Effects of exercise training on hepatic microsomal triglyceride transfer protein content in rats.
Microsomal triglyceride transfer protein (MTP) is a protein that exerts a central regulatory role in very-low-density lipoprotein (VLDL) assembly and secretion. The purpose of the study was to investigate the effects of an exercise-training program on hepatic content of MTP and its relation to hepatic VLDL-triglyceride (VLDL-TG) production in response to lipid infusion. Female rats either fed a standard (SD) or an obesity-induced high-fat (HF; 43% as energy) diet for 8 weeks were subdivided into sedentary (Sed) and trained (Tr) groups. Exercise training consisted of continuous running on a motor-driven rodent treadmill 5 times/week for 8 weeks. At the end of this period, all rats in the fasted state were intravenously infused with a 20% solution of Intralipid for 3 h followed by an injection of Triton WR1339 to block lipoprotein lipase. An additional control group consisting of Sed rats fed the SD diet was infused with saline (0.9% NaCl). Plasma TG accumulation was thereafter measured during 90 min to estimate VLDL-TG production. Under HF diet, hepatic MTP content and plasma TG accumulation after Triton blockade (thus reflecting VLDL-TG synthesis and secretion) were not changed in Sed rats, whereas liver TG content was highly increased (approximately 90%; p<0.01). On the other hand, training reduced liver MTP protein content in both SD (-18%) and HF (-23%) fed rats (p<0.05). Plasma VLDL-TG accumulation was also lower (p<0.05) in Tr than in Sed rats fed the HF diet. This effect was not observed in SD fed rats. Furthermore, the exercise training-induced decrease in VLDL-TG production in HF rats was associated with a decrease in liver TG levels. It is concluded that in addition to a reduction in liver TG content, exercise training reduces VLDL synthesis and/or secretion in HF fed rats probably via MTP regulation.
Chapados
N A
NA
Department of Kinesiology, University of Montreal, Montreal, Canada. natalie.chapados@umontreal.ca
Seelaender
M
M
Levy
E
E
Lavoie
J-M
JM
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D005081:Exercise Therapy; D005260:Female; D006801:Humans; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D009765:Obesity / Q000378:metabolism* / Q000628:therapy*; D010805:Physical Conditioning, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley; D014280:Triglycerides / Q000378:metabolism
D002352:Carrier Proteins; D008079:Lipoproteins, VLDL; D014280:Triglycerides; C106092:microsomal triglyceride transfer protein; C030106:very low density lipoprotein triglyceride