Two different mechanisms are involved in nutritional regulation of lipoprotein lipase in guinea-pig adipose tissue.

Lipoprotein lipase activity in adipose tissue responds rapidly to changes in the physiological state. To study what mechanisms are involved in the regulation, guinea pigs were fasted and the decrease in adipose-tissue lipoprotein lipase activity was compared with the decreases in mRNA and lipase synthesis. The mRNA pattern (three species) did not change. There was a close parallelism between the abundance of lipase mRNA and relative lipase synthesis (immunoprecipitable 35S-labelled lipoprotein lipase as fraction of total [35S]protein after pulse-labelling with [35S]methionine). Total protein synthesis decreased on fasting, compounding the decrease in relative lipase synthesis. Lipoprotein lipase mRNA changed similarly in fat-pads and in isolated adipocytes, whereas lipase activity changed more in the pads, indicating disproportionally large changes in extracellularly located lipase. In old guinea pigs the decreases in lipoprotein lipase activity and lipase synthesis were comparable, but in young animals the change in lipase activity was substantially larger than the change in lipase synthesis. Refeeding of fasted young guinea pigs with glucose resulted in a rapid increase in lipoprotein lipase activity, but there was only a small change in lipase mRNA. Old animals responded slowly to refeeding. The results indicate that in older animals the major mechanism for regulation of adipose lipoprotein lipase activity is a relatively slow change in lipase mRNA, whereas in younger animals an additional, more rapid, regulation is exerted on the transport and turnover of the enzyme.