INFLUENCE OF THE THYROID HORMONE ON THE EFFECTOR SYSTEMS OF THE MAMMALIAN HEART

Publisher Website
Google Scholar
Abstract
In hyperthyroid rabbits, cats, and rats, the effect of vagus stimulation on the heart is less marked than in normal animals. Often there is no vagus effect at all and sometimes the stimulation of the vagus leads to cardiac acceleration. The impaired vagus effect is returned to normal by eserine or prostigmine. In thyroidectomized cats, the effect of vagus stimulation on the heart is more marked and maintained than in normal animals. In isolated hearts of hyperthyroid cats and guinea pigs, acetylcholine has only a slight depressor action. This effect is always followed and overshadowed by a pronounced stimulation, similar to that produced by epine-phrine. In perfusates flowing from hyperthyroid hearts there appear, as a consequence of injns. of relatively low doses of acetylcholine, unusually high amts. of an epinephrine-like substance. On isolated hearts of thyroidectomized cats-and guinea pigs, AC exerts an intense depressor effect. The stimulating action of this drug is very weak and often completely absent. In perfusates of isolated hearts of hypothy-roid guinea pigs there appears an epinephrine-like substance only when high doses of AC are injected. A high sensitivity of the hyperthyroid heart to adrenaline and a low sensitivity to this agent of the myocardium of hypothyroid animals is always observed. The changes of the sensitivity of the heart effector systems to the neuro-transmitter substances contribute to the elucidation of the cardiac symptoms observed in thyroid disorders.

This publication has 5 references indexed in Scilit: