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Adult male rats were surgically provided with a drainage catheter in the left thoracic lymphatic channel and an indwelling duodenal catheter for constant infusion of physiological saline–5% glucose. After an overnight fast, animals were given a single duodenal dose of an aqueous emulsion containing one of the following: oleic acid, corn oil, menhaden oil or a fish oil concentrate (FOC) and [1,2-3H]cholesterol. Digestion and absorption were estimated by recovering the total fatty acids in the thoracic duct lymph over a 24-h collection period (after subtraction of the “baseline” endogenous fatty acids in the lymph). Cholesterol absorption in the thoracic duct lymph was significantly reduced (P< 0.05) in the presence of menhaden oil or FOC compared to that in the presence of corn oil. With various fat feedings, the major increases in lymph fatty acids were directly related to the dietary fatty acid content. The relative amounts of eicosapentaenoic acid (EPA) and arachidonic acid (AA) in the thoracic lymph were influenced by the lipid content of the emulsion. The EPA/AA ratio in control, oleic acid and corn oil feedings ranged from 0.12 to 0.25. When marine oil was administered, the EPA/AA ratio was 0.78–0.98. The total amount of fatty acids found in the lymph after marine oil feeding was significantly less (P< 0.01) than that found after corn oil feeding. The results suggested that the digestion and absorption of menhaden oil and FOC were decreased as compared with corn oil. The EPA/AA ratio was increased in the thoracic lymph after dietary fish oil feeding.

Adult male rats were surgically provided with a drainage catheter in the left thoracic lymphatic channel and an indwelling gastric catheter for constant infusion of saline-glucose. After an overnight fast, animals were given a single gastric dose of an aqueous emulsion containing one of the following 1-14C-labeled fatty acids: oleic, arachidonic or eicosapentaenoic acid, and [1,2-3H]cholesterol. Absorption was estimated by the appearance of radioactivity in lymph over a 24-h collection period, and the lymph lipoprotein distributions and lipoprotein lipid distribution were determined in the 24-h samples. Although there were apparent differences in the rates of eicosapentaenoic and arachidonic acid absorption, the overall appearance (after 24 h) of these acids in lymph was quantitatively equivalent to that of oleate. Furthermore, cholesterol absorption from each fatty acid medium was quantitatively similar. The distributions of each fatty acid among major lymph lipoproteins were similar with 93–95% recovered in chylomicrons and very low density lipoprotein (VLDL) fractions. Furthermore in these lipoproteins, 85–91% of each of the three fatty acids was recovered as triglycerides. With both polyunsaturated fatty acids, there was greater incorporation into phospholipids and their precursor partial glycerides than with oleate. These studies suggest that unesterified eicosapentaenoic acid is absorbed efficiently into the lymphatic system, and has lymph lipoprotein and lipid distribution comparable to those of the more typical mono- and polyunsatured fatty acids.

Digestion and absorption of cocoa butter and palm kernel oil and their effect on cholesterol absorption were studied in adult male rats. Duodenal and thoracic duct catheters were inserted surgically into the anesthetized rats. After an overnight fast, animals were given a single duodenal dose of an aqueous emulsion containing [1,2-3H]cholesterol and one of the following: corn oil, cocoa butter or palm kernel oil. Digestion and absorption were estimated by recovering the total fatty acids in the thoracic duct lymph over a 24-h collection period (after subtraction of the baseline “endogenous fatty acids” in the lymph). Intestinal absorption of cholesterol into the thoracic duct lymph was reduced significantly (P< 0.05) in the presence of cocoa butter, compared to absorption when palm kernel oil or corn oil was administered. Compared to the absorption of corn oil (arbitrarily defined as 100%), the absorption of palm kernel oil and cocoa butter was 82 and 63%, respectively. The present study suggests that palm kernel oil absorption was not significantly different from that of corn oil. The lower absorbability of cocoa butter and its inhibitory effect on cholesterol absorption may explain in part why cocoa butter is less hypercholesterolemic and atherogenic than other equally saturated fats.