Recent analysis of the structure-function relationship of human PTH-related peptide (hPTHrP) has led to the discovery that its direct inhibitory activity on osteoclastic bone resorption resides fully in the 107-111 sequence of the peptide, as assessed by a bone resorption assay using isolated rat osteoclasts. Here we report that hPTHrP-(107-111) is inactive in neonatal mouse calvariae in culture. hPTHrP-(107-111), at doses of 10(-12)-10(-6) M and incubation periods up to 96 h, did not affect either basal or agonist-stimulated 45Ca release from prelabeled neonatal mouse calvariae, while salmon calcitonin was a potent and powerful inhibitor of both basal and stimulated 45Ca release from bone. Moreover, salmon calcitonin, but not hPTHrP-(107-111), inhibited the increase in osteoclast number in hPTHrP-(1-34)-treated bones. Furthermore, hPTHrP-(107-139) also failed to inhibit 45Ca release and the hPTHrP-(1-34)-induced increase in osteoclast number in this organ culture model when tested under conditions identical to those for hPTHrP-(107-111). The addition of indomethacin to hPTHrP-(107-111)- or hPTHrP-(107-139)-treated bones was without effect, excluding the possibility that the direct inhibitory activity of these peptides on osteoclasts is ablated by a prostaglandin-mediated mechanism. Although the mechanism underlying the apparent inability of the carboxyl-terminal PTHrP fragments to inhibit osteoclastic bone resorption in neonatal mouse calvariae is unknown, it may involve the complex microenvironment of osteoclasts in intact bone, which contains a large variety of cell types other than osteoclasts.
Crohn's disease is a type of inflammatory bowel disease of unknown etiology. Administration of indomethacin (Indo) to rats induces acute mucosal lesions similar to those observed in Crohn's disease patients, but the damage can be prevented by feeding the animals an elemental diet (ED). In this study, we examined changes in intestinal macroscopic appearance, permeability, and immunoglobulin production after administration of Indo to male Sprague-Dawley rats fed normal lab chow or an ED. Intestinal damage was induced by subcutaneous injection of Indo on two successive days. Mucosal permeability, as measured by urinary excretion of phenolsulfonphthalein, peaked on day 2 after Indo injection, whereas the most severe intestinal damage, as scored by macroscopic inflammatory changes, was observed on day 3. Flow cytometric analysis of mesenteric lymph node cells revealed that the proportion of CD45RA 1 cells was increased after Indo treatment. Furthermore, in vitro-cultured mesenteric lymph node and spleen lymphocytes from Indotreated rats produced higher levels of IgA and IgG than did cells from vehicle-treated rats. In contrast, IgG and albumin concentrations in plasma were significantly decreased by Indo administration. Notably, none of the Indo-induced changes was observed in ED-fed rats. These findings suggest that an ED may prevent the appearance of Indo-induced mucosal lesions, at least in part, by modulating intestinal permeability and antibody production.
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