Splanchnic secretion rates of plasma triglycerides and total and splanchnic turnover of plasma free fatty acids in men with normo- and hypertriglyceridaemia.

Abstract

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 contributing factor in half the number of patients.