The effects of small-bowel resection or bypass on the rat skeleton.

The bones of adult rats became progressively osteopenic 1 to 5 weeks following jejunoileal bypass or resection. These changes were accompanied by increased levels of metaphyseal enzyme activities as well as by loss of histochemically identifiable osteoid. Osteoid tissue and the ability to mineralize skeletal collagen were recovered more rapidly and fully in the resection group than in the bypass group. Metaphyseal alkaline phosphatase concentrations increased in both groups coincident with the elevated lysosomal enzymes levels, and the skeletons showed a calcium deficit (low Ca/HOPr ratio) within the first 3 weeks. In resected rats the osteopenia and bone blood chemistry were consistent with hyperparathyroidism secondary to impared Ca absorption. In bypassed rats the results suggest that the osteopenia might be related to the release of a "resorptive factor" from the excluded intestinal segment.