Plasma post heparin lipoprotein lipase activity (LLA) has been studied in patients with hyper- and hypothyroidism and in rabbits made thyrotoxic with thyroxine. The hypothyroid patients had high triglyceride and low LLA values as compared with a control group of healthy subjects. Statistically highly significant negative correlation was found between the triglycerides in fasting patients and the post heparin LLA, indicating a causal relationship, possibly with disturbance of chylomicron degradation due to low LLA in the arterial wall. However, relatively low LLA values were also demonstrated in hyperthyroid patients as well as in rabbits following treatment with thyroxine for 3 weeks. A stimulating effect of the thyroid hormones on the synthesis and degradation of lipoprotein lipase may be a possible explanation for these apparently contradictory findings.

Studies of the fatty acid composition in cholesterol esters, phospholipids and triglycerides in serum have been made in 73 men with acute myocardial infarction (AMI) and in 32 healthy men of comparable age. Of the patients 36 had previously had a myocardial infarction or a history of angina pectoris, while for the other 37 the present attack was their first symptom of coronary heart disease (CHD). Significant differences in fatty acid composition were observed between the two groups of patients with higher percentages of linoleic acid in patients with old CHD. Since linoleic acid proportions in serum to a large extent reflect dietary habits, it is thought that patients with an old CHD have been more assiduous in following diet recommendations given to the whole population, advocating “cholesterol‐lowering diets”, than subjects with no history of cardiac disease. It is concluded that data concerning fatty acid composition in patients with a history of old CHD cannot be used to evaluate dietary habits prior to the manifestation of CHD. It was demonstrated that in patients with an AMI as the first manifestation of CHD linoleic acid percentages were lower than in controls. The finding indicates dietary habits in the patients characterized by a high intake of saturated and monosaturated fats, low intake of essential fatty acids, and possibly a high intake of simple sugars. Differences were also observed in pentaenoic and hexaenoic acids, with higher values in the patient group. This finding does not support the assumption that pentaenoic and hexaenoic acids are significant in the prevention of CHD. In a smaller number of patients, admitted to the hospital within 6 hours after the initial attack of pain, studies were made on admission and on the following morning. These studies gave no indication of important changes in fatty acid composition occurring during the first 24 hours of the disease; and since all studies reported here were performed within 24 hours after onset of the attack, the results are probably representative of preinfarction fatty acid composition.

Serum lipids and thyroxine were determined in 26 men participating in a 90‐km cross‐country ski race, before, immediately after, and on the following days. Serum cholesterol was unchanged immediately after the race, but then fell significantly and remained low during the observation period. During the race the fatty acid composition of serum free fatty acids changed towards the composition of ordinary adipose tissue. The composition of serum triglycerides showed similar but less pronouced changes. On the following days an increase in the arachidonic, and a decrease in the linoleic acid fraction of the total serum lipids were observed. Total thyroxine and free thyroxine in serum were significantly increased at the end of the race, but had returned to the pre‐race levels during the rest of the observation period. The observations correspond to the findings during acute, severe illness, and are compatible with the hypothesis that some of the changes In serum lipids following severe somatic stress are due to increased thyroid hormone activity.