The effect of actinomycin D, cycloheximide and glucocorticoids on the intestinal absorption of phosphate was studied. The effective intestinal absorption of 32P and 47Ca was determined simultaneously in intact rats in vivo using a whole body counter. Both, actinomycin D and cycloheximide caused a significant diminution of the intestinal absorption of phosphate whereas calcium absorption was not altered. Experiments with the in situ ligated loop technique were performed to eliminate the possibility that the action of the protein synthesis inhibitors could be due to an altered intestinal motility effect. Phosphate absorption was also significantly diminished under this condition. On the other hand, the administration of glucocorticoids produced a significant inhibition of phosphate and calcium absorption in the rat in vivo. The reported results indicate that proteins and/or enzymes with a rapid turn-over are involved in the mechanism of phosphate intestinal absorption, and confirm previous observations that phosphate and calcium are transported across the intestine by different mechanisms.

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The chronic ingestion of the leaves of the plant Solanum malacoxylon (SM) causes an endemic disease in the cattle of some areas of Buenos Aires province. The animals affected manifest loss of appetite and weight, hypercalcemia, hyperphosphatemia, and ectopic calcifications. In order to study the mechanism of the hypercalcemia provoked by the administration of SM, a calcium kinetic study was performed in control and treated adult intact rats. The animals receiving SM showed higher levels of serum calcium throughout the study. The body excretion of 47Ca and the size of the most rapidly exchangeable calcium pool were also elevated. On the other hand, the bone accretion rate and the urinary excretion of total hydroxyproline were significantly diminished. The results indicate that during the early phase of SM administration in intact rats, bone turnover rate is depressed.