Effects of mental stress on lipolysis in humans

Downregulating carnitine palmitoyl transferase 1 affects disease progression in the SOD1 G93A mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease characterized by death of motor neurons. The etiology and pathogenesis remains elusive despite decades of intensive research. Herein, we report that dysregulated metabolism plays a central role in the SOD1 G93A mouse model mimicking ALS. Specifically, we report that the activity of carnitine palmitoyl transferase 1 (CPT1) lipid metabolism is associated with disease progression. Downregulation of CPT1 activity by pharmacological and genetic methods results in amelioration of disease symptoms, inflammation, oxidative stress and mitochondrial function, whereas upregulation by high-fat diet or corticosterone results in a more aggressive disease progression. Finally, we show that downregulating CPT1 shifts the gut microbiota communities towards a protective phenotype in SOD1 G93A mice. These findings reveal that metabolism, and specifically CPT1 lipid metabolism plays a central role in the SOD1 G93A mouse model and shows that CPT1 might be a therapeutic target in ALS.

The Choice of Euthanasia Method Affects Metabolic Serum Biomarkers

The impact of euthanasia methods on endocrine and metabolic parameters in rodent tissues and biological fluids is highly relevant for the accuracy and reliability of the data collected. However, few studies concerning this issue are found in the literature. We compared the effects of three euthanasia methods currently used in animal experimentation (i.e. decapitation, CO₂ inhalation and pentobarbital injection) on the serum levels of corticosterone, insulin, glucose, triglycerides, cholesterol and a range of free fatty acids in rats. The corticosterone and insulin levels were not significantly affected by the euthanasia protocol used. However, euthanasia by an overdose of pentobarbital (120 mg/kg intraperitoneal injection) increased the serum levels of glucose, and decreased cholesterol, stearic and arachidonic acids levels compared with euthanasia by CO₂ inhalation and decapitation. CO₂ inhalation appears to increase the serum levels of triglycerides, while euthanasia by decapitation induced no individual discrepant biomarker level. We conclude that choice of the euthanasia methods is critical for the reliability of serum biomarkers and indicate the importance of selecting adequate euthanasia methods for metabolic analysis in rodents. Decapitation without anaesthesia may be the most adequate method of euthanasia when taking both animal welfare and data quality in consideration.

Adrenaline but not noradrenaline is a determinant of exercise-induced lipid mobilization in human subcutaneous adipose tissue

The relative contribution of noradrenaline (norepinephrine) and adrenaline (epinephrine) in the control of lipid mobilization in subcutaneous adipose tissue (SCAT) during exercise was evaluated in men treated with a somatostatin analogue, octreotide. Eight lean and eight obese young men matched for age and physical fitness performed 60 min exercise bouts at 50% of their maximal oxygen consumption on two occasions: (1) during i.v. infusion of octreotide, and (2) during placebo infusion. Lipolysis and local blood flow changes in SCAT were evaluated using in situ microdialysis. Infusion of octreotide suppressed plasma insulin and growth hormone levels at rest and during exercise. It blocked the exercise-induced increase in plasma adrenaline while that of noradrenaline was unchanged. Plasma natriuretic peptides (NPs) level was higher at rest and during exercise under octreotide infusion in lean men. Under placebo, no difference was found in the exercise-induced increase in glycerol between the probe perfused with Ringer solution alone and that with phentolamine (an alpha-adrenergic receptor antagonist) in lean subjects while a greater increase in glycerol was observed in the obese subjects. Under placebo, propranolol infusion in the probe containing phentolamine reduced by about 45% exercise-induced glycerol release; this effect was fully suppressed under octreotide infusion while noradrenaline was still elevated and exercise-induced lipid mobilization maintained in both lean and obese individuals. In conclusion, blockade of beta-adrenergic receptors during exercise performed during infusion of octreotide (blocking the exercise-induced rise in adrenaline but not that of noradrenaline) does not alter the exercise-induced lipolysis. This suggests that adrenaline is the main adrenergic agent contributing to exercise-induced lipolysis in SCAT. Moreover, it is the combined action of insulin suppression and NPs release which explains the lipolytic response which remains under octreotide after full local blockade of fat cell adrenergic receptors. For the moment, it is unknown if results apply specifically to SCAT and exercise only or if conclusions could be extended to all forms of lipolysis in humans.

Maternal and fetal fatty acid profile in normal and intrauterine growth restriction pregnancies with and without preeclampsia

The aim of this study was to evaluate maternal and fetal lipid profile in intrauterine growth restriction (IUGR) pregnancies with and without preeclampsia (PE). Thirteen normal pregnancies studied during the third trimester (control M) and 29 at elective cesarean section (control CS) were compared with 18 pregnancies complicated by IUGR (IUGR only) and with seven pregnancies complicated by both IUGR and PE (IUGR-PE). Total plasma fatty acids, triglycerides, cholesterol, and nonesterified fatty acids (NEFA) were determined in maternal and fetal plasma. Nutritional intake was analyzed. IUGR only mothers had lower percentage of linoleic acid (LA) and higher arachidonic acid (AA) than controls, partly explained by higher AA dietary intake. Higher levels of NEFA were observed both in IUGR only and in IUGR-PE mothers whereas triglyceride levels were increased in IUGR-PE mothers only. In IUGR-PE fetuses, LA and AA were significantly decreased, whereas triglyceride and NEFA concentrations were significantly increased compared with normal fetuses. In conclusion, IUGR only is associated with altered fatty acids profile not completely accounted by dietary changes. We hypothesize that the differences observed in IUGR with PE for triglycerides and other lipids could be related to a difference in maternal phenotype.

Cardiovascular stress responses among Asian Indian and European American women and men

Asian Indians have approximately 3 times the rate of coronary artery disease as do age-matched European Americans, but the increased risk cannot be explained by the presence of known physiological and behavioral risk factors. One previous study suggested that Asian Indians have diminished vasoactive responses to isoproterenol, but no published study has examined responses to psychological stressors. The purpose of this study was to test the hypothesis that the vasomotor response to stress, as indexed by hemodynamic measures, would be exaggerated in Asian Indian men and women, relative to European American individuals. Thirty-seven Asian Indian and 43 European American men and women were tested in a standard reactivity protocol, whereas heart rate, blood pressure, and cardiac impedance measures were assessed. Asian Indian men and women had significantly smaller changes in systolic blood pressure and mean arterial pressure during the stressors, relative to European American men and women. Asian Indian women, but not men, had significantly smaller diastolic blood pressure and total peripheral-resistance index changes to the stressors, relative to the other 3 groups. These data are in contrast to our expectation of decreased tendency of Asian Indians to vasodilate during psychological stress but do suggest that sex and Asian Indian ethnicity interact to influence vascular reactivity to stressors.

Postexercise ketosis in night-migrating passerine birds

This study investigated the postexercise metabolism of six species of free-living, night-migrating passerine birds (European robin, pied flycatcher, wheatear, redstart, blackcap, and garden warbler). The birds were caught during autumn migration out of their nocturnal flight, and their metabolism changed from a fasting, highly active state to a fasting, resting state. Concentrations of six plasma metabolites of the fat, carbohydrate, and protein metabolism were measured during up to 10 h of recovery time. The metabolic changes indicated a biphasic pattern: (a) a quick first response to the reduced energy demands during the first 20 min of recovery, suggested by an increase and subsequent decrease of free fatty acid levels, and (b) subsequently, a postexercise ketosis and a reduction of lipolysis and proteolysis, suggested by high beta-hydroxy-butyrate and low free fatty acid, glycerol, triglyceride, and uric acid levels. This metabolic pattern differs from that of humans and rats, in which ketosis starts immediately postexercise or is absent in trained subjects. Since migrating birds are naturally adapted to endurance exercise, it is hypothesized that the high and long-lasting postexercise ketosis does not evoke physiological problems (such as hypoglycemia) but, by contrast, increases the ability of birds to rely on lipids, to a very high extent, during and after flight and decreases the dependence on glucose and glucogenic amino acids. Differences between species in fat stores and metabolic pattern support this hypothesis.

Mechanism of increased tolerance to hypothermia after composite Indian herbal preparation II administration

OBJECTIVE

Investigation of the mechanism of increased tolerance to stress induced hypothermia after the administration of composite Indian herbal preparation II (CIHP II), a combination of several plant ingredients and minerals.

DESIGN

The effect of oral CIHP II administration (1 mg/g of body weight), prior to cold (5 degrees C)-hypoxia (428 mm Hg)-restraint (C-H-R) exposure in rats on cardiac and skeletal muscle oxidation was studied in vitro by estimating conversion of glucose-U-14C and Palmitate-1-(14)C to 14CO2. In vitro adipose tissue lipolysis and incorporation of glucose-U-14C into skeletal muscle glycogen was also studied.

RESULTS

A single dose of CIHP II-enhanced resistance to hypothermia (rectal temperature [T(rec)] 23 degrees C) during C-H-R exposure as evidenced by increased glucose turnover rate in heart and skeletal muscle tissue. The blood glucose and skeletal muscle glycogen were conserved. Cardiac free fatty acid oxidation was also increased. During recovery from hypothermia (T(rec) 37 degrees C) blood glucose and muscle glycogen levels were conserved. Five doses of CIHP II increased resistance to cold by increased adipose fat mobilization and cardiac oxidation. Glucose oxidation was spared. During recovery from hypothermia, the glucose turnover and oxidation in skeletal muscle was increased as was fat mobilization from adipose tissue and its oxidation by heart muscle.

CONCLUSIONS

CIHP II intake prior to C-H-R exposure resulted in increased glucose turnover rate and fat utilization. This perhaps helped increase the resistance to C-H-R-induced hypothermia and speeded recovery.

The effect of interday variation and a short-term stressor on insulin sensitivity in clinically normal cats

To determine whether there is a day-to-day variation in insulin sensitivity in cats, we subjected six clinically normal cats to four insulin-modified frequently sampled intravenous glucose tolerance tests (FSIVGTTs) over 7 days. The insulin-modified FSIVGTTs were analysed by the minimal model method. Minimal model insulin sensitivity (S(I)) averaged 2.9+/-0.4 x 10(-4) min(-1)/microU/ml (range 1.9-4.6 x 10(-4) min(-1)/microU/ml), with a mean interday coefficient of variation (CV) of 35.4+/-6.4% (range 12.8-58.5%). Glucose effectiveness (S(G)) averaged 0.029+/-0.002 min(-1)(range 0.024-0.037 min(-1)), and showed less interday variability with a mean CV of 24.7+/-4.3% (range 7.9-39.3%). Insulin sensitivity was also measured after a short-term stressor (5-min spray bath) of sufficient magnitude to elevate blood glucose levels. The mean insulin sensitivity after the stressor was 3.6+/-0.8 x 10(-4) min(-1)/microU/ml (range 1.6-7.3 x 10(-4) min(-1)/microU/ml), which was not significantly different to the mean insulin sensitivity before the short-term stressor (P=0.237). The mean glucose effectiveness after the stressor was 0.046+/-0.004 min(-1)(range 0.032-0.057 min(-1)), which was significantly different from mean glucose effectiveness before the short-term stressor (P=0.003). We conclude that insulin sensitivity is highly variable from day to day in normal cats, and that hyperglycaemia in response to short-term stressors is probably due to increased hepatic glucose production, rather than peripheral insulin resistance.

Stress, acute hyperglycemia, and hyperlipidemia role of the autonomic nervous system and cytokines

Stress is accompanied by metabolic alterations that could contribute to the etiology of diabetes mellitus, arteriosclerosis, and cardiovascular diseases; however, the mechanisms by which stress affects glucose and lipid metabolism remain to be resolved. Stress-induced effects on neurotransmission and interleukin-1 (IL-1) signaling rapidly produce hyperglycemia by increasing sympathetic outflow. Activation of the sympathetic nervous system can also rapidly stimulate lipolysis and hepatic triglyceride secretion. Furthermore, stress increases serum interleukin-6 (IL-6) and nerve growth factor (NGF) levels by activating neuroendocrine systems. IL-6 and NGF can rapidly increase lipolysis and hepatic triglyceride secretion without inducing hyperglycemia. The sympathetic nervous system does not mediate cytokine-induced hypertriglyceridemia. Thus, the central nervous system plays an important role in regulation of hepatic glucose and lipid metabolism via the sympathetic nervous system and cytokines. (Trends Endocrinol Metab 1997;8:192-197). (c) 1997, Elsevier Science Inc.

The day-to-day variation in insulin sensitivity in non-insulin-dependent diabetes mellitus patients assessed by the hyperinsulinemic-euglycemic clamp method

The objective was to study the day-to-day variation in insulin sensitivity in non-insulin-dependent diabetes mellitus (NIDDM) and to analyze within- and between-person variances in the glucose infusion rate during steady state (M value). Ten NIDDM patients attending the outpatient clinic at Aarhus Amtssygehus were studied three times under standardized conditions. Each time, a 120-minute hyperinsulinemic-euglycemic clamp was performed. Similar M values were found on the 3 study days, with difference between M values on the 3 days of (mean +/- SD) 0.3 +/- 1.8 mg glucose/kg lean body mass (LBM)/min. The total coefficient of variation (CV) for M values was 57% after the first clamp, 55% after the second, and 53% after the third. Ninety percent of the total day-to-day variation in M values could be ascribed to between-person variation and 10% to within-person variation. Within-person components of variance included all sources of variation other than between-person variation. The within-person CV for M values was 11.9% +/- 7.2% after two clamp studies and 12.1% +/- 7.3% after three (P < .55). In conclusion, under standardized conditions, a valid estimate of insulin sensitivity assessed by the hyperinsulinemic-euglycemic clamp in NIDDM patients is obtained after a single measurement. Because of large between-person variation, paired data should be used when comparing insulin sensitivity in NIDDM patients.

Systolic blood pressure is related to catecholamine sensitivity in subcutaneous abdominal fat cells

A relationship between abdominal obesity and hypertension is well established. In search for an early-onset defect in adipocyte function linking these two conditions, we compared catecholamine sensitivity in subcutaneous abdominal fat cells with 24-hour systolic, mean arterial and diastolic blood pressure in 16 healthy, normotensive subjects. Clear inter-individual variations in the adipocyte lipolytic adrenoceptor sensitivity (pD2) for noradrenaline were observed in dose-response experiments (i.e., about 4 log units). An inverse and independent correlation was found between the 24-hour systolic blood pressure and pD2 for noradrenaline (r = -0.67, p < 0.01). The mean arterial blood pressure was also negatively correlated to peripheral noradrenaline sensitivity (r = -0.58, p < 0.05). However, no significant relationship between the 24-hour diastolic blood pressure and pD2 for noradrenaline was demonstrated. In conclusion we suggest that catecholamine resistance in subcutaneous fat cells may be associated with autonomic dysfunction and impaired blood pressure regulation. This finding is supported by the fact that both noradrenaline sensitivity and 24-hour systolic blood pressure also are correlated to the individual orthostatic heart rate responses, reflecting the sympathetic nervous system tone (r = 0.61, p = 0.01 and r = -0.53, p = 0.03, respectively). The relationship between noradrenaline sensitivity and systolic blood pressure may be of importance in the early development of hypertension in man.

Adipocyte beta-adrenoceptor sensitivity influences plasma lipid levels

Catecholamine stimulation of lipolysis through adipocyte beta-adrenoceptors is of major importance for the regulation of lipid mobilization from adipose tissue. The influence of adipocyte beta-receptor sensitivity as assessed by an isoprenaline bioassay on circulating lipid levels was investigated in 46 healthy and drug-free subjects. beta-Receptor sensitivity was inversely related to total plasma triglycerides (r = -.62), very low density lipoprotein cholesterol (VLDL-C) (r = -.56), VLDL triglycerides (r = -.52), and apolipoprotein B (r = -.41). These relationships remained significant after adjustment for age, sex, body mass index, waist/hip ratio, fat cell volume, and circulating levels of insulin, noradrenaline, and adrenaline. beta-Receptor sensitivity accounted for 40% of the variance in total plasma triglycerides. beta-Receptor subtype sensitivity and binding capacity were also determined in fat cells using terbutaline (beta 2) and dobutamine (beta 1) bioassays and radioligand binding. Multiple regression analysis revealed that terbutaline sensitivity correlated inversely with total plasma triglycerides, apolipoprotein B, VLDL-C, and VLDL triglycerides (partial r from -.56 to -.42), but there was no correlation between dobutamine sensitivity and blood lipids (partial r from .05 to .18) or between receptor binding and blood lipids (partial r from .01 to .28). Thus, the lipolytic beta-receptor sensitivity in fat cells appears to play a hitherto-unrecognized role for lipoprotein metabolism, in particular that of VLDL. This relationship is receptor-subtype specific, particularly involving beta 2-receptors, and seems to be localized to a postreceptor step in lipolysis regulation. Low sensitivity may be of importance for the development of hypertriglyceridemia.

Lipolytic catecholamine resistance due to decreased beta 2-adrenoceptor expression in fat cells

The existence of lipolytic beta-adrenoceptor (BAR) resistance was investigated in vivo and in isolated abdominal subcutaneous adipocytes in 65 healthy and drug-free subjects. The concentration of isoprenaline (nonselective BAR agonist) causing half-maximum lipolysis effect (ED50) varied bimodally and 10(6)-fold between individuals but was almost constant in the same subject when measured two times at rest or before and 30 min after exercise. The subjects were categorized as having either high or low isoprenaline sensitivity. The former group had a 50% reduced in vivo lipolytic response to exercise and mental stress, despite a 50% increased plasma noradrenaline response (P < 0.01) and a 350% increased plasma adrenaline response (P < 0.02). In fat cells the lipolytic ED50 values for noradrenaline and terbutaline (BAR2 agonist) were 10 times lower (P < 0.001) in low-sensitive subjects, but the maximum lipolytic actions of these agents (and of isoprenaline) were similar in both groups. The action on lipolysis of dobutamine (BAR1 agonist), forskolin (stimulating adenylate cyclase), dibutyryl cyclic AMP (activating protein kinase), clonidine (alpha 2-adrenergic agonist), or phenyl isopropyladenosine (adenosine receptor agonist) were almost identical in high- and low-sensitivity subjects. ED50 for isoprenaline correlated with ED50 for terbutaline (r = 0.75), but not with ED50 for dobutamine. In high-sensitivity subjects the number of BAR2 was almost three-fold increased (P < 0.002) and the steady-state adipocyte mRNA level for BAR2 was sixfold increased (P < 0.005). BAR2 affinity as well as BAR1 number, affinity and mRNA expression were similar in both groups. In 11 cholecystectomy patients (otherwise healthy) lipolytic ED50 for beta agonists correlated in omental and subcutaneous fat cells (r = 0.85 for isoprenaline; r = 0.95 for terbutaline). In conclusion, lipolytic resistance to catecholamines is present in vivo in apparently healthy subjects due to reduced expression of BAR2 in adipocytes.