1. We have used young pigs, each prepared surgically with a Thiry-Vella loop of proximal small intestine, to study the time course of changes in the intestinal absorption of calcium, phosphate, sodium, glucose and water and on the plasma levels of 1,25-dihydroxyvitamin D after treatment of the animals with glucocorticoids.
2. Perfusion of the intestinal loop for 6 h with a solution containing hydrocortisone or betamethasone was without effect on the absorption of calcium or phosphate.
3. The oral administration of betamethasone stimulated the absorption of calcium and phosphate by 15–20% for 2–3 days before the trend was reversed and absorption was progressively reduced.
4. Chronic treatment with betamethasone inhibited only the active component of calcium and phosphate absorption.
5. Treatment with betamethasone was associated with a sustained 25–50% increase, to a maximum by 2 days, in the absorption of sodium, glucose and water.
6. Plasma levels of 1,25-dihydroxyvitamin D were reduced within 2 days of the start of treatment and reached a minimum (40–50% decrease) in 4–6 days.
7. We conclude that the initial stimulation of calcium and phosphate absorption is caused by the increased absorption of water. The long-term decrease in absorption may not be caused solely by the decreased circulating levels of 1,25-dihydroxyvitamin D since absorption continued to fall for several weeks after 1,25-dihydroxyvitamin D levels had reached a minimum.