Ileal pH and apparent absorption of magnesium in rats fed on diets containing either lactose or lactulose

Abstract

The hypothesis was tested that dietary lactose v. glucose stimulates Mg absorption in rats because lactose lowers pH of the ileal lumen, which improves Mg solubility which in turn enhances Mg availability for transport across the ileal epithelium. For comparison, the effects of lactulose were studied because it shares with lactose the characteristic of being poorly digestible. Replacement of glucose by lactose (100 g/Kg) significantly stimulated apparent absorption of Mg. Apart from Mg absorption, lactulose also significantly enhanced absorption of Ca and phosphate. Lactose v. glucose lowered the pH of the ileal lumen from 7.5 to 7.2, whereas lactulose significantly reduced it to 7.0. In in vitro incubations a decrease in pH within the range of fluctuation in vivo was found to cause an improved solubility of Mg, and to a lesser extent also of Ca and phosphate. The smaller fall of ileal pH induced by feeding lactose instead of lactulose may explain why lactose improved Mg absorption only. For all individual rats combined there were negative relationships between ileal pH and apparent absorption of minerals, the relationship being strongest for Mg. Neither lactose nor lactulose was found to raise ileal solubility of minerals, which could relate to the possibility that the time of sampling was not appropriate. It is suggested that lactose-induced stimulation of Mg absorption in rats is caused by a lowering of ileal pH.

Effect of Galactooligosaccharides on Calcium Absorption in Rats.

“…Key Words galactooligosaccharides, calcium, absorption, cecal content, fermentation Lactose, the main carbohydrate constituent of milk products, is known to stimulate the absorption of calcium (1)(2)(3). Various other carbohydrates (3-7) and sugar alcohols (8,9) have also been reported to increase calcium absorption in rats.…”

“…Heijnen et al (3) reported that the calcium absorption by rats fed lactulose, which is a poorly digestible carbohydrate in the small intestine but is hydrolyzed to volatile fatty acids in the large intestine, was significantly increased and that lactulose feeding lowered the ileum luminal pH and raised the absolute amount of calcium in the liquid phase of the ileum. Remesy et al (10) also reported that CHONAN and M. WATANUKI inulin feeding increased the concentration of soluble calcium in the cecum, and the calcium absorption from the cecum was also higher in rats fed inulin.…”

“…There have been many reports on the stimulatory effects of dietary lactose on calcium absorption (1)(2)(3). One hypothesis of the mechanism is that the reduced pH resulting from lactose fermentation in the large intestine would increase the concentration of soluble calcium (4).…”

Non-digestible oligosaccharides used as prebiotic agents: mode of production and beneficial effects on animal and human health

“…Differences between the rat and human mechanisms involved in digestibility of minerals are, however, very important. For instance, coprophagy in many rodent species [61,78] can alter the fermentation of undigestible carbohydrates in the hindgut and therefore may affect the absorption of minerals [43,67,124]. Thus, we could not directly extrapolate results obtained from animal models to humans.…”

Phytate hydrolysis in pigs fed a barley-rapeseed meal diet treated with Aspergillus niger phytase or steeped with whey

“…Steeping of the diet with whey was chosen as a treatment since no effect on phosphorus absorption was noticed due to water steeping for 3 h in a previous trial (Näsi and Helander 1994). Furthermore, dietary lactose supply has shown an augmenting effect on mineral absorption (Heijnen et al 1993). The effect of dried whey in replacement for barley (60 g kg -1 DM) on the chemical composition of the diets was negligible.…”