Enhanced intestinal excretion of hexachlorobenzene in rats by intraluminal injection of hexadecane.

The effect of hexadecane on the intestinal excretion of hexachlorobenzene was studied in female Sprague-Dawley rats dosed twice with 14C-hexachlorobenzene at 50 mg kg-1 per os. Injection of 75 mg n-hexadecane into ligated and unligated segments of the intestine increased concentrations of hexachlorobenzene in intestinal contents by about two- or three-fold in jejunal and ileal segments, and about two-fold in the cecal-colon segment. The jejunum appeared to be the site of greatest excretion of hexachlorobenzene followed by the ileum, the cecum and the colon. This order is opposite to our previous data from animals with an undisturbed intestinal passage. The apparently greater excretion of hexachlorobenzene into the small intestine is probably due to its much larger surface area than that of the large intestine. However, the residency time of luminal contents in the large intestine normally exceeds that in the small intestine by about 20--40-fold, which apparently more than compensates for the difference in relative surface area between small and large intestine. Thus, residency time appears to be a more important factor than surface area in determining the intestinal elimination of hexachlorobenzene. These results with hexachlorobenzene are probably typical of physiological disposition of lipophilic halogenated hydrocarbons generally.