SERUM AND URINARY BORON LEVELS IN RATS AFTER SINGLE ADMINISTRATION OFSODIUM TETRABORATE

The pharmacokinetics of boron was studied in rats by administering a 1 ml oral dose of sodium tetraborate solution to several groups of rats (n =20) at eleven different dose levels ranging from 0 to 0.4 mg/100 g body weight as boron. Twenty-four-hour urine samples were collected after boron administration. After 24 h the average urinary recoverv ra te for this element was 99.6 +/- 7.9. The relationship between boron d ose and excretion was Linear (r = 0.999) with a regression coefficient of 0.954. This result suggests that the oral bioavailability (F) of b oron was complete. Another group of rats (n = 10) was given a single o ral injection of 2 ml of sodium tetraborate solution containing 0.4 mg of boron/100 g body wt. The serum decay of boron was followed and fou nd to be monophasic. The data were interpreted according to a one-comp artment open model. The appropriate pharmacokinetic parameters were es timated as follows: absorption half-life. t(1/2a) = 0.608 +/- 0.432h; elimination half-life, t(1/2) = 4.64 +/- 1.19 h; volume of dis tributi on, Vd = 142.0 +/- 30.2 ml/100 g body wt.; total clearance, C-tot = 0. 359 +/- 0.0255 ml/min per 100 g body wt. The maximum boron concentrati on in serum after administration (C-max) was 2.13 +/- 0.270 mg/l, and the time needed to reach this maximum concentration (T-max) was 1.76 /- 0.887 h. Our results suggest that orally administered belie acid is rapidly and completely absorbed from the gastrointestinal tract into the blood stream. Boric acid in the intra vascular space does not have a strong affinity to serum proteins, and rapidly diffuses to the extr avascular space in proportion to blood flow without massive accumulati on or binding in tissues. The main route of boron excretion from the b ody is via glomerular filtration. It may be inferred that there is par tial tubular resorption at low plasma levels. The animal model is prop osed as a useful tool to approach the problem of environmental or indu strial exposure to boron or in cases of accidental acute boron intoxic ation.