Effect of age on duodenal 1,25-dihydroxyvitamin D-3 receptors in Wistar rats.
We confirmed our previous observation that duodenal Ca2+ absorption and serum 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels declined concurrently in old (24 months old) rats as compared to young (6 months old) rats. It is well known that 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3) expresses its action after binding to specific receptor molecules. In this paper, we compared certain properties of rat duodenal 1,25-(OH)2D3 receptors from old and young animals. Receptor preparations were incubated with [3H]1,25-(OH)2D3 to quantitate the number of unoccupied and total receptor sites and showed that total and unoccupied receptor sites decreased by 22 and 16%, respectively in old rats. Endogenously occupied sites were reduced by 43% in duodenum of the old rat and, consequently, the percentage of receptor occupancy also declined. Age did not affect the dissociation constant (KD) of 1,25-(OH)2D3 from the receptor; the sedimentation coefficient (3.3 S) of the tritiated 1,25-(OH)2D3-receptor complex in sucrose density centrifugation; or its affinity for DNA. The data are consistent with the hypothesis that the age-related decline in Ca2+ absorption in the intestine may be due, in part, to the decrement in the circulating level of 1,25-(OH)2D and a reduction of intestinal 1,25-(OH)2D3 receptor occupancy status.
Takamoto
S
S
Laboratory of Biological Chemistry, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224.
Seino
Y
Y
Sacktor
B
B
Liang
C T
CT
D000375:Aging / Q000378:metabolism*; D000818:Animals; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000378:metabolism; D002846:Chromatography, Affinity; D004247:DNA / Q000378:metabolism; D004386:Duodenum / Q000032:analysis*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000032:analysis*
D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D004247:DNA; D002117:Calcitriol; D002118:Calcium