Adiponutrin is a recently identified gene of unknown function that is expressed exclusively in adipose tissues. To provide information about its physiological regulation and possible function, the effect of meal-feeding rats on the expression of adiponutrin mRNA in white adipose tissue was studied. A high-sucrose meal increased adiponutrin mRNA levels by at least 5-fold within 3 h. Post-meal levels returned to pre-meal levels with a half-life of about 5 h. The induction was prevented by injection of actinomycin-D prior to the meal. This pattern of expression was very similar to that seen for leptin mRNA. There were only minimal, or no, effects on acrp30/adiponectin, resistin, adipsin, or stearoyl-CoA desaturase 1. Adiponutrin appears more like leptin with respect to its acute regulation by meal-feeding than to any of the other adipokines or to enzymes directly involved in lipogenesis. This suggests that adiponutrin could be involved in overall energy homeostasis, as is leptin.

States characterised by elevated plasma fatty acid levels are accompanied by increased UCP2 expression but the physiological regulation of UCP2 expression in white adipose tissue is not fully understood. We used 3T3-L1 preadipocytes to determine whether various dietary fatty acids (20:5, 18:3, 18:2, 18:1, 18:0) directly regulate UCP2 expression. Physiological concentrations of each class of polyunsaturated fatty acid and the monounsaturated fatty acid dramatically up-regulated UCP2 mRNA levels 5- to 8-fold, but the saturated fatty acid was not so effective (1.5-fold). The up-regulation occurred in a time- and dose-dependent manner, was evident by 4 h and maximum between 18 and 24 h, and was prevented by actinomycin D. Synthetic ligands selective for each PPAR isoform did not induce UCP2 expression, which suggests that fatty acids might not be acting solely via PPAR transcription factors. In conclusion, dietary unsaturated fatty acids may be physiological signals to alter energy balance by direct induction of UCP2.

Genetically separate lines of Coopworth sheep have been bred by selecting for (fat genotype) or against (lean genotype) backfat depth. Typically, the total fat content, adjusted for carcass weight, is 21.2 and 29.3% for the lean and fat lines, respectively. As a homologue of the obese gene, which shows altered expression in several forms of obesity, is also expressed in sheep, it was decided to determine whether the obese gene was differentially expressed in each line of sheep. The relative level of expression of obese mRNA was approximately twofold higher in the fat line compared with the lean line in back, omental and perirenal fat depots of ram lambs fed ad libitum or fasted for 48 h. This elevation in the fat line is most likely a secondary consequence of obesity rather than a cause. Fasting for 48 h decreased obese mRNA levels by 8.9-, 8.5-, and 4.2-fold in back, omental and perirenal fat, respectively, in the lean line, and by 8.3-, 5.7-, and 3.5-fold in back, omental and perirenal fat, respectively, in the fat line. The lean and fat lines of sheep, therefore, responded in a similar way to fasting.

Meal-feeding caused a rapid and specific induction of ob mRNA levels in rat adipose tissue. A high-carbohydrate meal caused a mean 5-fold increase in ob mRNA within 3 h after feeding and almost reached the levels of expression seen in rats fed ad lib. After the meal ob mRNA declined with a half-life of less than 2 h. The increase in ob mRNA in response to the meal was prevented by prior injection of actinomycin-D, an inhibitor of transcription. None of the mRNAs for other genes involved in lipid metabolism (lipoprotein lipase, fatty acid synthase, malic enzyme, hormone-sensitive lipase, S14 or adipsin) showed any significant difference between pre-meal and post-meal levels.

1.1. Uncoupling protein (UCP) was purified from perirenal adipose tissue of 2-day-old lambs by a procedure involving Triton solubilization and hydroxyapatite treatment. It has a apparent Mr of 34,000.2.2. Rabbit anti-sheep UCP and rabbit anti-rat UCP each cross-reacted with both rat and sheep UCP in Western blots, indicating that the major antigenic determinants of the sheep UCP and rat UCP are similar.3.3. In Western blots, the anti-sheep UCP showed tissue specifity by detecting a band corresponding to UCP only in brown adipose tissue, but not in heart or liver homogenates.4.4. The Western blotting procedure was used to analyse sheep tissues. UCP was detected in samples of perirenal, omental, back and lymph node fat from 2-day-lambs, but not in heart, liver, muscle or kidney samples.5.5. UCP was not detected in any tissue samples from 34-day-old or 7-month-old lambs.6.6. Comparison of the amount of UCP in perirenal fat of 2-day-old lambs from lean, fat and control selection lines, using the Western blotting procedure, showed no apparent difference.

Lactating rats have been fed either a protein-restricted diet (10 vs. 20% casein in the control diet) or the control diet at 80, 60 and 40% of the voluntary intake for 7 d from d 7 of lactation. Food consumption, changes in maternal live weight, litter live weight gain and the mass of several maternal tissues were determined together with the activity of several mammary and liver enzymes, including 10 that are essential for fatty acid and complex lipid synthesis. Milk production was estimated from the litter weight gain and litter weight. Lactating rats fed the 20% protein diet ad libitum consumed three times that of nonlactating rats; their liver and kidney masses were significantly higher and their adipose mass was lower. The livers of the lactating rats were fatty, containing 118 mg lipid/g compared with 42 mg/g for the nonlactating rats. Lactating rats fed either the protein-restricted diet or the control diet at 40 and 60% of the ad libitum intake of the control diet had lower mammary, liver and kidney masses than rats consuming the control diet ad libitum. Both protein and food restriction led to lower rates of milk production than those of ad libitum-fed control rats as evidenced by the decrease in litter live weight gains. The concentrations of total lipid, total protein and lactose in milk were not affected by these dietary treatments. The concentration of alpha-lactalbumin in milk of rats fed the low protein diet was, however, lower than that in the milk of all rats receiving the control diet, irrespective of intake. Consumption of the restricted diets resulted in only small changes in specific activities (mu/mg protein) of 15 mammary enzymes. In the livers, lactation led to higher specific activities of all four soluble lipogenic enzymes examined but did not affect the particulate enzymes involved in complex lipid synthesis. The dietary restrictions resulted in lower specific activities of the soluble enzymes compared with those of the lactating rats consuming the control diet ad libitum without affecting the particulate enzymes. Total activities of these enzymes were, however, lower than those for the control rats as a result of the smaller liver mass in the rats receiving the restricted diets.

Lactating rats consuming a control diet (20% casein) ad libitum and kept on a 12-h light-dark cycle produced milk during the dark phase at a rate 50% greater than that during the light period. Diurnal variations in the food consumptions of these animals, maternal live weights and litter weight gains were also observed. This diurnal variation with respect to milk production and food consumption appears to be abolished by feeding a low protein (10% casein) diet. However, the variation was amplified when the amount of the control diet was restricted to 25 g/d and made available at the middark period; this was probably related to the meal-feeding behavior of these rats because they consumed all their food within 6 h after it was made available. The rates of fatty acid synthesis in the mammary glands, livers and adipose tissue measured in vivo from [3H]H2O incorporation also varied diurnally with maximal rates at the middark period. Similar rates were obtained for the rats receiving restricted amounts of the control diet measured in the feeding period, whereas the values for the rats fed the low protein diet in the dark period tended to be significantly lower. The milk fatty acids were also analyzed, and whereas no diurnal differences were detected in the samples taken from control rats, a marked reduction in the proportion of the medium-chain acids was observed in the samples from rats receiving restricted amounts of the control diet taken immediately before the normal feeding period.

1.1. In tumour-bearing rats as the tumour grew the level of insulin declined to 15 μU/ml, compared to normal basal plasma insulin level of 46 μU/ml.2.2. The level of glucagon increased from 262 to 1110 pg/ml as the tumour grew.3.3. There was an inverse relationship between the molar insulin/glucagon ratio and the tumour/body wt ratio.4.4. The glucose tolerance of tumour-bearing rats was apparently normal. The rate of disappearance of glucose in tumour-bearing rats was within the normal range, but the insulin response to the glucose load was significantly impaired.5.5. Tolbutamide did not elicit any greater insulin response than glucose.

The biochemical basis for the observed depletion of adipose tissue in C57BL mice bearing a transplantable nonmetastasizing preputial gland tumor, ESR-586, has been investigated. The results have shown that there are a number of significant changes in both deposition and mobilization of lipid as the tumor grows. The first change, before the tumor reached 2 g, was a decline in the activity of adipose tissue lipoprotein lipase to levels normally found in starved animals. This was accompanied by a slight increase in lipoprotein lipase activity in heart and appearance of substantial activity in large tumors. Together, these would result in impaired uptake of exogenous fatty acids by adipose tissue, and dietary lipid would be directed away from storage. This was followed by a marked decline in endogenous lipid synthesis in adipose tissue which commenced when the tumor weighed between 2 and 3 g, as measured in vivo by the incorporation of radioactivity into lipid from tritiated water. The basal rate of lipolysis was enhanced 2-fold in epididymal fat pads from mice bearing tumors that weighed between 2 and 4 g, although there was no difference in the epinephrine-stimulated activity.

The importance of gluconeogenesis for the maintenance of normoglycemia in rats bearing a transplantable sarcoma has been studied. Blood glucose concentrations remained within the normal fed range until the tumor/body weight ratio was greater than 0.15. In rats with tumor/body weight ratios between 0.31 and 0.50, the blood glucose was significantly lower than normal but was similar to blood glucose levels measured in normal rats fasted overnight. A sharp decline in the liver glycogen content, from 200 to 50 µmol glucose per g wet weight occurred at a stage when the tumor/body weight ratios were between 0.20 and 0.25. No depletion of the muscle glycogen content occurred until the tumor/body weight ratios were greater than 0.40. The degree of hypoglycemia after the administration of 3-mercaptopicolinate, an inhibitor of gluconeogenesis, became successively more pronounced as the tumor/body weight ratio increased, indicating that gluconeogenesis becomes increasingly important for the maintenance of normoglycemia. This was confirmed by an observed 10-fold increase in the incorporation of label into glucose from [14C]lactate and [14C]alanine during tumor growth. The rates of gluconeogenesis from lactate were approximately 30 times greater than the estimated rates of gluconeogenesis from endogenous alanine. Corresponding to this increase in gluconeogenesis during tumor growth, there was an increase in the percentage of glucose carbon recycled via the Cori cycle, from 9% in rats bearing a small tumor to 52% in rats bearing a large tumor. The actual amount of glucose recycled showed a pattern of increase similar to that of the rates measured from [14C]lactate, and the rates of gluconeogenesis calculated using these two methods were in good agreement. Rates of gluconeogenesis in isolated perfused livers from fed and starved normal rats were in agreement with the estimated rates in vivo . However, the in vitro rates in livers from tumor-bearing rats were approximately 3 times lower than the estimated rates in vivo , even at lactate concentrations that were higher than expected physiological concentrations. The activities of key gluconeogenic enzymes in livers of tumor-bearing rats were similar to those in the livers of overnight-starved rats but were not sufficient to fully explain the high rates of gluconeogenesis in vivo .