Alain Géloën

Uric acid and urea in relation to protein catabolism in long-term fasting geese

SummaryFive ganders were subjected to an experimental fast comparable to that which spontaneously occurs during breeding in domestic geese, and during migration and breeding in various wild birds. Plasma uric acid and urea concentrations, and their excretion as a proportion of total nitrogen excretion, were studied in relation to daily change in body mass per unit body mass, dm/mdt. This variable has previously been found to reflect changes in protein catabolism over the three phases of fast: I, dm/mdt and protein utilization both decrease; II, they are maintained at a low value; and III, they increase. In the fed state, daily total nitrogen excretion was 5 gN·24 h−1; uric acid, ammonia and urea accounted for 51, 15 and 5% respectively. The high remaining proportion of, excreted nitrogen (29%), after subtraction of uric acid-N, ammonia-N and urea-N to total nitrogen, accords with the literature. During fasting, the changes in daily excretion of uric acid, urea, ammonia and total nitrogen followed a pattern essentially similar to that for dm/mdt. Uric acid accounted for a progressively increasing fraction of total nitrogen, up to 76% at the end of phase III, while urea remained at a constant 5%. Plasma concentrations of both uric acid and urea followed similar trends during the fast, in particular both increasing during phase III, i.e. when there was a rise in nitrogen exrection. This suggests they could be used as an index in field investigations, to determine whether birds which naturally fast in connection with specific activities have entered into the situation where proteins are no longer spared.

Differential regulation of uncoupling protein-1, -2 and -3 gene expression by sympathetic innervation in brown adipose tissue of thermoneutral or cold-exposed rats.

The control of uncoupling protein‐1, ‐2 and ‐3 (UCP‐1, UCP‐2, UCP‐3) mRNA levels by sympathetic innervation in rats was investigated by specific and sensitive RT‐PCR assays. In rats reared at thermoneutrality (25°C), unilateral surgical sympathetic denervation of interscapular brown adipose tissue (BAT) markedly reduced the UCP‐1 mRNA level (−38%) as compared with the contralateral innervated BAT pad, but was without significant effect on UCP‐2 and ‐3 mRNA levels. Cold exposure (7 days, 4°C) markedly increased UCP‐1 (+180%), UCP‐2 (+115%) and UCP‐3 (+195%) mRNA levels in interscapular BAT. Unilateral sympathetic denervation prevented the cold‐induced rise in BAT UCP‐1 and UCP‐2 mRNAs, but not that in BAT UCP‐3 mRNA. Results were confirmed by Northern blot analysis. These data indicate a differential endocrine control of UCP‐1, UCP‐2 and UCP‐3 gene expression in rat BAT both at thermoneutrality and during prolonged cold exposure.

Effects of Chronic Treatment with Noradrenaline or a Specific β3-Adrenergic Agonist, CL 316 243, on Energy Expenditure and Epididymal Adipocyte Lipolytic Activity in Rat

1. The effects of 7 days exposure to a specific beta3-adrenergic agonist, CL 316 243 (1 mg/kg x 24 hr), or to the physiological hormone, noradrenaline (5 mg/kg x 24 hr), were tested on energy expenditure and on in vitro lipolysis in male Sprague-Dawley rats. 2. At the second day of treatment, the total energy expenditure and the resting metabolic rate were increased by 20 and 30%, respectively, in the CL-treated group. Under the same conditions, a dose five times higher of NA increased the resting metabolic rate by 11% without any significant change in the total daily energy expenditure. 3. The CL-treated group showed a lower weight gain, correlated with a significant reduction in retroperitoneal adipose tissue weight. Both treatments resulted in a marked desensitization (increased EC50 values) of the NA stimulated lipolysis of epididymal adipocytes. The effects of both treatments on maximal lipolysis were opposite. Indeed, chronic NA-treatment decreased the responsiveness of lipolysis while chronic treatment with CL increased the maximal stimulation of lipolysis to NA. Furthermore, dose-response curve for CL on lipolysis showed a marked functional desensitization of beta3-adrenergic response. 4. Our results demonstrate the high selectivity of beta3-adrenergic agonists to stimulate whole body energy expenditure and lipid mobilization in rodents. The present results point out for the first time an adrenergic desensitization of the lipolytic response after chronic administration of a beta3-agonist.

Mechanism of carbon tetrachloride autoprotection: An in vivo study based on 13C-aminopyrine and 13C-galactose breath tests

This study was conducted to evaluate in vivo the hepatotoxic effects of CCl4 administration to rats using 13C breath tests: aminopyrine breath test (ABT) was used to monitor CCl4-induced cytochrome P450 inactivation, and galactose breath test (GBT) to quantitatively measure the CCl4-induced decrease of liver function. The ABT results showed profound aminopyrine demethylation inhibition lasting for three days and complete recovery at day 7, while GBT results were decreased only one day after CCl4. The protection induced by a first CCl4 dose against a second one paralleled cytochrome P450 inactivation: a second CCl4 dose given three days after the first one induced no GBT decrease and a mild increase of serum transaminase activities. On the other hand, the second dose administered 7 days after the first one produced a GBT decrease similar to the one observed after the first one. These results should be taken into consideration to determine the optimal CCl4 dosing schedule in the rat CCl4-induced cirrhosis model.

In situ regulation of lipolysis by insulin and norepinephrine: A microdialysis study during euglycemic-hyperinsulinemic clamp

Lipolytic responsiveness of subcutaneous and epididymal adipose tissue to norepinephrine (NE) was measured by microdialysis before and during a euglycemic-hyperinsulinemic clamp in male Sprague-Dawley rats (280 +/- 7g, n = 8). Microdialysis probes were perfused with standard Krebs-Ringer buffer without (basal condition [BC]) or with NE 10(-6) mol/L to determine basal and stimulated rates of lipolysis. The dialysate concentration of glycerol was measured (lipolytic index). NE infusion resulted in 3.0- and 4.2-fold increases in glycerol release in abdominal subcutaneous and epididymal adipose tissues, respectively. A euglycemic-hyperinsulinemic clamp at 6 mU/kg.min increased by ninefold the insulinemia (120 +/- 9 U/L). Hyperinsulinemia suppressed basal glycerol release by 57% and 42% in subcutaneous and epididymal adipose depots, respectively (BC + I). Lipolytic responses to NE infusion during a euglycemic-hyperinsulinemic clamp (NE + I) were reduced by 45% and 33% in subcutaneous and epididymal adipose tissues, respectively, as compared with BC. Under BC, the lipolytic response to NE was greater in epididymal than in subcutaneous adipose tissue. Physiological levels of insulin regulated basal lipolysis and counteracted adrenergic stimulation of lipolysis to a similar extent in both superficial (subcutaneous) and intraabdominal (epididymal) adipose tissue. Our findings show that lipolysis is more responsive to NE in epididymal than in subcutaneous adipose tissue. The antilipolytic effects of insulin are similar in both superficial and deep intraabdominal adipose tissues. Furthermore, physiological plasma insulin levels cannot fully antagonize the lipolytic effects of NE.

Short-Term Cold-Exposure Does Not Improve Insulin Sensitivity in Rats

Effects of noradrenergic activation induced by short-term cold-exposure (7 days at 4 degrees C) on whole-body glucose utilization and tissue glucose uptake were investigated in rats. Measurements were realized on anesthetized normothermic animals at four different levels of insulinemia, within physiological range, allowing calculation of insulin sensitivity and responsiveness. Whole-body glucose utilization increased as a logarithmic function of insulinemias, and was always higher in cold-exposed than in control rats. However, neither insulin sensitivity nor responsiveness, literally, appeared different between the two groups. In the diaphragm, the only studied working muscle, glucose uptake was largely higher than in restin muscles. At basal insulin concentration, glucose uptake was higher in cold-exposed than in control rats and increased in the two groups with insulinemia. Among resting muscles, glucose uptake was increased by previous cold exposure in gastrocnemius, soleus, and tibialis. However, insulin sensitivity and responsiveness were found augmented only in the two former. In interscapular brown adipose tissue, glucose uptake was largely higher in cold-exposed than in control rats, but no difference could be evidenced in insulin sensitivity or responsiveness. In white adipose tissues, glucose uptake increased with insulinemia. Insulin responsiveness and sensitivity were higher only in the retroperitoneal depot.

Continuous monitoring of 13C-aminopyrine metabolism in rats: effects of cold exposure and noradrenaline.

A system was developed to allow constant monitoring of hepatic cytochrome P450 activity in awake and unrestrained rats. A continuous 13C-aminopyrine perfusion was performed, and breath samples obtained for endogenous CO2 production and 13C measurements, to calculate 13C O2 production due to aminopyrine demthylation. Increasing doses of 13C-aminopyrine produced a hyperbolic increase of expired 13CO2, compatible with an in vivo measurement of enzymatic activity. Acute-cold exposure of the rats during 13C-aminopyrine perfusion produced a two-fold increase of endogenous CO2 production, together with a 27% increased 13C-aminopyrine metabolism (p<0.05 vs basal conditions). In contrast, noradrenaline (20 microg/kg BW/min), despite a similar effect on energy expenditure, did not significantly change 13C-aminopyrine metabolism. Acute-cold exposure is known to stimulate both adrenal catecholamine secretion and the sympathetic nervous system. The observed difference in 13C-aminopyrine demthylation during cold exposure and nonadrenaline perfusion, therefore, could be due to a more specific effect of adrenal catecholamines on liver aminopyrine metabolism. These results suggest the possibility of prolonged in vivo monitoring of liver metabolism pathways such as aminopyrine demethylation, thus allowing the study of drug acute interactions with cytochrome P450 system.

Oleic Acid Uptake Reveals the Rescued Enterocyte Phenotype of Colon Cancer Caco-2 by HT29-MTX Cells in Co-Culture Mode

Gastrointestinal epithelium is the unique route for nutrients and for many pharmaceuticals to enter the body. The present study aimed to analyze precisely whether co-culture of two colon cancer cell lines, mucus-producing cells HT29-MTX and enterocyte-like Caco-2 cells, ameliorate differentiation into an in vitro intestinal barrier model and the signaling pathways involved. Differentiated Caco-2 cells gene datasets were compared first to intestinal or cancer phenotypes and second to signaling pathway gene datasets. Experimental validations were performed in real-time experiments, immunochemistry, and gene expression analyses on Caco-2 versus co-cultures of Caco-2 and HT29-MTX (10%) cells. Partial maintenance of cancer-cell phenotype in differentiated Caco-2 cells was confirmed and fatty acids merged as potential regulators of cancer signaling pathways. HT29-MTX cells induced morphological changes in Caco-2 cells, slightly increased their proliferation rate and profoundly modified gene transcription of phenotype markers, fatty acid receptors, intracellular transporters, and lipid droplet components as well as functional responses to oleic acid. In vitro, enterocyte phenotype was rescued partially by co-culture of cancer cells with goblet cells and completed through oleic acid interaction with signaling pathways dysregulated in cancer cells.