Absorption and metabolic fate of dietary 3H-squalene in the rat.

The absorption and metabolic fate of dietary squalene was investigated on the rat by administering a single oral dose of 3H-squalene and 14C-cholesterol. Experiments on rats with cannulated thoracic duct revealed that 3H-squalene was, like 14C-cholesterol, absorbed through the lymphatic vessels and that ca. 20% of absorbed 3H-squalene was cyclized to sterols during the transit through the intestinal wall. Feces contained 3H-sterols, indicating that newly synthesized mucosal sterols had been secreted into the gut lumen. In intact animals, 3H-squalene appeared in the circulation more rapidly than 14C-cholesterol and did not persist to any significant extent in the squalene-rich adipose and muscle tissues. The increase in dietary squalene load (8-48 mg) decreased the absorption percentage of 3H-squalene (45-26%) but did not affect the absorption of 14C-cholesterol (47%). Determination of fecal steroids revealed that during the first days absorbed 3H-squalene was eliminated to a significantly higher extent than 14C-cholesterol as fecal bile acids (34% vs 11%). The experiments indicate that the rat intestine has a marked capacity for absorbing dietary squalene and that the absorbed squalene is preferentially converted to bile acids in the liver.