Effect of epinephrine on the relationship between nonesterified fatty acid availability and ketone body production in postabsorptive man: evidence for a hepatic antiketogenic effect of epinephrine

Metabolic effect of adrenaline infusion in people with type 1 diabetes and healthy individuals

AIMS/HYPOTHESIS

As a result of early loss of the glucagon response, adrenaline is the primary counter-regulatory hormone in type 1 diabetes. Diminished adrenaline responses to hypoglycaemia due to counter-regulatory failure are common in type 1 diabetes, and are probably induced by exposure to recurrent hypoglycaemia, however, the metabolic effects of adrenaline have received less research attention, and also there is conflicting evidence regarding adrenaline sensitivity in type 1 diabetes. Thus, we aimed to investigate the metabolic response to adrenaline and explore whether it is modified by prior exposure to hypoglycaemia.

METHODS

Eighteen participants with type 1 diabetes and nine healthy participants underwent a three-step ascending adrenaline infusion during a hyperinsulinaemic-euglycaemic clamp. Continuous glucose monitoring data obtained during the week before the study day were used to assess the extent of hypoglycaemia exposure.

RESULTS

While glucose responses during the clamp were similar between people with type 1 diabetes and healthy participants, plasma concentrations of NEFAs and glycerol only increased in the group with type 1 diabetes (p<0.001). Metabolomics revealed an increase in the most common NEFAs (p<0.01). Other metabolic responses were generally similar between participants with type 1 diabetes and healthy participants. Exposure to hypoglycaemia was negatively associated with the NEFA response; however, this was not statistically significant.

CONCLUSIONS/INTERPRETATION

In conclusion, individuals with type 1 diabetes respond with increased lipolysis to adrenaline compared with healthy participants by mobilising the abundant NEFAs in plasma, whereas other metabolic responses were similar. This may suggest that the metabolic sensitivity to adrenaline is altered in a pathway-specific manner in type 1 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05095259.

Endocrine regulation of the fasting response by PPARalpha-mediated induction of fibroblast growth factor 21

Peroxisome proliferator-activated receptor alpha (PPARalpha) regulates the utilization of fat as an energy source during starvation and is the molecular target for the fibrate dyslipidemia drugs. Here, we identify the endocrine hormone fibroblast growth factor 21 (FGF21) as a mediator of the pleiotropic actions of PPARalpha. FGF21 is induced directly by PPARalpha in liver in response to fasting and PPARalpha agonists. FGF21 in turn stimulates lipolysis in white adipose tissue and ketogenesis in liver. FGF21 also reduces physical activity and promotes torpor, a short-term hibernation-like state of regulated hypothermia that conserves energy. These findings demonstrate an unexpected role for the PPARalpha-FGF21 endocrine signaling pathway in regulating diverse metabolic and behavioral aspects of the adaptive response to starvation.

Lipolytic responsiveness to epinephrine in nondiabetic and diabetic humans

To determine whether the sensitivity of adipose tissue lipolysis to catecholamines is increased in poorly controlled insulin-dependent diabetes, the lipolytic response to epinephrine was measured in seven nondiabetic volunteers and seven poorly controlled diabetic subjects with use of [1-(14)C]palmitate as a tracer. Subjects received sequential 1-h infusions of epinephrine, which produced epinephrine concentrations of approximately 1,000, approximately 1,750, approximately 3,500, and approximately 6,000 pmol/l. A pancreatic clamp was used to maintain constant plasma hormone levels. Concentration-response curves were constructed for each subject from the integrated lipolytic response during each epinephrine infusion. There was no difference in maximal lipolytic response (117 +/- 19 vs. 152 +/- 11 mumol.kg-1.h-1) or in maximally effective (3,171 +/- 267 vs. 3,357 +/- 349 pmol/l) or half-maximally effective (1,081 +/- 109 vs. 1,015 +/- 120 pmol/l) epinephrine concentrations between nondiabetic and diabetic subjects, respectively (all P = NS). In control subjects, maximum beta-hydroxybutyrate concentrations were achieved at lower epinephrine concentrations than those required for a maximum lipolytic effect. Thus, under pancreatic clamp conditions, the lipolytic response to epinephrine in nondiabetic and diabetic subjects was similar.

Differential effects of physiological versus pathophysiological plasma concentrations of epinephrine and norepinephrine on ketone body metabolism and hepatic portal blood flow in man

Few studies that have examined the effects of catecholamines on ketogenesis have considered the effects of catecholamines on hepatic portal blood flow. Since hepatic blood flow is a major determinant of hepatic ketogenesis (via modification of free fatty acid availability), interpretation of these studies is difficult. To better define the relative contributions of these variables, we studied the effects of physiological and pathophysiological plasma concentrations of epinephrine and norepinephrine on plasma ketone body concentrations and hepatic portal blood flow in controlled paired studies in young healthy male volunteers. To assess the effects of physiological catecholamine concentrations, each of eight subjects received 60-minute sequential infusions of epinephrine (10 ng/kg/min) and norepinephrine (32.5 ng/kg/min) together with a control infusion of heparin (0.4 U/kg/min) separated by 60-minute washout periods. Similar increments in plasma nonesterified fatty acid ([NEFA] to approximately 1 mmol/L) were observed during each infusion. The ketotic ratios, calculated as the ratio of plasma ketone bodies to fatty acids integrated above baseline for 90 and 120 minutes, respectively, for epinephrine and norepinephrine infusions were both significantly greater (P < .005 for each) than for the heparin control infusion. To assess the effects of pathophysiological plasma catecholamine concentrations, each of eight subjects also received sequential 60-minute infusions of epinephrine 60 ng/kg/min, norepinephrine 80 ng/kg/min (plus heparin 0.1 U/kg/min), and a separate control infusion of heparin with or without Intralipid (KabiVitrum, Alameda, CA). Whereas integrated plasma fatty acid levels were approximately twofold greater than those observed in the physiological protocol, the absolute integrated ketone body response to the pathophysiological concentration of epinephrine was significantly lower than that observed for the physiological dose of the hormone (P < .05). In contrast, the ketotic ratio for norepinephrine was significantly greater (P < .005) than for both epinephrine and the control infusion of heparin with or without Intralipid. Significant (P < .01) increases above baseline fasting levels were observed in plasma glucose and immunoreactive insulin concentrations during infusion of pathophysiological concentrations of epinephrine. Because of the technical difficulties of simultaneously measuring portal blood and sampling blood frequently, studies were repeated in six additional subjects using noninvasive image-guided flowmetry to measure percentage changes in hepatic portal blood flow during catecholamine infusion. Norepinephrine reduced hepatic portal blood flow significantly at the low-physiological concentration by 12% (P < .05) and at the pathophysiological concentration by 18% (P < .05). In summary, (1) both epinephrine and norepinephrine were associated with significant ketotic effects at physiological plasma concentrations; and (2) when infused at pathophysiological concentrations, only norepinephrine exerted a significant additional ketotic effect. Since norepinephrine has a significant simultaneous effect of reducing hepatic portal blood flow, we conclude that previous studies may have underestimated the effect of norepinephrine on hepatic ketogenesis.

Respective role of plasma nonesterified fatty acid oxidation and total lipid oxidation in lipid-induced insulin resistance

To investigate the respective role of nonesterified fatty acids (NEFA) oxidation and total lipid oxidation in lipid-induced insulin resistance, we measured the response of glucose metabolism to insulin in normal subjects without (control study) or with either heparin (heparin study) or triglycerides (TG) emulsion (Ivelip study) infusion. Three-step euglycemic-mild-hyperinsulinemic clamp studies were performed. Lipid and glucose metabolism were studied using indirect calorimetry and [6,6-2H2]glucose and [1-13C]palmitate infusions. NEFA concentration and turnover and oxidation rates were decreased by insulin in the control study, but were maintained during the heparin and Ivelip infusion studies. Total lipid oxidation was decreased similarly in the control and heparin studies, but was increased during the Ivelip infusion. Stimulation of glucose oxidation and utilization by insulin was reduced in the Ivelip study, but not in the heparin study. Thus, peripheral insulin resistance was observed in the presence of a combined increase in total lipid and NEFA oxidation, but not during an isolated increase in NEFA oxidation. On the other hand, insulin-induced inhibition of glucose production was impaired in both the heparin and Ivelip studies. We conclude that total lipid oxidation is a major determinant of peripheral insulin resistance, whereas hepatic insulin resistance could be induced even by a moderate increase in NEFA availability.

Differential control of glucoregulatory hormone response and glucose metabolism by NMDA and kainate

The aim of the present study was to elucidate the effect of kainate and N-methyl-D-aspartate (NMDA), two different excitatory amino acid (EAA) agonists, on glucoregulatory hormone production and whole body glucose metabolism. Rates of hepatic glucose production (HGP) and peripheral glucose utilization (GU) were assessed in overnight fasted, catheterized, conscious rats using [3-3H]glucose. At the highest dose of kainate examined (16 mg/kg), glucose levels increased 97% after 1 h; thereafter, glucose fell towards basal values but was still elevated 25% at the end of the 3 h experiment. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of GU. Both HGP and GU were elevated 86% throughout the final 2 h of the experiment. NMDA induced changes in glucose flux that were qualitatively similar, yet of smaller magnitude and of shorter duration, than those produced by kainate. Kainate-induced increases in glucose metabolism were associated with an early transient hyperinsulinemia followed by a period of insulinopenia, and sustained increases in the plasma concentrations of glucagon, corticosterone, epinephrine and norepinephrine. In contrast, sustained increases in glucagon and catecholamines, as well as the late hypoinsulinemia were not detected in NMDA-treated rats. Adrenergic blockade attenuated the kainate- but not the NMDA-induced increase in glucose metabolism. These results indicate that EAA agonists that bind preferentially to different receptor subtypes produce qualitatively similar changes in glucose metabolism. Whereas the increased HGP in kainate-injected rats was associated with sustained elevations in glucagon, catecholamines and corticosterone, NMDA only transiently elevated circulating glucocorticoid levels, suggesting a different mechanism of action. These data, support the involvement of EAA in various aspects of glucoregulation.

Inhibition of hepatic ketogenesis by tumor necrosis factor-alpha in rats

Tumor necrosis factor-alpha (TNF-alpha) stimulates hepatic lipogenesis. Therefore, it could play a role in the control of ketogenesis. To test this hypothesis, we measured simultaneously free fatty acids (FFA; [1-13C]palmitate) and ketone body (KB; [3,4-13C2]acetoacetate) kinetics, before and after intraperitoneal injection of saline or TNF-alpha, in postabsorptive rats or rats starved for 24 h. In both groups of rats, TNF-alpha injection did not modify insulinemia and induced a moderate increase of FFA concentrations and appearance rates (P < 0.05). Despite increased FFA availability, ketogenesis was impaired after TNF-alpha injection, as shown by lower KB concentrations and appearance rates; this effect was more important in postabsorptive than in starved rats. The percentage of FFA flux used for ketogenesis was decreased by TNF-alpha in the postabsorptive group (P < 0.05) and starved (P < 0.05) rats. In both groups, maximal liver acetyl-coenzyme A carboxylase activity and estimated phosphorylation state were not modified by TNF-alpha injection, but hepatic concentrations of citrate were increased (P < 0.05). This increased citrate level could be related to a mobilization of glucose stored as glycogen since liver glycogen was decreased by TNF-alpha injection (P < 0.05). In conclusion, TNF-alpha injection in rats decreased hepatic ketogenesis. This action could be related to an increased mobilization and utilization of carbohydrate stores.

Epinephrine's ketogenic effect in humans is mediated principally by lipolysis

To quantify epinephrine's effects on acetoacetate and beta-hydroxybutyrate kinetics, we infused subjects with 0.3 and 2.5 micrograms/min epinephrine, either alone or with a concomitant somatostatin infusion with insulin, glucagon, and growth hormone replaced at postabsorptive levels (islet clamp). Additional subjects received no epinephrine but sequential infusions of heparin plus 10% Intralipid at rates of 0.5 and 3.0 ml/min. Both epinephrine and Intralipid increased ketone body appearance (unaffected by islet clamp), augmented the interconversion rates between ketone bodies and, during the 2.5 micrograms/min infusion, caused a marked increase in beta-hydroxybutyrate appearance. The fraction of plasma free fatty acid (FFA) flux appearing as plasma ketones increased from 6 to 7% in the basal state to 11% at the high-epinephrine infusion. This fraction was also unaffected by the islet clamp and was not different from values obtained at similar Intralipid plus heparin-induced elevations in plasma FFA levels. We conclude that epinephrine's ketogenic effect in humans is primarily the result of its lipolytic effect, is accompanied by a significantly increased rate of ketone body interconversion, is manifest largely as an increase in plasma beta-hydroxybutyrate appearance at high plasma epinephrine values, and is not limited by portal insulin at post-absorptive levels.

Hypoglycemic effects of a beta-agonist, Ro 16-8714, in streptozotocin-diabetic rats: decreased hepatic glucose production and increased glucose utilization in oxidative muscles

Streptozotocin (STZ)-induced diabetic rats are glycosuric, hyperglycemic, hyperketonemic, overproduce glucose, and have a decreased glucose utilization in oxidative muscles. Treatment with a beta-agonist, Ro 16-8714, decreases the glycosuria, hyperglycemia, hyperketonemia, and hepatic glucose production. Tissue glucose utilization was unchanged, except in oxidative muscles, where it was increased.

The effects of different plasma insulin concentrations on lipolytic and ketogenic responses to epinephrine in normal and type 1 (insulin-dependent) diabetic humans

This study was performed to verify: (1) the ability of different insulin concentrations to restrict the lipolytic and ketogenic responses to exogenous epinephrine administration; (2) whether the ability of insulin to suppress the lipolytic and ketogenic responses during epinephrine administration is impaired in Type 1 (insulin-dependent) diabetic patients. Each subject was infused on separate occasions with insulin at rates of 0.2, 0.4, and 0.8 mU.kg-1.min-1 while normoglycaemic. To avoid indirect adrenergic effects on endocrine pancreas secretions, the so-called "islet clamp" technique was used. Rates of appearance of palmitic acid, acetoacetate, and 3-hydroxybutyrate were simultaneously measured with an infusion of 13C-labelled homologous tracers. After a baseline observation period epinephrine was exogenously administered at a rate of 16 ng.kg-1.min-1. At low insulin levels (20 microU/ml) the lipolytic response of comparable magnitude was detected in normal and Type 1 diabetic patients. However, the ketogenic response was significantly higher in Type 1 diabetic patients. During epinephrine administration, similar plasma glucose increments were observed in the two groups (from 4.74 +/- 0.53 to 7.16 +/- 0.77 mmol/l (p less than 0.05) in Type 1 diabetic patients and from 4.94 +/- 0.20 to 7.11 +/- 0.38 mmol/l (p less than 0.05) in normal subjects, respectively). At intermediate insulin levels (35 microU/ml) no significant differences were found between Type 1 diabetic patients and normal subjects, whereas plasma glucose levels rose from 4.98 +/- 0.30 to 6.27 +/- 0.66 mmol/l (p less than 0.05) in Type 1 diabetic patients, and from 5.05 +/- 0.13 to 6.61 +/- 0.22 mmol/l (p less than 0.05) in normal subjects. At high insulin levels (70 microU/ml) the lipolytic response was detectable only in Type 1 diabetic patients; the ketogenic response was reduced in both groups. During the third clamp, a significant rise in plasma glucose concentration during epinephrine infusion was observed in both groups. In conclusion this study shows that at low insulin levels Type 1 diabetic patients show an increased ketogenic response to epinephrine, despite their normal nonesterified fatty acid response. Instead, high insulin levels are able to restrict the ketogenic response to epinephrine in both normal and Type 1 diabetic subjects, although there is a still detectable lipolytic response in the latter. In the presence of plasma free insulin levels that completely restrict the ketogenic response in the same group, there is still a distinct glycaemic response. Plasma insulin levels in Type 1 diabetic patients are a major determinant of the metabolic response to epinephrine.

Effect of physiological concentrations of insulin and glucagon on the relationship between nonesterified fatty acids availability and ketone body production in humans

To determine the effect of insulin and glucagon on the transformation of nonesterified fatty acids (NEFA) into ketone bodies (KB), we measured simultaneously in normal subjects NEFA and KB kinetics at different NEFA levels in the presence of basal (control test) or increasing insulin concentrations with glucagopenia (somatostatin + insulin infusion, insulin test) and without glucagopenia (somatostatin + insulin + glucagon infusion, glucagon test). NEFA levels were controlled during these tests by an intravenous (IV) infusion of a triglyceride emulsion. During the control test, a moderate increase of NEFA (464 +/- 30 to 715 +/- 56 mumol/L) increased the percentage of NEFA converted into KB (13.3% +/- 1.4% to 26.4% +/- 2.1%, P less than .05), and there was a linear relationship between this percentage and NEFA levels (r = .788, P less than .01). During the insulin and glucagon tests, the progressive increase in NEFA induced by the triglyceride emulsion infusion was associated, despite the increase of insulinemia, with an increase in KB production rate (P less than .05) and in the proportion of NEFA used for ketogenesis in the presence (8.1% +/- 1.2% to 14.2% +/- 6.3%, P less than .05) and absence (15.7% +/- 2.8% to 25.2% +/- 3.99%, P less than 0.05) of glucagopenia. In both tests, this percentage was always linearly related with NEFA levels (P less than .05) and the slopes of these relationships were comparable to that observed in the control test. However, the fraction of NEFA used for ketogenesis was always higher (P less than .05) during glucagon substitution than in its absence.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of epinephrine on ketogenesis in the dog after a prolonged fast

The effects of a selective increase in epinephrine on ketogenesis and lipolysis were determined in the conscious dog following a prolonged fast (7 days). Plasma insulin and glucagon were fixed at basal levels by infusion of somatostatin (0.8 micrograms/kg/min) and basal intraportal replacement amounts of insulin (210 +/- 20 microU/kg/min) and glucagon (0.65 ng/kg/min). Following a 40-minute control period, saline or epinephrine (0.04 microgram/kg/min) was infused for 3 hours. Plasma insulin, glucagon, and norepinephrine levels did not change during saline (6 +/- 1 microU/mL, 83 +/- 17 pg/mL, and 137 +/- 38 pg/mL, respectively) or epinephrine (10 +/- 1 microU/mL, 73 +/- 18 pg/ml, 98 +/- 13 pg/mL, respectively) infusion. Plasma epinephrine levels increased from 80 +/- 26 to 440 +/- 47 pg/mL in response to infusion of the catecholamine, but remained unchanged during saline infusion. Glycerol levels (93 +/- 10 mumol/L) remained unchanged during saline infusion, but increased in response to epinephrine (108 +/- 9 to 170 +/- 18 mumol/L by 30 minutes). The glycerol level had returned to baseline and to the value apparent in saline controls by 60 minutes. The nonesterified fatty acid (NEFA) level declined slowly during the 3-hour saline infusion, but was elevated in response to epinephrine infusion (1.27 +/- 0.16 to 1.97 +/- 0.25 mmol/L at 30 minutes). After the initial epinephrine-induced increase, the NEFA level declined so that by 3 hours it was not significantly different from the basal or saline values.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of ketone body flux in septic patients

To assess the effect of sepsis on ketone body (KB) kinetics in humans, we measured in normal and septic subjects KB appearance rate (Ra) before (initial state) and during a rise of free fatty acids (FFA) level (intravenous infusion of a triglycerides emulsion). We studied normal subjects in postabsorptive state and septic patients when receiving an hypocaloric intravenous infusion of glucose and amino acids or 12 h after its interruption. When receiving glucose and amino acids infusion, septic patients had higher glucose and insulin levels than normal subjects, and despite lower FFA concentrations (255 +/- 44 vs. 480 +/- 51 mumol/l, P less than 0.05) comparable initial KB Ra (2.50 +/- 0.10 vs. 2.48 +/- 0.30 mumol.kg-1.min-1). Triglyceride infusion increased FFA to comparable values (septic 780 +/- 130, normal 730 +/- 45 mumol/l), but KB Ra rose in septic patients only to 3.7 +/- 1.1 instead of 7.7 +/- 1.1 mumol.kg-1.min-1 as in normal subjects (P less than 0.05). Somatostatin infusion decreased the hyperinsulinemia of septic patients but did not restore a normal ketogenesis. After interruption of nutriment infusion, septic patients had normal FFA levels and only mild hyperglycemia and hyperinsulinemia. Their initial KB Ra was not modified. However, their response of KB Ra (increase to 6.27 +/- 2.0 mumol.kg-1.min-1) to raised FFA levels (842 +/- 170 mumol/l) was comparable to the response of normal subjects. In conclusion, although septic patients receiving an hypocaloric parenteral nutrition had a depressed ketogenesis they were able to restore a normal ketogenic capacity after a short-time caloric deprivation. Glucose and/or insulin appears to have a major role in this modulation of hepatic ketogenesis.

Human ketone body production and utilization studied using tracer techniques: regulation by free fatty acids, insulin, catecholamines, and thyroid hormones

Ketone body concentrations fluctuate markedly during physiological and pathological conditions. Tracer techniques have been developed in recent years to study production, utilization, and the metabolic clearance rate of ketone bodies. This review describes data on the roles of insulin, catecholamines, and thyroid hormones in the regulation of ketone body kinetics. The data indicate that insulin lowers ketone body concentrations by three independent mechanisms: first, it inhibits lipolysis, and thus lowers free fatty acid availability for ketogenesis; second, it restrains ketone body production within the liver; third, it enhances peripheral ketone body utilization. To assess these effects in humans in vivo, experimental models were developed to study insulin effects with controlled concentrations of free fatty acids, insulin, glucagon, and ketone bodies. Presently available data also support an important role of catecholamines in increasing ketone body concentrations. Evidence was presented that norepinephrine increases ketogenesis not only by stimulating lipolysis, and thus releasing free fatty acids, but also by increasing intrahepatic ketogenesis. Thyroid hormone availability was associated with lipolysis and ketogenesis. Ketone body concentrations after an overnight fast were only modestly elevated in hyperthyroidism resulting from increased peripheral ketone body clearance. There was a significant correlation between serum triiodothyronine levels and the ketone body metabolic clearance rate. Thus, ketone body homeostasis in human subjects resulted from the interaction of hormones such as insulin, catecholamines, and thyroid hormones regulating lipolysis, intrahepatic ketogenesis, and peripheral ketone body utilization.