Effect of Thyroxine on Oxygen Consumption of the Toadfish

Abstract

It has been commonly assumed that thyroid medication increases the metabolic rate of all vertebrates. For cold-blooded animals, however, the evidence is very scanty. Negative results on frogs and several other poikilotherms have been reported. 1 2 Positive results on metamorphosing amphibia had been frequently reported but upon critical review were found unconvincing by one of the present authors who obtained negative results. 3 It was therefore thought desirable to investigate the question in a fish where the complications of metamorphosis could be avoided.

A continuous flow apparatus was set up in which oxygen determinations were made by the Winkler technique. 4 By this method repeated determinations can be made on individual animals over a period of days without the slightest disturbance of the animals. With proper precautions for constant temperature (24°C), elimination of light, etc., it was found that 8–24 hours after introduction into the chambers the oxygen consumption of the fish fell to a fairly constant “standard”level.

The toadfish, Opsanus tau (Linnaeus), was used. The animals, weighing about 350 gm., were paired off, starved for at least 3 days before and throughout the course of an experiment. The experimental animals were injected with synthetic thyroxine (disodium salt “Roche”, 1 mg. per ml.). Usually 2–3 mg. were injected per day for 4–5 days. The dose was varied, however, a single massive dose of 10 mg. being tried as well as daily 1 mg. doses. The total dose varied from 10 to 23.5 mg. The controls were injected with distilled water brought to pH 11 with KOH. Oxygen determinations were made for a preliminary period of 3 days and for successive similar periods 12 to 18 days after the first injections.