Characterization of the renal and intestinal adaptations to dietary calcium deprivation in growing female rabbits.

To characterize the time courses and efficiencies of the renal and intestinal adaptations to dietary Ca deprivation, growing female albino rabbits were fed a low-Ca diet for up to 44 days while they were housed in metabolism cages. Urinary Ca excretion decreased markedly within 8 h of Ca restriction and became essentially undetectable after 14 days. This persisted as long as dietary Ca was low. The intestinal Ca absorption observed during the predeprivation control period was initially changed to net secretion with dietary Ca restriction. However, after 21 days of the low-Ca diet, intestinal Ca absorption was observed. Fecal Ca contents decreased appropriately with Ca deprivation, but never became undetectable. Hyperphosphaturia, which occurred within 8 h of Ca deprivation and persisted as long as dietary Ca was restricted, diminished positive P balance, despite increased intestinal P absorption. Intestinal hyperabsorption and renal conservation of Ca were observed after dietary Ca repletion, suggesting the presence of driving forces for the restitution of Ca deficits incurred by Ca deprivation during growth. We conclude that there are appropriate intestinal and renal homeostatic adaptations to dietary Ca deprivation in the growing female rabbit and that the latter are more rapidly induced and ultimately more efficient than the former.