MYOCARDIAL METABOLISM OF EXOGENOUS PLASMA TRIGLYCERIDES IN RESTING MAN

Imagining a habitable planet through food and health

BACKGROUND AND OBJECTIVES

Whether and how it might be possible to imagine a habitable planet through food and health.

METHODS

Reflection on childhood happenstances, sociodemographic circumstances, educational opportunities, persons of influence and lifetime experiences insofar as they might have shaped a view of the past, present and future world as the sole rational home of us all. Confirmation of these notions by personal, kindred, and other contemporary records and publications.

RESULTS

The need to live with uncertainty and an appreciation of connectedness with things animate and inanimate; and for this to be belief, identity, reason and professional imprimatur. That these things have unwittingly informed a near lifetime of interest and enthusiasm for how food and health systems are best served by socioecological approaches.

CONCLUSIONS

That we are socioecological beings with a destiny dependent on reconciling ourselves, as earthlings, as to how well we keep our place in the cosmos habitable. To that end we must dream and work.

Removal of exogenous triglycerides in subjects with massive obesity before and after jejunoileal shunt operation

The fractional removal rate of exogenous triglycerides (TG) in 12 obese subjects with a mean body weight of 132+/-5 kg (S.E.M.) has been studied before a jejunoileal shunt operation. The study was repeated postoperatively at stable body weights 30-54 months later. The weight loss ranged from 13 to 65 kg (mean weight reduction 27%). In 8 patients, 0.3-6.0 kg of skin and subcutaneous tissue were removed surgically for cosmetic reasons during the weight reduction period. Serum cholesterol fell from 220+/-8 to 141+/-11 mg/100 ml (p less than 0.001). The serum TG reduction was not significant, 1.80+/-0.25 before and 1.50+/-0.19 mmol/l after operation. The fractional removal rate of exogenous TG, determined by the intravenous fat tolerance test (IVFTT) with the Intralipid fat emulsion, was not significantly changed. The IVFFT k2 value was 3.5+/-0.5%/min before and 4.3+/-0.6 after surgery (p greater than 0.05). Previous studies have shown that a major part of Intralipid is removed initially in skeletal muscle. The unchanged fractional removal rate of Intralipid, despite the marked reduction in the amount of adipose tissue, supports the concept that the adipose tissue may play a minor role in the initial elimination of exogenous TG from the bloodstream.

Fatty acids and insulin modulate myocardial substrate metabolism in humans with type 1 diabetes

OBJECTIVE

Normal human myocardium switches substrate metabolism preference, adapting to the prevailing plasma substrate levels and hormonal milieu, but in type 1 diabetes, the myocardium relies heavily on fatty acid metabolism for energy. Whether conditions that affect myocardial glucose use and fatty acid utilization, oxidation, and storage in nondiabetic subjects alter them in type 1 diabetes is not well known.

RESEARCH DESIGN AND METHODS

To test the hypotheses that in humans with type 1 diabetes, myocardial glucose and fatty acid metabolism can be manipulated by altering plasma free fatty acid (FFA) and insulin levels, we quantified myocardial oxygen consumption (MVo(2)), glucose, and fatty acid metabolism in nondiabetic subjects and three groups of type 1 diabetic subjects (those studied during euglycemia, hyperlipidemia, and a hyperinsulinemic-euglycemic clamp) using positron emission tomography.

RESULTS

Type 1 diabetic subjects had higher MVo(2) and lower myocardial glucose utilization rate/insulin than control subjects. In type 1 diabetes, glucose utilization increased with increasing plasma insulin and decreasing FFA levels. Myocardial fatty acid utilization, oxidation, and esterification rates increased with increasing plasma FFA. Increasing plasma insulin levels decreased myocardial fatty acid esterification rates but increased the percentage of fatty acids going into esterification.

CONCLUSIONS

Type 1 diabetes myocardium has increased MVo(2) and is insulin resistant during euglycemia. However, its myocardial glucose and fatty acid metabolism still responds to changes in plasma insulin and plasma FFA levels. Moreover, insulin and plasma FFA levels can regulate the intramyocardial fate of fatty acids in humans with type 1 diabetes.

Fat emulsion catabolism in vitro and in vivo--sex related differences

The removal rates of an intravenously administered 10% fat emulsion (Intralipid) from plasma in male and female conscious rats are described. The plasma concentration of fat emulsion particles at various time intervals following a bolus administration (0.2 g/kg) was measured by nephelometry. At the dose employed, the removal of fat emulsion from the plasma followed first order kinetics, ie, a constant fraction was removed from the plasma per unit of time, K2 (%/min). Females exhibited a significantly greater fractional removal rate (K2) than comparably aged males (21.0 +/- 1.0 vs 15.0 +/- 1.4, p less than 0.05). Postheparin lipoprotein lipase, measured using fat emulsion as substrate, also was significantly greater in female rats compared with males. Our results demonstrate that, in rats, fat emulsion (Intralipid) is catabolized more rapidly in females than in males and a greater lipoprotein lipase activity in female rats may be the causative factor.

Removal of exogenous plasma triglycerides in forearm muscle and subcutaneous tissue of hyper-and normotriglyceridaemic men

Absolute arterio-venous removal and fractional removal of blood-borne exogenous triglyceride particles by skeletal and subcutaneous tissues were determined in eight normotriglyceridaemic and six hypertriglyceridaemic men. Estimations were made by simultaneously sampling blood from catheters inserted into a brachial artery, and in the distal direction, into a superficial and deep vein, draining subcutaneous tissue and skeletal muscle respectively. During the infusion of the fat emulsion IntralipidR for 3 hours steady arterial concentrations of exogenous TG particles were found, indicating first order kinetics. In all subjects absolute arterio-venous and fractional removal of triglycerides were about twice as high in skeletal muscle as in subcutaneous tissue. In skeletal muscle the fractional removal and absolute removal were significantly higher in normotriglyceridaemic than in hypertriglyceridaemic subjects (p less than 0.001). No decrease in removal with time was observed, which would have suggested saturation of removal sites. Mean fractional removal in skeletal muscle was significantly correlated with the k2 value determined by an intravenous fat tolerance test before the infusion study (r = 0.61, p less than 0.05). In subcutaneous tissue fractional removal was also significantly higher in normotriglyceridaemic subjects (p less than 0.05). The results suggest that in both skeletal muscle and subcutaneous tissue the removal system is impaired in hypertriglyceridaemic subjects. This finding supports the concept that a decreased elimination capacity in these tissues may partly account for triglyceride elevation in hypertriglyceridaemic subjects.

Removal of exogenous triglycerides in human forearm muscle and subcutaneous tissue

The removal of exogenous triglyceride (TG) in forearm muscle and subcutaneous tissue of 7 healthy male volunteers has been studied by nephelometric determinations of arterial-deep venous (a-dv) and arterial-superficial venous (a-sv) differences in concentration of fat particles. Exogenous TG was administered as a constant i.v. infusion of Intralipid over a period of 30 min at reat and another 15 min during forearm work. At rest a significant positive a-dv difference in fat particle concentration of 121 plus pr minus 21 mumol TG/l (mean plus or minus S.E.M.) was found, which correspondens to a fractional extraction of 1093 plus or minus 2.0%. Also the a-sv difference was significant, 81 plus or minus 14 mumol TG/l, 5.7 plus or minus 0.8% of the arterial concentration. During exercise no further significant removal was found. Thus both skeletal muscle and subcutaneous tissue seem to be able to remove exogenous TG in substantial amounts under resting conditions. In the exercising muscle, however, the direct removal of exogenous TG does not seem to be of significant importance.

Changes in insulin immunoreactivity across the coronary circulation in man during infusions of glucose and a fat emulsion

The extraction of immunoreactive insulin by the human heart has been examined using the technique of coronary sinus catheterisation. The subjects were 12 male volunteers. During the study infusions of a fat emulsion and glucose were given in an effort to create a "steady fed state". The higher arterial insulin immunoreactivities which were observed during the infusions were associated with greater arterial coronary sinus differences in insulin immunoreactivity. The possibility of insulin degradation by the heart is discussed. During prolonged exercise the process of insulin removal by the heart appeared more active.