Lipolysis, lipogenesis, and adiposity are reduced while fatty acid oxidation is increased in visceral and subcutaneous adipocytes of endurance-trained rats

Abstract

(2015) Lipolysis, lipogenesis, and adiposity are reduced while fatty acid oxidation is increased in visceral and subcutaneous adipocytes of endurance-trained rats, Adipocyte, 4:1, 22-31, DOI: 10.4161/21623945.2014 This study examined the alterations in triglyceride (TG) breakdown and storage in subcutaneous inguinal (SC Ing) and epididymal (Epid) fat depots following chronic endurance training. Male Wistar rats were either kept sedentary (Sed) or subjected to endurance training (Ex) at 70-85% peak VO 2 for 6 weeks. At weeks 0, 3, and 6 blood was collected at rest and immediately after a bout of submaximal exercise of similar relative intensity to assess whole-body lipolysis. At week 6, adipocytes were isolated from Epid and SC Ing fat pads for the determination of lipolysis under basal or isoproterenol-and forskolin-stimulated conditions, basal and insulin-stimulated glucose incorporation into lipids, and fatty acid oxidation (FAO). Body weight, fat pad mass, and insulin were reduced by endurance training. Also, circulating non-esterified fatty acids (NEFAs) were 33% lower in Ex than Sed rats when exercising at the same relative intensity. This coincided with reduced isoproterenol-stimulated lipolysis in the Epid (27%) and SC Ing (25%) adipocytes in Ex rats. Similarly, forskolin-stimulated lipolysis was reduced in Epid (51%) and SC Ing (49%) adipocytes from Ex rats. Insulinstimulated glucose incorporation into lipids in adipocytes from both fat depots from Ex rats was also lower (»43%) than Sed controls. Conversely, FAO was increased in Epid (1.71-fold) and SC Ing (1.82-fold) adipocytes of Ex rats. In conclusion, chronic endurance exercise reduced lipolysis and lipogenesis while increasing FAO in Epid and SC Ing adipocytes. These are compatible with an energy-sparing adaptive response to reduced adiposity under chronic endurance training conditions.

Physical exercise remodels visceral adipose tissue and mitochondrial lipid metabolism in rats fed a high‐fat diet

“…Unexpectedly and, in contrast with other studies, no alterations on mitofusin‐related proteins were observed in HFD‐fed animals. However, the decrease in both eWAT mass and adipocyte size induced by exercise and a concomitant decreased plasma NEFA levels might have contributed to the improvements of mitochondrial content and biogenesis, which are in agreement with some studies . In liver mitochondria, ET positively modulated fusion‐related proteins in HFD‐induced obese animals .…”

“…In the present study, we further demonstrate that ET impact was evident on eWAT lipolysis, which were observed by reduced plasma NEFA and glycerol levels. This is in agreement with an inhibitory exercise effect on the adipocyte lipolytic activity of obese rats . However, until now and to our best knowledge, limited information is available regarding the effects of chronic exercise on NEFA and glycerol transporters in eWAT in the context of an HFD‐induced obesity.…”

“…Some studies described an increased lipolysis, while others suggested a reduced lipolysis in isolated rat adipocytes or unaltered condition when assessed in situ by microdialysis technique in humans in response to ET. Moreover, it has been reported that an increased mitochondrial oxidative capacity in VAT could reduce the availability of NEFA for esterification and the utilization of glucose for the formation of glycerol in white adipocytes . Few studies have reported that exercise induces positive alterations on VAT mitochondrial metabolism, including increases on mitochondrial content and activity and on critical factors involved in the regulation of mitochondrial biogenesis, such as peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) .…”

“…15 However, discrepant data regarding the effects of chronic exercise on lipolytic capacity in adipocytes have been reported. Some studies described an increased lipolysis, 16,17 while others suggested a reduced lipolysis in isolated rat adipocytes 18,19 or unaltered condition when assessed in situ by microdialysis technique in humans 20 in response to ET. Moreover, it has been reported that an increased mitochondrial oxidative capacity in VAT could reduce the availability of NEFA for esterification 21 and the utilization of glucose for the formation of glycerol in white adipocytes.…”

Exercise-Mediated Effects on White and Brown Adipose Tissue Plasticity and Metabolism

“…In our model, exercise intensity was kept constant at 70%Y85% of peak V O 2 throughout the training period, so circulating catecholamines are expected to be increased during exercise bouts. This was confirmed by our findings that circulating epinephrine was increased during an exercise bout of similar relative intensity (80% of peak V O 2 ) at the beginning and after 3 and 6 wk of endurance training (21). Therefore, it is surprising that thermogenic capacity was reduced markedly in iBAT and peri-aortic BAT (aBAT) of endurance-trained rats (34), despite repeated daily transient increases in circulating epinephrine.…”