Interrelationship of the Effects of Aldosterone and Thyroid Hormones on Sodium Transport and Electrical Properties of Rat Colon

Abstract

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\g=m\g/100gbody 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 \g=m\g/100g body weight) abolished the effect of T3 but this did not influence the action of aldosterone in euthyroid animals.

Hormones and Water Movement Through the Vertebrate Intestine

“…This gives a convenient measure of the sodium pump and results indicate that aldosterone exerts a powerful stimulatory influence on rat colon fluid absorption, whether it is given by intravenous perfusion or indirectly by salt depletion to stimulate the adrenal cortex. A recent and very interesting observation is that thyroidectomy abolishes the effect of aldosterone and a single injection of tri-iodo-L-thyronine restores it [36]. This might be a clue to some of the equivocal results that have been obtained when examining the effect of thyroid hormones on intestinal trans port [74,88].…”