Free fatty acid and carbohydrate metabolism of the working forearm muscle in type IV hyperlipoproteinaemia

Abstract. Substrate utilization of the working forearm was studied in nineteen patients with hypertriglyceridaemia (HLP) and compared to nineteen normolipidaemic (NLP) subjects, matched with regard to body weight, body height, intravenous glucose tolerance and age. Arterial-deep venous differences of oxygen, carbon dioxide, free fatty acids (FFA), glucose, lactate and pyruvate was measured. The fractional extraction and oxidation of fatty acids was assessed by intravenous infusion of albumin-bound [³H]palmitate and [¹⁴C]oleate. Measurements were made both in the postabsorptive state and after plasma FFA lowering by nicotinic acid. The HLP subjects had, before nicotinic acid, higher arterial concentrations, higher turnover rates of palmitate and oleate and higher plasma glycerol concentrations indicating a greater mobilization of FFA. However, the forearm extraction and oxidation of FFA as well as the calculated total body fatty acid oxidation was similar in HLP and NLP subjects. Nicotinic acid decreased arterial concentrations and turnover rates of FFA to the same extent in HLP and NLP groups, the effect being the same for palmitic and oleic acid. Fractional extraction both of palmitic and of oleic acid increased after nicotinic acid in the NLP but not in the HLP group. Plasma glycerol decrease after nicotinic acid was of the same magnitude in HLP and NLP groups. Thus, (1) an increased uptake of FFA in HLP subjects must occur in other tissues than skeletal muscle and with another fate of the fatty acids than oxidation. The explanation might be an increased incorporation of fatty acids into triglycerides which are subsequently secreted from the liver. (2) The impaired triglyceride removal in skeletal muscle which has been found in HLP subjects is more likely due to an impaired lipolytic activity than to an abnormality in uptake and utilization of hydrolysed fatty acids. No abnormalities in carbohydrate metabolism were found in these HLP subjects with normal glucose tolerance.