Effects of fasting, adrenalectomy and cortisol on bone composition and density

¹ Department of Pediatrics, University of Wisconsin Medical School, Madison, Wisconsin

Cortical marrow-free bone from white rats was analyzed for water, sodium, calcium and citrate content after fasting for 24 and 120 hours with and without adrenalectomy or cortisol administration. Density of fresh cortical bone from all animals was calculated from determinations of volume made by weighing fragments in air and below the surface of water. The rapidly exchangeable fraction of bone sodium was determined, using radiosodium, in all animals killed at 120 hours. There were no observed changes in the sodium content, its exchangeability, or citrate content of bone with any treatment despite an average decrease in serum sodium of 7 mEq/l. and a twofold increase in serum citrate with adrenalectomy at 120 hours. An unexplained slight increase in bone density occurred in cortisol-treated animals after 120 hours which did not make changes in sodium and citrate content more apparent when calculated on a volume basis. With fasting alone there were no observed differences in bone composition but there was an increase in serum citrate at 120 hours which did not occur in fasted rats given cortisol. It was concluded that the hyponatremia and salt depletion of fasted adult rats subjected to adrenalectomy are not sufficient to cause depletion of bone sodium and that changes in serum citrate concentration associated with alterations in adrenal function do not have a detectable effect on bone citrate content.