Triiodothyronine stimulates 2-deoxy-D-glucose uptake by organ cultured embryonic chick small intestine

The possible contribution of increased D-glucose absorption from the intestine to the impairment of oral glucose tolerance in hyperthyroidism was evaluated by investigating the influence of T3 on different pathways of D-glucose transport, utilizing an organ culture system of embryonic chick small intestinal explants. T3, when present in the culture medium at a concentration between 10(-10)-10(-8) mol/l, had no effect on uptake of alpha-methyl-D-glucoside, but stimulated uptake of 2-deoxy-D-glucose by the intestinal epithelium in a dose-dependent fashion. T3 thereby enhanced the maximal velocity of a saturable, cytochalasin B-sensitive but phloretin-insensitive 2-deoxy-D-glucose transport system with an apparent Km of 7 mmol/l. The combined data are consistent with the assumption that T3 can enhance D-glucose entry into the intestinal epithelium through stimulation of a low-affinity transport system at the brush-border membrane of enterocytes. Our findings provide a basis for the explanation of adaptive modulation of intestinal glucose absorption in hyperthyroidism.

Modified behavioral and olfactory bulb responses to maternal odors in preweanling rats

Rat pups acquire an attraction for maternal odors, which can vary with maternal diet. In the two experiments reported here, maternal diet was modified and both pup behavioral responses and pup olfactory bulb neural responses [( 14C]2-DG uptake) to maternal odors were examined. In experiment 1, pups were reared from birth to postnatal day 19 with either a dam fed normal rat chow or a dam fed a sucrose-based diet which suppressed her normal maternal odor. In experiment 2, pups were raised from birth to postnatal day 19 with either a dam fed the sucrose-based diet adulterated with peppermint, or the non-scented sucrose-based diet. Pups selectively expressed both a behavioral attraction and an enhanced olfactory bulb neural response to odors that they experienced in the nest.

Desmopressin, but not vasopressin, decreases activity of the hypothalamo-neurohypophysial system in Brattleboro rats

The pituitary neural lobe of homozygous Brattleboro rats has high rates of glucose utilization not affected by chronic treatment with exogenous vasopressin, despite attenuation of polydipsia and polyuria. We evaluated whether this effect may result from the inability of vasopressin to affect the hypothalamo-neurohypophysial metabolism or from the development of resistance to chronic vasopressin treatment. We used the [14C]deoxyglucose method to compare 28-h effects of vasopressin treatment (5 U/kg, i.m., twice a day) with that of desmopressin (100 micrograms/kg, i.p., once a day), a long-lasting antidiuretic hormone, on glucose utilization of the hypothalamo-neurohypophysial system and related structures in conscious homozygous Brattleboro rats. Vasopressin and desmopressin reduced water intake, plasma osmolality and plasma Na+ concentration similarly. Vasopressin decreased glucose utilization in the supraoptic nucleus, subfornical organ and median preoptic nucleus, but did not alter activity in the paraventricular nucleus and neural lobe. Desmopressin decreased glucose utilization in all these structures. The results indicate that desmopressin has a more potent inhibitory action on the hypothalamo-neurohypophysial system than vasopressin over this short duration of treatment. The lack of response in the neural lobe from chronic treatment with vasopressin seems to be due to its inability to affect the paraventricular nucleus metabolism. The maintenance of metabolic activity in the paraventricular nucleus of vasopressin-treated Brattleboro rats suggests that this structure contributes importantly to the metabolism of neural lobe.

Regional brain glucose metabolism and blood flow in streptozocin-induced diabetic rats

Brain regional glucose metabolism and regional blood flow were measured from autoradiographs by the uptake of [3H]-2-deoxy-D-glucose and [14C]iodoantipyrine in streptozocin-induced diabetic (STZ-D) rats. After 2 days of diabetes, glucose metabolism in the neocortex, basal ganglia, and white matter increased by 34, 37, and 8%, respectively, whereas blood flow was unchanged. After 4 mo, glucose metabolism in the same three regions was decreased by 32, 43, and 60%. This reduction was paralleled by a statistically nonsignificant reduction in blood flow in neocortex and basal ganglia. It is suggested that the decrease of brain glucose metabolism in STZ-D reflects increased ketone body oxidation and reduction of electrochemical work.

Measurement of cerebral glucose utilization from brain uptake of [14C]2-deoxyglucose and [3H]3-O-methylglucose in the mouse

Glucose utilization (GU) in the mouse brain in vivo was measured by the simultaneous use of [14C]2-deoxyglucose (2DG), the glucose analogue that can be phosphorylated in the brain, and [3H]3-O-methylglucose (3MG), the nonmetabolizable glucose analogue. Originally, this method was developed by Gjedde et al. (1985) in the rat and in humans. The present study examined the validity of this method in the mouse brain. The effects of urethane and pentobarbital (PB) on GU were also studied. Whereas the distribution volume of 3MG reached a constant value under each condition after 10 min of the tracer circulation, the apparent volume of distribution of 2DG, which increased with time in the awake mice, did not increase so greatly in the anesthetized and hypothermic mice, indicating that the net rate of 2DG phosphorylation is lowered under these conditions. These data were fitted for the conventional three-compartmental model and the values of rate constants of influx (K1), efflux (k2), phosphorylation, and dephosphorylation for 2DG, and K1 and k2 for 3MG were computed by nonlinear least square regression method. No significant difference in the value of K1/k2, the distribution volume of the precursor pool, was observed between 2DG and 3MG, indicating that 3MG can be used to estimate the distribution volume of unmetabolized 2DG in the brain. The values of GU calculated from the values of estimated parameters were not significantly different from those calculated from blood and tissue radioactivities obtained during 10 min after the injection of the tracers in both awake and PB-anesthetized mice. These findings indicate that the double tracer technique is useful for measuring GU in a short duration experiment.

Metabolic consequences of hyperinsulinaemia imposed on normal rats on glucose handling by white adipose tissue, muscles and liver

The effects of hyperinsulinaemia imposed on normal rats on the subsequent insulin-responsiveness in vivo of 2-deoxy-D-glucose uptake of white adipose tissue and of various muscle types were investigated. This was done by treating normal rats with insulin via osmotic minipumps, and by comparing them with saline-infused controls. Hyperinsulinaemia produced by prior insulin treatment resulted in a well-tolerated hypoglycaemia. At the end of the treatment, the glucose utilization index of individual tissues was determined by euglycaemic/hyperinsulinaemic clamps associated with the labelled 2-deoxy-D-glucose method. Prior insulin treatment resulted in increased insulin-responsiveness of the glucose utilization index of white adipose tissue, and in increased total lipogenesis in white adipose tissue and fat-pad weight. In contrast, prior insulin treatment resulted in a decreased glucose utilization index of several muscles. These opposite effects of hyperinsulinaemia on glucose utilization in white adipose tissue and muscles persisted when the hypoglycaemia-induced catecholamine output was prevented (adrenomedullectomy, propranolol treatment), as well as when hypoglycaemia was normalized by concomitant insulin treatment and glucose infusion. Insulin suppressed hepatic glucose production during the clamps in insulin-treated rats as in the respective controls, whereas total hepatic lipid synthesis and liver fat content were greater in rats treated with insulin than in controls. It is concluded that hyperinsulinaemia itself could be one of the driving forces responsible for producing increased glucose utilization by white adipose tissue, increased total lipid synthesis with fat accumulation in adipose tissue and the liver, together with an insulin-resistant state at the muscular level.

Increased glucose use in the hypoglossal nucleus after hypoglossal nerve transection in aged rats

We used [2-14C]deoxyglucose as a marker of increased metabolism of the hypoglossal nucleus after transection of its nerve. We studied this metabolism in 3-, 12-, and 24-month-old rats. We found an increase in glucose uptake in the control nucleus of 24-month-old rats which was significant when compared to that of 3-month-old rats. We also found a twofold increase in the difference between glucose uptake on the side of nerve transection compared to the control side in old rats.

Determination of the role of polyphosphate in transport-coupled phosphorylation in the yeast Saccharomyces cerevisiae

The role of polyphosphate in 2-deoxy-D-glucose transport was studied in yeast cells, pulse-labeled with [32P]orthophosphate, by comparing the concentrations and specific activities of polyphosphate, orthophosphate and 2-dGlc-phosphate. When 2-dGlc transport was measured under aerobic conditions, it appeared that polyphosphate replenished the orthophosphate pool, indicating that polyphosphate has, at least mainly, an indirect role in sugar phosphorylation. Also in cells with a reduced respiratory capacity, due to a treatment with antimycin A, no direct role for polyphosphate in 2-dGlc transport could be detected. Under these conditions, only a very limited breakdown of polyphosphate occurred, probably because of the small decrease in the orthophosphate concentration.

Acid lability of metabolites of 2-deoxyglucose in rat brain: implications for estimates of kinetic parameters of deoxyglucose phosphorylation and transport between blood and brain

The steady-state brain/plasma distribution ratios of [14C]deoxyglucose ([14C]DG) for hypoglycemic rats previously determined by measurement of DG concentrations in neutralized acid extracts of freeze-blown brain and plasma exceeded those predicted by simulations of kinetics of the DG model. Overestimation of the true size of the precursor pool of [14C]DG for transport and phosphorylation could arise from sequestration of [14C]DG within brain compartments and/or instability of metabolites of [14C]DG and regeneration of free [14C]DG during the experimental period or extraction procedure. In the present study, the concentrations of [14C]DG and glucose were compared in samples of rat brain and plasma extracted in parallel with perchloric acid or 65% ethanol containing phosphate-buffered saline. The concentrations of both hexoses in acid extracts of brain were higher than those in ethanol, whereas hexose contents of plasma were not dependent on the extraction procedure. The magnitude of overestimation of DG content (about 1.2-to fourfold) varied with glucose level and was highest in extracts isolated from hypoglycemic rats; contamination of the [14C]DG fraction with 14C-labeled nonacidic metabolites also contributed to this overestimation. Glucose concentrations in acid extracts of brain exceeded those of the ethanol extracts by less than 40% for normal and hypoglycemic rats.

Exchange of fluorinated glucose across the red-cell membrane measured by 19F-n.m.r. magnetization transfer

The 19F n.m.r. spectrum of 3-fluoro-3-deoxy-D-glucose (3FG) in a red-cell suspension was observed to contain separate resonances from the intra- and extra-cellular populations of both the alpha- and beta-anomers. This phenomenon was used with an n.m.r. spin-transfer procedure to measure the rate of exchange of the anomers across the human red-cell membrane under equilibrium-exchange conditions at 37 degrees C. The beta-anomer crossed the membrane significantly more quickly than the alpha-anomer. At a total 3FG concentration of 9.3 mM; the first-order rate constants for the efflux of the alpha- and beta-anomers were 0.41 +/- 0.15 and 0.88 +/- 0.20 s-1 respectively. The measurable 3FG exchange was inhibited by 75 and 100% respectively by the glucose-transport inhibitors cytochalasin B and phloretin. Glucose inhibited the exchange of 3FG, and the results were consistent with glucose and 3FG binding to the hexose-transport protein with similar affinity.

The distribution of changes in local cerebral energy metabolism associated with brain stimulation reward to the medial forebrain bundle of the rat

Using the quantitative 2-[14C]deoxyglucose autoradiographic method, local rates of glucose utilization were measured in rats during brain stimulation reward to the medial forebrain bundle. Metabolic activation was observed both rostral and caudal to the site of stimulation. These sites included the nucleus accumbens, olfactory tubercle, lateral septum, and ventral tegmental area. In many cases, increases in glucose utilization occurred bilaterally. These data suggest the involvement of both ascending and descending systems in brain stimulation reward. Furthermore, despite the unilateral nature of the electrical stimulation, increases in glucose utilization were observed both ipsilateral and contralateral to the site of stimulation.

2-Deoxy-D-glucose uptake in cultured human muscle cells

Hexose uptake was studied with cultured human muscle cells using 2-deoxy-D-[1-3H]glucose. At a concentration of 0.25 and 4 mM, phosphorylation rather than transport was the rate-limiting step in the uptake of 2-deoxy-D-glucose. This was not due to inhibition of the hexokinase activity by either ATP depletion or 2-deoxyglucose 6-phosphate accumulation. In cellular homogenates, hexokinase showed a lower Km value for glucose as compared to 2-deoxyglucose. Intact cells preferentially phosphorylated glucose instead of 2-deoxyglucose. Therefore, transport instead of phosphorylation may be rate limiting in the uptake of glucose by cultured human muscle cells. These data suggest caution in using 2-deoxyglucose for measuring glucose transport.

Effects of phorbol ester on immunoreactive protein kinase C, insulin binding, and glucose uptake in astrocytic glial and neuronal cells from the brain

Phorbol esters, potent stimulators of protein kinase C (PKC), stimulate [3H]2-deoxy-D-glucose (dGlc) uptake and [125I] insulin binding in cultured glial cells but not neuronal cells from neonatal rat brains. Using an antibody to the alpha and beta forms of PKC we have demonstrated that both neuronal and glial cells contain an immunoactive PKC of Mr approximately 80 kD, although the PKC level in neurons is greater than 4-fold that in glia. The majority of immunoactive PKC (63%) is cytosolic in glial cells although the reverse is true in neuronal cells, in which 88% of the PKC is membrane-bound in the basal state. The most potent phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), stimulates a redistribution of this enzyme in neuronal and glial cells. The TPA-stimulated translocation of PKC from cytosol to membrane precedes TPA's effects on [3H]dGlc uptake and insulin binding in glial cells.

Local cerebral glucose metabolism after global ischemia: treatment by ventriculocisternal perfusion with a fluorocarbon emulsion

The local cerebral metabolic rate for glucose (LCMRg) was measured in cats subjected to global cerebral ischemia (GCI). Control (nonperfused) cats showed decreased LCMRg (P less than 0.01) in the frontal, temporal, parietal, and occipital cortex 9.5 hours after a 10-minute exposure to GCI. Cats perfused ventriculocisternally with oxygenated nutrient solution (ONS) for 8 hours showed significant increases in the LCMRg (p less than 0.05) at 9.5 hours postischemia in the parietal and occipital areas over the levels found in untreated ischemic cats. Supplementing the ONS perfusion medium with fluorocarbon (OFNS) increased the LCMRg (P less than 0.05) in the frontal, as well as the parietal and occipital areas, over that seen in untreated ischemic brains. The increase of LCMRg in three (rather than only two) cortical areas may be a result of the ability of the fluorocarbon in OFNS to deliver greater quantities of oxygen to the brain than ONS without fluorocarbon. Perfusion with OFNS without glucose, or with low (50 mg%) glucose, was more effective than OFNS with high (200 mg%) glucose in restoring LCMRg to normal in all four cortical areas affected by GCI. In five brain areas not affected by GCI, perfusion with OFNS having no glucose significantly increased LCMRg as compared to normal animals. This study demonstrates that OFNS perfused by the ventriculocisternal route can restore toward normal the LCMRg following GCI and that different concentrations of glucose in the perfusing fluid will have variable effects on LCMRg in certain brain areas.

Local glucose utilization changes caused by subarachnoid contrast media in the rabbit

The glucose metabolism effects of six hour exposures to subarachnoid injections of metrizamide, iohexol, iodixanol and control solutions were studied in vivo in 18 rabbits. The brain tissue uptake of intravenously injected 14C labelled deoxyglucose was measured using autoradiographic techniques. Metrizamide and iodixanol caused significant (p less than 0.05) decreases in deoxyglucose uptake in the outer cortical areas where the contrast medium concentrations were highest. Iohexol and the control CSF solution did not cause significant effects. The results appear to indicate that iohexol has less effect on brain tissue glucose metabolism than either metrizamide or the new non-ionic dimer iodixanol.

Mechanism for acute reduction of 1,5-anhydroglucitol in rats treated with diabetogenic agents

The mechanism for acute reduction of plasma 1,5-anhydroglucitol (AG) in experimental diabetic rats was studied. Acute AG decrease was induced not only by diabetogenic agents, such as streptozotocin (STZ) and alloxan, but also by phloridzin, which caused glucosuria but not hyperglycemia. A similar reduction also occurred in hyperglycemia induced by glucose injection. The AG reduction induced by STZ was completely abolished by bilateral nephrectomy or by euglycemia with insulin treatment. The decrease of plasma AG was well correlated with the degree of urinary excretion of AG, which in turn reflected the degree of urinary glucose excretion, irrespective of the kind of agent causing the glucosuria. Under conditions of continuous glucose infusion, AG concentration decreased not only in plasma but also in various tissues and organs. The amount of AG lost was estimated to be almost equal to that excreted into urine during the period of infusion. These observations suggest that the degree of reduction of plasma AG depends simply on the urinary excretion of glucose, and it was assumed that the urinary excretion of 0.5 mg AG corresponds to the urinary excretion of 100 mg glucose during a short period after the onset of glucosuria.

18Fluorodeoxyglucose positron emission tomography studies in presumed Alzheimer cases, including 13 serial scans

Positron emission tomographic (PET) data on local cerebral metabolic rates for glucose (LCMR) are reported for 32 regions of interest (ROI)s in cross-sectional studies on 57 patients with clinically diagnosed Alzheimer's disease (AD) and 20 neurologically normal controls, and in serial studies on 13 of the AD cases, including a familial, young-onset case where the diagnosis has been confirmed at autopsy. Extensive psychological testing was done on all the AD cases. Almost all cortical regions showed a significant decline in LCMR with age in the control subjects. There were the expected cortical metabolic deficits in AD and the serial studies showed a general increase in such deficits over time in 12 of the 13 cases. The regions showing the greatest declines with time in serial studies are the same as those showing the most severe deficiencies in cross-sectional studies. The young-onset case did not show a greater rate of metabolic decline than many of the older cases studied. Results on individual psychological tests tended to correlate with metabolic rates in multiple, rather than single, cortical regions, suggesting intact neuronal networks are required for good performance. The correlations with cortical metabolic activity found were of a sign indicating that the higher the metabolic rates and the better the left:right asymmetry index, the better was the performance.

Use of nonradioactive 2-deoxyglucose to study compartmentation of brain glucose metabolism and rapid regional changes in rate

A method is presented for measuring rapid changes in the rate of glucose phosphorylation in mouse brain with nonradioactive 2-deoxyglucose (DG). After times as short as 1 min after DG injection, the mouse is frozen rapidly, and selected brain regions are analyzed enzymatically for DG, 2-deoxyglucose 6-phosphate (DG6P), and glucose. The rate of glucose phosphorylation can be directly calculated from the rate of change in DG6P, the average levels of DG and glucose, and a constant derived from direct comparison of the rate of changes in glucose and DG6P after decapitation. Experiments with large brain samples provided evidence for a 2% per min loss of DG6P and at least two compartments differing in their rates of glucose metabolism, one rapidly entered by DG with glucose phosphorylation almost double that of average brain and another more slowly entered with a much lower phosphorylation rate. The method is illustrated by changes in phosphorylation within 2 min after injection of a convulsant or an anesthetic and over a 48-min time course with and without anesthesia. The sensitivity of the analytical methods can be amplified as much as desired by enzymatic cycling. Consequently, the method is applicable to very small brain samples. Examples are given for regions with volumes of 5 x 10(-4) microliters, but studies with samples as small as single large cell bodies are feasible.

Dissection of the growth versus metabolic effects of insulin and insulin-like growth factor-I in transfected cells expressing kinase-defective human insulin receptors

We have recently reported that the expression of an in vitro mutated, kinase-defective insulin receptor (A/K1018) leads to cellular insulin resistance when expressed in Rat 1 fibroblasts. That is, despite the presence of normal numbers of activatable native insulin receptors in the host cell, the A/K1018 receptors prevent the normal receptors from phosphorylating endogenous substrates and from signalling insulin action, perhaps by competing for limiting amounts of these substrates. We report here that insulin-like growth factor I-stimulated phosphorylation of two endogenous substrate proteins, pp220 and pp170, is also inhibited in cells expressing A/K1018 receptors. Because insulin-like growth factor I stimulation of glucose uptake is not inhibited in cells with A/K1018 receptors while pp220 and pp170 phosphorylation is inhibited, it is unlikely that either pp220 or pp170 are involved in mediating the stimulation of glucose transport. In contrast, insulin-like growth factor I-mediated stimulation of mitogenesis is inhibited in cells with A/K1018 receptors. Thus, pp170 or pp220 could be involved in mitogenic signalling. We also report that both H2O2 and tetradecanoylphorbolacetate stimulate glucose transport normally in cells with A/K1018 receptors. Phorbol esters also lead to the phosphorylation of both normal and A/K1018 receptors on serine and/or threonine. This argues that phorbol esters or H2O2 bypass the normal proximal steps in signalling insulin action.

Clonidine attenuates increased brain glucose metabolism during naloxone-precipitated morphine withdrawal

The effect of two doses of clonidine on regional cerebral metabolic rates for glucose were measured during morphine withdrawal in rats. In the first study, 0 or 200 micrograms/kg clonidine was administered to rats subjected to naloxone-precipitated morphine withdrawal (naloxone, 0.5 mg/kg, s.c.), and to non-dependent control rats. In a second study of similar design, 0 or 20 micrograms/kg clonidine were administered. Withdrawal signs in rats subjected to naloxone-precipitated morphine withdrawal and receiving 0, 20 or 200 micrograms/kg clonidine were also assessed. Naloxone-precipitated morphine withdrawal stimulated regional cerebral metabolic rates for glucose (59 of 83 regions in study no. 1; 73 of 83 regions in study no. 2). At 200 micrograms/kg, clonidine attenuated this effect (33 of 59 regions). Although 200 micrograms/kg clonidine directly suppressed regional cerebral metabolic rates for glucose in many regions (significant main effect of clonidine), it attenuated the naloxone-precipitated morphine withdrawal effect specifically in the lateral septal nucleus, medial habenula, subiculum and gracile nucleus (significant interactions between clonidine and morphine withdrawal). The 20 micrograms/kg dose of clonidine had no statistically significant effect. In behavioral experiments, both doses of clonidine diminished withdrawal in that there was no diarrhea, fewer wet-dog shakes and less abnormal posturing. However, locomotion, grooming and jumping were increased by clonidine. Most of these effects were statistically significant only with the 200 micrograms/kg dose. The results of these studies show that clonidine reduces morphine withdrawal-induced increases in regional cerebral metabolic rates for glucose in many brain regions, irrespective of the distribution of alpha 2-adrenoceptors. Although clonidine has been thought to ameliorate morphine withdrawal by actions primarily at the locus coeruleus and central amygdala, it may play a major role in other regions as well.

High activity neurons in the reticular formation of the medulla oblongata: a high-resolution autoradiographic 2-deoxyglucose study

Accumulation of radioactivity in the medulla oblongata of the rat was assessed with high resolution autoradiography after injection of [3H]2-deoxyglucose or [14C]2-deoxyglucose. The autoradiographic approach employed allowed analysis at the cellular level. A salient feature of autoradiograms was the presence of foci of very high silver grain density in the reticular formation. These heavily labeled foci were shown to be associated with neurons by combined Acridine Orange staining and autoradiography. The high activity neurons in the ventral lateral medulla were predominantly located in the caudal portion of the paragigantocellular reticular nucleus. In addition, a group of high activity neurons was present in the dorsal reticular formation. The potential involvement of the high activity neurons in cardiovascular and respiratory regulation is discussed. In dry-mount autoradiograms produced after injection of [3H]2-deoxyglucose, certain small cells, presumably glial cells, were observed throughout the brainstem to accumulate radioactivity to a greater extent than the surrounding tissue. High activity neurons and high activity glial cells were observed for 5 min and 45 min survival intervals after intravenous injection of [3H]2-deoxyglucose. The similar appearance of autoradiograms at 5 min and 45 min after injection of [3H]2-deoxyglucose indicates that the utility of a 5-min survival period deserves further evaluation for assessment of functional activity patterns in brain.

Local as well as remote functional and metabolic changes after focal ischemia in cats

Behavior and limb placing ability were analyzed acutely and subacutely (up to 21 days) following unilateral occlusion of the middle cerebral artery (MCA) in cats. Immediately following occlusion, all tested cats started to display a sequence of different behaviors, characteristic for 1) an ipsilateral inhibition of dopaminergic activity in the caudate nucleus (CN); 2) an inhibition of GABAergic activity in the reticular substantia nigra (SNR); 3) a stimulation of GABA receptors in the deeper layers of the colliculus superior (CSDL) (starting-time of these phases: about 4, 12 and 25 min, respectively). The latter behavior was also present subacutely. In addition, unilateral orofacial dyskinetic movements were observed acutely as well as subacutely. Contralateral limb placing was deficient in all cats 60 min postocclusion; it was at least partly restored subacutely. Twenty-one days after the occlusion, [14C]-2-D-deoxyglucose uptake was relatively reduced in the ipsilateral CN (especially in its posterior part), the ipsilateral SNR and the ipsilateral CSDL. The anterior CN appeared to be less affected than the posterior CN. Metabolism was relatively reduced in the sensorimotor cortex only in part of the tested cats. The data show that unilateral MCA occlusion produces consistent functional changes in all structures studied apart from the sensorimotor cortex, viz. the CN, the SNR and the CSDL.

3,5,3'-tri-iodothyronine enhances sugar transport in rat thymocytes by increasing the intrinsic activity of the plasma membrane sugar transporter

We have shown that 3,5,3'-tri-iodothyronine (T3) produces a prompt increase in sugar transport in rat thymocytes by increasing the maximal velocity without changing the Michaelis-Menten constant of the plasma membrane sugar transport system. To elucidate further the mechanism of this effect, we have now assessed the influence of T3 on the number and affinity of sugar transporters in thymocytes, measured as the sugar (2-deoxyglucose; dGlc)-displaceable binding of cytochalasin B. Cytochalasin B inhibited in a dose-related manner the uptake of dGlc by rat thymocytes with inhibition constant values of 0.19 and 0.22 mumol/l in the presence and absence of T3 respectively. Binding of cytochalasin B by the sugar-displaceable sites was rapid and saturable, demonstrating a single class of sites having an apparent dissociation constant of 0.33 +/- 0.02 (S.D.) mumol/l and maximal binding capacity of 3.73 +/- 0.48 pmol/20 x 10(6) cells (11.2 +/- 1.4 x 10(4) sites/thymocyte). In the rat thymocyte, sugar transporters were found to be located in two major subcellular pools, the plasma membrane and microsomes, the latter being about twice the size of the former. In these subcellular compartments, as well as in the intact cell, binding of [3H]cytochalasin B by the sugar-displaceable sites constituted about 40% of total cytochalasin B binding. 3,5,3'-Tri-iodothyronine in concentrations that stimulated uptake of dGlc by thymocytes had no effect on [3H]cytochalasin B binding (total and sugar-displaceable) in the intact cell and in the plasma membrane and microsomal compartments, nor did it influence the affinity and number of sugar transporters.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cytochalasin B on the uptake of ascorbic acid and glucose by 3T3 fibroblasts: mechanism of impaired ascorbate transport in diabetes

Hyperglycemia and/or hypoinsulinemia have been found to inhibit L-ascorbic acid cellular transport. The resultant decrease in intracellular ascorbic acid may de-inhibit aryl sulfatase B and increase degradation of sulfated glycosaminoglycans (sGAG). This could lead to a degeneration of the extracellular matrix and result in increased intimal permeability, the initiating event in atherosclerosis. The present studies show that the glucose transport inhibitor cytochalasin B blocked the uptake of 3H-2-deoxy-D-glucose (2.5 mg%) by mouse 3T3 fibroblasts. Cytochalasin B also blocked the uptake of 14C-L-ascorbic acid (1.25 mg%). The results of these studies further support the hypothesis that glucose and ascorbate share a common transport system. This may have important implications concerning the vascular pathology associated with diabetes mellitus.