Stimulation by low phosphorus and low calcium diets of duodenal absorption of phosphate in betamethasone-treated chicks.

Although the inhibitory effect of glucocorticoids on the intestinal absorption of calcium is well recognized, their effect on the absorption of phosphate is less well documented. We studied the effect of the oral administration of betamethasone (BM; 25 micrograms/kg per day) on the duodenal absorption of phosphate in chicks fed normal calcium, normal phosphorus (NCaNP), normal calcium, low phosphorus (NCaLP) or low calcium, normal phosphorus (LCaNP) diets using the ligated loop technique in vivo. The daily oral administration of BM for 8 days significantly reduced the absorption of phosphate in chicks fed the NCaNP diet (21% decrease) but had less effect in chicks fed the NCaLP (14% decrease) or LCaNP (9% decrease) diets in which birds the absorption of phosphate was significantly raised (49 and 87% respectively). In one group of chicks, BM was administered for 9 days before the birds were transferred to the NCaLP or LCaNP diets. Adaptation was again unaffected by the treatment. Thirty-four per cent of the absorbed phosphate was retained in the duodenal tissue. Treatment with BM reduced the amount retained but this may have been caused by the lower weight of the duodenal segment in these chicks as BM administration markedly reduced growth rate. We have concluded that the duodenal absorption of phosphate in the chick can be inhibited by treatment with BM, although this may be secondary to the reduced rate of growth, but the increase in the absorption of phosphate caused by feeding NCaLP or LCaNP diets was unaffected by the steroid.