The gastrointestinal absorption and retention of niobium in adult and newborn guinea pigs.

The gastrointestinal absorption of 95Nb ingested in milk by adult guinea pigs on a milk-supplemented diet was estimated as 0.8 +/- 0.2% (SEM; n = 4) and a value of 1.4 +/- 0.2% was obtained for guinea pigs fasted for 24 h before and 2 h after the oral administration of 95Nb in a citrate solution. The absorption in 2-day-old animals given the 95Nb-citrate solution was estimated as 1.5 +/- 0.2% (SEM; n = 3). These results support the values currently used for radiological protection purposes to calculate doses from the ingestion of niobium isotopes; these are 1% for adults and 2% for infants in the first year of life. Intestinal retention of niobium in newborn guinea pigs was low, unlike retention in other species, but consistent with observations of the retention of other elements in guinea pigs. It is considered that retention in human neonates is likely to be most similar to that in guinea pigs. Whole-body retention of 95Nb after systemic administration in citrate solution was slightly lower in 2-day-old guinea pigs than in adults, with rapid excretion of about 50% over the first day compared with 40% in adults. Subsequent clearance was similar in the two age groups with a retention half-time of about 30 days.