Arterialized Hand Vein Research Articles

11β-Hydroxysteroid dehydrogenase activity in the brain does not contribute to systemic interconversion of cortisol and cortisone in healthy men.

Context and Objective:11β-hydroxysteroid dehydrogenase type 1 (11βHSD1) catalyses regeneration of cortisol in liver, adipose tissue, and skeletal muscle, making a substantial contribution to circulating cortisol as demonstrated in humans by combining stable isotope tracer infusion with arteriovenous sampling. In the brain, 11βHSD1 is a potential therapeutic target implicated in age-associated cognitive dysfunction. We aimed to quantify brain 11βHSD1 activity, both to assess its contribution to systemic cortisol/cortisone turnover and to develop a tool for measuring 11βHSD1 in dementia and following administration of 11βHSD1 inhibitors.Design, Setting, and Participants:With ethical approval and informed consent, 8 healthy men aged 38.1 years (sd 16.5) underwent an ECG-gated phase-contrast magnetic resonance scan to quantify internal jugular vein blood flow and were infused with 1,2 [2H]2-cortisone and 9,11,12,12 [2H]4-cortisol for 3 h before samples were obtained from the internal jugular vein and an arterialized hand vein. Steroids were quantified by liquid chromatography-tandem mass spectrometry.Main Outcome Measures and Results:Steady state tracer enrichments were achieved and systemic indices of cortisol/cortisone interconversion were consistent with previous studies in healthy men. However, there was no measurable release or production of cortisol, 9,12,12 [2H]3-cortisol or cortisone into the internal jugular vein.Conclusions:Although cerebral 11βHSD1 reductase activity may be greater in cognitively impaired patients, in healthy men any contribution of 11βHSD1 in the brain to systemic cortisol/cortisone turnover is negligible. The influence of 11βHSD1 in the brain is likely confined to subregions, notably the hippocampus. Alternative approaches are required to quantify pharmacodynamics effects of 11βHSD1 inhibitors in the human brain.

Increased Whole-Body and Sustained Liver Cortisol Regeneration by 11β-Hydroxysteroid Dehydrogenase Type 1 in Obese Men With Type 2 Diabetes Provides a Target for Enzyme Inhibition

OBJECTIVEThe cortisol-regenerating enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) amplifies glucocorticoid levels in liver and adipose tissue. 11β-HSD1 inhibitors are being developed to treat type 2 diabetes. In obesity, 11β-HSD1 is increased in adipose tissue but decreased in liver. The benefits of pharmacological inhibition may be reduced if hepatic 11β-HSD1 is similarly decreased in obese patients with type 2 diabetes. To examine this, we quantified in vivo whole-body, splanchnic, and hepatic 11β-HSD1 activity in obese type 2 diabetic subjects.RESEARCH DESIGN AND METHODSTen obese men with type 2 diabetes and seven normal-weight control subjects were infused with 9,11,12,12-[2H]4cortisol (40%) and cortisol (60%) at 1.74 mg/h. Adrenal cortisol secretion was suppressed with dexamethasone. Samples were obtained from the hepatic vein and an arterialized hand vein at steady state and after oral administration of cortisone (5 mg) to estimate whole-body and liver 11β-HSD1 activity using tracer dilution.RESULTSIn obese type 2 diabetic subjects, the appearance rate of 9,12,12-[2H]3cortisol in arterialized blood was increased (35 ± 2 vs. 29 ± 1 nmol/min, P < 0.05), splanchnic 9,12,12-[2H]3cortisol production was not reduced (29 ± 6 vs. 29 ± 6 nmol/min), and cortisol appearance in the hepatic vein after oral cortisone was unchanged.CONCLUSIONSWhole-body 11β-HSD1 activity is increased in obese men with type 2 diabetes, whereas liver 11β-HSD1 activity is sustained, unlike in euglycemic obesity. This supports the concept that inhibitors of 11β-HSD1 are likely to be most effective in obese type 2 diabetic subjects.

Restoration of early insulin secretion after a meal in type 2 diabetes: effects on lipid and glucose metabolism.

In type 2 diabetes (T2D) insulin secretion after a meal is delayed; this may have an impact on the development of hyperglycaemia and hyperlipidaemia. To investigate this, a meal was given to 15 T2D (age 52 +/- 2 years, BMI 25 +/- 0.8 kg m(-2)) on three different occasions: (1) without treatment, (2) after 120 mg of nateglinide before the meal (acute treatment), and (3) after 3 months of nateglinide (120 mg t.i.d., chronic treatment). Fifteen healthy subjects (CON, age 48 +/- 2 years, BMI 24 +/- 0.5 kg m(-2)) were also studied. Blood was withdrawn for 360 min from veins draining the anterior abdominal subcutaneous adipose tissue (AD) and from an arterialized hand vein. Blood flow (BF) in AD was measured with (133)Xe. Lipoprotein lipase activity (LPL) was calculated as the triacylglycerol (TAG) flux across AD, and hormone-sensitive lipase (HSL) as the glycerol flux minus LPL. (1) In T2D the increase in prandial insulin secretion was delayed; postprandial nonesterified fatty acid (NEFA) and TAG levels in blood were increased, while BF, LPL and TAG clearance were blunted vs. CON. (2) Acute or chronic nateglinide treatment induced a prompt increase in prandial insulin secretion, resulting in a decrease in blood glucose and NEFA levels owing to suppression of HSL, while BF, LPL and TAG clearance remained suppressed. In T2D, restoration of early phase insulin secretion improved postprandial hyperglycaemia and suppressed endogenous lipolysis, resulting in suppression of NEFA levels. These results suggest that in nonobese T2D, metabolic defects may result, to a large extent, from the delay in prandial insulin secretion.

Catecholamine Response is Attenuated During Moderate Intensity Exercise in Response to the “Lactate Clamp”.

0149 Plasma catecholamines are known to respond to feedforward and feedback mechanisms. Norepinephrine (NE) and epinephrine (E) rise in response to stresses, such as exercise, that compromise blood glucose homeostasis. Both NE and E have been correlated with blood pH, blood lactate, and ATP demand as assessed by relative exercise intensity. PURPOSE: To assess the hypothesis that the lactate anion (La-) is involved in feedback control of catecholamine release plasma concentrations of norepinephrine and epinephrine were determined at rest and during exercise at 55% of VO2peak with (LC) and without (CON) exogenous lactate infusion. METHODS: Six apparently healthy recreationally active young men were recruited to participate in this study (26 ± 2 yr, 82 ± 2 kg, 50.7 ± 2.1 ml·kg−1·min−1 VO2peak). Participants were studied on 5 occasions. Exercise intensities were 65% of VO2peak for the first trial, and 55% of VO2peak for all remaining trials. The blood lactate profile of the first (65%) trial was matched during the subsequent LC trials, target [lactate] > 4 mM. Participants were studied after an overnight fast; exogenous lactate was infused in a forearm vein; blood was sampled from an arterialized hand vein during 90 min of rest and 90 min of exercise, and catecholamines were determined using HPLC with electrochemical detection. RESULTS: Plasma concentrations of NE and E increased from rest (NE: 241 ± 98 pg/ml, E: 63 ± 25 pg/ml) to exercise (NE: 1498 ± 611 pg/ml, E: 207 ± 187 pg/ml; P <0.05). There was also a condition effect during exercise with NE and E lower during the LC trial (NE: LC = 1211 ± 494 pg/ml, CON = 1785 ± 728 pg/ml, E: LC = 145 ± 59 pg/ml CON = 269 ± 109, P <0.05). As reported previously, LC did not affect endogenous lactate Ra, but raised total [La-], Ra and Rd to levels seen in the 65% trial. Neither glucose, insulin (I), or glucagon (G) concentrations or the I/G were affected, but RER was decreased, and blood pH raised by LC. CONCLUSIONS: NE and E responses were attenuated during moderate intensity (55% of VO2peak) exercise with the exogenous lactate infusion. Results indicate an effect of lactate or an associate parameter of acid-base balance on regulation of catecholamine secretion during physical activity. Supported by NIH grant: AR-42906

Regulation of dietary fatty acid entrapment in subcutaneous adipose tissue and skeletal muscle.

Using stable isotopic labeling of dietary fatty acids in conjunction with arteriovenous difference measurements, we have assessed the regulation of lipoprotein lipase-derived fatty acid entrapment in subcutaneous adipose tissue and forearm muscle in healthy subjects in the postprandial state. Eight volunteers fasted overnight and were then given a mixed meal containing [ 1-(13)C]palmitic acid and [1-(13)C]oleic acid. At baseline and for 6 h after the meal, blood samples were obtained from an arterialized hand vein and veins draining subcutaneous abdominal adipose tissue and forearm muscle, and arteriovenous differences were calculated. Entrapment of labeled fatty acids released by circulating triacylglycerol hydrolysis was close to 100% at 60 min, decreasing to 10-30% by 360 min. Entrapment of labeled fatty acids in forearm muscle was >100% and did not change with time. This study shows that entrapment of dietary fatty acids in adipose tissue in the postprandial period is a highly regulated process (varying with time) and that this can be studied in humans using stable isotope- labeled fatty acids in combination with measurement of appropriate arteriovenous differences. Also, fatty acid trapping in skeletal muscle is fundamentally different from that in adipose tissue, in that all the fatty acids released by lipoprotein lipase in skeletal muscle are taken up by the tissue.

Carbohydrate and fat have different effects on plasma leptin concentrations and adipose tissue leptin production

Leptin is secreted by adipocytes and plays a role in the regulation of food intake. However, the regulation of leptin production by adipose tissue is unclear. We have investigated whether a mixed meal or a high-fat load given orally, or a pure fat load given intravenously, stimulates adipose tissue leptin production. Six volunteers were studied on two occasions following an overnight fast. On one occasion they consumed tomato soup containing 40 g of triacylglycerol (as Intralipid) and 9.6 g of carbohydrate; on the other occasion Intralipid was infused intravenously over 4 h to give the same fat load. A further eight subjects consumed a mixed meal (containing 37 g of fat and 100 g of carbohydrate) after an overnight fast. Paired blood samples were obtained from an arterialized hand vein and a vein draining subcutaneous adipose tissue at baseline and for 6 h following the meals or the start of the infusion. After both the intravenous and oral fat loads, the arterialized and adipose venous plasma leptin concentrations decreased over 6 h (both P<0.001), as did the leptin veno--arterial difference (P=0.01). Following the mixed meal, there was a slight increase in the arterialized plasma leptin concentration (P=0.02) and a more marked increase in the adipose venous plasma leptin concentration (P=0.03) and in the adipose tissue leptin veno--arterial difference (P=0.01), all peaking at 240 min. We conclude that the increase in plasma leptin concentration observed after meals is not simply a result of an energy load, but is in response to a signal that is not present following a fat load without carbohydrate.

Renal substrate metabolism and gluconeogenesis during hypoglycemia in humans.

To examine the potential contribution of precursor substrates to renal gluconeogenesis during hypoglycemia, 14 healthy subjects had arterialized hand vein and renal vein (under fluoroscopy) catheterized after an overnight fast. Net renal balance of lactate, glycerol, alanine, and glutamine was determined simultaneously with systemic and renal glucose kinetics using arteriovenous concentration differences and 6-[2H2]glucose tracer dilution. Renal plasma flow was measured by para-aminohippurate clearance and was converted to blood flow using the mathematical value (1-hematocrit). Arterial and renal vein samples were obtained in the postabsorptive state and during a 180-min hyperinsulinemic period during either euglycemia or hypoglycemia. Insulin increased from 49 +/- 14 to 130 +/- 25 pmol/l (hypoglycemia) and to 102 +/- 10 pmol/l (euglycemia). Arterial blood glucose decreased from 4.5 +/-0.2 to 3.0 +/- 0.1 mmol/l during hypoglycemia but did not change during euglycemia (4.3 +/- 0.2 mmol/l). After 150 min, endogenous glucose production reached a plateau value that was higher during hypoglycemia (10.3 +/0.6 micromol x kg(-1) x min(-1)) than during euglycemia (5.73 +/-0.6 micromol x kg(-1) x min(-1), P < 0.001). Hypoglycemia was associated with a rise in renal glucose production (RGP) from 3.0 +/- 0.7 to 5.4 +/- 0.6 micromol x kg(-1) x min(-1) (P < 0.05), although glucose utilization remained the same (2.0 +/- 0.8 vs. 2.1 +/-0.6 micromol x kg(-1) x min(-1)). As a result, net renal glucose output increased from 1.0 +/- 0.3 to 3.3 +/- 0.40 micromol x kg(-1) x min(-1). Elevations in net renal uptake of lactate (2.4 +/- 0.5 to 3.5 +/- 0.7 vs. 2.8 +/- 0.4 micromol x kg(-1) x min(-1)), glycerol (0.6 +/- 0.3 to 1.3 +/- 0.5 vs. 0.4 +/- 0.2 micromol x kg(-1) x min(-1)), and glutamine (0.7 +/- 0.2 to 1.1 +/- 0.3 vs. 0.1 +/- 0.3 micromol x kg(-1) x min(-1)) during hypoglycemia versus euglycemia (P < 0.05) could account for nearly 60% of all glucose carbons released in the renal vein during hypoglycemia. Our data indicate that extraction of circulating gluconeogenic precursors by the kidney is enhanced and responsible for a substantial fraction of the compensatory rise in RGP during sustained hypoglycemia. Increased renal gluconeogenesis from circulating substrates represents an additional physiological mechanism by which the decrease in blood glucose concentration is attenuated in humans.

Uptake of individual fatty acids into adipose tissue in relation to their presence in the diet

The fatty acid composition of adipose tissue triacylglycerol reflects, but is not identical to, the fatty acid composition of the habitual diet. We investigated whether the fatty acid composition of adipose tissue is explained by differences between fatty acids in early storage in adipose tissue after a meal. Nine healthy men ate a meal containing several fatty acids. Blood samples were taken for 6 h after the meal from an arterialized hand vein and a vein draining the anterior abdominal subcutaneous adipose tissue. Net storage of fatty acids in adipose tissue occurred between 1 and 4 h after the meal. In relation to the amount fed, storage of fatty acids differed (P < 0. 01) between classes (n-3 polyunsaturated < saturated < n-6 polyunsaturated < monounsaturated); oleic acid was stored in the greatest amounts. These differences agreed closely with published data, except for n-3 polyunsaturated fatty acids. The only individual metabolic step at which significant differences between fatty acids was shown was incorporation of fatty acids into chylomicron triacylglycerol. Differences between fatty acids in rate of extraction from chylomicron triacylglycerol and net uptake into adipose tissue in the postprandial period were significant (P < 0. 01), but not when expressed in relation to proportions in chylomicron triacylglycerol. The characteristic fatty acid pattern of adipose tissue may predominantly reflect the early metabolic handling of different fatty acids. Adipose tissue uptake of n-3 polyunsaturated fatty acids is slow in relation to that of other fatty acids.

Application of high-performance liquid chromatography of plasma fatty acids as their phenacyl esters to evaluate splanchnic and renal fatty acid balance in vivo

Plasma fatty acids from renal and hepatic veins, and arterialized hand vein obtained in 20 subjects before and after insulin infusion were separated by reversed-phase high-performance liquid chromatography following phenacyl esterification. Separation and quantification over the range 1.0–100 nmol per injection of nine fatty acids was achieved within 60 min using [ 2H 31]palmitic acid as internal standard. Analytical recoveries were greater than 90% and the intra- and inter-assay coefficients of variation were less than 2.5 and 4.0%, respectively. Following insulin infusion, net splanchnic uptake of total fatty acids decreased from 3.0±0.3 to 1.0±0.1 μmol/kg min ( p<0.01), whereas net renal balance remained neutral (−0.04±0.04 vs. −0.06±0.03 μmol/kg min, p=N.S.). Individual fatty acid balance varied from a low of 0.012±0.005 (myristic acid) to a high of 0.95±0.08 (oleic acid) μmol/kg min across the splanchnic tissues and from 0.005±0.002 (stearic acid) to 0.21±0.1 (oleic acid) μmol/kg min across the kidney. There is a substantial diversity in changes in plasma concentration and regional balance of individual fatty acid during short-term fasting and hyperinsulinemia. This method is simple, accurate, and can be applied to assess individual fatty acid metabolism in vivo.

Coordinated release of acylation stimulating protein (ASP) and triacylglycerol clearance by human adipose tissue in vivo in the postprandial period

The objective of this study was to determine whether Acylation Stimulating Protein (ASP) is generated in vivo by human adipose tissue during the postprandial period. After a fat meal, samples from 12 subjects were obtained (up to 6 h) from an arterialized hand vein and an anterior abdominal wall vein that drains adipose tissue. Veno-arterial (V-A) gradients across the subcutaneous adipose tissue bed were calculated. The data demonstrate that ASP is produced in vivo (positive V-A gradient) with maximal production at 3–5 h postprandially. The plasma triacylglycerol (TAG) clearance was evidenced by a negative V-A gradient. It increased substantially after 3 h and remained prominant until the final time point. There was, therefore, a close temporal coordination between ASP generation and TAG clearance. In contrast, plasma insulin and non-esterified fatty acid (NEFA) had an early (1–2 h) postprandial change. Fatty acid incorporation into adipose tissue (FIAT) was calculated from V-A glycerol and non-esterified fatty acid (NEFA) differences postprandially. FIAT was negative during the first hour, implying net fat mobilization. FIAT then became increasingly positive, implying net fat deposition, and overall followed the same time course as ASP and TAG clearance. There was a direct positive correlation between total ASP production and total FIAT (r = 0.566, P < 0.05). These data demonstrate that ASP is generated in vivo by human adipocytes and that this process is accentuated postprandially, supporting the concept that ASP plays an important role in clearance of TAG from plasma and fatty acid storage in adipose tissue.—Saleh, J., L. K. M. Summers, K. Cianflone, B. A. Fielding, A. D. Sniderman, and K. N. Frayn. Coordinated release of acylation stimulating protein (ASP) and triacylglycerol clearance by human adipose tissue in vivo in the postprandial period. J. Lipid Res. 1998. 39: 884–891.

Effect of physical training on the capacity to secrete epinephrine.

Epinephrine responses to hypoglycemia and to identical relative work loads have been shown to be higher in endurance-trained athletes than in untrained subjects. To test the hypothesis that training increases the adrenal medullary secretory capacity, we studied the effects of glucagon (1 mg/70 kg iv), acute hypercapnia (inspired O2 fraction = 7%), and acute hypobaric hypoxia (inspired Po2 = 87 Torr), respectively, on the epinephrine concentration in arterialized hand vein blood in eight endurance-trained athletes [T, O2 uptake = 66 (62-70) ml.min-1.kg-1] and seven sedentary males [C, O2 uptake = 46 (41-50)]. In response to identical increments in glucagon concentrations, plasma epinephrine increased more in T than in C subjects [0.87 +/- 0.11 vs. 0.38 +/- 0.14 (SE) nmol/l, P less than 0.05]. In response to hypercapnia [arterial PCO2 = 56 +/- 0.7 Torr (T) and 55 +/- 0.4 (C), P greater than 0.05], the increment in epinephrine was significant in T (0.38 +/- 0.11 nmol/l) but not (P less than 0.1) in C subjects (0.22 +/- 0.11). Hypoxia [arterial PO2 = 42 +/- 2 Torr (T) and 41 +/- 2 (C), P greater than 0.05] increased epinephrine in T (0.22 +/- 0.10 nmol/l, P less than 0.05) but not in C subjects (0.01 +/- 0.07). The plasma norepinephrine concentration never changed, whereas heart rate always increased, the increase being higher (P less than 0.05) in T than in C subjects only during hypercapnia. The results indicate that training increases the capacity to secrete epinephrine.

Role of motor center activity for hormonal changes and substrate mobilization in humans.

The study evaluated the hypothesis that during exercise autonomic neuroendocrine activity and, in turn, substrate mobilization, is subjected to feed-forward stimulation from motor centers. Eight young healthy men bicycled for two 20-min periods without (control, C) as well as during partial neuromuscular blockade with tubocurarine (Cu). 3-[3H]glucose was infused, and arterialized hand vein blood was sampled. In period 1 O2 consumption (VO2) (56% VO2 max), heart rate, and blood lactate were identical in Cu compared with C experiments, whereas hand grip strength was lower and perceived exertion [14.0 +/- 1.5 vs. 9.1 +/- 1.2 (SE) points, P less than 0.01] higher in Cu experiments, indicating higher motor center activity. Concentrations of norepinephrine [7.39 +/- 1.18 (Cu) vs. 5.14 +/- 1.06 (C) nmol/l], epinephrine (1.69 +/- 0.33 vs 0.87 +/- 0.16 nmol/l), growth hormone (25.9 +/- 7.3 vs. 11.5 +/- 4.7 mU/l), and adrenocorticotropin hormone (11.3 +/- 1.3 vs. 5.5 +/- 0.7 pmol/l) attained higher values in Cu than in C experiments (P less than 0.05). The initial increase in glucose production was enhanced in Cu (8.1 +/- 1.6 mumol.min-1.kg-1) compared with C experiments (3.9 +/- 1.9, P less than 0.05), and plasma glucose only increased in Cu experiments. Free fatty acid (P less than 0.05) and glycerol (P less than 0.1) concentrations were higher in Cu than in C experiments. In period 2 identical perceived exertion was achieved in the two experiments by reducing work load in Cu experiments. In this period hormonal responses were similar in the two experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of leucine infusion on substrate flux across the human forearm

In this study we examine the role of leucine infusion on amino acid and carbohydrate flux across the human forearm. Thirteen male volunteers of ideal body weight (103 ± 3%) were studied after an overnight fast. Five received an infusion of l-leucine (2.1 ± 0.07 μmol/kg/min) for 5 hr and 8 received physiologic saline as controls. Blood samples were obtained from arterialized hand vein and a deep forearm vein at 15-min intervals for 1 hr basal period and at 1-hr intervals for a 5-hr experimental period. Blood flow to the forearm was measured by capacitance plethysmography and balance ( Q ̇ ) across the forearm was calculated according to the Fick principle. Leucine infusion resulted in a reversal of Q ̇ leu ) from a net production of 17 ± 5 to a net uptake of 249 ± 23 nmol/100 g muscle/min ( P < 0.001) or 15% of the infused load. α-Keto-isocaproate release increased from 23 ± 4 to 48 ± 7 nmol/100 g muscle/min ( P < 0.05). Alanine output dropped by 57% (125 ± 22 to 53 ± 12 nmol/100 g muscle/min, P < 0.005), while glutamine output increased by 150% (131 ± 20 to 326 ± 31 nmol/100 g muscle/min, P < 0.005). Total alpha amino nitrogen (AAN output) by the forearm dropped by 60 and 48% within 1 and 2 hr of leucine infusion and returned thereafter to basal levels. The output of amino acids, other than the BCAA, progressively increased such that they were 75% of basal values by the end of leucine infusion (370 ± 75 vs 645 ± 115 nmol/100 g muscle/min, P < 0.005). Glucose uptake dropped and lactate release increased by 80% each. Insulin levels increased by 82%. These changes resulted in a 10% drop in glucose and a 25% increase in lactate levels. Ketone bodies and plasma FFA increased by 85 and 21%, respectively. We conclude that leucine infusion in overnight fasted man results in (a) a transient positive effect on nitrogen balance, followed by (b) an increase in glutamine output across the forearm to account for all the leucine retained, and (c) a minimal change in KIC output, thus suggesting that most of the leucine retained was completely oxidized across the forearm tissue. Furthermore leucine infusion exerted a glucose sparing effect by directly inhibiting glucose uptake across the forearm.