We examined in rats the intestinal absorption of 4 different dietary fats (rapeseed oil (RO), rapeseed oil interesterified with decanoic acid (R/C10), olive oil (OO), and butter) after feeding a high-fat (30 wt-%) diet rich in trans-fatty acids (mainly trans-C18:1) for 3 weeks. The trans-fatty acids were used as markers for the contribution from the endogenous stores to the circulating pool of fatty acids during the absorption, thereby enabling us to measure differences in release of endogenous fatty acids caused by differences in the administered fats. Rats with cannulated left carotid artery were divided into 4 groups after a 24 h fast and fed intragastrically with a fat load. Blood samples were collected regularly and fatty acid compositions as well as insulin and glucagon concentrations were determined (experiment 1). In 2 other groups of rats the mesenteric lymph duct was cannulated and they were fed intragastrically either R/C10 or butter. Lymph was collected and analyzed for fatty acid composition (experiment 2). The fatty acid composition of plasma lipids changed rapidly according to the administered fats and a biphasic response was observed for nearly all fatty acids investigated. Although decreasing during the early absorptive phase a continuous contribution of endogenous trans-C18:I and arachidonic acid was observed in plasma. Small differences were observed between the 4 dietary fats. In lymph, the transport of trans-C18:1 rose markedly after butter administration partly caused by the content of this fatty acid in butter, while the transport of trans-C18:1 after R/C10 was unchanged although still transported at a reasonable high rate. The transport of arachidonic acid increased after administration of both butter and R/C10. Minor changes were observed in plasma concentrations of insulin and glucagon during the absorption. (C) Elsevier Science Inc.