A new low-molecular-weight calcium-binding ligand in rat small intestine

Three calcium-binding ligands in the cytosol of rat small intestine have been separated using Sephadex G-75 column chromatography. The estimated molecular weights of these ligands were 85,000, 10,000, and 800, respectively. The two high-molecular-weight ligands were found only in young rats, while the low-molecular-weight calcium-binding ligand was found in all age groups and appeared to be a calcium-bound prostaglandin metabolite. Oral administration of arachidonic acid increased and PGE₂ decreased $\text{in vivo}$ calcium absorption, while PGF₂ administration showed no discernible effect on this parameter. These results suggest that the intestinal calcium transport mechanism may be modulated by prostaglandins and related metabolites.