Vitamin D3 effect on the calcium content in subcellular fractions of rat intestinal mucosa.

IITOYO et al. and LAWSON et al. reported that vitamin D3 caused a slight de crease in the activities of Mg-activated DNA-dependent RNA polymerase (1, 2) and Mn++-activated DNA-dependent RNA polymerase (2). However, it is known that calcium inhibits RNA polymerase (3). Since the calcium content of the in testine in vitamin D-treated animals must be higher, the decrease in RNA poly merase activities by vitamin D3 might be considered to be derived from the increases in nuclear calcium. Gounelle and Raoul demonstrated that the calcium content in rat liver nuclei was slightly increased by vitamin D3 (4). However, there is no information about the calcium content in the subcellular fractions of rat intestinal mucosa. Thus, in this report, calcium content in the subcellular fractions of rat intestinal mucosa with various vitamin D3 status was determined by atomic absorp tion spectroscopy, and the effect of vitamin D3 on RNA polymerase activities was discussed. Vitamin D-deficient rats and their intestinal mucosal subce1lular fractions were prepared as described by IITOYO et al. (1). Female rats of Wistar strain weigh ing 40-50 g were raised on Rachitogenic diet No. 2, U. S. P. (N. B. Co.) for 4 weeks in a dark room. Vitamin D3 was dissolved in the mixture of ethanol and propylene glycol (1:9) and a part of the solution equivalent to 2,000 IU of vitamin D3 was orally administered to vitamin D-deficient rats 1, 3 and 16 hr before sacrifice. Animals were fasted 24 hr before sacrifice. The calcium contents of rat intestinal mucosal subcellular fractions were measured by the method of atomic absorption spectroscopy after ashing of cellular fractions (5). As shown in Table 1, the calcium content in homogenate of intestinal mucosa was not significantly changed by vitamin D3 administration, whereas the subcellular distribution of calcium was changed significantly. The intestinal mitochondria the calcium in vitamin D-deficient rat was high, and it was decreased significantly