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Abstract. Plasma triglyceride (TG) “turnover rates” were estimated in the fasting state in three different ways: splanchnic chemical TG secretion, splanchnic isotope TG secretion and plasma TG clearance. Forty‐two men with a wide range of fasting plasma TG concentrations, from 0.53 to 16.50 mmol/l were investigated. A constant intravenous infusion of albumin‐bound 3H‐labelled palmitate was given and blood was simultaneously sampled from the hepatic vein and an artery for determination of hepatic venous‐arterial differences of labelled and unlabelled plasma TG. In addition total and splanchnic turnovers of plasma FFA were measured. Similar values were obtained for plasma TG “turnover rate” by the splanchnic chemical TG secretion and the plasma TG clearance method. The values for these two methods varied between 3 and 74 μmol/min. and m2 body surface area, except for two cases who had considerably higher values. The splanchnic isotope TG secretion method gave lower values varying from 1 to 34 μmol/min. and m2 body surface area. This method probably measures only that fraction of the splanchnic TG secretion which is derived from plasma FFA. No correlations were found among normotriglyceridaemic subjects between plasma total TG or VLDL‐TG concentrations and plasma TG “turnover rates” measured by any of the three methods. For patients with hypertriglyceridaemia significant positive correlations were found between plasma VLDL‐TG concentrations and plasma “turnover rates”. The “fractional turnover rate” decreased with increasing TG levels in an apparently hyperbolic fashion. The results suggest an impaired plasma TG removal capacity in patients with hypertriglyceridaemia. In 7 out of 14 patients the plasma TG “turnover rates” were in the upper part of the normal range and seemed to have contributed to the hypertriglyceridaemia in these patients. Plasma FFA turnover rate ranged between 102 and 439 μmol/min. and m2 body surface area. On the average splanchnic FFA mobilization and uptake were about 30 and 60 per cent respectively of total FFA turnover rate. Significant positive correlations were found for the interrelationships between the three plasma FFA total and splanchnic transport parameters. Significant positive correlations were found between the three plasma TG “turnover rates” and total and splanchnic turnover of plasma FFA in subjects with normal plasma TG concentrations. Some patients with hypertriglyceridaemia fell outside the intervals of 99 per cent confidence of the regression analyses for the normo‐triglyceridaemic subjects. This group had higher TG “turnover rates” than “expected” from plasma FFA turnover rates and may represent a distinctive group of hypertriglyceridaemia from the point of view of pathogenesis. It was concluded that all patients with hypertriglyceridaemia who were investigated had decreased “fractional turnover rates” of plasma TG indicating a decreased removal capacity which might be a primary cause of the hypertriglyceridaemia although inflow of plasma TG seemed to be an essential con...

Myocardial metabolism of lipid and carbohydrate substrates wns studied in 17 healthy men a t rest by measuring the arterial-coronary sinus [ (a-cs)] concentration differences. A continnoas int.ravenous infusion of albumin-bound 3H-palmitate was given to provide a tracer for the plasma free fatt.y acids (FFAj and to procluce endogenous labelling of plasma triglycerides (TGj.-4 statistically significant positive (a-cs) difference in triglyceride (TG) concentration was detected in 10 of the 17 subjects and averaged l 8 i 4 (SEN) pmolJ plirsma for the 17 subjects. This was 1.6% of the average arterial TC, concentration. A significant positive (a-cs) difference in TG radioactivity was found in 12 of the 17 subjects but it was not possible to quantitate myoc*arclial TG extr:ict,ion from these radioisotope data.Myocardial extraction of FF-4 based on the radiopalmitate data was on ;iverape 39"6 greater than the extraction of FF-4 measured c:liemically. This was interpreted as indicating an efflux of cinlabelletl fatty acids into tlie coronary sinus, most prolmhly froni i i ylyceridc p o l within thc niyocardium. The fintling that this cffltix of fittty acids \ri~s not accompanied by free glywrol suggested citlier that the fatty acids were derived from partial hydrolysis of glycerides, or that glycerol wiu metabolised within the myocardium. Seven of the subjects had significant, positive (a-cs) differences in free glycerol concentration suggesting that the human heart is capable of metabolising glycerol.There were significant, negative linear correlations between arterial FFA concentration and niyocardial extraction of glucose, lactate and pyruvate with significant efflux of pyruvate from the heart a t higher FPA concentrations. These findings suggested that FFA can decrease glucose extraction by the hunian heart and that one possible mechanism for this may be the inhibition of pyruvate dehydrogertase. The average ( & SEM) oxygen extraction ratios (OERs) for the subst,rates were: TG l 6 + 4oA; FF-4 &3& 3% ; glucose 20 f 3% ; liictate 8 & 2 ' % ; pyriivate 1 + 0.3%. The total OER for these substrates averaged 9700 suggesting that in the resting. fasting, state there is little change in the total energy content of endogenous myocardial substrate pools. K e y words: Jlyocnrdial subst.rate metabolism, myocardial energy metabolism. coronary sinus, endogenous myocardial lipid metabolism. t,riglycerides, free fatty acids, glycerol, glucose. lactate. pyriiwite, 3H-p;~lmitiitc.

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