Rachitogenic activity of dietary strontium. I. Inhibition of intestinal calcium absorption and 1,25-dihydroxycholecalciferol synthesis.
نویسندگان
چکیده
Inhibition of calcium absorption by dietary strontium is the result of a block in the renal synthesis of 1,25-dihydroxycholecalciferol (1,25-(OH)&C) from 25-hydroxycholecalciferol (25-OHCC). The administration of 1,25-(OH)&C but not 25-OHCC restores to normal calcium absorption in strontium-fed chicks. Kidney mitochondria from strontium-fed chicks do not metabolize 25-OHCC to 1,25-(OH)&C, but rather to a metabolite designated Peak V,. The function of Peak V, is unknown while it is believed that 1,25-(OH)&C is the metabolically active form of vitamin D in the stimulation of calcium absorption from intestine and mobilization from bone. The changes in the kidney metabolism of 25-OHCC in response to dietary strontium occur over a period of several days and correlate closely with changes in intestinal calcium absorption. Feeding a normal calcium diet can correct the strontiuminduced inhibition of intestinal calcium absorption. This restoration of calcium absorption correlates with an increased rate of in vitro 1,25-(OH)&C synthesis. The exact mechanism whereby strontium alters the renal metabolism of 25-OHCC is unknown. However, indirect evidence suggests that it may operate through humoral agents such as parathyroid hormone, or calcitonin, or both, which are responsible for maintenance of plasma calcium concentration.
منابع مشابه
Rachitogenic Activity of Dietary Strontium I. INHIBITION OF INTESTINAL CALCIUM ABSORPTIOS AND 1,25-DIHYDROX1-CHOLECALCI Ipk:ROL
Inhibition of calcium absorption by dietary strontium is the result of a block in the renal synthesis of 1,25-dihydroxycholecalciferol (1,25-(OH)&C) from 25-hydroxycholecalciferol (25-OHCC). The administration of 1,25-(OH)&C but not 25-OHCC restores to normal calcium absorption in strontium-fed chicks. Kidney mitochondria from strontium-fed chicks do not metabolize 25-OHCC to 1,25-(OH)&C, but r...
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Administration of 60 pmoles of 1,25-dihydroxycholecalciferol to vitamin D-deficient rats on a low calcium diet gives a maximal intestinal calcium transport response in 7 hr and a maximal bone calcium mobilization response in 12 hr. During the 48 hr after injection of radioactive 1,25-dihydroxycholecalciferol, unchanged 1,25-dihydroxycholecalciferol accounts for 71-98% of the radioactivity found...
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Stimulation of intestinal calcium transport by the hormone 1,25-dihydroxycholecalciferol appears to involve RNA transcriptions and the synthesis of new proteins. Although one of these proteins has been identified as calcium-binding protein, no RNA molecules specifically induced by the hormone in the nucleus have been identified. Nuclear RNA from intestine of vitamin D-deficient chicks before an...
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ورودعنوان ژورنال:
- The Journal of biological chemistry
دوره 247 17 شماره
صفحات -
تاریخ انتشار 1972