Effects of lα,25-Dihydroxyvitamin D3andSolanum Glaucophyllumon Intestinal Calcium and Phosphate Transport and on Plasma Ca, Mg, and P Levels in the Rat
The responses elicited by a single dose of either S. glaucophyllum (SG) or 1.alpha.,25-dihydroxyvitamin D3 (1.alpha.,25-(OH)2D3) in vitamin D-deficient rats were qualitatively identical. Both compounds stimulated duodenal absorption of Ca and PO4 3 h after administration, and the effects persisted for 96 h. The SG effects on Ca transport were maximal at 6 h and exceeded the greatest response to 1.alpha.,25-(OH)2D3 which occurred at 48 h. While the early SG effects on PO4 absorption exceeded those of 1.alpha.,25-(OH)2D3, the latter compound had a much greater effect at 48 h. Both SG and 1.alpha.,25-(OH)2D3 produced marked hyperphosphatemia that was accompanied by hypocalcemia and transient hypermagnesemia at 3-6 h. The phosphatemia increased for 48 h in the 1.alpha.,25-(OH)2D3 group and fell toward baseline between 48-96 h, while this parameter was maximal in the SG group at 3-12 h and returned to baseline values by 96 h. Plasma Ca levels tended to vary inversely with PO4 concentrations and did not exceed baseline values until 48 h for the SG grcup and 96 h for the 1.alpha.,25-(OH)2D3 group. The hypocalcemia is due to Ca3(PO4)2 precipitation. The quantitative differences in the effects on Ca and P metabolism may be dose-related. The responses to SG suggest that a gram of dried leaf has approximately the same activity as 1 .mu.g of 1.alpha.,25-(OH)2D3. The water-soluble SG factor has the same biological effects on Ca and P metabolism as does 1.alpha.,25-(OH)2D3.