Deuterium oxide stimulates glucose metabolism and inhibits lipolysis in rat epididymal adipose tissue.

Incubation of segments of rat epididymal adipose tissue in media prepared with deuterium oxide results in increased glucose oxidation, increased lipogenesis, accelerated sugar transport and decreased lipolysis in response to epinephrine or theophylline. In view of the well documented action of heavy water to “stabilize” cytoplasmic microtubules, the foregoing observations are in support of a link between cytoplasmic microtubules and metabolic process in adipose tissue.     

Amino-acid metabolism enzyme activities in rat white adipose tissue

The activities of alanine-, aspartate- and branched-chain amino-acid transaminases, glutamine synthetase, glutamate dehydrogenase and adenylate deaminase in white adipose tissue of adult male rats have been determined in animals submitted to 12-h cold exposure (4 degrees C) or to 24-h food deprivation. Starvation resulted in small changes in glutamate dehydrogenase and alanine transaminase when expressed per unit of protein weight, inducing an increase in branched-chain amino-acid transaminase and glutamine synthetase. Cold exposure showed the same effects as starvation with respect to glutamate dehydrogenase and alanine transaminase, but induced increases in glutamine synthetase and aspartate transaminase. It is concluded that starvation increases the handling of some amino acids by white adipose tissue and the detoxification of the ammonia thus evolved. The changes observed suggest a different pattern of amino-acid metabolism enzyme changes with either cold or starvation.     

Light modulates glucose metabolism by a retina-hypothalamus-brown adipose tissue axis

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Insulin insensitivity and altered glucose utilization in cultured rat adipose tissue

Glucose utilization was studied in isolated fat cells prepared from rat adipose tissue which had been cultured for 18 hr in TC 199 medium. When 1% bovine serum albumin (BSA) was in the culture medium, basal rates of (14)CO(2) and [(14)C]triglyceride production from [1-(14)C]glucose were markedly depressed and there was no effect of insulin. With 4% BSA, basal (14)CO(2) production was the same as in cells prepared from fresh tissue and basal triglyceride production was greatly increased. Insulin effect on these cells was minimal. One-minute uptake of [(14)C]2-deoxyglucose was stimulated by 800-1000% in fresh cells and 300-500% in cells cultured with either 1% or 4% BSA. Oxidation of [U-(14)C]glucose showed a much smaller impairment in cultured cells than for [1-(14)C]glucose, suggesting that the pentose phosphate shunt was more severely impaired than glycolysis. Glyceride-glycerol production was increased in cultured cells relative to preculture (fresh) cells. There was no effect of insulin in the culture medium in any of these systems. Rates of free fatty acid and glycerol release were markedly increased in cultured cells, especially when insulin was present in the culture medium. The acute antilipolytic effect of insulin was retained, so that insulin in the test incubation decreased lipolysis by 40-80%. Nevertheless, cell-associated fatty acids were increased in cultured cells and FFA/albumin ratios in the medium often reached potentially toxic levels. The reduction in pentose phosphate shunt activity, lipogenesis, and insulin effect resembles other models of insulin insensitivity. The impaired metabolism is probably due to an intracellular defect. A possible toxic role of either intracellular or extracellular fatty acids cannot be excluded. This system should be a useful model in which to study the cellular mechanisms of insulin insensitivity in adipocytes.-Bernstein, R. S. Insulin insensitivity and altered glucose utilization in cultured rat adipose tissue.     

The effect of glucose, insulin and adrenaline on glycerol metabolism in vitro in rat adipose tissue.

The uptake and utilization of [1-14C]glycerol was determined in pieces of rat epididymal fat-pads incubated in Krebs--Ringer bicarbonate buffer containing albumin. Insulin (200 muunits/ml), adrenaline (epinephrine; 0.5 mug/ml) and glucose (0, 5, 15 and 20 mM) were added to the medium. Changes in the specific radioactivity of the tracer during the incubation were taken into account in calculating the rate of glycerol utilization. Adrenaline decreased glycerol uptake, whereas insulin plus adrenaline increased it. The rate of incorporation of glycerol into glycerides was decreased by adrenaline and insulin, singly or together. Insulin increased the rate of formation of CO2 and fatty acids from glycerol. The formation of CO2 and fatty acids was further enhanced by insulin plus adrenaline. The decrease in glycerol uptake induced by adrenaline, the decrease in incorporation of glycerol into glycerides induced by insulin and insulin plus adrenaline and the synthesis of fatty acids were dependent on the presence of glucose in the medium. Thus insulin and adrenaline act on glycerol utilization in adipose tissue and some of their effects are mediated by action on glucose metabolism, but others are independent of this.     

Carnitine and brown adipose tissue metabolism in the rat during development

1. The content of carnitine, acylcarnitine and total acid soluble carnitine in brown adipose tissue of rats increases rapidly after birth, attaining a peak on about day 10 and then decreases. Similar changes with age were found for carnitine acetyltransferase activity in mitochondria from brown adipose tissue and heart. The activity of this enzyme in brain and in liver is much smaller, but also increases postnatally. 2. The activity of carnitine palmitoyltransferase in brown adipose tissue, however, decreases after birth then increases later in life. 3. Exposure of 18-day-old rats to the cold for 20 days leads to an increase in carnitine content in brown adipose tissue and raises the activity of carnitine acetyltransferase. The activity of carnitine palmitoyltransferase is not affected by cold adaptation.     

Co-ordination of hepatic and adipose tissue lipid metabolism after oral glucose.

The integration of lipid metabolism in the splanchnic bed and in subcutaneous adipose tissue before and after ingestion of a 75 g glucose load was studied by Fick's principle in seven healthy subjects. Six additional subjects were studied during a hyperinsulinemic euglycemic clamp. Release of non-esterified fatty acids (NEFA) from adipose tissue and splanchnic NEFA extraction followed a similar time-course after oral glucose, and there was a highly significant relationship between adipose tissue NEFA release and splanchnic NEFA uptake. There was no immediate inhibition of splanchnic very low density lipoprotein (VLDL)-triacylglycerol (TAG) output when plasma insulin levels increased after glucose. Adipose tissue extraction of VLDL-TAG tended to vary in time in a manner similar to splanchnic VLDL-TAG output and the two were significantly related. The area-under-curves (AUC) for splanchnic extraction of NEFA was significantly lower than that for output of VLDL, implying depletion of hepatic TAG stores during the experiment. In the hyperinsulinemic clamp experiments, there was on average suppression of splanchnic VLDL-TAG output although between-person variability was marked. This suppression could be explained by a very low supply of NEFA during the clamp.We conclude that there is an integrated pattern of metabolism in splanchnic and adipose tissues in the postabsorptive and post-glucose states. Flux of NEFA from adipose tissue drives splanchnic NEFA uptake. Splanchnic VLDL-TAG secretion appears to be regulated by a number of factors and in turn controls TAG extraction in adipose tissue. Insulin does not seem to play a key role in the acute regulation of hepatic VLDL metabolism under these particular conditions in vivo.     

The effects of duodenal glucose and dextrin infusion on adipose tissue metabolism in sheep

Three groups of 3 sheep were penned individually and provided with pelleted dried grass. In addition two of the groups received either dextrin or glucose via duodenal cannulae. The rate of in vitro lipogenesis, from acetate of glucose, in subcutaneous adipose tissue was significantly increased in the carbohydrate-infused sheep. The increase in lipogenesis in response to glucose infusion was much greater than that to dextrin infusion. The changes in lipogenesis induced by dextrin or glucose infusion were reflected in the specific activities of the various lipogenic enzymes examined. These results are discussed in relation to the capacity of the sheep small intestine to hydrolyse alpha-linked glucose polymer.