Postexercise Muscle Triacylglycerol and Glycogen Metabolism in Obese Insulin‐Resistant Zucker Rats

Aug 5, 2004Obesity research

Muscle fat and sugar storage after exercise in obese insulin-resistant Zucker rats

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Abstract

Resting muscle triacylglycerol (IMTG) content was 4-fold higher in obese insulin-resistant Zucker rats compared to lean Zucker rats.

IMTG levels in muscles remained unchanged immediately after exercise for both lean and obese rats.
Exercise led to about 85% glycogen use in lean rats, while obese rats showed only a 30% decrease in glycogen content.
Postexercise recovery in lean rats supplemented with carbohydrates resulted in decreased IMTG levels in their muscles.
In contrast, fasting obese rats had increased IMTG levels in their muscles after 360 minutes.
Carbohydrate refeeding restored glycogen levels in lean rats, but glycogen content in obese rats remained lower than resting levels after fasting.

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OBJECTIVE: To determine the impact of insulin resistance and obesity on muscle triacylglycerol (IMTG) and glycogen metabolism during and after prolonged exercise.

RESEARCH METHODS AND PROCEDURES: Female lean (fa/?; N = 40, ZL) and obese insulin-resistant (fa/fa; N = 40, ZO) Zucker rats performed an acute bout of swimming exercise (8 times for 30 minutes) followed by 6 hours of carbohydrate supplementation (CHO) or fasting (FAST). IMTG and glycogen were measured in the extensor digitorum longus (EDL) and red vastus lateralis (RVL) muscles.

RESULTS: Despite resting IMTG content being 4-fold higher in ZO compared with ZL rats, IMTG levels were unchanged in either EDL or RVL muscles immediately after exercise. Resting glycogen concentration in EDL and RVL muscles was similar between genotypes, with exercise resulting in glycogen use in both muscles from ZL rats (approximately 85%, p < 0.05). However, in ZO rats, there was a much smaller decrease in postexercise glycogen content in both EDL and RVL muscles (approximately 30%). During postexercise recovery, there was a decrease in EDL muscle levels of IMTG in ZL rats supplemented with CHO after 30 and 360 minutes (p < 0.05). In contrast, IMTG content was increased above resting levels in RVL muscles of ZO rats fasted for 360 minutes. Six hours of CHO refeeding restored glycogen content to resting levels in both muscles in ZL rats. However, after 6 hours of FAST in ZO animals, RVL muscle glycogen content was still lower than resting levels (p < 0.05). At this time, IMTG levels were elevated above basal (p < 0.05).

DISCUSSION: In both healthy and insulin-resistant skeletal muscle, there was negligible net IMTG degradation after a single bout of prolonged exercise. However, during postexercise recovery, there was differential metabolism of IMTG between phenotypes.

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Postexercise Muscle Triacylglycerol and Glycogen Metabolism in Obese Insulin‐Resistant Zucker Rats

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