Plasma Triglyceride Concentration and Plasma Free Fatty Acid Changes in Response to Norepinephrine in Man.

Hypertriglyceridemia is frequently observed in subjects with coronary artery disease and is particularly common in young males (1, 2). A number of factors undoubtedly contribute to the increased levels of plasma triglycerides; among these, the role of exogenous dietary fat has been established (3). The magnitude of endogenous triglyceride synthesis has not been measured in patients with hypertriglyceridemia, although it is known that in fasting man, plasma triglycerides are derived from free fatty acids (FFA) (4). Since the flux of FFA from adipose tissue stores is, to a large extent, determined by the activity of the sympathetic nervous system (5), it seems possible that the level of plasma triglycerides in a given individual might be related to the responsiveness of the adipose tissue to catecholamines. This paper presents evidence to support this hypothesis. The increment in plasma FFA in response to a standard infusion of norepinephrine has been measured in subjects with and without coronary artery disease and related to their plasma triglyceride levels. The depression of plasma FFA by nicotinic acid has also been measured and related to the initial plasma FFA and tri-glyceride levels, since nicotinic acid has been shown to inhibit catecholamine-induced mobilization of FFA (6). Materials and Methods Seventeen men with coronary artery disease, ages 34 to 49 (mean age, 44), and another group of 8 men, ages 32 to 53 (mean age, 43), were studied. The subjects with coronary artery disease had survived a myocardial infarction at least 3 months previously and were leading a normal ambulant life at the time of the investiga-Supported by a grant from the National Heart Foundation of Australia. tion. The other group consisted of men attending the hospital for minor surgical complaints who were otherwise healthy and ambulant. All the men were therefore familiar with such hospital procedures as venipunc-ture. Patients with obviously hyperlipemic plasma were excluded. The subjects, who had not smoked since the previous day, were studied after an overnight fast. After the subjects had rested for half an hour, an indwelling cathe-ter was placed into a vein, and the first sample of blood was obtained after a further half-hour. Three control samples of blood were usually obtained during the following 30 minutes. Norepinephrine was infused at a constant rate of 0.2 ,g per kg per minute for 15 minutes. Further samples of blood were collected at the end of the infusion and 5, 15, 30, and …