Experimental Angina Pectoris in the Dog. Effect of Total Thyroidectomy

Abstract

The clinical observation that the beneficial effect of total thyroidectomy in angina pectoris is an almost immediate one, and so cannot be due entirely to the fall in the basal metabolic rate which does not begin to occur for over a week, has given rise to speculation as to the possible mechanism involved.

We investigated the possibility that this effect might be due to interruption of nerve impulses from the heart. Our method was that described by Sutton and Lueth 1 for producing “experimental angina pectoris” in the dog consisting in placing a ligature about the anterior descending branch of the left coronary artery and compressing the coronary vessels by traction on this ligature. This method was successfully employed by White and his associates 2 to test the efficacy of various surgical procedures in interrupting the afferent nervous pathways of the heart. Five dogs were tested in this manner after removal of both thyroids. One animal was tested 5 hours after thyroidectomy, and 4 dogs on the eleventh, thirteenth, fourteenth, and twenty-eighth day respectively. A definite discomfort response was elicited in each instance. Two of the dogs had been similarly tested previous to the thyroidectomy and in these no diminution was noted in the amount of traction required to produce the typical response.

The relief of angina by removal of the thyroid may be due to the diminished sensitiveness to adrenalin 3 which has been demonstrated clinically as early as 24 hours following the operation. This implies that the individual attacks of angina pectoris in a patient suffering from this disorder may be precipitated by a sudden increase in the patient's physiological output of adrenalin. We attempted to precipitate the discomfort response in dogs by injecting adrenalin. This was successfully accomplished in 9 dogs by applying a constant subminimal traction on the coronary suture by means of weights suspended over pulleys, and then raising the blood pressure suddenly by injecting adrenalin into the femoral vein.