Intestinal Absorption of Mercury in Vitro from Intestinal Contents of Methylmercury Administered Mice.

Abstract

Intestinal flora plays an important role in the decomposition and fecal excretion of methylmercury. The assumed mechanism is that decomposition of organic mercury (o-Hg) to inorganic mercury (i-Hg) by intestinal flora in cecum decreases the reabsorption of mercury in large intestines. To confirm this hypothesis, we examined the large intestinal mercury absorption in vitro from intestinal contents of methylmercury administered mice. Methylmercury (2 mg Hg/kg) was administered intraperitoneally to adult female mice, and the contents of small intestine (ileum) and cecum were taken out 24 hr after the administration. Ratios of organic mercury to total mercury in small intestinal content and cecal content were 86% and 49%, respectively. Contents fo both samall intestine and cecum were packed into cecum and colon of normal mice, respectively, and were incubated in a medium (Tyrode’s solution) at 37°C for 2 hr. 73% of total mercury (t-Hg) was absorbed from small intestinal content into the cecum and medium after the incubation. On the other hand, only 34% of t-Hg was absorbed from cecal content; most i-Hg remained unabsorbed. However, the absorption rate of t-Hg increased to 57% when the cecal content from antibiotics treated mice was used, because of the high percentage (90%) of o-Hg contained. These results suggest that o-Hg in small intestinal and cecal contents can be reabsorbed by cecum and colon in vivo, and that the decomposition of o-Hg to i-Hg by intestinal flora decreases the intestinal reabsorption rate of t-Hg in methylmercury exposed mice.