Search PubMed⌕ Search

Biomedical subjects

C J Edmonds

Publications and source records attributed to C J Edmonds.

At least 91 records · Page 5Linked to original sources
PubMed1972

Effect of luminal ions on the transepithelial electrical potential difference of human rectum.

Skin electrodes are the most convenient reference electrodes for clinical measurements of electrical potential differences (pd) across the epithelium of the alimentary tract but the presence of an electrical charge on normal skin introduces an error. In the present study, by comparison with results obtained using subcutaneous and intravenous electrodes, it was shown that an intradermal injection of saline abolished the skin potential differences. This simple method, therefore, allows skin electrodes to be used to measure the true transepithelial potential differences of gut mucosa. The method was applied to investigate the effect on the rectal potential difference of altering the composition of the luminal solutions. Changes in the cations (sodium, potassium, magnesium) showed that sodium was the most important cationic determinant of the potential difference, especially when sodium absorption was stimulated by giving mineralocorticoids. Changes in the anions (chloride, iodide, bromide, nitrate, bicarbonate, sulphate, phosphate, citrate, and acetate) indicated that the molecular size of the anion rather than its chemical nature was the significant factor and suggested that the ions had to cross a barrier relatively impermeable to anions of radius greater than 3.5 to 4 A degrees . Changes in osmolality and glucose concentration were without effect.

Aldosterone↗
PubMed1971

Absorption of sodium and water by human rectum measured by a dialysis method.

A dialysis method for the study of intestinal absorption is described. Its use has been assessed in animals and normal human subjects and it has been applied to the measurement of rectal transport of sodium and water.When the luminal solution was of high sodium concentration (145 m-equiv/1), the sodium influx rate (lumen to plasma) was about five times greater than the sodium efflux rate (plasma to lumen). The luminal sodium concentration associated with zero net sodium flux was very low (<15 m-equiv/1). As the mucosa was charged with the luminal side negative, the epithelium must therefore possess a powerful sodium absorbing ;pump'. With isotonic solutions in the lumen, the amount of water absorbed depended on the sodium concentration and when this was 30 m-equiv/1 or less, no significant water absorption was detectable. When, however, water absorption was altered by imposing osmotic gradients, sodium absorption was not significantly affected. The luminal solution tended to become issomolar with plasma; osmotic gradients across the epithelium did not develop. The particular transport properties of rectal epithelium enabling it to remove sodium from the lumen against considerable electrochemical gradients are well adapted to its function.

Adult↗
PubMed1970

Sodium transport and short-circuit current in rat colon in vivo and the effect of aldosterone.

1. A method for measurement of short-circuit current and for applying a voltage clamp to segments of rat colon in vivo is described.2. The mucosa behaved as an ohmic resistor of average resistance 154 Omega/cm(2) although brief transient effects were frequently observed. Tissue resistance was independent of considerable changes in ionic strength and composition of the luminal solution.3. The short-circuit current averaged 120 muA/cm(2) in normal rats. Aldosterone intravenously raised the p.d., short-circuit current rising proportionately and tissue resistance being unchanged. The effects of various modifications of the intraluminal solution in respect to composition, hydrostatic pressure and pH were examined. An increase in the osmolality of the luminal solution sufficient to abolish water absorption did not affect p.d. or short-circuit current.4. The short-circuit current measured with 150 mM-NaCl in the lumen was almost completely accounted for by active Na absorption both in normal and aldosterone-treated rats. The changes in Na efflux rate produced by voltage clamping suggested that only part of Na efflux was due to simple diffusion. With lower [NaCl] in the lumen, the short-circuit current exceeded that atributable to active Na absorption, the discrepancy increasing with reduction of [NaCl].5. The luminal [Na] at which Na efflux and influx rates were equal was reduced by aldosterone, an effect which is probably responsible for the low stool [Na] of aldosterone treated animals. The significance of this finding in terms of the mode of action of aldosterone is discussed.

Aldosterone↗
PubMed1970

Electrical potentials of the sigmoid colon and rectum in irritable bowel syndrome and ulcerative colitis.

Using a simple and rapid method, electrical potential differences across rectal and colonic mucosa have been measured at routine sigmoidoscopy in patients with irritable bowel syndrome and ulcerative colitis. In patients with irritable bowel syndrome, all of whom had diarrhoea, the mucosa was charged negatively on the luminal side and potential differences were not significantly different from those of normal subjects. In acute exacerbations of ulcerative colitis, the potential difference was reversed, the luminal side being positive. This characteristic change was seen even in mild attacks. The potential difference was usually restored to normal within a few weeks of commencing treatment. In some cases, however, it was persistently abnormal for months and failed to show the normal response to stimulation by the mineralocorticoid, fludrocortisone. The way in which measurements of potential difference can be useful in diagnosis, prognosis, and as a guide to treatment is discussed.

Acute Disease↗
PubMed1970

Measurement of electrical potentials of the human rectum and pelvic colon in normal and aldosterone-treated patients.

A method is described which allows rapid measurement of the electrical potential difference across colonic mucosal epithelium to be carried out during routine sigmoidoscopy. The potential differences measured had a mean value of 25 mV (range 4 to 51 mV) in 27 subjects with normal bowel. Six hours after two intravenous injections of 0.5 mg aldosterone the potential difference had risen to 60 mV (range 37 to 101 mV). The time course of responses studied after a single injection of aldosterone showed that the potential allowance rose within four hours and had fallen again after 18 hours. Urinary sodium concentrations and sodium/potassium ratios fell after aldosterone injections, the time course of the changes being similar to that of the potential differences of the colon. Sodium concentration of stool fluid also fell. The concentration of chloride in the stool fluid was consistent with a passive distribution of chloride according to the electrochemical gradient, but that of potassium was considerably greater than expected from a passive distribution, suggesting that potassium is actively secreted into the lumen of the colon.

Aldosterone↗