Responses of fetal rat bones to Solanum malacoxylon in vitro: A possible explanation of previous paradoxical results

A partially purified extract of Solanum malacoxylon was tested for its actions on fetal rat bone in vitro. The extract had a biphasic effect on bone resorption in vitro, stimulating at low concentrations (0.3-0.3 mg/ml) and inhibiting at concentrations of 1 mg/ml and higher. The stimulatory effect could be anatgonized with calcitonin or glucagon. At a concentration of 1.0 mg/ml, the S. malacoxylon extract anatagonized the bone-resorbing effect of 1α,25-dihydroxyvitmin D₃[1,25-(OH)₂D₃] and parathyroid hormone. To determine whether effects in vitro could be due to 1,25-(OH)₂D₃ released into the medium during incubation, bones were cultured with equieffective concentrations of parathyroid hormone, 1,25-(OH)₂D₃ or S. malacoxylon, and the culture medium was extracted with organic solvents. Chloroform or benzene extracts from control or parathyroid hormone treated cultures were inactive, whereas those from 1,25-(OH)₂D₃-treated cultures retained most or all of the activity of the original media. Benzene extracts of S. malacoxylon culture, media inhibited resorption. The inhibitory material could be removed by high-pressure liquid chromatography, but the benzene extract was still ineffective. The results would be consistent with S. malacoxylon acting in vitro as the unhydrolyzed glycoside conjugate. However, it is also possible that the bone cells hydrolyze the glycoside to release small amounts of 1,25-(OH)₂D₃ which then interacts with the receptor.