Effects of methylprednisolone on electrolyte transport by in vitro rat ileum

Systemic Disease Associations with Disorders of Gut-Brain Interaction and Gastrointestinal Transit: A Review

Functional gastrointestinal disorders (FGID) are now classified within the Rome IV framework as disorders of gut-brain interaction (DGBI). Disorders of gastrointestinal transit (as defined by abnormalities on contemporary gastrointestinal motility testing) frequently are associated with symptoms that are also characteristic of DGBIs. In this narrative review, we outline a non-inclusive set of systemic diseases or risk factors that have been classically associated with DGBIs and disorders of gastrointestinal transit; these include diabetes mellitus, paraneoplastic syndromes, surgery, Parkinson's disease, systemic sclerosis, endocrinopathies, polypharmacy, and post-infectious syndromes.

Regulatory Binding Partners and Complexes of NHE3

NHE3 is the brush-border (BB) Na+/H+exchanger of small intestine, colon, and renal proximal tubule which is involved in large amounts of neutral Na+absorption. NHE3 is a highly regulated transporter, being both stimulated and inhibited by signaling that mimics the postprandial state. It also undergoes downregulation in diarrheal diseases as well as changes in renal disorders. For this regulation, NHE3 exists in large, multiprotein complexes in which it associates with at least nine other proteins. This review deals with short-term regulation of NHE3 and the identity and function of its recognized interacting partners and the multiprotein complexes in which NHE3 functions.

Mechanism of glucocorticoid-mediated reversal of inhibition of Cl(-)/HCO(-)(3) exchange during chronic ileitis

In the normal ileum, coupled NaCl absorption occurs via the dual operation of Na(+)/H(+) and Cl(-)/HCO(-)(3) exchange on the brush-border membrane (BBM) of villus cells. In a rabbit model of chronic small intestinal inflammation we determined the cellular mechanism of inhibition of NaCl absorption and the effect of steroids on this inhibition. Cl(-)/HCO(-)(3) but not Na(+)/H(+) exchange was reduced in the BBM of villus cells during chronic ileitis. Cl(-)/HCO(-)(3) exchange was inhibited secondary to a decrease in the affinity for Cl(-) rather than an alteration in the maximal rate of uptake of Cl(-) (V(max)). Methylprednisolone (MP) stimulated Cl(-)/HCO(-)(3) exchange in the normal ileum by increasing the V(max) of Cl(-) uptake rather than altering affinity for Cl(-). MP reversed the inhibition of Cl(-)/HCO(-)(3) exchange in rabbits with chronic ileitis. However, MP alleviated the Cl(-)/HCO(-)(3) exchange inhibition by restoring the affinity for Cl(-) rather than altering the V(max) of Cl(-) uptake. These data suggest that glucocorticoids mediate the alleviation of Cl(-)/HCO(-)(3) exchange inhibition in chronically inflamed ileum by reversing the same mechanism that was responsible for inhibition of this transporter rather than exerting a direct effect on the transporter itself, as was the case in normal ileum.

Na,K-ATPase in diabetic rat small intestine. Changes at protein and mRNA levels and role of glucagon

Na,K-ATPase activity and isoform expression were measured in rat small intestinal mucosa taken from both normal and streptozocin-treated diabetic rats. Enzyme activity and abundance was 1.7-2.3-fold higher in rats diabetic for 2 wk than in controls. This was associated with 1.4-1.7-fold increases in small intestinal protein and DNA content. Ouabain inhibition curves of Na,K-ATPase were monophasic with Kis of 2.6 +/- 1.4 x 10(-4) and 2.0 +/- 1.2 x 10(-4) M for control and diabetic rats, respectively (NS). Northern blot analysis revealed a 2.5-fold increase in mRNA alpha 1 and a 3.4-fold increase in mRNA beta 1 in diabetic rats relative to controls. Two thirds of this increase occurred within 24h after injection of streptozocin. Immunoblots of intestinal enzyme preparations from diabetic and control rats indicated the presence of alpha 1 and beta 1 subunits but not of alpha 2 or alpha 3. Administration of glucagon (80 micrograms/kg) to normal rats daily for 14-16 d increased mRNA alpha 1 3.1-fold but did not increase mRNA beta 1 or enzyme activity. In experimental diabetes, alpha 1 and beta 1 isoforms of Na,K-ATPase are coordinately upregulated at both protein and mRNA levels, an effect which appears to be partially mediated by the associated hyperglucagonemia.

Regulation of cation transport by low doses of glucocorticoids in in vivo adrenalectomized rat colon

A dose response curve for glucocorticoid-induced proximal and distal colonic cation transport in vivo was established in adrenalectomized rats. All doses (0.5-50 nmol/100 g body wt) stimulated sodium absorption. Distal sodium absorption did not saturate at dexamethasone levels that saturate the glucocorticoid receptor but also bind to greater than 35% of aldosterone receptors. Saturation of the pure glucocorticoid response occurred in both segments with RU26988, a synthetic glucocorticoid that does not occupy aldosterone receptors. Maximum velocities for pure glucocorticoid-induced sodium absorption were 15 and 16 mu eq/min per g dry tissue, and Michaelis constants (Km) were 4.2 and 4.6 X 10(-9) mol/liter for proximal and distal colon. Kms are similar to the dissociation constant for the colonic glucocorticoid receptor and too low for significant aldosterone receptor occupancy. Dexamethasone increased sodium absorption significantly within 30 min of injection, suggesting the response is not dependent on new protein synthesis. Similar time and dose responses in proximal and distal colon suggest glucocorticoids stimulate the same pathway in both segments.

Cellular and paracellular calcium transport in the rat ileum and the influence of 1 alpha, 25-dihydroxyvitamin D3 and dexamethasone

Concentration dependence of unidirectional calcium fluxes across the rat ileum freed from the serosa and the muscularis externa were measured in a modified Ussing-chamber. Mucosa (m) to serosa (s) calcium flux showed a saturable component, whereas s to m calcium flux was linearly related to the calcium concentration between 0.125 mmol/l and 5 mmol/l. At all calcium concentrations used net secretion of calcium was observed. The s to m flux of the simultaneously measured paracellular marker mannitol at all calcium concentrations was remarkably higher than the m to s flux, resulting in net mannitol secretion. The results obtained from the calcium fluxes when clamping the transepithelial electrical potential agree well with those of the concentration dependence of the calcium fluxes: 1. Only m to s flux has a voltage independent, transcellular component. 2. Calcium s to m flux is totally voltage dependent, i.e. diffusive. 3. Diffusional s to m calcium flux is about 80% greater than the diffusional fraction of the m to s flux. Omitting glucose from the bathing solution effected a decrease of the transepithelial electrical potential and of the short circuit by 91% and 85% respectively; net calcium secretion was almost abolished and net mannitol secretion remarkably reduced. Addition of glucose, which stimulates water absorption in the ileum as a metabolic substrate, activated m to s but significantly more pronounced s to m calcium flux parallel to that of mannitol.(ABSTRACT TRUNCATED AT 250 WORDS)