Biomedical subjects

B Cousin

Publications and source records attributed to B Cousin.

27 records · Page 2Linked to original sources

PubMed1993

Local sympathetic denervation of white adipose tissue in rats induces preadipocyte proliferation without noticeable changes in metabolism.

The direct influence of the sympathetic nervous system on white adipose tissue was studied by performing a unilateral surgical denervation of the retroperitoneal fat pad in rats, the contralateral pad being used as a control. One week after surgery, the weight of the denervated pad was significantly higher than that of the intact pad. In vivo, glucose utilization was not altered by denervation. The expression of GLUT4 as well as the expression and activity of fatty acid synthase, lipoprotein lipase, and hormone-sensitive triglyceride lipase were similar in the two pads. Lipolysis in response to norepinephrine, determined in vitro, was not modified by denervation although the ratio between alpha 2- and beta-adrenergic receptors was changed. Denervation induced an increase in DNA content without change in the number of mature adipocytes. The expression of A2COL6/pOb24, a marker of the early step of adipocyte differentiation, was significantly enhanced in the denervated pad, suggesting an increased number of preadipocytes. This was confirmed by an increased cell number observed in the denervated fat pad 1 month after surgery. In conclusion, surgical denervation of the white fat pad does not alter the glucose and lipid metabolisms. By contrast, it accelerated adipocyte differentiation and led to the recruitment of new precursors.

Adipose Tissue↗

PubMed1992

Molecular and metabolic changes in white adipose tissue of the rat during development of ventromedial hypothalamic obesity.

We have previously shown that rats made obese by lesion of ventromedial hypothalamus (VMH) nuclei, demonstrate an hyper-responsiveness to insulin with regard to whole-body glucose utilization one week after injury. This is mainly due to an increased glucose uptake in white adipose tissue. Six weeks after the lesion, glucose utilization in white adipose tissue returns to normal values. These modifications in insulin responsiveness could be mediated by altered activity and/or concentration of intracellular insulin effectors. In this study, we have measured the expression of the insulin-sensitive glucose transporter, Glut 4 and the activities and expression of key lipogenic enzymes (fatty-acid synthase and acetyl-CoA carboxylase) in white adipose tissue, one and six weeks after the lesion. All these parameters, as well as glucose transport and metabolism determined in white adipocytes, were markedly increased one week after the lesion. They returned to control values within six weeks in VMH-lesioned rats. These results indicate the existence of an increased expression of Glut 4 and lipogenic enzymes in white adipose tissue of VMH-lesioned rats which decreased with time and were parallel to glucose utilization determined in vivo.

Adipose Tissue↗

PubMed1992

Insulin receptor kinase activity in muscles and white adipose tissue during course of VMH obesity.

Early after lesion of the ventromedial hypothalamus nuclei (VMH), insulin-induced glucose utilization is increased in white adipose tissue (WAT), whereas oxidative and glycolytic muscles are, respectively, normoresponsive or resistant to insulin. Five weeks later, all of the muscles are resistant, whereas WAT returns to normal responsiveness. The aim of this study was to characterize the insulin receptor kinase activity in WAT and muscles 1 and 6 wk after lesion. The number and affinity of insulin receptors were not modified in any of the tissues studied. Autophosphorylation and phosphorylation of an exogenous substrate were similar in oxidative and glycolytic muscles of VMH and control rats both 1 and 6 wk after the lesion. Insulin receptors from WAT of 1-wk VMH rats exhibited a 2.5-fold increase in insulin-stimulated autophosphorylation and phosphorylation. Six weeks after the lesion, both autophosphorylation and phosphorylation returned to normal values. This suggests that insulin receptor tyrosine kinase activity does not play a significant role in the insulin resistance of skeletal muscles but has a crucial role in mediating the variations of insulin action on WAT observed during the development of VMH obesity.

Adipose Tissue↗

PubMed1992

Occurrence of brown adipocytes in rat white adipose tissue: molecular and morphological characterization.

Brown adipocytes are thermogenic cells which play an important role in energy balance. Their thermogenic activity is due to the presence of a mitochondrial uncoupling protein (UCP). Until recently, it was admitted that in rodents brown adipocytes were mainly located in classical brown adipose tissue (BAT). In the present study, we have investigated the presence of UCP protein or mRNA in white adipose tissue (WAT) of rats. Using polymerase chain reaction or Northern blot hybridization, UCP mRNA was detected in mesenteric, epidydimal, retroperitoneal, inguinal and particularly in periovarian adipose depots. The uncoupling protein was detected by Western blotting in mitochondria from periovarian adipose tissue. When rats were submitted to cold or to treatment with a beta-adrenoceptor agonist, UCP expression was increased in this tissue as in typical brown fat. Moreover, the expression was decreased in obese fa/fa rats compared to lean controls. Morphological studies showed that periovarian adipose tissue of rats kept at 24 degrees C contained cells with numerous typical BAT mitochondria with or without multilocular lipid droplets. Immunocytochemistry confirmed that multilocular cells expressed mitochondrial UCP. Furthermore, the number of brown adipocytes and the density of mitochondrial cristae increased in parallel with exposure to cold. These results demonstrate that adipocytes expressing UCP are present in adipose deposits considered as white fat. They suggest the existence of a continuum in rodents between BAT and WAT, and a great plasticity between adipose tissue phenotypes. The physiological importance of brown adipocytes in WAT and the regulation of UCP expression remain open questions.

Adipose Tissue↗

PubMed1984