The "enteque seco" is a disease of calcinosis, i.e., pathological
deposition of calcium phosphate in soft tissues, which occurs in grazing
cattle in Argentina and is of considerable economic importance.
The
ingestion of leaves of Solanum malacoxylon has been identified as the
cause of the disease. Hypercalcemia and/or hyperphosphatemia and
mineralization of the cardiovascular and pulmonary systems are usually
seen in bovines or experimental animals exposed to this plant. The
symptoms of the disease resemble those of vitamin D intoxication. In
agreement with these observations, a glycoside derivative of
1,25-dihydroxyvitamin D3 (1,25(OH)2D3), the hormonally active form of
vitamin D in animals, has been identified as the toxic principle of S.
malacoxylon. Glycoside conjugates of its precursors, 25-hydroxyvitamin
D3 and vitamin D3, may also be present. Recent studies indicate that the
plant factor is modified in the rumen of bovines through cleavage of
the glycosidic linkage and further conversion of the released
1,25(OH)2D3 to a more polar metabolite, possibly
1,24,25-trihydroxyvitamin D3. Excess free 1,25(OH)2D3 may alter
extracellular and intracellular Ca homeostasis in intoxicated animals
through a receptor-mediated mechanism and activation of membrane Ca
channels. In addition, 1,24,25(OH)3D3 may potentiate the effects of
1,25(OH)2D3 on intestinal Ca transport.
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