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Search for other papers by C. J. EDMONDS in
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SUMMARY
The effect of adrenalectomy on the increase of the transmucosal potential difference (p.d.) of the colon of the rat induced by Na depletion, together with the action of aldosterone on the p.d. and on colonic Na+ and Cl− transport, and K+ and bicarbonate secretion have been investigated. Adrenalectomy increased the Na+ content in the stool, an effect reversed by treatment with aldosterone. When Na+-depleted rats were adrenalectomized and maintained on cortisone, the elevated p.d. fell to levels below those found in normal rats. Aldosterone given intravenously (i.v.) in physiological doses increased the p.d. in normal, adrenalectomized and Na+-depleted adrenalectomized rats after a latency period of 80–110 min., and the p.d. tended to rise further when injections were continued for several days. The p.d. gradient along the colon after treatment with aldosterone was similar to that of Na+-depleted rats, the highest p.d. being at the distal end of the descending colon. Cortisol intravenously increased the p.d. but the effect was small in comparison with that of aldosterone.
Measurement of ionic fluxes in the descending colon of adrenalectomized rats showed that treatment with aldosterone produced an increase in Na+ and water absorption, and in K+ secretion, but had no effect on bicarbonate secretion. The effects of aldosterone on the transmucosal p.d. and ion transport were similar to those of Na+ depletion.
Search for other papers by C. J. EDMONDS in
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Search for other papers by JANE C. MARRIOTT in
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SUMMARY
The effect of aldosterone on the colonic transmucosal potential difference (p.d.) was examined in normal, adrenalectomized and Na+ depleted rats. Continuous intravenous infusion of aldosterone in conscious animals was more effective than single i.v. injection and over the dose range 0·5–50 μg./hr. for 6 hr., p.d. increased linearly with log dose and returned to the pre-infusion levels 16–24 hr. after stopping infusion. Only a region 2–4 cm. from the anus responded to low doses, but with high doses an increasing length of colon responded. Cortisone (250 μg. daily) intramuscularly maintained adrenalectomized rats even when severely Na+ depleted without affecting the p.d. Cortisone (2·5 mg. daily, i.m.) raised the p.d. but the effect of low doses of aldosterone was unchanged. Neither Na+ depletion nor pentobarbitone anaesthesia affected the action of aldosterone but large doses of spironolactone reduced it. Aldosterone was effective when applied locally by submucosal injection in very low dose but was almost ineffective even in very large dose in the lumen. Again the most sensitive region was 2–4 cm. from the anus. Ouabain (10-3 m) injected into the submucosa rapidly reduced the increased p.d. but was ineffective in the lumen.
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Search for other papers by B. D. THOMPSON in
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SUMMARY
Transmucosal electrical potential difference (p.d.), short-circuit current, electrical resistance and Na+ influx rate of the descending colon were similar in euthyroid and hypothyroid rats, the latter having been treated earlier with an ablation dose of 131I. However, in contrast to the considerable p.d. increase found in normal rats, little change of p.d. was found in hypothyroid rats when they were Na+ depleted or given an intravenous aldosterone infusion. A single small dose of tri-iodothyronine (T3) (1 μg/100g body weight) or a larger dose of thyroxine given to hypothyroid rats 10–16 h before aldosterone, restored the p.d. response to normal, although these doses did not influence the animal's oxygen consumption. Fasting for 3 days or giving actinomycin D (8 μg/100 g body weight) abolished the effect of T3 but this did not influence the action of aldosterone in euthyroid animals.
