Boron affects energy metabolism in the streptozotocin-injected, vitamin D3-deprived rat

Dietary boron, in amounts usually found in human diets comprised mainly of fruits and vegetables, apparently affects both mineral and energy metabolism. Therefore, the effects of boron on a model system with a perturbed metabolic insulin-vitamin D3 axis was examined. Weanling male rats were fed a ground corn-high protein casein-corn oil-based diet (0.06 micrograms B/g and no supplemental vitamin D3) supplemented with B (as orthoboric acid) at 0 or 2.4 mg/kg. After 55 days, all rats were equilibrated in individual metabolic cages. After another 6 days, one half of the rats in both dietary groups were injected intraperitoneally with streptozotocin (STZ). All rats were killed 3 days after STZ treatment. STZ affected many aspects of energy metabolism. In the non-STZ rats, supplemental dietary boron substantially depressed plasma insulin, plasma pyruvate concentrations, and creatine kinase activity and increased plasma thyroxine (T4) concentrations. The finding that boron did not affect growth, but did affect several indices of energy metabolism in the non-STZ animals suggests that boron functions as a regulator of energy metabolism in the rat. A decrease in plasma aspartate transaminase activity (an indicator of enhanced cell membrane integrity) in the non-STZ rats suggests that boron exerts a protective influence over normal liver metabolism.