Relationship between plasma and tear fluoride levels in rabbit and man

Tear fluoride concentrations were determined in rabbits and man. Tear fluoride levels in reflex tears were higher in rabbits (2-10 mumol/l) than in man (1.4-4 mumol/l), while plasma levels were quite similar in both species (1.5-4 mumol/l). Chronic fluoride ingestion in rabbits over 29 days of 1, 5, 10, 25 or 50 (2.65 mmol/l) ppm fluoride in drinking water caused a dose-related increase in plasma, but not tear, levels of fluoride. The plasma:tear ratio went from 0.5 at baseline (1 ppm) to 1.8 after drinking water that contained 50 ppm F. Acute fluoride ingestion in man led to an increase in both plasma and tear fluoride levels that changed such that the plasma:tear ratio remained constant despite a 2-fold increase in plasma fluoride.