Earlier reports have shown that absorbed U4-labeled stearic (l), palmitic (2), and pentadecanoic (3) acids can be recovered, almost quantitatively, in intestinal or thoracic duct lymph. In the case of myristic acid, however, the highest recovery in lymph was about 80, and the lowest about 60 per cent of the absorbed C14. Still lower values (15 to 55 per cent) were observed with lauric acid, and, when decanoic acid was studied, the recoveries in lymph did not exceed 20 per cent of the amount absorbed (1). The above findings were taken to indicate that the major portion of absorbed shorter chain fatty acids is transported from the intestine via the portal pathway.

These earlier findings were obtained with rats in which cannulae had been inserted into either the thoracic duct or intestinal lacteals. In the present study, we investigated fatty acid absorption in normal rats that were not subjected to operative manipulations. It is shown that when C14-labeled palmitic acid is fed the ratio of plasma fatty acid-C” of the portal vein to that of the inferior vena cava is about unity, whereas in similar experiments with C14-labeled decanoic acid, the ratio exceeds unity. These results with intact rats are thus in agreement with the concept that long chain, saturated fatty acids are transported primarily, if not solely, via lymph, whereas short chain fatty acids enter by way of the portal system.