Further Observations on Lactose Stimulation of the Gastrointestinal Absorption of Calcium and Strontium in the Rat

Abstract

Investigations were performed to study the mechanism by which lactose enhances the gastrointestinal absorption of calcium and strontium using short-term, radioisotope techniques. The absorption of Sr³⁵ and Ca⁴⁵ was proportional to the lactose concentration in the test dose up to a maximum response at 0.4 millimoles of lactose. In the presence of an antibiotic, neomycin, the lactose effect was still observed. Neomycin, itself, also was found to enhance Sr³⁵ absorption. Metabolic inhibitors, such as phlorrhizin, sodium fluoroacetate, sodium iodoacetate, 2,4-dinitrophenol and sodium azide, did not inhibit lactose action when given as an integral part of the dosing solution. The enhancing effect of lactose could not be duplicated when the hydrostatic pressure within the intestinal lumen was maintained at 10.5 or 12.0 cm with distilled water, saline or bovine serum ultrafiltrate. In vitro studies showed that lactose, xylose and glucose at concentrations up to 0.5 M were unable to increase the solubility of CaHPO₄; however, the amino acids, lysine and glycine, were able to double the solubility of CaHPO₄ at this concentration. These data were discussed in regard to the possible mechanism of action of lactose in enhancing alkaline earth absorption.