Pinealectomy impairs adipose tissue adaptability to exercise in rats

This study investigated the effects of pinealectomy and exercise training on rat adipose tissue metabolism. Pinealectomized (PINX) and sham-operated (CONTROL) adult male Wistar rats were subdivided into four subgroups, including PINX untrained, PINX trained, CONTROL untrained and CONTROL trained. At the end of the training period (8 wk), the rats were killed and peri-epididymal adipocytes were isolated for in vitro insulin-stimulated glucose uptake, conversion of D-[U-14C]-glucose, l-[U-14C]-lactate, [2-14C]-acetate and [1-14C]-palmitate into 14CO2, and insulin binding. Pinealectomy resulted in a significantly decreased insulin-stimulated glucose uptake in adipocytes without affecting insulin-binding capacity. However, in intact control animals only, training promoted a higher baseline glucose uptake in adipocytes. Training influenced the adipocyte ability to oxidize the different substrates: the rates of glucose and palmitate oxidation increased while the rates of lactate and acetate diminished. Nevertheless, these effects of exercise training were not seen in pinealectomized rats. Additionally, an increase in palmitate oxidation was observed in sedentary pinealectomized animals. In conclusion, these data show that the pineal gland alters the patterns of substrate utilization by the adipocyte, in such a way that its absence disrupts the ability to adapt to the metabolic demands evoked by exercise training in rats.     

Pinealectomy reduces hepatic and muscular glycogen content and attenuates aerobic power adaptability in trained rats

The current study emphasizes the crucial role of the pineal gland on the effects of chronic training in different tissues focusing on carbohydrate metabolism. We investigated the maximal oxygen uptake (aerobic power), muscle and liver glycogen content, and also the enzymes involved in the carbohydrate metabolism of rat adipose tissue. Pinealectomized and sham-operated adult male Wistar rats were distributed into four groups: pinealectomized (PINX) untrained, pinealectomized trained, control untrained and control trained. The maximal oxygen uptake capability was assayed before and after the training protocol by indirect open circuit calorimetry. The rats were killed after 8 wk of training. Blood samples were collected for glucose and insulin determinations. The glycogen content was assayed in the liver and muscle. Maximal activities of epididymal adipose tissue enzymes (hexokinase, pyruvate kinase, lactate dehydrogenase, citrate synthase and malic enzyme) as well as adipocyte size were determined. The exercise training in control animals promoted an increase in the aerobic power and in liver glycogen content but caused a reduction in the malic enzyme activity in adipose tissue. However, PINX trained animals, in contrast to trained controls, showed a decrease in the aerobic power and in liver and muscle glycogen content, as well as an increase in the activity of the adipocyte enzymes involved in carbohydrate metabolism. In conclusion, these data show that the pineal gland integrity is necessary for the homeostatic control of energy metabolism among adipose, muscle and hepatic tissues. The pinealectomized animals showed alterations in adaptive responses of the maximal oxygen uptake to training. Therefore, the pineal gland must be considered an influential participant in the complex adaptation to exercise and is involved in the improvement of endurance capacity.     

Melatonin and the circadian entrainment of metabolic and hormonal activities in primary isolated adipocytes

The aim of this work was to investigate the effect of the in vitro circadian-like exposure to melatonin [in the presence or absence of insulin (Ins)] on the metabolism and clock gene expression in adipocytes. To simulate the cyclic characteristics of the daily melatonin profile, isolated rat adipocytes were exposed in a circadian-like pattern to melatonin added to the incubating medium for 12 hr (mimicking the night), followed by an equal period without melatonin (mimicking the day) combined or not with Ins. This intermittent incubation was interrupted when four and a half 24-hr cycles were fulfilled. At the end, either during the induced night (melatonin present) or the induced day (melatonin absent), the rates of lipolysis and D-[U-(14)C]-glucose incorporation into lipids were estimated, in addition to the determination of lipogenic [glucose-6-phosphate dehydrogenase and fatty acid synthase (FAS)] and lipolytic (hormone sensitive lipase) enzymes and clock gene (Bmal-1b, Clock, Per-1 and Cry-1) mRNA expression. The leptin release was also measured. During the induced night, the following effects were observed: an increase in the mRNA expression of Clock, Per-1 and FAS; a rise in lipogenic response and leptin secretion; and a decrease in the lipolytic activity. The intermittent exposure of adipocytes to melatonin temporally and rhythmically synchronized their metabolic and hormonal function in a circadian fashion, mimicking what is observed in vivo in animals during the daily light-dark cycle. Therefore, this work helps to clarify the physiological relevance of the circadian pattern of melatonin secretion and its interactions with Ins, contributing to a better understanding of the adipocyte biology.     

Brown adipose tissue metabolism in hypothalamic-obese rats

Studies were performed to evaluate the metabolic changes of brown adipose tissue (BAT) in rats with hypothalamic obesity (VMNL). In vitro 14C-palmitate oxidation and incorporation into triglycerides were similar in VMNL and control rats. However, protein and fatty acid content and incorporation of 14C-palmitate into phospholipid were significantly less in both hyperphagic and normophagic VMNL rats. In order to assess in vivo BAT lipogenesis, rats were injected with 3H2O. Plasma H2O incorporation into BAT lipids was significantly greater in VMNL rats. Likewise, BAT lipid content was higher in obese rats. In another experiment BAT was incubated with U-14C-glucose to evaluate glucose utilization by BAT. 14C-glucose was oxidized and incorporated into both lipids and glycogen more rapidly by obese than by normal rat BAT. Glycogen content was greater in VMNL rats. Tissues were also incubated with 1-14C-pyruvate and 2-14C pyruvate. Pyruvate incorporation into glyceride glycerol and oxidation of 2-14C pyruvate through the Krebs cycle were similar in both obese and control rats. However, the incorporation of pyruvate into glyceride fatty acids was increased in VMNL rats. The results indicate that both fatty acid and lipid synthesis are increased in BAT of obese rats whereas lactate production is decreased and Krebs cycle activity is normal. Some of these changes appear to be independent of the level of food intake.     

Metabolic adaptations in the adipose tissue that underlie the body fat mass gain in middle-aged rats

Little is known about adipocyte metabolism during aging process and whether this can influence body fat redistribution and systemic metabolism. To better understand this phenomenon, two animal groups were studied: young—14 weeks old—and middle-aged—16 months old. Periepididymal (PE) and subcutaneous (SC) adipocytes were isolated and tested for their capacities to perform lipolysis and to incorporate D-[U-¹⁴C]-glucose, D-[U-¹⁴C]-lactate, and [9,10(n)-³H]-oleic acid into lipids. Additionally, the morphometric characteristics of the adipose tissues, glucose tolerance tests, and biochemical determinations (fasting glucose, triglycerides, insulin) in blood were performed. The middle-aged rats showed adipocyte (PE and SC) hypertrophy and glucose intolerance, although there were no significant changes in fasting glycemia and insulin. Furthermore, PE tissue revealed elevated rates (+50 %) of lipolysis during beta-adrenergic-stimulation. There was also an increase (+62 %) in the baseline rate of glucose incorporation into lipids in the PE adipocytes, while these PE cells were almost unresponsive to insulin stimulation and less responsive (a 34 % decrease) in the SC tissue. Also, the capacity of oleic acid esterification was elevated in baseline state and with insulin stimulus in the PE tissue (+90 and 82 %, respectively). Likewise, spontaneous incorporation of lactate into lipids in the PE and SC tissues was higher (+100 and 11 %, respectively) in middle-aged rats. We concluded that adipocyte metabolism of middle-aged animals seems to strongly favor cellular hypertrophy and increased adipose mass, particularly the intra-abdominal PE fat pad. In discussion, we have interpreted all these results as a metabolic adaptations to avoid the spreading of fat that can reach tissues beyond adipose protecting them against ectopic fat accumulation. However, these adaptations may have the potential to lead to future metabolic dysfunctions seen in the senescence.     

Effects of insulin on the utilization of 14C-glycerol and 14C-glucose in hepatectomized nephrectomized rats

Insulin (i.v.) administration to functionally hepatectomized-nephrectomized rats did not alter circulating levels of glycerol and only slightly affected plasma radioactivity when animals received (U-14C)-glycerol, whereas after (U-14C)-glucose administration insulin enhanced hypoglycemia and greatly accelerated the rate of radioactivity loss from plasma. At 15 min after i.v. injection of (U-14C)-glycerol, radioactivity in total lipids was reduced in heart and lungs by insulin administration and enhanced in carcass and brown adipose tissue. These effects involved the 14C-glyceride glycerol fraction in the case of heart and 14C-fatty acids in carcass and adipose tissue. When (U-14C)-glucose was administered, insulin enhanced the appearance of 14C-water-soluble material in heart and carcass and 14C-total lipids in heart, carcass, and both brown and white adipose tissue. The effect in heart corresponded mainly to the 14C-glyceride glycerol fraction whereas it corresponded to the 14C-fatty acids in the other tissues. Therefore, insulin effects on glycerol metabolism substantially differ from those on glucose. Opposite effects on heart and lung glycerol utilization as compared to those in carcass and brown adipose tissue may account for the difficulties in observing changes in plasma glycerol levels after insulin treatment.     

Family history of diabetes is associated with enhanced adipose lipolysis: Evidence for the implication of epigenetic factors

Aims

Type 2 diabetes is associated with insulin resistance, adipose hypertrophy and increased lipolysis. The heritability of these traits has been determined by associating them with a family history of diabetes.

Effect of protein malnutrition on glycoprotein, protein and lipid synthesis in the rat cerebellum during the period of brain growth spurt

Female Wistar rats were fed a normal-protein diet (25% casein) or a low-protein diet (8% casein) during pregnancy and lactation. The two diets were isocaloric and contained appropriate amounts of mineral salts and vitamins. Pups from dams submitted to the low-protein diet had a lower body weight than normally fed controls as early as on the day of birth, but a difference in cerebellar weight between the two groups was observed only on the 15th postnatal day. Malnutrition had no effect on cerebellar protein concentration, which increased with age in both groups. The cerebellar DNA concentration was higher at 7 and 15 days of age in normally fed rats than in malnourished rats, whereas at 21 days of age it was higher in the malnourished animals. [U-14C]Leucine and [2-3H]mannose incorporation into proteins and lipid synthesis from acetyl coenzyme A (CoA) derived from [U-14C]leucine markedly decreased with age in the cerebellum of rats fed both diets. [2-3H]Mannose incorporation into cerebellar glycoproteins was greater in malnourished rats during the period of brain growth spurt than in normally fed rats at all ages studied. Prenatal and postnatal protein malnutrition had no effect on [U-14C]leucine incorporation into cerebellar proteins or on cerebellar lipid synthesis from acetyl-CoA derived from [U-14C]leucine during the period of brain growth spurt.     

Genetic obesity in rats. II. The effect of food restriction on the metabolism of adipose tissue

The metabolism of adipose tissue from genetically obese rats (Fatty) and lean animals was studied in two experiments. In the first experiment, food intake was regulated at three levels in Fatty rats. One group ate ad lib., a second group was pair fed to lean controls, and the third group received two-thirds of the food eaten by the lean rats. Serum insulin was reduced by restricting food intake. Fat cells were largest in the ad lib.-fed Fatties and smallest in the lean rats. Lipolysis, as measured by glycerol release, was comparable in lean and Fatty rats. Several lipolytic drugs were as effective in fat from the obese as the lean animals. Metabolism of ¹⁴C-glucose with or without insulin was reduced in the tissue from Fatty rats and was not corrected by restricting food intake. In the second experiment, lipolysis and lipogenesis were studied by serial biopsies during starvation-induced weight loss. Rats were allowed to eat for 3 days before each biopsy. Reduction of fat cells to the same size as normals did not restore lipogenesis or lipolysis to normal. Reesterification of fatty acids remained high in all experiments with tissues from Fatty rats.     

Effect of okadaic acid in rat adipocytes: differential stimulation of glucose and lipid metabolism and induction of refractoriness to insulin and vanadate.

The insulin-like effects of okadaic acid (OKA) in rat adipocytes were further characterized. Okadaic acid did not alter insulin receptor function. This includes undisturbed insulin binding and receptor-mediated ligand internalization in OKA-treated cells. Also, the tyrosine kinase activity of the insulin receptor was not modified in a cell-free system. The stimulating effects of OKA were significantly increased by preincubating (40 min) the cells at 37 C. At lower temperatures (i.e. 26-30 C), OKA did not mimic insulin. Maximal stimulation of lipogenesis occurred at 0.5 microM and then declined at higher concentrations. The insulin-like effects of OKA on lipogenesis did not persist after removal of the agent by washing at 37 C. Okadaic acid maximally stimulated the incorporation of [1-14C]glucose into lipids and the oxidation of [6-14C]glucose into 14CO2, but unlike insulin, it had little if any effect of oxidizing [1-14C]glucose to 14CO2 or incorporating [6-14C]glucose into lipids. Okadaic acid was equivalent to insulin in stimulating 3-O-methyl-glucose uptake. Since the insulin-like effects of OKA did not persist after preincubation and washing, the effects of insulin in OKA-treated cells could be evaluated. The adipocytes were found to be fully refractory to the modulating actions of insulin. Thus, insulin did not stimulate glucose transport, its oxidation, or its incorporation into lipids, and failed to reverse lipolysis. Unresponsiveness was fully developed after 40-min preincubation at 37 C with 3 microM OKA and was half-maximal at 0.13 microM OKA. It persisted at least over a period of 150 min. The effect of OKA was restricted to the stimulating actions of insulin and vanadate. Basal activities were not altered, nor was the ability of the desensitized cells to respond to isoproterenol. The lack of an insulin-like effect of OKA on some metabolic pathways enabled us to demonstrate that OKA (0.25 microM) also rendered adipocytes fully unresponsive to insulin in the continuous presence of the agent. Western blotting of the 40,000 x g pellets with antibodies to phosphotyrosine revealed the appearance of a protein with an apparent mol wt of 43,000 in OKA-desensitized cells. In summary, OKA mimics some of insulin bioeffects, but concomitantly renders the cells tolerant to the modulating action of the hormone itself.     

Effects of cafeteria diet feeding on beta3-adrenoceptor expression and lipolytic activity in white adipose tissue of male and female rats

OBJECTIVE: To investigate the effects of short term (15 days) cafeteria diet feeding on the expression of beta3-AR in vivo and its association with lipolytic stimulation induced by beta3-AR agonist CGP12177A in isolated white adipocytes. ANIMALS: Six female and 6 male Wistar rats (at 4 weeks of age) were fed on a cafeteria diet plus standard diet for 15 days. The remaining 12 age- and sex-matched rats always received standard diet only. MEASUREMENTS: White gonadal adipose tissue was isolated and used for the determination of beta3-AR and leptin expression, and for in vitro studies of lipolytic activity. RESULTS: Control male rats had higher levels of both beta3-AR and leptin mRNA in white adipose tissue than their female counterparts. Both male and female rats up-regulated the levels of both beta3-AR and leptin mRNA in response to 15 day cafeteria diet feeding. Noradrenaline- and isoprenaline-induced lipolysis were significantly increased in fat cells from control females compared to their male counterparts. CGP12177A stimulation resulted in significantly higher glycerol release in fat cells from cafeteria diet-fed female rats, whereas there were no differences due to dietary treatment in male rats. The maximal lipolytic response of forskolin (stimulating adenylyl cyclase) and dibutyryl cyclic AMP (cyclic AMP analogous) was not affected by sex or cafeteria diet feeding. CONCLUSION: Cafeteria diet feeding brings about higher excess body weight and impaired adipose tissue lipolytic activity in female rats compared to male rats. Thus, the higher levels of beta3-AR mRNA induced by cafeteria feeding are not indicative per se of an increase of the lipolytic response of the adipocytes. The changes seen in other adrenoceptor subtypes (beta1 and beta2) may be more determinant of the overall lipolytic response of adipocytes.     

Effects of gastric inhibitory polypeptide on glucose and lipid metabolism of isolated rat adipocytes

The effects of gastric inhibitory polypeptide (GIP) on glucose and lipid metabolism of isolated rat adipocytes were investigated. In a dose-dependent manner, GIP stimulated 2-deoxy-glucose uptake increasing the glucose transport rate by up to 140% at a concentration of 10(-7) mol/l. GIP also stimulated the conversion of 14C-glucose into extractable lipids by up to 81% at 10(-7) mol/l. Insulin-stimulated 2-deoxy-glucose uptake and lipogenesis were additively enhanced by the presence of GIP. Insulin binding was slightly but not significantly increased by addition of GIP, mainly due to an increase in receptor affinity. GIP had a weak lipolytic activity, but lipolysis elicited by glucagon or isoproterenol was potently reduced. In conclusion, independent of its insulinotropic action, GIP showed a insulin-like activity on glucose metabolism and lipolysis in rat adipose tissue. The possible role of GIP for the development of obesity is discussed.     

The effect of O-acetylsalicylic acid on lipid synthesis by guinea pig gastric mucosa in vitro

The aim of this work was to investigate the involvement of lipids as possible components of the gastric mucosal barrier by studying the synthesis and secretion of lipids by the epithelial cell lining of gastric mucosa and the effect of salicylate on these processes. O-Acetylsalicylic acid reversibly reduced in vitro incorporation of [U-14C]acetate and of DL-[2-14C]mevalonic acid into lipids by isolated epithelial cells and by intact mucosa of guinea pig stomach, indicating reversible inhibition of lipid synthesis by the tissue in the presence of the drug. Inhibition of incorporation of both precursors into total lipids, into their fatty acid components, and into cholesterol is demonstrated.     

Swim training increases glucose output from liver perfused in situ with glucagon in fed and fasted rats

The effect of endurance swim training (3 hours per day, 5 days/week, for 10 weeks) on hepatic glucose production (HGP) in liver perfused in situ for 60 minutes with glucagon and insulin was studied in Sprague-Dawley rats. The experiments were performed in fed rats and in rats fasted for 24 hours, but with lactate (8 mmol/L) added to the perfusion medium. Liver glycogen content was significantly lower in fasted than fed rats (fasted untrained and trained: 14 +/- 4 and 11 +/- 3 micromol glycosyl U/g of liver wet weight (WW); fed untrained and trained: 205 +/- 11 and 231 +/- 11 micromol glycosyl U/g of liver WW; not significantly different in trained and untrained rats). Glucagon increased HGP in the 4 experimental groups, but the increases were more rapid and pronounced in trained than in untrained rats in both fed and fasted states. HGP values (area under the curve [AUC] in micromol/g of liver WW) were significantly higher in trained fed (112.1 +/- 7.1 v 85.9 +/- 12.2 in untrained rats) than in trained fasted rats (50.8 +/- 4.4 v 34.7 +/- 3.6 in untrained rats). When compared with untrained rats, the total amount of glucose released by the liver in response to glucagon in trained rats was approximately 30% higher in the fed state and approximately 45% larger in the fasted state. These results indicate that endurance training increases the response of both glycogenolysis and gluconeogenesis to glucagon.     

Age-related changes in the response of rat adipocytes to insulin: evidence for a critical role for inositol phosphoglycans and cAMP

Adipose tissue plays a pivotal role in ageing and longevity; many studies, both human and animal, have focussed on the effects of food limitation. Here we present a new model based on striking differences between two ‘normal’ inbred strains of albino Wistar rats the Charles River (CR) and Harlan Olac (HO) that have marked differences in age-related accumulation of fat and insulin-stimulated rates of glucose incorporation into lipid in the epididymal fat pads (EFP). The incorporation [U-¹⁴C]glucose into lipid by adipocytes showed that the CR group had a twofold higher basal rate of lipogenesis and a greater response to insulin in vitro, exceptionally, adipocytes from CR group maintained the high response to insulin to late adulthood while retaining the lower EFP weight/100 g body weight. Inositol phosphoglycan A-type (IPG-A), a putative insulin second messenger, was 3.5-fold higher and cAMP significantly lower per EFP in the CR versus HO groups. Plasma insulin levels were similar and plasma leptin higher in CR versus HO groups. The anomaly of a higher rate of lipogenesis and response to insulin and lower EFP weight in the CR group is interpreted as the resultant effect of a faster turnover of lipid and stimulating effect of leptin in raising fatty acid oxidation by muscle, potentially key to the lower accumulation of visceral fat. The metabolic profile of the CR strain provides a template that could be central to therapies that may lead to the lowering of both adipose and non-adipocyte lipid accumulation in humans in ageing.     

The postprandial rates of glycogen and lipid synthesis of lean and obese female Zucker rats

OBJECTIVE: To determine the relative rates of glycogenesis and lipogenesis following administration of a test meal in lean and obese Zucker rats. PROTOCOL: Nine-week-old lean and obese Zucker rats were fasted overnight, then tube-fed a test meal of balanced composition amounting to 16kJ (lean rats and one group of obese rats) or 24kJ (one group of obese rats) and containing 200 mg 1-(13)C glucose. Immediately after the meal the rats were injected intraperitoneally with 5 mCi of 3H2O and killed 1 h later. METHODS: Glycogenesis was calculated from the incorporation of 3H into liver glycogen divided by the specific activity of plasma water. Lipogenesis was calculated similarly from the incorporation of 3H into saponifiable lipids in liver and perirenal adipose tissue. The proportion of glycogen synthesized by the indirect pathway via pyruvate was determined from the ratio of 3H labelling at positions C6 and C2 in the glycogen glucose residues. Glycogen synthesis from glucose was determined from the ratio of 13C enrichment in liver glycogen to that in plasma glucose. RESULTS: The rate of synthesis of glycogen was considerably lower in the livers of obese rats than those of lean controls, with the larger meal causing a small but significant increase in glycogenesis. The proportion of glycogen synthesized via pyruvate showed a non-significant increase in the obese rats, while the amount of glycogen synthesized from glucose was significantly decreased. Hepatic lipogenic rates were about five times higher in both groups of obese rats than the lean controls. In adipose tissue, lipogenesis per g tissue was slightly reduced in the obese rats, although there was clearly an increase in adipose tissue lipogenic activity per whole animal. The larger meal caused a greater rise in plasma glucose and insulin concentrations but did not affect lipogenic rates, although it did cause a greater suppression of lipolysis, as indicated by a lower plasma glycerol concentration. CONCLUSION: Ingested carbohydrate is partitioned predominantly into hepatic fatty acid synthesis in obese Zucker rats. Hepatic glycogen synthesis is suppressed and comes mainly from precursors other than glucose. The suppression of hepatic glycogen synthesis may contribute to the increased energetic efficiency of obese Zucker rats.     

Effects of mental stress on lipolysis in humans.

Lipid mobilization was investigated in subcutaneous adipose tissue specimens obtained before and after a standardized mental-stress test in 14 non-obese healthy subjects. All participants responded with an increased heart rate and elevation of plasma glycerol levels. Plasma norepinephrine concentrations remained unchanged throughout the test. In six subjects, mental stress induced a significant increase in plasma epinephrine levels, to more than 0.26 nmol/L (responders), while the remaining eight individuals showed a response of less than 0.12 nmol/L (nonresponders). In the responders, a 30% increase in catecholamine-stimulated in vitro lipolysis was found after the mental-stress test, while the lipolytic response in isolated fat cells in vitro decreased slightly in the nonresponders after mental stress. A strong correlation (r = .84) was observed between the increased in vitro lipolytic responsiveness due to mental stress and circulating plasma epinephrine levels. In vitro data suggest that the augmentation in lipolytic activity induced by acute mental stress was caused by alterations between the beta-adrenoceptor and adenylate cyclase, ie, probably an increased coupling between beta-receptors and the stimulatory guanosine triphosphate [GTP]-binding protein (G2). This, in combination with elevated levels of circulating epinephrine, may explain the increased lipolysis during mental stress in some individuals (ie, responders). However, other parallel mechanisms for activation of lipolysis during mental stress must also exist in certain individuals (ie, nonresponders), and seem not to involve the adrenergic system.     

Diabetes causes marked changes in lymphocyte metabolism

An enhanced susceptibility to infections is well known to occur in a poorly controlled diabetic state. Since glucose and glutamine are essential for lymphocyte function, we investigated whether their metabolism is changed in lymphocytes obtained from mesenteric lymph nodes of alloxan-induced diabetic rats (40 mg/kg body weight). The activities of hexokinase, phosphofructokinase, glucose-6-phosphate dehydrogenase (G6PDH), citrate synthase and phosphate-dependent glutaminase were determined. Decarboxylation of metabolites [U-14C]-, [1-14C]- and [6-14C]-glucose, [1-14C]- and [2-14C]-pyruvic acid, [U-14C]-palmitic acid and [U-14C]-glutamine was evaluated in incubated lymphocytes isolated from mesenteric lymph nodes. The measurements were carried out in cells following three experimental protocols: (1) lymphocytes freshly obtained from control and alloxan-induced diabetic rats, (2) lymphocytes from insulin-treated (2 U/rat per day) diabetic rats and (3) lymphocytes obtained from control and diabetic rats and cultured in the presence of insulin (1 mU/ml) for 6 h. The activities of hexokinase, G6PDH and citrate synthase were decreased by the diabetic state, whereas that of phosphofructokinase was raised. Decarboxylation of [U-14C]- and [6-14C]-glucose, [1-14C]- and [2-14C]-pyruvate and [U-14C]-glutamine were also decreased in lymphocytes from diabetic rats, whereas [U-14C]-palmitic acid decarboxylation was increased. Insulin administration in vivo or added to the culture medium reversed the changes observed in freshly obtained lymphocytes. Alloxan-induced diabetes did change lymphocyte metabolism and this may be an important mechanism leading to impairment of lymphocyte function.     

Effects of exogenous growth hormone on lipid metabolism in the isolated epididymal fat pad of the growth hormone-deficient little mouse

The effects of two preparations of highly purified human GH (hGH) on lipid metabolism were studied in the GH-deficient little mouse (50-60 days old). Marked decreases in incorporation of [14C]glucose into fatty acid and in the activity of acetyl-CoA carboxylase in the epididymal fat pads were observed after i.p. injection of hGH at a dose of 1.0 microgram/g body weight or after continuous infusion of hGH by osmotic minipump. The rate of glucose incorporation into fatty acid decreased from 107.0 +/- 27.6 (S.E.M.) to 38.1 +/- 19.6 mumol/g tissue per h after a single injection of hGH and from 174.1 +/- 28.5 to 56.3 +/- 20.3 mumol/g tissue per h after continuous infusion of hGH for 2 days. Activity of the lipogenic enzyme acetyl-CoA carboxylase was also reduced by more than 50% in the epididymal fat pad from hGH-treated mice in comparison with the corresponding control animals. Incubation of isolated fat pads with hGH (0.1 microgram/ml) revealed similar inhibitory effects of the hormone on fatty acid synthesis and acetyl-CoA carboxylase activity. No lipolytic effect of hGH was found as determined by the rate of glycerol release from epididymal fat pads of little mice following hormone treatment in vivo or in vitro. The results lend strong support to the conclusion that GH inhibits lipogenesis but has no effect on lipolysis in adipose tissues, and indicate that the physiological role of GH in lipid metabolism is concerned mainly with the regulation of anabolic rather than catabolic processes.