Studies on the Enhancement of Radiocalcium and Radiostrontium Absorption by Lactose in the Rat

Abstract

The influence of lactose on Ca⁴⁵ and Sr⁸⁵ absorption was studied in the rat using a simple technique based on the appearance of the radionuclides in the femur after oral administration. Lactose enhanced calcium absorption when the latter was given as either the chloride, gluconate, lactate, or acetate salt. The chelating agent, sodium ethylendiaminetetraacetate (NaEDTA) had no effect on Sr⁸⁵ absorption, but at high enough concentration was able to suppress completely the action of lactose. Lactose increased calcium absorption in the absence or presence of vitamin D in the rachitic rat and did so as effectively as vitamin D. In the intact animal the enhanced absorption of Ca⁴⁵ and Sr⁸⁵ due to lactose was noted within two hours after gavage. The increased gastric emptying time in the presence of lactose was not alone sufficient to account for the lactose action. When solutions were injected into ligated segments of the gastrointestinal tract, it was observed that lactose was most effective in the ileum although an appreciable response was seen in the duodenum and jejunum. The lactose effect was apparent within 30 minutes following injection into the ileum. Without lactose, all of the absorption of Sr⁸⁵ took place within 30 minutes, whereas, in the presence of lactose, absorption continued for two hours.