Edmond Balasse

Kinetics of ketone body metabolism in fasting humans.

The rates of production of total ketone bodies (acetoacetate + beta-hydroxybutyrate) were determined using an isotope tracer technique in 23 obese subjects submitted to a fast of variable duration (15 hr--23 days). Constant infusions of 14C-acetoacetate were used in most studies, but similar results were obtained with pulse injections of this tracer or with constant infusions of 14C-D(-)-beta-hydroxybutyrate. Blood concentration, production rate, and urinary elimination of total ketones rose during approximately the first 3 days of fast and plateaued thereafter at values amounting, respectively, to 7.09 +/- 0.32 mumole/ml, 1908 +/- 80 mumole/min and 167 +/- 14 mumole/min. The rates of ketogenesis are significantly higher than those usually reported in the literature. Ketonemia was an exponential function of production rate suggesting that tissue uptake becomes progressively saturated as inflow rate rises. The same type of relationship between concentration and inflow rate was observed in nine control overnight fasted obese subjects rendered hyperketonemic with infusions of variable amounts of unlabeled acetoacetate. The comparison between the fasted and the control subjects at ketone concentrations of 3--10 mumole/ml showed that on an average, starvation is associated with a 35% decrease in the metabolic clearance rate of ketones. These data suggest that fasting is associated with an impairment of mechanisms for utilizing ketones, this defect contributing to the hyperketonemia of food deprivation.

Operation of the “Glucose-Fatty Acid Cycle” during Experimental Elevations of Plasma Free Fatty Acid Levels in Man

Abstract. In order to determine whether increased plasma free fatty acid (FFA) levels inhibit glucose utilization in man, glucose metabolism was studied in 8 normal subjects both under basal conditions and during experimental elevations of plasma FFA concentrations induced by the administration of high fat meals and heparin. A primed constant infusion of 1‐14C‐glucose was used to measure the rate of turnover, the fractional removal rate and the rate of oxidation of plasma glucose under both experimental conditions. Elevations of FFA levels (+117%) were accompanied by a 9% reduction in both the fractional removal rate of glucose and the hepatic glucose production so that glycaemia remained unchanged. The % glucose converted to CO2, and the % CO2 derived from plasma glucose decreased respectively by 13.5% and 21.7%, while unlabelled CO2 production remained unchanged. This reduction in glucose utilization occurred despite a significant rise in insulin concentration indicating that high FFA levels reduce sensitivity to insulin. The tissue implicated in the inhibitory effect of FFA on overall glucose utilization cannot be determined from these experiments but it is suggested that muscle participated in these metabolic changes. These data provide further arguments supporting the view that plasma FFA participate in the regulation of glucose metabolism in man.

Ketone Body Production and Disposal in Diabetic Ketosis: A Comparison with Fasting Ketosis

This work compares the metabolism of total ketone bodies in 13 insulin-deprived, type I diabetic subjects and 26 control subjects fasted for 15 h to 23 days, with the two groups showing a similar range of ketone body levels (1–12 mM). Ketone turnover rate was measured using a primed, constant infusion of either 14C-acetoacetate or 14C-β-hydroxybutyrate, both tracers yielding comparable results. The major conclusions of this study are the following: the kinetics of ketone bodies are comparable in the two groups within the range of concentrations tested. The hyperketonemia of fasting and diabetes is primarily caused by an increased production of ketone bodies, but the phenomenon is amplified by a progressive limitation in the ability of tissues to remove ketones from blood as the concentration rises. The inverse relationship between the metabolic clearance and the plasma levels of ketones, which underlies this process, represents a general characteristic of ketone body metabolism that applies to both types of ketosis. A maximal metabolic disposal rate of about 2.3 mmol/min/1.73 m2 is attained in both groups at concentrations of 10–12 mM, which correspond to the highest ketone body levels encountered during prolonged fasting. Thus, up to these levels, there is no evidence for the existence of a ketone body removal defect specific to diabetes.

Hole of plasma free fatty acids in the control of insulin secretion in man

SummaryThe aim of the present work was to study the effects of experimental changes in plasma free fatty acid (FFA) levels on basal insulin (IRI) concentration and onβ cell response to IV glucose, tolbutamide or glucagon in man. Each of the 53 subjects tested was studied on two separate occasions: i) in the basal state; ii) after an experimental decrease or increase in plasma FFA levels induced, respectively, by administration of nicotinic acid or the combination of a fat meal and heparin. The lowering of plasma FFA resulted in a small but significant fall in basal insulin concentration and in a 30% decrease in. IRI response whatever the insulinotropic agent used. On the other hand, experimental elevation of plasma FFA enhanced pancreatic response to glucose (+178%) and tolbutamide (+58%), but did not alter significantly the IRI response to glucagon. Both the increase and the decrease in FFA concentration resulted in a reduction in the rate of glucose assimilation. — These results provide arguments for a role of plasma FFA in the control of insulin secretion and of insulin sensitivity in man.

Influence of nicotinic acid on the rates of turnover and oxidation of plasma glucose in man

Abstract The effects of antilipolysis induced by nicotinic acid on the rates of turnover and oxidation of plasma glucose were studied in normal overnight fasted, obese overnight fasted, and obese starved subjects, using a 14 C-glucose infusion technique. Changes induced by nicotinic acid were similar whatever the nutritional state of the subjects. Plasma FFA levels and blood concentrations of glycerol and ketones decreased by about 60%; glycemia remained essentially unchanged but both the removal rate of plasma glucose and the hepatic glucose output increased by about 25%. Moreover, the fraction of glucose taken up by tissues and promptly oxidized and the fraction of expired CO 2 derived from plasma glucose increased, respectively, by 18% and 33%. This enhancement of glucose utilization occurred despite a small but significant decrease in plasma IRI concentration, indicating that nicotinic acid increased sensitivity to insulin. The above-mentioned results were obtained in 8 of the 10 patients studied. The remaining two subjects did not respond to the administration of nicotinic acid by any significant decrease in FFA nor in glycerol concentrations and showed no change in the rates of glucose turnover and oxidation. These data indicate that the effects of nicotinic acid on glucose metabolism may be partly mediated through changes in plasma FFA concentration and are consistent with the idea that the “glucose-fatty acid cycle” plays a significant role in the control of glucose metabolism in man.

Differential Effects of Sodium Acetoacetate and Acetoacetic Acid Infusions on Alanine and Glutamine Metabolism in Man

It has been suggested that ketone bodies might participate in the nitrogen-sparing process occurring during prolonged starvation by inhibiting the muscular production of alanine and glutamine, which are the main gluconeogenic amino acids. The results of the ketone infusion studies on which this theory is based have been reevaluated in this study by following the plasma levels of ketone bodies, alanine, glutamine, and other substrates during 11.5 h in five groups of normal overnight-fasted subjects. Subjects of groups I, II, and III were infused for 3 h, respectively, with Na acetoacetate, Na bicarbonate, or free acetoacetic acid administered in comparable amounts (about 20 mumol/kg per min), whereas group IV was infused with hydrochloric acid (7.0 mumol/kg per min). A control group (V) received no infusion. Na acetoacetate induced a rise in blood pH (+0.1+/-0.003) and a fall in the plasma levels of alanine (-41.8+/-4.6%) and glutamine (-10.6+/-1.4%), whereas free acetoacetic acid had a barely detectable lowering effect on blood pH and induced a rise in alanine (+22.5+/-8.0%) and glutamine (+14.6+/-3.2%) levels. Both infusions were associated with a lowering of plasma glucose, which therefore seems independent of the changes in alanine and glutamine concentrations. Sodium bicarbonate reproduced the alkalinizing effect and the hypoalaninemic action of Na acetoacetate, which seems thus unrelated to hyperketonemia. On the other hand, acidification of blood with hydrochloric acid did not mimic the effects of acetoacetic acid. If the hyperalaninemic and hyperglutaminemic effects of ketone bodies infused in their physiological form (free acids) reflect a stimulation of the muscular output of these amino acids, the participation of ketone bodies in the nitrogen-sparing process of prolonged fasting seems very unlikely. On the other hand, during brief starvation, when both ketogenesis and gluconeogenesis are markedly stimulated, ketone bodies might indirectly contribute in supplying the liver and the kidney with gluconeogenic substrates.

Inhibition of ketogenesis by ketone bodies in fasting humans

Although there exists some indirect evidence that circulating ketone bodies might inhibit their own production rate, the direct demonstration of this homeostatic feed-back phenomenon is still lacking. The present work aims at demonstrating the operation of this control mechanism in human fasting ketosis. Six obese subjects, who fasted 2-23 days, were given a primed constant i.v. infusion of 3- 14C-acetoacetate for 4 hr. After a control period of 2 hr, unlabeled sodium acetoacetate was administered as a primed constant i.v. infusion at the rate of 0.688-1.960 mmol/min until the end of the study. During both periods, the rates of inflow of ketones were estimated from the specific activity of total ketones measured under near isotopic steady state conditions. During the control period, total ketone concentration amounted to 3.98-9.65 mumol/ml and production rates of total ketones ranged between 1.450 and 2.053 mmol/min. The levels of free fatty acids, glycerol, glucose, and insulin averaged respecitvely 1.30 mumol/ml, 0.11 mumol/ml, 74 mg/100 ml, and 5.2 muU/ml. The administration of exogenous ketones during the second phase of the study induced a 47%-92% increase in total ketone levels. During this period, the endogenous production of ketones (calculated as the difference between total inflow rate and acetoacetate infusion rate) amounted only to 67%-90% of control values. Among other factors, this inhibition of ketogenesis was probably partially related to the direct antilipolytic effect of infused ketones. Indeed, there was a concomitant fall in FFA and in glycerol levels averaging respectively 13.5% and 17.3%, without significant changes in peripheral insulin concentrations. Our results demonstrate that during fasting, circulating ketone bodies exert an inhibitory influence on the rate of ketogenesis. This mechanism might play an important role in preventing the development of uncontrolled hyperketonemia during starvation.

Effects of metformin on the pathways of glucose utilization after oral glucose in non—insulin-dependent diabetes mellitus patients☆

To analyze the effects of metformin (M) on the kinetics and pathways of glucose utilization after glucose ingestion, nine non-insulin-dependent diabetes mellitus (NIDDM) patients underwent two 5-hour oral glucose tolerance tests (OGTTs) preceded in random order by a 3-week treatment with either M (850 mg twice per day) or placebo. Each test included intravenous infusion of 3-3H-glucose and labeling of the oral dose (75 g) with 1-14C-glucose, with measurements of glucose kinetics, glycolytic flux (3H2O production), and glucose oxidation (indirect calorimetry and expired 14CO2). Basal glycemia was decreased by M (6.6 v 8.2 mmol/L, P < .01) with no changes in insulin levels, with the hypoglycemic effect correlating strongly (P < .001) with a decrease in glucose production. Mean 0- to 5-hour postprandial glycemia was also decreased by the drug (9.9 v 12.2 mmol/L, P < .04), lactate concentration was increased (1.79 v 1.44 mmol/L, P < .01), and absolute insulin levels were increased, but not to a significant extent. The rates of appearance (Ra) of exogenous and endogenous glucose were not modified, and the hypoglycemic effect of M in the postprandial state was entirely related to an increase in systemic glucose disposal (85.1 v 77.5 g/5 h, P < .001). Carbohydrate oxidation was unchanged, and glycolytic flux and nonoxidative glycolysis were increased by approximately 13 g/5 h (P < .01), with the excess lactate produced probably being converted to glycogen in the liver. Whole-body glycogen synthesis through the direct pathway tended to be reduced (-8 g/5 h, P > .05). Thus, M decreases postprandial glycemia by increasing glucose disposal and stimulates lactate production. The data also suggest that the drug increases the proportions of glycogen deposited through the indirect rather than the direct pathway.

Early Effects of Anti-Insulin Serum on Hepatic Metabolism of Plasma Free Fatty Acids in Dogs

SUMMARY:Hepatic metabolism of free fatty acids was studied in six anesthetized fasted dogs before and for several hours after the abrupt induction of insulin deficiency. This was produced by injecting guinea pig anti-insulin serum in amounts capable of binding all circulating insulin for several hours. During each study, albumin-bound-I-C-14-palmitate and I-131-rose bengal were infused at a constant rate and serial sanv pies of arterial, portal and hepatic venous blood were obtained through appropriate intravascular catheters. Maximal changes were observed three to four hours after administration of anti-insulin serum. Mean arterial concentrations of glucose, free fatty acids, glycerol and triglyceride fatty acids of very low density lipoproteins increased twofold and that of ketone bodies, fourfold. Hepatic extraction ratio of free fatty acids was unchanged after anti-insulin serum so that the hepatic uptake of free fatty acids approximately doubled. During the control period, about 25 per cent of free fatty acids removed by the liver were converted to CO2, 11 per cent to triglyceride fatty acids of very low density lipoproteins and 25 per cent to ketones (assuming that ketones derived entirely from FFA). After anti-insulin serum, corresponding values were 14 per cent, 26 per cent and 51 per cent. The increased relative and absolute conversion of free fatty acids to ketones resembles that observed in chronically diabetic dogs withdrawn from insulin for forty-eight hours. However, the increased conversion of free fatty acids to triglyceride fatty acids of very low density lipoproteins observed in short-term deficiency of insulin contrasts with the greatly depressed conversion observed after two days of insulin lack.

Glucose Metabolism During the Starved-To-Fed Transition in Obese Patients With NIDDM

To analyze the effects of short-term fasting on postprandial glucose metabolism in non-insulin-dependent diabetes mellitus (NIDDM), two groups of nine obese NIDDM patients and two comparable groups of control subjects underwent a 5-h oral glucose tolerance test after either 14 h or 4 days of fasting. The fluxes and the rates of oxidation and storage of glucose were measured using a dual isotope technique combined with indirect calorimetry. The effect of fasting on insulin action and beta-cell responsiveness was tested in an additional group of six obese NIDDM patients with a euglycemic hyperinsulinemic clamp followed by an intravenous glucagon test. In the diabetic patients, fasting enhanced beta-cell response to glucose and glucagon and did not modify insulin action. This response differs from that of nondiabetic subjects in whom fasting is known to impair insulin secretion and action. Regarding glucose fluxes, it was observed that in the overnight-fasted state, the incremental tissular disposal following glucose ingestion was reduced by ∼ 50% in the diabetic versus control subjects in relation to an ∼ 62% impairment in glucose storage. After fasting, incremental tissular disposal was restored to normal, glucose oxidation was virtually abolished, and storage was increased ∼ threefold. Thus, in NIDDM patients, fasting corrects the defect in glycogen storage without modifying the action of insulin on glucose uptake and improves beta-cell responsiveness, the latter two effects being opposite to those observed in nondiabetic subjects.