase in the respiration rate at both ages. Respiration rates with glucose as the substrate were not affected under these conditions.     

Effects of duration of gonadectomy,sex and age on adrenal steroid 5α-reductase activity in the rat

Summary Within 6–8 weeks, gonadectomy in male and female rats leads to an increase in adrenal 5-steroid reductase activity. However, long-term post-orchiectomy enzyme activity decreases to the control level and this effect is not related to the age of animals.Supported in part by grant No.564/VI from Polish Academy of Sciences. Generous gift of hormones applied in these studies from The Upjohn Company, Kalamazoo, Michigan, USA is acknowledged.     

Effect of acute administration of Δ1-tetrahydrocannabinol on β-endorphin levels in plasma and brain tissue of the rat

Summary Acute treatment with ¹-tetrahydrocannabinol (¹-THC) elevated the concentration of -endorphin-like immunoreactivity (-ELIR) in plasma and in the hypothalamus, but not in the hippocampus of rats habituated to the injection procedure. These effects were not obtained with the psychotropically inert analog of (¹-THC), cannabidiol. In animals that had not been habituated to the injection procedure, placebo treatment induced a decrease in hippocampal -ELIR.The authors acknowledge the skillful technical assistance of Mrs Willeke Logtenberg.     

May K+ ions stimulate the formation of cyclic AMP in the brain independently on their depolarizing action?

Summary The effect of potassium ions on the formation of adenosine 3,5-monophosphate (cAMP) in the rat cerebral cortex in vivo was studied under conditions where development of spreading depression had been blocked by pretreatment of the cerebral cortex by topically applied magnesium ions. A linear relationship between potassium concentrations applied to the cortical surface and levels of cAMP has been found. Moreover, potentiation of the K⁺-effect by magnesium ions has been observed.     

The molecular link between β- and γ-secretase activity on the amyloid β precursor protein

Alzheimer’s disease (AD) is characterized by an accumulation in the brain of amyloid β peptides (Aβ). The production of Aβ requires two sequential cleavages induced by β- and γ-secretases on the β-amyloid precursor protein (APP). Altered activity of these secretases is involved in the pathogenesis of AD. The expression and activity of β-secretase (BACE1) is augmented in the brain in late-onset sporadic AD. Mutant presenilin 1 (PS1), the major genetic defect of early-onset familial AD (FAD), alters the activity of γ-secretase, leading to increased production of Aβ42. Here we review the role of oxidative stress as a molecular link between the β- and the γ-secretase activities, and provide a mechanistic explanation of the pathogenesis of sporadic late-onset AD. We also discuss evidence for a role of the same mechanism in the pathogenesis of familial AD carrying PS1 mutations.     

Thyroid hormone controls carnitine status through modifications of γ-butyrobetaine hydroxylase activity and gene expression

The carnitine system plays a key role in β-oxidation of long-chain fatty acids by permitting their transport into the mitochondrial matrix. The effects of hypothyroidism and hyperthyroidism were studied on γ-butyrobetaine hydroxylase (BBH), the enzyme responsible for carnitine biosynthesis in the rat. In rat liver, BBH activity was decreased in the hypothyroid state and increased in hyperthyroid animals. The modifications in BBH activity correlated with changes in the enzyme Vmax values. These changes were shown to be related to hepatic BBH mRNA abundance. Thyroid hormones are known to interact with lipid metabolism, in particular by increasing long-chain fatty acid oxidation through activation of carnitine-dependent fatty acid import into mitochondria. Our study showed that thyroid hormones also increased carnitine bioavailability. Received 23 October 2001; received after revision 11 January 2002; accepted 15 January 2002     

Hepatic α-tocopherol binding protein in the rat: Absence of an effect of selenium deficiency on binding activity

Summary Selenium deficiency produces no effect on either the total content of or the binding properties of rat liver -tocopherol binding protein.     

Effects of N2, O2′-dibutyril cyclic GMP on the nucleoside phosphotransferase activity of the retina of the chick embryos

Summary In the retina of the chick embryo, 2 different forms of nucleoside phosphotransferase take part in the phosphorylation of thymidine. One is an unstable form with higher molecular weight. The other with lower m. wt is a stable form. This paper shows that N², O²-dibutyril cyclic GMP causes a marked decrement of the activity of the unstable nucleoside phosphotransferase.     

The effects of γ-aminobutyric acid and picrotoxin on the junctional potential and the contraction of crayfish muscle

Résumé L'acide-amino-butyrique et la-alanine reproduisent l'action du transmetteur inhibiteur du système neuromusculaire de l'écrevisse. Ces deux acids aminés diminuent la contraction musculaire. L'acide-amino-butyrique réduit la différence de potentiel et augmente sa décomposition. L'action de ces acides aminés est bloquée par la picrotoxine comme l'est celle du transmetteur inhibiteur.

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The study was supported by Grants B-1089 and B-31 from the National Institute of Neurological Diseases and Blindness, United States Public Health Service. Some of this work was done at the Department of Zoology, Cornell University. We are grateful to Prof.S. C. Wang, Columbia University, for generous assistance.     

An immunohistochemical and ultrastructural comparison of the effects of 2-bromo-α-ergocryptine on intrasellar and transplanted rat pituitaries

Summary Following 2 weeks of administration of 2-bromo--ergocryptine, a marked decrease was observed in prolactin immunoreactivity of the grafted pituitaries, whereas no reduction was noted in the intrasellar pituitaries. No evidence of crinophagy was revealed by electron microscopy in prolactin cells of 2-bromo--ergocryptine-treated rats.Acknowledgments. This work was supported in part by the Medical Research Council of Canada (grant MA-6349). The excellent technical assistance of Mrs Cynthia Edwards and secretarial help of Mrs Wanda Wlodarski are gratefully acknowledged.     

Opposite effects ofβ-adrenoceptor stimulation and 8-bromo-cyclic AMP on potassium efflux in mammalian heart muscle

Summary -adrenoceptor stimulation by isoprenaline increases the potassium efflux in beating guinea-pig atria. This effect is not mimicked by 8-bromo-cyclic AMP, a cyclic AMP analogue which exerts a positive inotropic effect in this preparation.     

Effects of two kinds of social deprivation on testosterone and estradiol-17β plasma levels in the male rat

Summary The effect of complete and tactile isolation on plasma testosterone and estradiol-17 was studied in male rats at the age of 60 and 180 days. A decrease in the plasma levels of the two hormones was observed.     

Influence of cyproterone acetate on the activity ofβ-glucuronidase in the hypothalamus and cerebral cortex of the male mouse

Summary Daily s.c. injections of cyproterone acetate greatly decrease the protein content and-glucuronidase activity in the mouse hypothalamus. These effects are reversible and the recovery capacity of the animal seems to be inversely related to the duration of antiandrogenic treatment.Financial aid was given by CNR (finalized project Biologia della Riproduzione) and Ministry of Education. Thanks are also due to Prof. G. Chieffi for suggestions and to Mr R. Auriemma for maintenance of experimental animals.     

Action ofβ-(4-chlorophenyl-GABA) on uptake and metabolism of GABA in different subcellular fractions of rat brain

Summary -(4-chlorophenyl)-GABA, a GABA mimetic compound, acts as an inhibitor of GABA metabolism in both synaptosomal and extrasynaptosomal compartments. It has no significant action on GABA or Glu uptake by synaptosomes.