Relationship of calcium uptake and calcium-binding protein synthesis in chick and rat intestine in response to Solanum malacoxylon

Abstract

It now seems clear that one of the ways by which vitamin D affects calcium absorption is by the stimulation of the de novo synthesis of calcium-binding protein [l-3]. How calcium-binding protein acts to promote calcium absorption is still a matter for discussion, but the correlation between vitamin D-stimulated calcium absorption and the production of calcium-binding protein is such that the protein must play an intimate part in this process [3,4]. To determine whether calcium-binding protein plays an obligatory role in calcium absorption the effect has been studied of other substances capable of changing calcium absorption, to see if there is always a corresponding change in the level of calcium-binding protein. Experiments of this nature have so far produced conflicting results. Nicarbazin for instance has been shown to inhibit both calcium-binding protein levels and egg formation in the hen [5] but cortisone, given with vitamin D to rachitic chicks, inhibits the action of vitamin D on calcium absorption without affecting the vitamin D-dependent synthesis of calcium-binding protein [6]. Another agent, capable of changing calcium metabolism in different animals, has recently been found in the leaves of the shrub Solanum malacoxylon. Used in the dried form or as an extract, active principles in the leaf act to raise plasma calcium and phosphate levels and to increase calcium absorption [7-lo]. It has been claimed that the effect of the