Screening of Vitamin D activity (VDA) of Solanum glaucophyllum leaves measured by radioimmunoassay (RIA)

The ingestion of Solanum glaucophyllum (SG) causes a calcinosis of cattle named Enteque Seco (ES). The toxic principle is the 1,25-(OH)2D3, mainly conjugated as glycoside. This study aims to validate a simple novel method of evaluation of the VDA of SG leaves. Aqueous extracts of SG were purified using C18 minicolumns and assayed by RIA with an antibody raised in rabbits by injection of the acid—C22, 1α-(OH)Vitamin D3. Data were expresed as glycoside equivalent to 1,25-(OH)2D3 in ng/g of dry leaves. We compared this data with 1,25-(OH)2D3 levels measured, in the same samples, by liquid chromatography (HPLC) after enzyme cleavage. This procedure involved the incubation of SG leaves with rumen fluid, followed by C18-OH solid phase extraction. The 1,25-(OH)2D3 fraction was run by HPLC and detection was achieved using a photodiode array detector. Data were expressed as micrograms of 1,25-(OH)2D3/g dry leaves. A significant regression of 1,25-(OH)2D3 levels (Y) as a function of glycoside RIA 1,25-(OH)2D3 equivalents (X) was found: Y = 12.02 + 0.35X [R = 0.81; P = 0,0002; N = 15], allowing us to conclude that this novel assay could be used to estimate the amount of this active principle contained in SG leaves.