Bioactive Lipids And IMTG Are Not Influenced By 14 Days Prolonged Exercise In Older Men

Abstract

In a recently published study (Rosenkilde et al., 2015) we observed that older men were able to sustain near maximal energy expenditure during very prolonged exercise, but their energy balance was negative -4.8 ± 2 MJ/day. The effect of prolonged exercise on muscle bioactive lipid content is unresolved and the coupling to and importance of bioactive lipids for insulin sensitivity is controversial. PURPOSE: We investigated the effect of 14 days of very prolonged exercise on muscle content of ceramide and IMTG and the muscle expression of lipid handling proteins in lean trained older individuals. METHODS: Six lean (BMI; 24 ± 1 kg/m2) trained (VO2max: 48 ± 2 mlO2/kg/min) men (age 61 ± 4 yrs.) participated in the study (described in full detail in Rosenkilde et al.). During 14 days the subjects cycled a total of 2706 km averaging a duration of 631 ± 37 min cycling per day. Before and after the 14 days a basal blood sample and a biopsy from the vastus lateralis were obtained. The post testing was done after 28-33 hours of rest. Muscle protein expression was measured by Western blotting. RESULTS: Subjects maintained their body weight but were in negative energy balance (Rosenkilde et al. 2015). VO2max was decreased by 6 ± 2 % across the 14 days. The plasma glucose and adiponectin concentration remained unchanged whereas the plasma insulin concentration and an index of insulin sensitivity (HOMA) tended (P<0.07) to increase after 14 days. The plasma FFA concentration decreased from 560 ± 70 to 160 ± 35 μmol L-1 (P < 0.002) after 14 days. Muscle triacylglycerol and muscle total ceramide content remained unchanged. The muscle expression of DGAT1 and 2, CD36, FABPpm and HSL and PLIN2, 3, and 5 remained unchanged whereas ATGL protein expression was increased (P<0.05) and LPL protein expression tended to increase (P=0.06) after 14 days. CONCLUSION: In the present study no effect of prolonged repeated exercise on muscle ceramide or muscle TG was observed after the 14 days despite a trend towards lower insulin sensitivity. Interestingly only the lipolytic capacity in muscle indicated by ATGL and LPL content was up regulated after 14 days very prolonged exercise. Supported by the Center of Healthy Aging. Rosenkilde et al. Am J Clin Nutr. 2015 Oct 21. pii: ajcn109918. (Epub ahead of Print)