The present study was addressed to determine whether the high expression of peroxisome proliferator-activated receptor-a (PPAR-a) in rat liver during the perinatal stage plays a role in the induction of liver lipoprotein lipase (LPL) expression and activity. Parallel increases in liver mRNA PPAR-a and LPL activity were found in newborn rats, and after a slight decline, values remained elevated until weaning. Anticipated weaning for 3 days caused a decline in those two variables as well as in the mRNA LPL level, and a similar change was also found in liver triacylglycerol concentration. Force-feeding with Intralipid in 10-day-old rats or animals kept fasted for 5 h showed high mRNA-PPARa and -LPL levels as well as LPL activity with low plasma insulin and high FFA levels, whereas glucose and a combination of glucose and Intralipid produced low mRNA-PPARa and -LPL levels as well as LPL activity. Under these latter conditions, plasma insulin and FFA levels were high in those rats receiving the combination of glucose and Intralipid, whereas plasma FF A levels were low in those force-fed with glucose. It is proposed that the hormonal and nutritional induction of liver PPAR-a expression around birth and its maintained elevated level throughout suckling is responsible for the induction of liver LPLexpression and activity during suckling.