Abstract
In the pregnant rat, the yolk sac, which possesses true placental functions, is a vitamin D target organ. We tested its ability to hydroxylate 25-hydroxy- and 1,25-dihydroxyvitamin D3 (25-OHD3 and 1,25-(OH)2D3). 24,25-Dihydroxy- and 1,24,25-trihydroxyvitamin D3 were produced by rat yolk sac homogenates incubated with tritiated 25-OHD3 and 1,25-(OH)2D3. Rat yolk sac homogenates also formed small amounts of 25,26-dihydroxyvitamin D3. These newly synthesized metabolites were isolated and identified by Sephadex LH-20 chromatography, high performance liquid chromatography, and periodate cleavage. Yolk sac 25-OHD3- and 1,25-(OH)2D3-24-hydroxylases were present in mitochondria and were of a mixed function oxidase nature. They were detected in the yolk sac as early as day 12 in the embryonic period and until the end of gestation. No hydroxylation occurred in maternal liver, amnion, fetal brain, or skin homogenates. Both 24-hydroxylases were detected in pure isolated rat yolk sac endodermal cells. This may be of physiological importance, since they are the 1,25-(OH)2D3 target cells in the yolk sac. Injection of 1,25-(OH)2[3H]D3 into rat yolk sac vitelline veins strongly suggested that the yolk sac vitelline veins strongly suggested that the yolk sac produced 1,24,25-(OH)3D3 in vivo. We conclude that the yolk sac and more precisely its endodermal cells may help to control vitamin D metabolism within the fetoplacental unit.
Highlights
In the pregnant rat, the yolk sac, which possesses 24,25-dihydroxyvitamin D3 and 1,24,25-trihydroxyvitamin D3. true placental functions, is a vitamin D target organ
Yolk sac 25-OHD 3- and 1,25-(OH) 2D 3-24-hydroxylases were present in mitochondria and were of a mixed function oxidase nature
The residue after rotatory evaporation under vacuum was redissolved in a small amount of ethanol and aliquots were or Sephadex LH-20 chromatography in the control experiments in which 25-OH[ 3H]D 3 was incubated with Tris buffer alone or when the homogenates were boiled for 15 min prior to incubation
Summary
Animals and Materials-Normal pregnant Wistar rats were obtained from Lessieux (France) and fed ad libitum with a normal diet (UAR 103). In Vivo Metabolism of 1,25-(OH)2[3H/D3 after Its Injection into the Vitelline Vein of the Yolk Sac-In vivo experiments were performed on normal pregnant rats, on day 20 of gestation. Blood was collected from the injected fetuses via the axillary vessels and yolk sacs were carefully removed and immediately frozen in liquid nitrogen. In vitro experiments were performed on tissues obtained from the water solvent system, run at a rate of 1.2 ml/min, was used to identify normal pregnant rats on days 18 and 19 of gestation. Yolk sacs were cut into small pieces and homogenized LH-20 chromatography and HPLC were used and gave the same in 5 volumes of Tris buffer by 4 passes in a Potter-Elvehjem homog- results.
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