Effect of fasting on free fatty acid, glycerol and cholesterol concentrations in blood plasma and lipoprotein lipase activity in adipose tissue of cattle.

Contributing factors in the regulation of triglyceride deposition in and fatty acid release from bovine adipose tissue were investigated. Six Holstein steers were fasted for 9 days and then refed for 41 days. Blood samples from the jugular vein and adipose tissue samples from backfat biopsies were taken during fasting and refeeding periods. Concentrations of plasma free fatty aids, glycerol and cholesterol and activity of lipoprotein lipase in adipose tissue from fasted and refed steers were measured. Plasma free fatty acid concentration increased almost eightfold during fasting. After 4 days of refeeding, free fatty acids in plasma had returned to basal concentration. Fasting had no effect on plasma cholesterol concentration; during refeeding, concentration decreased slightly and then returned to the basal concentration. Lipoprotein lipase activity decreased to 37% of the basal concentration during fasting and increased to 100% above prefasting values during refeeding. Significant changes in plasma free fatty acid and glycerol concentrations and in activity of lipoprotein lipase in adipose tissue during fasting and refeeding suggest that fatty acid mobilization and triglyceride uptake by adipose tissue of cattle adapt to great changes in energy intake. Correlations of measured blood metabolites in fasted and refed steers demonstrate that changes in rates of lipolysis and of triglyceride uptake by adipose tissue vary in a reciprocal manner.