1,25-Dihydroxyvitamin D$\sb3$ (1,25(OH)$\sb2$D$\sb3$) acts through specific nuclear receptors (VDR) to bring about its biological effects. The following studies were performed to test the hypothesis that 1,25(OH)$\sb2$D$\sb3$ receptors in rat testis are different from those in kidney. Scatchard analysis revealed that VDR sites in testis have a 10-fold higher binding affinity than do the principal VDR sites in kidney. This analysis also demonstrated heterogeneity of VDR sites in kidney, with the lower affinity site being the most abundant Administration of 1,25(OH)$\sb2$D$\sb3$ upregulated VDR in kidney, but not in testis, heart, or lung. Scatchard analysis revealed that 1,25(OH)$\sb2$D$\sb3$ treatment upregulated the low affinity VDR site in kidney, while the high affinity site was no longer detectable. Intestine displayed upregulation of the single, low affinity VDR site, while testis showed no regulation of the single, high affinity site. Dexamethasone administration affected VDR levels as follows: increased in intestine, decreased in kidney, and no change in testis, heart, or lung. Scatchard analysis revealed that dexamethasone treatment upregulated the single, low affinity VDR site in intestine, but did not regulate the single, high affinity site in testis. In kidney, dexamethasone treatment completely downregulated the low affinity binding component, leaving only the high affinity site, whose binding affinity was similar to that of testis Competition for VDR revealed that synthetic analogs Ro24-2287 and KH-1060 display higher affinity for the principal kidney VDR form than for testis VDR, while analog EB-1089 showed the opposite pattern. Although the major VDR forms in kidney and testis showed no size differences based on immunoblot analysis, comparing the ability of VDR sites from kidney and testis to bind to DNA-cellulose revealed differences in the KCl concentration at which peak elution occurred Overall, these studies provide evidence in support of the hypothesis that the principal 1,25(OH)$\sb2$D$\sb3$ receptors in kidney and testis are different. In addition, the kidney appears to contain a second, high affinity binding site, which may be the same as the high affinity site in testis. These data thus provide evidence in support of the novel concept that there are multiple forms of the vitamin D receptor / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_26447 |
| Date | January 1993 |
| Contributors | Gensure, Robert Charles (Author), Walters, Marian R (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
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