Effect of cortisol on [3H] 1,25-dihydroxyvitamin D3 uptake and 1,25-dihydroxyvitamin D3-induced DNA-dependent RNA polymerase activity in chick intestinal cells

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Abstract
Summary The influence of cortisol on intestinal DNA-dependent RNA polymerase activity was studied in purified nuclei of vitamin D-deficient or 1,25-dihydroxyvitamin D3-treated chicks. Six- to 7-week-old vitamin D-deficient cockerels were given 5 mg of cortisol or vehicle intraperitoneally 24 and 48 hours before sacrifice. Three hours before sacrifice, 200 ng of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was administered intracardially. Cortisol did not alter the uptake or metabolism of 1,25(OH)2D3 in the intestinal mucosa. After a 200 ng dose of 1,25(OH)2D3 thein situ intestinal ligated loop technique revealed a 39% increase in calcium absorption compared to control birds (P2D3, however, resulted in a significant decrease in intestinal calcium transportin vivo (P2D3-treated and 1,25(OH)2D3 plus cortisol-treated chicks had intestinal RNA polymerase II transcriptional activities that were significantly greater than those of vitamin D-deficient controls (P≤0.02,P≤0.005). There was no difference between RNA polymerase II and I+III activities of the 1,25(OH)2D3-treated birds and that of the cortisol plus 1,25(OH)2D3-treated birds. Vitamin D-deficient chicks treated with cortisol alone showed RNA polymerase I+III activity that was significantly higher (P≤0.01) than that of birds treated with vehicle alone. As transcription is not altered by cortisol following 1,25(OH)2D3 treatment, we suggest that cortisol may inhibit intestinal calcium transport by altering posttranscriptional or other events such as basolateral membrane calcium transport.