NICKEL METABOLISM IN HUMANS INVESTIGATED WITH AN ORAL STABLE-ISOTOPE

We report the results of the first complete study of nickel metabolism in human subjects using a stable nickel isotope (Ni-62) as tracer. Fo ur healthy adult subjects (two women and two men) fasted overnight bef ore ingesting 10 mu g Ni-62/kg body wt. Blood samples were drawn after fixed intervals of time and the total daily output of urine and feces was collected for the first 5 d after dose ingestion. Ni-62 in, plasm a, urine, and feces was determined by isotope-dilution inductively cou pled plasma-mass spectrometry with Ni-61. The direct measurement of th e fecal excretion of the tracer allowed a reliable assessment of nicke l absorption from the gastrointestinal tract and we found no evidence of the excretion of absorbed nickel via the gut. The percentage absorp tion calculated from the amount of Ni-62 excreted in the feces ranged from 29% to 40%. Urinary excretion over 5 d ranged from 51% to 82% of the absorbed dose. Plasma Ni-62 peaked between 1.5 and 2.5 h after ing estion and decreased by a factor of > 10 over the next few days. We ob served low between-subject variability of nickel absorption and excret ion. Confounding factors such as contamination and dietary intake of n ickel, which hampered earlier measurements in subjects dosed with natu rally abundant nickel, were eliminated by using the tracer isotope Ni- 62.