Potentiation of the effects of Solanum malacoxylon extracts on rat intestinal phosphate and calcium absorption by incubation with ruminal fluid.

The effects of a partially purified aqueous extract of Solanum malacoxylon (SM) leaves and of an SM extract incubated with ruminal fluid (RF) prior to administration on intestinal phosphate and calcium absorption in rachitic rats were compared with 1α, 25-dihydroxy-vitamin D[1α,25-(OH)-D] using a duodenal loop in situ method. The time course responses elicited by both extracts were qualitatively similar to that of 1α, 25-(OH)-D. However, a single dose of SMRF was significantly more effective in stimulatingP absorption than an equivalent dose of SM. Part of this difference can be accounted for by incomplete saturation of the phosphate transport system with the level of SM employed. Treatment with rumen potentiated the effects of SM onCa absorption to a lesser extent. Extraction of SMRF with nonpolar organic solvents and purification of the lipid extract by chromatography on Silica Gel G thin-layer plates and on Sephadex LH-20 columns yield two fractions which promote intestinalP absorption. The bioactive fraction eluting first from the Sephadex LH-20 column migrates similarly as 1α,25-(OH)-D. The greater effectiveness of SMRF extracts on intestinal phosphate and calcium absorption may be tentatively attributed to the release of 1α,25-(OH)-D from the corresponding glycoside, shown previously to be present in SM, and to steroid modification during incubation with rumen. [ABSTRACT FROM AUTHOR]