Glucose Metabolism by Isolated Fat Cells from Diabetic Rats

Methyl-β-cyclodextrin alters adipokine gene expression and glucose metabolism in swine adipose tissue

This study was designed to determine whether methyl-β-cyclodextrin (MCD) can substitute for albumin in incubation medium for neonatal swine adipose tissue explants, or whether MCD affects metabolism and cytokine expression. Subcutaneous adipose tissue explants (100 ± 10 mg) were prepared from 21-day-old pigs. Explants were incubated in medium 199 supplemented with 25 mM HEPES, 1.0 nM insulin at 37°C. The medium also contained bovine serum albumin (BSA) or MCD at 0%, 0.05%, 0.1%, 0.2% or 0.3%. Tissue explants were treated with these media for 1 h and then switched to the same basal incubation medium containing 0.05% BSA. Explants were removed from basal medium at 2 or 8 h of incubation, and real-time PCR was performed to assess expression of tumor necrosis α (TNF) and interleukin 6 (IL6), acetyl CoA carboxylase (ACAC) and fatty acid synthase (FASN). Alternatively, rates of 14C-glucose oxidation and lipogenesis were monitored ± insulin (100 nM), following MCD treatment. Incubation with BSA had minimal effects on gene expression or adipose tissue metabolism, only producing a doubling in TNF mRNA abundance (P < 0.01). Treatment with MCD increased TNF mRNA abundance by eightfold (P < 0.009), whereas IL6 gene expression increased a 100-fold (P < 0.001) with a suppression in ACAC and FASN expression (P < 0.01). This was paralleled by MCD inhibition of insulin-stimulated glucose oxidation and lipogenesis (P < 0.001). Addition of a TNF antibody to the incubation medium alleviated this inhibition of insulin-stimulated glucose metabolism by ~30% (P < 0.05).

Endocrine Regulation of Fetal Adipose Tissue Metabolism in the Pig: Role of Hydrocortisone

Glucocorticoids have been shown to be essential for the excessive fat deposition and development of obesity in several animal models. This study was performed to characterize the role of glucocorticoids in the developmental regulation of adipose tissue metabolism. On day 70 of gestation, pig fetuses were hypophysectomized by micro-cauterization. Hypophysectomized fetuses were implanted subcutaneously with hydrocortisone pellets or received no hormone replacement. Fetuses were removed by laparotomy on day 90 of gestation. Additional fetuses were hypophysectomized on day 70, implanted with hydrocortisone pellets on day 90 and removed on day 105 of gestation. Several intact fetuses were also implanted subcutaneously with hydrocortisone pellets during this later gestational period. Serum cortisol concentrations were reduced in hypophysectomized pigs at both fetal ages and were restored to intact levels by hydrocortisone treatment. Hydrocortisone supplementation enhanced lipolytic response to isoproterenol in intact fetuses but failed to restore lipolytic response to isoproterenol in hypophysectomized animals at either fetal age. Hydrocortisone induced a slight increase in lipogenesis in hypophysectomized fetuses when administered from 70 to 90 days of gestation and a more dramatic increase when administered from days 90 to 105 of gestation. However, hydrocortisone had no effect on basal or insulin stimulated lipogenesis in intact fetuses when administered from days 90 to 105 of gestation. These results indicate that hydrocortisone may have a primary influence on adipose tissue metabolism during late fetal development only in the absence of inhibition from counterregulatory hormones of pituitary origin.

Regulation of uncoupling proteins 2 and 3 in porcine adipose tissue

This study was performed to determine whether or not uncoupling protein 2 (UCP2) and UCP3 expression in porcine subcutaneous adipose tissue are hormonally regulated in vitro and whether their expression is correlated with changes in metabolic activity. Tissue slices (approximately 100 mg) were placed in 12-well plates containing 1 mL of DMEM/F12 with 25 mM Hepes, 0.5% BSA, pH 7.4. Triplicate slices were incubated with basal medium or hormone supplemented media at 37 degrees C with 95% air/5% CO2. Parallel cultures were maintained for either 2 or 24 h to evaluate metabolic viability of the tissue. Slices were transferred to test tubes containing 1 mL of DMEM/F12 with 25 mM Hepes, 3% BSA, 5.5 mM glucose, 1 microCi 14C-U-glucose/mL and incubated for an additional 2 h at 37 degrees C. Glucose metabolism in 2-h incubations did not differ from 24-h (chronic) incubations, indicating viability was maintained (P>0.05). Expression of UCP2 and UCP3 was assessed in slices following 24h of incubation with various combinations of hormones by semi-quantitative RT-PCR. Expression of UCP2 was induced by leptin (100 ng/mL; P<0.05). Growth hormone (100 ng/mL) inhibited UCP2 expression (P<0.05). Expression of UCP3 was inhibited by growth hormone (100 ng/mL; P<0.05), tri-iodothyronine (10 nM; P<0.05) or leptin (100 ng/mL; P<0.05). Changes in UCP expression could not be associated with overall changes in glucose metabolism by adipose tissue slices in chronic culture.

Porcine leptin alters isolated adipocyte glucose and fatty acid metabolism

This study examined if leptin can acutely affect glucose or fatty acid metabolism in pig adipocytes and whether leptin's actions on lipogenesis are manifested through interaction with insulin or growth hormone. Subcutaneous adipose tissue was obtained from approximately 55 kg crossbred barrows at the USDA abattoir. Isolated adipocytes were prepared using a collagenase procedure. Experiments assessed U-14C-glucose or 1-14C-palmitate metabolism in isolated adipocytes exposed to: basal medium (control), 100 nM insulin, 100 ng/ml porcine growth hormone, 100 ng/ml recombinant porcine leptin, and combinations of these hormones. Treatments were performed in triplicate and the experiment was repeated with adipocytes isolated from five different animals. Cell aliquots (250 microl) were added to 1 ml of incubation medium, then incubated for 2h at 37 degrees C for measurement of glucose and palmitate oxidation or incorporation into lipid. Incubation of isolated adipocytes with insulin increased glucose oxidation rate by 18% (P<0.05), while neither growth hormone nor leptin affected glucose oxidation (P>0.5). Total lipid synthesis from glucose was increased by approximately 25% by 100 nM insulin or insulin+growth hormone (P<0.05). Insulin+leptin reduced the insulin response by 37% (P<0.05). The combination of all three hormones increased total lipid synthesis by 35%, relative to controls (P<0.05), a rate similar to insulin alone. Fatty acid synthesis was elevated by insulin (32%, P<0.05) or growth hormone (13%, P<0.05). Leptin had no effect on fatty acid synthesis (P>0.05). Leptin reduced the esterification rate by 10% (P<0.05). Growth hormone and insulin could overcome leptin's inhibition of palmitate esterification (P>0.05).

Endocrine regulation of fetal adipose tissue metabolism in the pig: interaction of porcine growth hormone and thyroxine

OBJECTIVE

This study tested the hypothesis that combined treatment of thyroxine (T4) and growth hormone (GH) could normalize cellular and metabolic aspects of adipose tissue development of hypophysectomized fetal pigs.

RESEARCH METHODS AND PROCEDURES

On day 70 of gestation, pig fetuses were hypophysectomized by microcauterization or remained intact. Hypophysectomized fetuses remained untreated or were treated from day 90 to day 105 of gestation with T4, GH, or a combination of both hormones.

RESULTS

Body weights were unaffected by hypophysectomy or hormone treatment. De novo lipogenesis in subcutaneous adipose tissue was increased 10-fold by hypophysectomy, consistent with our previous results. This increase was abolished by GH treatment in the hypophysectomized fetuses. In contrast, T4 treatment of the hypophysectomized fetuses resulted in a 12-fold further increase in adipose tissue lipogenesis, an effect that was negated by concomitant administration of GH. Lipolytic response to isoproterenol was decreased by hypophysectomy, unaffected by GH treatment, and restored to intact values by T4 or by T4+GH treatment in the hypophysectomized fetuses.

DISCUSSION

In contrast to T4, GH does not influence serum insulin-like growth factor-I or adipose tissue lipolysis, but decreases lipogenesis in the fetal pig. However, replacing both T4 and GH normalized hypophysectomized fetuses to a greater extent than either GH or T4 alone. Thus, any influence of thyroid hormones on stimulating adipose tissue lipogenesis in the developing fetal pig may be normally counterregulated by pituitary-derived growth hormone.

Hibernation depth influences the edible dormouse pancreatic B cell during the spring arousal

In order to determine the influence of hibernation depth upon the secretion and the effect of insulin, two groups of edible dormice were maintained in winter under different climatic and nutritional conditions, and their pancreatic B-cell function was tested during the spring arousal. The first group of animals was exposed to a moderate temperature and fed ad libitum. Their periods of hypothermia were short and irregular and the active periods sometimes lasted several days; their body weight increased during the winter months; in spring, the sensitivity of B cells to glucose was low, decreasing insulin secretion in vivo and in vitro, and the adipocytes were insulin resistant. The second group of fasting animals was exposed to a low and constant temperature (5 degrees). Their phases of lethargy were long and regular (about 15 days), separated by active periods (6-8 hr); their body weight decreased during the winter months; in spring the B-cell secretion was increased and the sensitivity of the tissues to insulin ensured a high peripheral glucose utilization. These data show that the winter climatic and nutritional conditions which influence the depth of hibernation modify the edible dormouse B-cell activity during the spring arousal.