Placental strontium

Calcidiol la-hydroxylase is not restricted to the kidney, but is also found in placenta, bone cells (in culture), mammary glands, and keratinocytes. The placental enzyme makes a significant contribution to fetal calcitriol, but it is not clear whether the calcidiol 1-hydroxylase activity of other tissues is physiologically significant or not. Acutely nephrectomized animals given a single dose of calcidiol do not form any detectable calcitriol, but there is some formation of calcitriol in anephric patients, which increases on the administration of cholecalciferol or calcidiol. However, thus extrarenal synthesis is not adequate to meet requirements, so that osteomalacia develops in renal failure (Section 3.4.1). The enzyme is inhibited, or possibly repressed, by strontium ions this is the basis of strontium-induced vitamin D-resistant rickets, which responds to the administration of calcitriol or la-hydroxycalciol, but not calciferol or calcidiol (Omdahl and DeLuca, 1971). 

Although placental transfer of strontium has been demonstrated in humans and animals exposed to strontium by other routes of exposure (see Section 3.4.2.2), only one study has examined placental transfer after a dose to the respiratory tract. Pregnant rats received an intratracheal dose of 89Sr-enriched fly ash (sieved to have a particle diameter of distribution of 90% less than 20 pm) on days 14-18 of gestation. 

Hartsook EW, Hershberger TV. 1973. Strontium-calcium discrimination during placental transfer and fetal uptake in rats Effect of gestation duration. Proc Soc Exp Biol Med 143(2) 343-349. 

Sikov MR, Meznarich HK, Traub RJ. 1991. Comparison of placental transfer and localization of caesium strontium and iodine in experimental animals and women. Int J Radiat Biol 60(3) 553-555. 

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