Magnesium and calcium as regulators of intestinal permeability

Abstract

The absorption of phenolsulfonphthalein (phenol red) was used as a measure of intestinal permeability in rats anesthetized with sodium pentobarbital. All solutions placed in the intestinal lumen were adjusted to pH 7.0 and 300 mosmoles/liter. When 5 ml of a 1 mm solution of phenol red were placed in either proximal or distal halves of the small intestine the mean hourly absorption was 1.1%. The presence of 25 mm/liter ethylenediaminetetraacetate (EDTA) as the calcium salt did not alter phenol red absorption. With 25 mm/liter NaEDTA in the lumen, the absorption of phenol red was increased tenfold. After NaEDTA had been present for 1 hr, rinsing the lumen produced results which varied with the ionic composition of the rinsing solution. Balanced physiologic saline did not reverse the increased permeability. A CaCl2 rinse produced a permeability intermediate between NaEDTA and control levels. A MgCI2 rinse reinstated normal permeability. It is concluded that magnesium and calcium, loosely bound in the structure of the membrane, regulate the aqueous permeability of the intestinal epithelium.

An Experimental Model for Measuring Intestinal Permeability

“…This resulted in an increased jejunal permeability for phe nol red. inulin and PVP confirming the re sults of other authors [4,7,19,30]. We inter preted the lack of change in jejunal perme ability for mannitol in our own experiments as opening of channels for the larger mole cules which were already available for man nitol.…”

Magnesium Metabolism: A Review

“…Howr ever, it could also mean that magnesium is taken up by simple diffusion, which is reduced at higher magnesium concentrations by a limited magnesium permeability. Increasing Mg concentration decreases intestinal and renal tubular water permeability (67,68). Evidence for magnesium uptake by "solvent drag" was obtained in the rat ileum.…”

Effect of Viscosity on Drug Absorption

“…Methylcellulose, rather than sucrose or glucose, was used as the viscosity enhancing agent because the latter contribute not only viscosity but also osmotic pressure and specific effects on gastric emptying (3). Phenol red was used as a marker because it is poorly absorbed (21). The slight absorption occurs by passive diffusion (22) and, due to its low rate, will be rate limited by the membrane permeation process and, therefore, will not be affected by viscosity.…”