In:
Journal of Bone and Mineral Research, Wiley, Vol. 14, No. 1 ( 1999-01), p. 57-64
Kurzfassung:
The sex steroid 17β‐estradiol (17β‐E 2 ) has a broad range of actions, including effects on calcium and bone metabolism. This study with 3‐month‐old Brown Norway rats was designed to investigate the role of 17β‐E 2 in the regulation of calcium homeostasis. Rats were divided in four groups, sham‐operated, ovariectomized (OVX), and OVX supplemented with either a 0.025‐mg or 0.05‐mg 17β‐E 2 pellet implanted subcutaneously. After 4 weeks, in none of the groups was serum calcium, phosphate, or parathyroid hormone altered compared with the sham group, while only in the OVX rats was a significant reduction in urinary calcium found. Bone mineral density and osteocalcin were modified, as can be expected after OVX and 17β‐E 2 supplementation. OVX resulted in a nonsignificant increase in serum 1,25‐dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ). Supplementation with either one of the 17β‐E 2 dosages resulted in an 80% reduction of 1,25(OH) 2 D 3 and only a 20% reduction in 25‐hydroxyvitamin D 3 levels. OVX, as well as supplementation with 17β‐E 2 , did not affect serum levels of vitamin D binding protein. As a consequence, the estimated free 1,25(OH) 2 D 3 levels were also significantly decreased in the 17β‐E 2 ‐supplemented group compared with the sham and OVX groups. Next, the consequences for intestinal calcium absorption were analyzed by the in situ intestinal loop technique. Although the 1,25(OH) 2 D 3 serum level was increased, OVX resulted in a significant decrease in intestinal calcium absorption in the duodenum. Despite the strongly reduced 1,25(OH) 2 D 3 levels (18.1 ± 2.1 and 16.4 ± 2.2 pmol/l compared with 143.5 ± 29 pmol/l for the OVX group), the OVX‐induced decrease in calcium absorption could partially be restored by supplementation with either 0.025 mg or 0.05 mg of 17β‐E 2 . None of the treatments resulted in a significant change in calcium handling in the jejunum, although the trends were similar as those observed in the duodenum. 17β‐E 2 did not change the VDR levels in both the intestine and the kidney. In conclusion, the present study demonstrates that 17β‐E 2 is positively involved in intestinal calcium absorption, and the data strengthen the assertion that 17β‐E 2 exerts this effect independent of 1,25(OH) 2 D 3 . In general, 17β‐E 2 not only affects bone turnover but also calcium homeostasis via an effect on intestinal calcium absorption.
Materialart:
Online-Ressource
ISSN:
0884-0431
,
1523-4681
DOI:
10.1359/jbmr.1999.14.1.57
Sprache:
Englisch
Verlag:
Wiley
Publikationsdatum:
1999
ZDB Id:
2008867-X
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