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Biomedical subjects

C J Edmonds

Publications and source records attributed to C J Edmonds.

30 records · Page 2Linked to original sources
PubMed1976

Potassium transport across the distal colon in man.

1. The mechanism of potassium transport across human distal colon was investigated in twenty-two individuals without evidence of bowel disease, by using a dialysis method in conjunction with measurements of the transepithelial potential difference (p.d.). 2. Whether potassium was absorbed or secreted depended on its initial concentration in the lumen. The potassium net flux was approximately zero when the luminal potassium concentration was between 30 and 50 mmol/l. 3. Potassium secretion rate was little affected by sodium absorption rate, or by the luminal sodium concentration or by the osmolality of the luminal solution. 4. Potassium secretion rate was increased by partial substitution of other cations for sodium, in the descending order Li greater than NH4 greater than Rb greater than Na. Potassium concentration increased on average to over 80 mmol/l when lithium was in the lumen. 5. The observed transepithelial p.d. was inadequate to account for the intraluminal potassium concentrations attained, the discrepancy being most marked when ammonium or lithium was in the lumen. It is suggested that some potassium is secreted by the epithelial cells and this component of the total potassium flux into the lumen is increased when rubidium, ammonium or lithium is substituted for sodium.

Adult↗
PubMed1976

Lithium transport by the colon of normal and sodium-depleted rats.

1. The transport of Li by colonic epithelium has been examined in normal and Na-depleted rats. 2. Substitution of Li for Na with lumen of the conon causes the transepithelial electrical potential difference (p.d.) and short-circuit current to fall to low levels and the electrical resistance of fall moderately. Recovery occurs by fairly slowly after removal of Li. 3. Li absorption increases linearly with increasing concentration in the lumen and is significantly faster in Na-depleted rats. Increasing the luminal Na concentration reduces Li absorption from solutions of low Li concentration. 4. Comparison of absorption rates with secretion rates in rats given Li systemically, together with measurements of Li distribution across the epithelium in relationship to the transepithelial p.d. indicate that Li transport is predominatly or entirely passive. Interference with Li absorption by Na suggests, however a mucosal membrane carrier which, since Li absorption rises after Na depletion, may be increased in the Na-depleted state.

Animals↗
PubMed1976

The effect of lithium on the transport of sodium, potassium and chloride by the colon of normal and sodium-depleted rats.

1. The effect of Li, given systemically or placed in the gut lumen, on the transport of Na, K and C1 and on the transepithelial electrical potential difference (p.d.) was studied in vivo in the distal colon of normal and Na-depleted rats. 2. The specific effect of Li appeared to be on the Na transport system with K and C1 transport affected only indirectly. Active Na absorption was impaired and p.d. reduced when either Li was in the lumen or given systemically. In addition with Li in the lumen, a considerable rise in the plasma-to-lumen Na flux was observed, the flux increasing progressively with rising intraluminal Li concentration. The effects were greater in Na-depleted rats. 3. The greater part of Li absorption from the colon of the rat takes place by exchange for Na, the secretion of which is much enhanced while the p.d. is reduced. This contrasts with human colon in which potassium is the ion exchanged for Li with the p.d. increased.

Animals↗
PubMed1976

Effect of aldosterone on lithium permeability of rat colon mucosa.

The effect of aldosterone on the ionic composition of colonic epithelial cells and on lithium absorption rate was studied by experiments on rats in vivo. Aldosterone considerably increased the rate of sodium absorption without measurably altering the sodium and potassium content of the epithelium. Aldosterone did not alter the electrical resistance of the tissue. With lithium in the lumen, the net sodium fluxes in the colon were similar in normal and aldosterone-stimulated rats but the rate of diffusion of lithium across the epithelium was greater in the aldosterone-stimulated group. The amount of lithium accumulating in the epithelial layer was also considerably increased by aldosterone stimulation. Aldosterone appears to increase the permeability of the mucosal (luminal) barrier allowing increased entry of lithium into the colonic epithelial cells.

Aldosterone↗
PubMed1975

Total body potassium and body fat estimation in relationship to height, sex, age, malnutrition and obesity.

1. Total body potassium was estimated by 40-K measurement with a high-sensitivity whole body counter in normal individuals over a wide age range and in patients who were obese or were grossly wasted as a result of various conditions which restricted food intake. 2. Potassal males and females, but when individuals of different age groups were matched for height, a significant fall in total body potassium with increasing age was observed only in males. Total body potassium of females was about 75% that of males of similar height when young, the sex difference decreasing with ageing. In the normal population, total body potassium was significantly correlated with height and with weight; regression equations for various relationships are given. 3. Fat-free mass was estimated from total body potassium, values of 65 and 56 mmol of potassium/kg fat-free mass being used for males and females respectively. Body fat estimated by this method correlated well with skinfold measurements over a wide range of body weight but in malnourished individuals having inadequate food intake there was considerable fat-free mass from total body potassium appear unsatisfactory in malnutrition. Considerable differences between expected and observed values of total body potassium were found in muscular individuals and in normal individuals who were thin but whose body weight was relatively constant. 4. The patients with malnutrition were low both in body fat as estimated by skinfold thcikness and in total body potassium estimated on the basis of height. Plasma potassium was, however, normal and potassium supplements did not increase the total body potassium. 5. Total body potassium of obese individuals was not significantly different from that of normal weight individuals on the basis of height. Total body potassium fell on weight reduction with a very low energy diet of 1260 kJ (300 kcal.) daily but changed little with a 3300 kJ (800 KCAY POTASSIUM WAS BEST PREDICTED FROM THE INDIVIDUAL'S HEIGHT. For those whose body weight was less than expected, the use of weight gave the best prediction but the error was considerable when the weight deviation was large.

Adipose Tissue↗
PubMed1975

The effect of aldosterone and the renin-angiotensin system on sodium, potassium and chloride transport by proximal and distal rat colon in vivo.

1. The roles of aldosterone and angiotensin in the direct control of epithelial sodium transport in vivo have been investigated by measurement of electrical p.d. changes and of the fluxes of sodium, potassium and chloride in rat colon, an organ actively involved in electrolyte homoeostasis. Exogenous angiotensin and aldosterone were given by both short- and long-term infusions and endogenous secretion of the hormones was varied by dietary sodium variation and by nephrectomy and/or adrenalectomy. 2. In vitro angiotensin has been shown to influence colonic salt and water absorption but in the present in vivo experiments administered angiotensin had no significant action on p.d. or on the ionic fluxes of the proximal or distal colon. The increase in p.d. produced by infusing aldosterone was unaffected by giving angiotensin concurrently. The effect of sodium depletion in stimulating sodium absorption and potassium secretion was completely abolished by adrenalectomy but was unaffected by nephrectomy. 3. During prolonged infusion of angiotensin into adrenalectomized rats, a small fall in faecal fluid and sodium content was observed, but this change would have little significance in sodium homoeostasis. 4. Aldosterone and sodium depletion stimulated sodium absorption in both proximal and distal colon but significant increase in potassium secretion was demonstrable only in the distal colon. Bicarbonate secretion (by calculation) was unaffected. In the proximal colon, the increased sodium absorption appeared to be accompanied by increased chloride absorption while in the distal colon it was principally the sodium-potassium exchange that was increased. 5. Adrenalectomy reduced potassium secretion in both proximal and distal colon but sodium absorption was only significantly reduced in the proximal colon. 6. It was concluded that there is no evidence that angiotensin in the living animal has a role as an important salt retaining hormone by direct epithelial action. Aldosterone has a considerable effect which is independent of the presence of angiotensin, and which differs in proximal and distal colon in regard to the relative effects on chloride absorption and potassium secretion.

Adrenalectomy↗
PubMed1975

Electrical potential difference, sodium absorption and potassium secretion by the human rectum during carbenoxolone therapy.

The transmucosal electrical potential difference (pd) and the sodium and potassium net fluxes were measured in the rectum of subjects taking carbenoxolone. There was a rise in transmucosal pd persisting throughout treatment in all subjects which was accompanied by an increase in sodium absorption and potassium secretion. Comparison of the pd changes produced by carbenoxolone with those due to the mineralocorticoid 9-alpha-fluorocortisol showed that carbenoxolone had about 1/1000th the potency on a weight basis and the two drugs appeared to be additive in their effects. Topical instillation of carbenoxolone into the rectum produced an elevation of pd which persisted for three days. Amiloride and bendrofluazide did not interfere with these actions of carbenoxolone but spironolactone abolished them. One patient who developed fluid retention and hypokalaemia had a rectal pd similar to that of the other patients who had no side effects.

Adult↗