Disposition of metals after portal and systemic administration to rats

To determine if metals undergo significant hepatic presystemic elimination, male Sprague-Dawley rats were administered solutions of ionic 109Cd, 64Cu, 203Hg and CH3 203Hg, 210Pb, and 113Sn at 1.0 mumol metal/kg into either the ileocolic (portal administration) or femoral vein (systemic administration). Serial blood and bile samples were obtained for 90 min after administration. Whereas the area under the blood concentration vs time curve after portal administration was not less than that following systemic administration or any metal, route-dependent differences in distribution did occur. Portal, in comparison to systemic administration, resulted in a higher blood/plasma concentration ratio for mercury and lower ratio for lead. These data suggest that the liver may play a role in the distribution of these metals within the blood. In addition, the biliary excretion of mercury, methylmercury, cadmium, and lead was higher after portal than after systemic administration. These route-dependent differences in disposition suggest that some degree of hepatic presystemic elimination occurs for several metals.