Distribution of orally administered 45Ca in rat intestinal tissues and vitamin D3 effect.

Abstract

The effects of vitamin D3 and actinomycin D on the radioactive calcium distribution were studied in the rat intestinal mucosa and muscle 5 and 30 minutes after the oral administration of 45Ca.1. Serum 45Ca concentration at 30 min was increased significantly in the vitamin D3 treated rat, and this vitamin D3 effect was inhibited by actinomycin D. The action of vitamin D3 and actinomycin D was not observed at 5 min. 2. 45Ca was observed in the proximal parts of intestinal mucosa (from pyloric end to 30cm) at 5 min, and at 30 min it came to be observed in the distal (40-60cm). 45Ca in the proximal parts at 5 min was reduced with vitamin D3, and actinomycin D did not seem to be influenced on this vitamin D3 action. 45Ca in the distal (at 30 min) was enhanced with vitamin D3 and this action was partially inhibited by actinomycin D. 3. 45Ca in muscle was lower than in mucosa. Observed pattern of 45Ca distribution at 5 min in muscle was not so different in vitamin D deficient and D3 treated rats. Actinomycin D did not exert its action on muscle at 5 min. Distribution patterns of 45Ca in muscle at 30 min were almost similar to the mucosal patterns. 4. Subcellular distribution of 45Ca was observed in the duodenal mucosa. Nuclei and cell debris (brush borders) have relative amounts of 45Ca 5 min after 45Ca administration. At 30 minutes, 45Ca of subcellular fraction was significantly decreased, especially in nuclei, cell debris and mitochondria. This reduction was moderated by vitamin D3. Actinomycin D inhibited this vitamin D3 action in microsomes and supernatants.From these results, it was suggested that calcium transport would be carried out in two ways, membrane permeable system (actinomycin D insensitive) and the system involving calcium carrier protein (actinomycin D sensitive).