INFLUENCE OF THYROIDECTOMY ON BLOOD LIPIDS OF THE DOG1

Abstract

The levels of blood cholesterol both free and esterified, phospholipids and total fatty acids were compared in 10 dogs before and after thyroidectomy. The caloric intake in 9 of these dogs was maintained constant throughout the period of observation, both before and after thyroidectomy. Lipid detns. of the blood were made at short intervals for as long as 214 days after thyroidectomy. From the data presented, the characteristic response of each lipid constituent may be pointed out. Although lipid levels of the blood rose after thyroidectomy, the various lipid constituents did not respond to the same degree. The most pronounced increases occurred in cholesterol and in total fatty acids. Striking changes in cholesterol esters occurred after thyroidectomy. The highest values observed after thyroidectomy represented increases of 37-380% above the highest preoperative values; in 4 cases the increases were over 300%. Changes in the levels of cholesterol esters may appear early after thyroidectomy. An 87% increase in esterified cholesterol was observed as early as 7 days after excision of the thyroid glands, and in 7 of the dogs significant changes in the levels of this lipid constituent were present when 16 days had elapsed after thyroidectomy. Increases in the total fatty acid content of the blood occurred in 7 of the 10 dogs after thyroidectomy. In no case did the extent of the rise in total fatty acids approach that recorded for esterified cholesterol. In a single animal the maximum increase in total fatty acids represented an increase of 125% above the preoperative value. In the 6 other dogs that responded, the maximum values after thyroidectomy were 47 to 88% above the preoperative. A significant rise in total fatty acids may occur as early as 1 wk. after thyroidectomy. In 7 of the 10 dogs examined, definite changes were present by the time 29 days had elapsed. Pronounced changes in the levels of free cholesterol or of phospholipids were observed infrequently after thyroidectomy. The types of response of the blood lipids to thyroidectomy differed widely. The responses among the 10 dogs examined were not uniform as regards either the extent of the rise, or the time of onset of lipid increases, or the maintenance of elevated levels, or the degree of fluctuations. Rapidly changing levels of esterified cholesterol and total fatty acids were observed in a number of the dogs after removal of the thyroid glands.