Boron and silicon: Effects on growth, plasma lipids, urinary cyclic amp and bone and brain mineral composition of male rats

Because boron resembles silicon in its chemical properties, an experiment was performed to determine if excessive dietary boron would affect the response to silicon deprivation and, conversely, if silicon would influence the effects of an excessive intake of boron. Male weanling Sprague‐Dawley rats were assigned to groups of six or 12 in a two‐by‐two factorially arranged experiment. Supplemented to a ground corn/casein diet containing 1.2 μg silicon and 3 μg boron per gram were silicon as sodium metasilicate at 0 or 50 μg/g and boron as orthoboric acid at 0 or 500 μg/g diet. At nine weeks, animals fed high dietary boron had significantly decreased final body weights, liver‐weight‐to‐body‐weight ratios, urinary cAMP concentrations, plasma triglyceride, cholesterol, glycine, valine, leucine, and lysine concentrations and skull copper, sodium, and manganese concentrations. High dietary boron also significantly increased brain‐weight‐to‐body‐weight ratios, magnesium concentrations of femur, brain, and plasma, zinc concentration of femur, and iron concentration of skull. The bone mineral findings suggest that excess dietary boron exerts subtle effects on bone composition. Dietary silicon affected blood urea nitrogen, hematocrit, hemoglobin, and the concentrations of plasma threonine and aspartic acid in animals fed excess boron. Depression of the testes‐weight‐to‐body‐weight ratio of animals fed 500 μg boron per gram diet was most marked in animals not fed silicon. Although excessive dietary boron did not markedly enhance the response of rats to silicon deprivation, dietary silicon affected their response to high dietary boron. Thus, dietary silicon apparently can influence boron toxicity.