Modification by rumen of vitamin D-like activity of Solanum malacoxylon in rats

The biological activity of aqueous extracts of Solanum malacoxylon (SM) and of extracts preincubated with ruminal fluid (SMRF) on calcium and phosphate metabolism in vitamin D depleted rats was compared. The responses in intestinal 32P and 45Ca absorption, measured in an isolated duodenal loop in situ after a single oral dose, were qualitatively similar to that of 1,25-OH2-vit.D3. However, the effects elicited by SMRF were significantly higher than those caused by SM. Both extracts were equally effective in promoting bone resorption when administered orally or subcutaneously. These results provide a basis to explain the greater effectiveness of SMRF to produce calcinosis in rats. The hypothesis is advanced that biologically active steroidal metabolites with predominant action on intestine, are formed during incubation with rumen.