Is the Effect of Thyroid and Thyroxin upon the Metabolic Rate Specific for Vertebrates?

Abstract

The author, while conducting experiments on insect metabolism, measured the metabolic rate of two species of insects under the influence of thyroid and thyroxin feeding. The forms used were the wasp, Polistes pallipes, and the roach, Periplaneta australasiae. Armour's desiccated thyroid was fed mixed with honey. Squibb's thyroxin crystals were also given in a honey mixture. Carbon dioxide output was measured per hour before and after feeding. In most cases of thyroid feeding results were not pronounced enough to be considered of consequence. In one case in which one wasp fed for approximately 4 minutes (a comparatively long time) the basal metabolic rate increased to more than twice normal for the first 2 hours following feeding. After the 4th hour the rate had again returned to normal. The very slight increases and decreases obtained with feeding desiccated thyroid to roaches were not consequential. It was assumed that proportionately a very great amount of desiccated thyroid gland was necessary to produce an increase in metabolism in these insects.

Thyroxin feeding, however, produced strongly positive results with the wasps. Each time it was fed and with each individual a very definite increase in the basal rate occurred. In one instance the rate was increased 6.5 times normal for the first hour after feeding, with a return to normal at the end of the third hour. Other records of an increase of 3 to 5 times the normal rate were not rare. With roaches the results were not so striking. In many cases no effects were noted but usually a slight rise in the rate occurred, which soon returned to normal. In no case was the increase as great as 1.5 times the normal rate.