title: Can information on the gastrointestinal absorption of actinide elements by neonatal rats, guinea pigs, dogs and swine be extrapolated to man?
abstract: Neonatal mammals that acquire passive immunity by absorbing immunoglobulins from mother's milk (colostrum), as well as species that develop immunity prenatally, absorb macromolecules from the gut. This permeability of the GI tract to large molecules also serves as a route of entry for actinides in quantities greatly in excess of adult absorption. Administration of 238Pu nitrate to piglets results in absorption that is 1000 times the adult value but neonatal dogs, guinea pigs and rats absorb only 100 times more 238Pu than adults. Neonatal pigs and rats retain as much as 60% of the dose in the gut mucosa for several days but dogs and guinea pigs retain much less. We have also found this difference in GI tract 238Pu retention to occur after inhalation, indicating that the gut is an important route of entry for actinides that are inhaled by neonates. Although retention of different gavaged actinides by suckling rats is within the same range (1-3%) we found retention by piglets to range between 35% for 233U and about 2% for 237Np, 244Cm and 241Am nitrate. Piglets that were gavaged with 238Pu nitrate retained 19% in the liver and carcass a week later. After one year, half of that still remained. Neonatal rats, on the other hand, retained 3% initially and only 0.1% at one year. While the GI tract of the human infant is probably not nearly as permeable to macromolecules as that of the swine, it is known to be more permeable to macromolecules than that of the adult human. If actinide absorption is also increased in the child, the retention of these elements would probably be more like that in swine than in rats, because of the greater similarity between man and swine in skeletal maturation, in retention of actinides in liver and their longer life span. These studies suggest a need for further information on neonatal absorption of actinides in a large animal species that has a developing GI function more similar to that of humans.
mesh_terms: D008671:Actinoid Series Elements / Q000378:metabolism*; D000284:Administration, Oral; D000818:Animals; D000831:Animals, Newborn; D004064:Digestive System / Q000378:metabolism; D004285:Dogs; D004781:Environmental Exposure; D006168:Guinea Pigs; D006801:Humans; D007408:Intestinal Absorption / Q000528:radiation effects*; D051381:Rats; D011919:Rats, Inbred Strains; D013552:Swine
chemical_list: D008671:Actinoid Series Elements