Sensitivity of Isolated Intestine of Athyroid,Normal and Thyroxinized Rabbits to Physostigmine and Adrenalin.

Abstract

It is generally accepted that increased thyroid secretion “sensitizes” the autonomic nerves, particularly the sympathetic. Evidence that this is so has been presented by Eppinger, Asher, Oswald, Cannon, Levy, 1 and others. The usual experimental method has been the quantitative determination of the blood pressure change induced by adrenalin, but “acute” experiments with thyroid substance or thyroxin have been generally negative. 2 The isolated intestine is such a delicate physiological test-agent, responding to both sympathetic and parasympathetic stimuli, that it was thought that investigation of the behavior of such segments in the presence of greater or less amounts of thyroid product might disclose significant differences. “Acute” experiments (i. e., dropping thyroxin in one bath and not in the other of parallel segments) were done some years ago and were uniformly negative.

The plan of the present work was as follows: rabbits were thyroidectomized under local anesthesia without disturbing the parathyroids and about 2 or 3 weeks later their isolated intestinal responses were studied in the usual fashion in a Tyrode bath. During the same period other rabbits were given 2, 3 or more 0.1 mg. doses of thyroxin intravenously, and the sensitivity to autonomic stimulating drugs compared quantitatively with segments from the thyroidectomized and normal animals. Comparisons were always made simultaneously in order to be sure of uniform temperature, oxygen and other environment.∗ To insure a fair distribution of the drugs administered, a double-chamber bath as shown in Fig. 1 was used. The recording segments were suspended in chamber A. The drug was run into chamber B through the oxygen tube C and allowed to diffuse throughout this chamber before it was mixed with the fluid in A by gentle blowing through tube D. The whole system was immersed all the while in a constant temperature bath.