Uptake, distribution, and excretion of ³¹silicon in normal rats

This study examines the uptake, distribution, and excretion of ³¹-labeled silicic acid in rat tissues at 1, 2, and 4 h after intracardiac injection of ³¹Si(OH)₄. Plasma levels of ³¹Si deccrease rapidly from 0.71 ± 0.04% at 1 h to 0.07 ± 0.06% of the dose administered per milliliter at 4 h. ³¹Si in plasma was found to be virtually entirely nonprotein bound. Kidney, liver, and lung accumulated the greatest amounts of ³¹Si per gram of wet weight, with concentrations at 4 h suggesting both relatively avid uptake and retention. Bone, skin, spleen, muscle, and testes also accumulated ³¹Si, but the levels were considerably lower than the aforementioned organs. Brain, however, contained negligible concentrations of ³¹Si throughout the study, indicating active exclusion by the blood-brain barrier. The major portion of the administered ³¹Si, 77 ± 12%, was recovered in the urine within 4 h.