Effects of magnesium deficiency and thyroparathyroidectomy on calcium active transport by rat duodenum

Mg deficiency was produced in rats by feeding a Mg-free diet. Ten days of dietary Mg depletion led to an increase in active duodenal Ca absorption in sham-operated animals, but this increase was abolished by thyroparathyroidectomy (TPTX). In addition, TPTX reduced Ca absorption in control aminals fed a Mg-containing diet. More prolonged Mg deficiency was produced by feeding sham-operated animals the Mg-free diet for 19 days. This condition resulted in more marked hypomagnesemia and a depression of Ca transport rates to the level observed in the TPTX groups. These results are consistent with the concept that adaptation of duodenal Ca transport in response to Mg deficiency occurs through an increase in parathyroid hormone (PTH) secretion; however, direct blood PTH measurements will be required to prove this point.