Effect of acute acidosis and alkalosis on leucine kinetics in man

Summary. The effects of acute pH changes on whole body leucine kinetics (1-¹³C-leucine infusion technique) were determined in normal subjects. Plasma insulin, glucagon, and growth hormone concentrations were kept constant by somatostatin and replacement infusions of the three hormones. When acidosis was produced by ingestion of NH4CI (4 mmol kg^-1 p. os; n = 8) arterialized pH decreased within 3 h from 7.39±0.01 to 7.31 ±0.01 (P<0.001) and leucine plasma appearance increased by 0.13 ±0.04 μmol kg^-1 min^-1 (P<0.02); in contrast, when alkalosis was produced by intravenous infusion of 4 mmol kg^-1 NaHCO₃ (n= 1, pH 7.47 ±0.01), leucine plasma appearance decreased by -0.09 ± 0.04 (xmol kg^-1 min^-1 (P<0.01 vs. acidosis). Whole body leucine flux also increased during acidosis compared to alkalosis (P<0.05), suggesting an increase in whole body protein breakdown during acidosis. Apparent leucine oxidation increased during acidosis compared to alkalosis (P=0.05). Net forearm leucine exchange remained unaffected by acute pH changes. Plasma FFA concentrations decreased during acidosis by -107 ±67 μmol l^-1 (P<0.05) and plasma glucose increased by 1.90±0.25 mmol l^-1 (P<0.02); in contrast, alkalosis resulted in an increase in plasma FFA by 83 ± 40 (μmol 1^-1 (P<0.02; P<0.01 vs. acidosis), suggesting an increase in lipolysis; plasma glucose decreased compared to acidosis (P<0.01). The data demonstrate that acute metabolic acidosis and alkalosis, as they occur in clinical conditions, influence protein breakdown, and in the opposite direction, lipolysis.     

Abdominal and femoral adipose tissue lipolysis and cardiovascular disease risk factors in men

Abstract. The relationships between subcutaneous abdominal and femoral fat cell lipolyses, plasma free-fatty acid (FFA) levels and metabolic variables considered as risk factors for cardiovascular disease (CVD) (plasma glucose, insulin and lipoprotein levels) were investigated in 54 men, aged 36 ± 3 (SD) years, covering a wide range of body fatness values (body mass indices from 19 to 34 kg m^-2). Although there were no consistent relationships between femoral fat cell weight and the metabolic profile, positive and significant associations were found between abdominal fat cell weight and most of the metabolic indices. However, abdominal fat cell lipolysis measured with an α₂:-(clonidine) or a β-agonist (isoproterenol) was unrelated to metabolic variables. In contrast, femoral fat cell lipolysis measured in the presence of clonidine was positively associated with fasting plasma insulin, cholesterol (CHOL) and apolipoprotein (apo) B levels, as well as with LDL-CHOL and LDL-apo B concentrations. No association was found between isoprotere-nol-stimulated lipolysis of femoral adipocytes and the metabolic profile. Comparison of two subgroups of men with either low or high femoral residual lipolysis with clonidine revealed that subjects with the lowest femoral α₂-adrenergic component (i.e. the highest residual lipolysis) displayed significant alterations in both plasma lipid-lipoprotein and glucose-insulin levels which could be predictive of an increased risk of CVD. Free fatty acid (FFA) levels measured in the fasting state and during an oral glucose tolerance test (OGTT) were positively associated with fasting plasma insulin and triglyceride levels as well as with both glucose and insulin areas measured during the OGTT. However, regional adipose tissue lipolysis measured in riiro was unrelated to plasma FFA levels. These results support the view that both femoral adipose tissue lipolysis and plasma FFA levels are significant correlates of plasma glucose-insulin homeostasis and lipoprotein-lipid levels, in men. However, as adipose tissue lipolysis and plasma FFA are unrelated to each other, they may be associated with risk variables through independent mechanisms.     

Inosine causing insulin release and increased myocardial uptake of carbohydrates relative to free fatty acids in dogs

Summary. The aim of the present study was to determine the effect of i.v. inosine on myocardial substrate uptake and function in the in situ dog heart. Inosine was infused i.v. at a rate of 5 mg kg min^-1 in eight closed-chest pentobarbital anaesthetized dogs. Inosine caused a 46% decrease (P<0.01) in plasma free fatty acids (FFA), a 15% decrease (P<0.05) in plasma glycerol, an 18% decrease (P<0.05) in plasma glucose and a 46% increase (P<0.01) in blood lactate. This was associated with a 55% decrease (P<0.01) in myocardial FFA uptake and a 72% increase in lactate uptake, while glucose uptake remained unchanged. These metabolic changes were associated with a five-fold increase (P<0.05) in arterial insulin. Inosine caused an 18% increase (P<0.01) in myocardial blood flow without changing MVO₂. There was a 33% increase (P<0.01) in LV dP/dt_max, a decrease in LVEDP from 4.9 ± 0.9 (mean ± SEM) to 0.9 ± 0.3 mmHg (P<0.05) and a 24% decrease (P<0.01) in systemic vascular resistance. Inosine caused a transient 38% increase (P<0.05) in pulmonary vascular resistance. In conclusion, in addition to a positive inotropic effect and vascular effects inosine was found to cause release of insulin and to shift myocardial metabolism towards increased uptake of carbohydrates relative to FFA.     

Causal linkage between insulin suppression of lipolysis and suppression of liver glucose output in dogs.

Suppression of hepatic glucose output (HGO) has been shown to be primarily mediated by peripheral rather than portal insulin concentrations; however, the mechanism by which peripheral insulin suppresses HGO has not yet been determined. Previous findings by our group indicated a strong correlation between free fatty acids (FFA) and HGO, suggesting that insulin suppression of HGO is mediated via suppression of lipolysis. To directly test the hypothesis that insulin suppression of HGO is causally linked to the suppression of adipose tissue lipolysis, we performed euglycemic-hyperinsulinemic glucose clamps in conscious dogs (n = 8) in which FFA were either allowed to fall or were prevented from falling with Liposyn plus heparin infusion (LI; 0.5 ml/min 20% Liposyn plus 25 U/min heparin with a 250 U prime). Endogenous insulin and glucagon were suppressed with somatostatin (1 microgram/min/kg), and insulin was infused at a rate of either 0.125 or 0.5 mU/min/kg. Two additional experiments were performed at the 0.5 mU/min/kg insulin dose: a double Liposyn infusion (2 x LI; 1.0 ml/min 20% Liposyn, heparin as above), and a glycerol infusion (19 mg/min). With the 0.125 mU/min/kg insulin infusion, FFA fell 40% and HGO fell 33%; preventing the fall in FFA with LI entirely prevented this decline in HGO. With 0.5 mU/min/kg insulin infusion, FFA levels fell 64% while HGO declined 62%. Preventing the fall in FFA at this higher insulin dose largely prevented the fall in HGO; however, steady state HGO still declined by 18%. Doubling the LI infusion did not further affect HGO, suggesting that the effect of FFA on HGO is saturable. Elevating plasma glycerol levels did not alter insulin's ability to suppress HGO. These data directly support the concept that insulin suppression of HGO is not direct, but rather is mediated via insulin suppression of adipose tissue lipolysis. Thus, resistance to insulin control of hepatic glucose production in obesity and/or non-insulin-dependent diabetes mellitus may reflect resistance of the adipocyte to insulin suppression of lipolysis.     

Persistence of counter-regulatory abnormalities in insulin-dependent diabetes mellitus after pancreas transplantation

Abstract Conventional insulin therapy does not correct the counter-regulatory abnormalities of insulin-dependent diabetes mellitus. Pancreas transplantation is an alternative therapy that restores the endogenous insulin secretion in diabetes. In this study, the effects of segmental pancreas transplantation on counter-regulation to mild hypoglycaemia were evaluated. Glucose kinetics and the counter-regulatory hormonal responses were assessed in eight insulin-dependent diabetics with end-stage renal failure who had received pancreas and kidney transplantation 1 year previously, seven diabetic uraemic subjects (candidates for combined transplantation), five patients with chronic uveitis on immunosuppressive therapy comparable to pancreas recipients and 10 normal subjects. Insulin (0·3 mU kg^-1 min^-1) was infused for 2h to induce mild hypoglycaemia (plasma glucose 3·2–3·5-mmol l^-1) and exogenous glucose was infused as required to prevent any glucose decrease below 3·1 mmol l^-1. After transplantation, two of eight recipients had hypoglycaemic episodes reported in their medical records. During the study, hepatic glucose production was rapidly suppressed in the controls and in the patients on immunsuppression (–80 ± 7 and –54 ± 7%, P < 0·001 vs. basal), and rebounded to the baseline values within 1 h (–3 ± 1 and –6 ± 2%, P= NS vs. basal). The transplant recipients had similar suppression in the first hour (–88 ± 8%, P < 0·001 vs. basal), but the suppression persisted in the second hour (–69 ± 11%, P < 0·001 vs. basal) indicating a lack of glucose counter-regulatory response. The uraemic-diabetics had reduced suppression of hepatic glucose production (–45 ± 14%, P < 0·001 vs. basal) with respect to the recipients (P < 0·001), but had the same lack of response in the second hour (suppression: –39 ± 12%, P < 0·001 vs. basal). In addition, the response of glucagon to hypoglycaemia was blunted in both the recipients and in the diabetic subjects. In conclusion, the alterations in glucose counter-regulation of insulin-dependent diabetes persists after segmental pancreas transplantation. Specifically, the increased sensitivity of hepatic glucose production to the action of insulin renders this defect more evident after transplantation.     

Four week administration of an ACE inhibitor and a cardioselective β-blocker in healthy volunteers: no influence on insulin sensitivity

Abstract. In most, but not all, studies antihypertensive treatment with angiotensin converting enzyme inhibitors (ACE inhibitors) improves insulin sensitivity, whereas β-blockers decrease insulin sensitivity. However, there was a significant increase in body weight with β-blockers and changes in the body potassium homeostasis with ACE inhibitors. In order to compare the drug specific metabolic effects of an ACE inhibitor and a cardioselective β-blocker controlling these factors, we measured insulin sensitivity in a randomized, double-blind cross-over study in 22 healthy volunteers (age 27 ± 3 years; BMI 22.0± 1.5kg m^-2 (mean ± SD)) during euglycaemic glucose clamps before and after 4 weeks' administration of 5mg Lisinopril or 5mg Bisoprolol. Both drug phases were separated by 4 weeks of no drug administration. During the insulin sensitivity measurements potassium concentrations were clamped at basal levels by means of a variable i.v. potassium infusion. Body weight was monitored at weekly intervals and kept constant within ± 1 kg of the subjects' baseline weight throughout the entire study period. Insulin sensitivity did not change significantly during either drug administration period. The insulin sensitivity index of the 22 volunteers after administration of the ACE inhibitor was 7.9±2.4 mL min^-1 m²μU^-1 mL^-1 (basal index 8.3 ± l.9mL min^-1 m²μ^-1 mL^-1, and 7.5 ± 2.1 mL min^-1 m²μU^-1 mL^-1 after administration of the β-blocker (basal index 8.2 ± l.9mL min^-1 m²μ^=-1 mL^-1; NS). In order to maintain blood potassium concentrations during the glucose c lamps at basal levels of 3.9 ± 0.3 mmol l^-1 a mean of 7.9±4.2 mval of potassium had to be infused during the low insulin step and a mean of 24.1 ±9.7mval during the high insulin step. Systolic and diastolic blood pressure were lowered significantly by Lisinopril (5±8 mmHg and 7 ± 9 mmHg) and Bisoprolol (7 ± 7 mmHg and 4 ± 8 mmHg; NS between both drugs), respectively. In healthy normo-tensive subjects administration of Lisinopril or Bisoprolol for 4 weeks does not influence insulin sensitivity, when appropriate experimental conditions are maintained.     

Myocardial Metabolism and Performance during Sodium Salicylate Infusion in Dogs

The effect of sodium salicylate on net myocardial free fatty acid (FFA) uptake, myocardial oxygen consumption (MVO₂), and the mechanical activity of the heart was studied in eight intact, anesthetized dogs. Sodium salicylate was given intravenously under basal conditions and during isoproterenol-stimulated lipolysis. Under basal conditions, sodium salicylate significantly reduced arterial FFA concentration, but did not influence net myocardial uptake of FFA, and MVO₂ was unchanged. During isoproterenol infusion sodium salicylate reduced arterial FFA concentration by 28% (P0.01) and significantly reduced net myocardial uptake of FFA from 44.5 ±9.0 (mean±S.E.M.) to 22.3 ±2.1 μmol/min-100 g tissue (P<0.05) and MVO₂ from 20.3±2.2 to 16.0±1.9 ml/min-100 g tissue (P<0.05). The reduction in MVO₂ could not be explained by reduced mechanical activity of the heart. Most probably the mechanism for the reduction in MVO₂ effected by sodium salicylate during isoproterenol infusion was mediated by reduced myocardial FFA consumption.     

Effect of danazol-induced chronic hyperglucagonaemia on glucose tolerance and turnover

Abstract. It has been shown that danazol (14-ethinyl-testosterone) induces hyperglucagonaemia. To investigate the effect of chronic glucagon excess on carbohydrate metabolism, we studied six patients before and after treatment with danazol for immuno-thrombopenia. Glucose tolerance and insulin, C-pep-tide and glucagon secretion during an oral glucose tolerance test (oGTT) as well as peripheral and hepatic insulin sensitivity were determined by means of euglycaemic clamp technique (40mUm^-2 min^-1) before and after 3 months of danazol therapy. Overall glucose turnover (R₂) was assessed radioisotopically. (1) Plasma glucagon levels rose significantly from 88 ±16 pgmL^-1 before to 683 ± 148pgmL^-1 after therapy (P < 0.01). (2) Glucose levels during an oGTT were not significantly different before and after therapy. Glucose-stimulated insulin secretion at 60 and 120min and the area under the curve (AUC) for insulin during the oGTT. were significantly increased after danazol treatment compared with pre-treatment values (P < 0.05), whereas glucagon secretion showed a similar decrease at both time points of investigation (NS). (3) R_d during steady state showed a significant decrease during the entire period of euglycaemic clamp following therapy (after 240min, 3.8 ±0.6 vs. 5.3 ±0.7 mg kg^-1 min^-1, P < 0.05). The decline in glucagon during the clamp was similar during steady state before and after therapy. (4) Basal hepatic glucose output did not differ significantly before and after therapy (1.74 ±0.41 vs. 1.45 ±0.22 mg kg^-1, NS), whereas hepatic glucose output during the clamp was significantly less suppressed after danazol therapy. The authors conclude that chronic glucagon excess leads to a decrease in peripheral and hepatic insulin action which is accompanied by an increase in insulin secretion.     

No differential effects of porcine and human insulin on muscle sympathetic nerve activity during euglycaemia or hypoglycaemia

Summary. On the basis of some clinical studies in diabetic patients, and experimental studies in normal humans, it has been suggested that hypoglycaemic autonomic responses are augmented with porcine (PI) compared to human insulin (HI). A difference in sensory processing has been reported following insulin-induced hypoglycaemia with PI compared to HI, and has been interpreted as different insulin effects on the central nervous system. In a double blind crossover comparison of HI and PI in nine healthy subjects, microneurographic recordings of muscle sympathetic nerve activity (MSNA) were performed, as well as measurements of cardiovascular and hormonal responses during a low dose hyperinsulinaemic euglycaemic glucose clamp (plasma insulin 60.1 ±1.9 mU ml^-1 (mean ± SEM)), followed by a period of insulin-induced hypoglycaemia. Plasma insulin and glucose were identical in the two sessions. Plasma glucose nadir during hypoglycaemia was 2.4 ± 0.2 mmol 1^-1 for HI and 2.5 ±0.1 mmol l^-1 for PI. During euglycaemia, MSNA increased from 24 ± 2 to 34 ± 3 and 23 ± 2 to 30 ± 2 burst/min (P:NS) for HI and PI, respectively, and during hypoglycaemia to 49 ± 4 and 45 ± 2 bursts min^-1 (P:NS), respectively. The maximal hypoglycaemic increments of MSNA were not different (HI 15 ± 4; PI 15 ± 2 bursts min^-1 (P: NS)) Responses of plasma noradrenaline and haemodynamic parameters did not differ either. This study does not indicate differing sympathetic responses to PI and HI in healthy humans. Evidence for a modulating effect of insulin on central sympathetic outflow was not found.     

Oxygen supplementation increases glucose tolerance during euglycaemic hyperinsulinaemic glucose clamp procedure in patients with severe COPD and chronic hypoxaemia

Investigations in chronic obstructive pulmonary disease (COPD) patients have shown impaired glucose tolerance in hypoxic COPD patients, compared with COPD patients with normal arterial blood gases. In healthy subjects, hypoxaemia or stay at altitude, have been shown to alter glucose metabolism. At altitude the effect seems to be dependent on duration of stay. A short stay is associated with insulin resistance, a longer stay gives rise to increased glucose uptake. The euglycaemic hyperinsulinaemic glucose clamp technique is a method to study glucose tolerance and enables determinations of glucose clearance in peripheral tissues. We investigated six COPD patients [forced expiratory volume in 1 s 0.7 +/- 0.2 l (mean +/- SD)] with chronic hypoxaemia (PaO(2) 7.9 +/- 0.6 kPa at rest, breathing air), with and without oxygen supplementation, using the glucose clamp technique. Net peripheral glucose uptake was 5.5 +/- 1.2 and 7.1 +/- 1.6 mg (kg*min)(-1) (+29%) breathing air and supplemental oxygen, respectively (P = 0.03). The tissue sensitivity to insulin increased 32% (P = 0.03) with oxygen supplementation. The results indicate that normalization of oxygen saturation in COPD patients with chronic hypoxaemia may have an immediate effect on glucose tolerance and tissue sensitivity to insulin in these patients.     

A hyperinsulinaemic, sequentially eu- and hypoglycaemic clamp test to characterize autonomous insulin secretion in patients with insulinoma

To better characterize autonomous insulin secretory behaviour in insulinoma patients and to establish diagnostic criteria with high accuracy, hyperinsulinaemic, sequentially eu- and hypoglycaemic clamp tests were performed in insulinoma patients and control subjects. Ten patients with insulinoma (benign in nine, histologically proven in nine) and 10 patients with suspected episodes of hypoglycaemia, in whom thorough clinical evaluation excluded an insulinoma, were examined. Five insulinoma patients were restudied after successful extirpation of the tumour. Suppression of C-peptide during low-dose [2 pmol kg^–1 min^–1 (20 mU kg^–1h^–1) for 90 min, plasma insulin approximately 120 pmol L^–1 (20 mU L^–1)] and high-dose [8 pmol kg^–1 h^–1 (80 mU kg^–1 h^–1) for 90 min, plasma insulin approximately 450 pmol L^–1 (75 mU L^–1)] insulin infusion under euglycaemic conditions [plasma glucose 4.4–5.0 mmol L^–1 (80–90 mg dL^–1)]) and during high-dose insulin infusion under hypoglycaemic conditions [glucose 2–2.2 mmol L^–1 (40–45 mg dL^–1)] was evaluated by radioimmunoassay (RIA). Euglycaemic hyperinsulinaemia suppressed C-peptide in control subjects (P < 0.0001), whereas in insulinoma patients apparently irregular changes in C-peptide concentrations (with spontaneous or paradoxical increments, P = 0.0006 vs. controls) were observed. The combination of hyperinsulinaemia and controlled hypoglycaemia led to a nearly complete suppression of C-peptide in normal subjects (from basal, 0.76 ± 0.08–0.06 ± 0.01 nmol L^–1; maximum observed value 0.10 nmol L^–1), which was more pronounced than at the point of discontinuation of prolonged fasting (> 48 h; 0.26 ± 0.16 nmol L^–1; P = 0.005). In insulinoma patients, C-peptide remained elevated under all conditions (P = 0.51 vs. prolonged fasting). All these findings were reversible after successful surgical removal of the insulinoma. Insulinoma patients could be identified as abnormal by (a) non-suppression of C-peptide even under hyperinsulinaemic/hypoglycaemic conditions (10 out of 10 patients) and (b) irregular increments in C-peptide under conditions that led to at least partial suppression in all normal subjects (9 out of 10 patients) and/or by an apparent shift to the left of insulin secretion relative to glucose concentrations (7 out of 10 patients). Controlled exposure to hyperinsulinaemic/hypoglycaemic conditions can help to characterize autonomous secretion in insulinoma patients and may be used as a diagnostic procedure when conventional methods yield equivocal results.     

Effects of physical exercise on insulin absorption in insulin-dependent diabetics. A comparison between human and porcine insulin

Summary. Nine insulin-dependent diabetics with undetectable plasma C-peptide (<0·05 nmol 1^-1) and without insulin antibodies (insulin binding to IgG<0·05 Ul^-1) received subcutaneous injections of 10 U ¹²⁵I-labelled soluble human or porcine insulin in the thigh on 2 consecutive days. Disappearance rates of ¹²⁵I were monitored continuously by external counting and plasma insulin levels were determined during rest for 30 min, bicycle exercise of moderate intensity for 40 min, and 60 min recovery. Subcutaneous blood flow was measured concomitantly in the contralateral thigh by the ¹³³Xenon clearance technique. During the initial period of rest human insulin was absorbed approximately 40% faster than its porcine analogue (first order rate constants 0·37±0·06 vs 0·27±0·06% min^-1, P<0·05) and the increment of the area under the plasma insulin curve was greater after hum-ii than after porcine insulin (184±46 vs 112±42 mUl^-1 min, P<0·05). Exercise enhanced the absorption rates for both ¹²⁵I-insulins to 0·50±0·06 and 0·48±0·10% min^-1 for human and porcine insulin, respectively (P<0·05). This increase was less pronounced for human compared to porcine insulin (49±19 vs 105±40%, P=0·06). During exercise plasma insulin rose to 37±5 mUl^-1 after human and 30±5 mUl^-1 after porcine insulin and the areas under the plasma insulin curves were similar. During the recovery phase the absorption rates decreased slightly compared to the exercise value for both insulins. The blood glucose lowering effect was similar for the two insulins. Subcutaneous blood flow was not significantly altered by exercise in either group. It is concluded that during rest human soluble insulin is more rapidly absorbed than porcine insulin. Physical exercise tends to increase porcine insulin absorption more and eliminates the basal difference in the absorption kinetics between human and porcine insulin. The increased insulin absorption during exercise is not coupled to corresponding changes in the subcutaneous blood flow.     

Role of basal glucagon levels in the regulation of splanchnic glucose output and ketogenesis in insulin-deficient humans

Summary. The aim of the present study was to investigate the influence of hepatic glycogen depletion and increased lipolysis on the response of splanchnic glucose output and ketogenesis to combined glucagon and insulin deficiency in normal man. Healthy subjects were studied after a 60-h fast and compared with a control group studied after an overnight fast, Net splanchnic exchange of glucose, gluconeogenic precursors, free fatty acids (FFA) and ketone acids were measured in the basal state and during intravenous infusion of somatostatin (9 μg/min) for 90–140 min (overnight fasted subjects) or for 5 h (60-h fasted subjects). During the infusion of somatostatin, euglycemia was maintained by a variable intravenous infusion of glucose. Prior to somatostatin infusion, after an overnight (12–14 h) fast, splanchnic uptake of glucose precursors (alanine, lactate, pyruvate, glycerol) could account for 26% of splanchnic glucose output (SGO) indicating primarily glycogenolysis. Somatostatin infusion resulted in a 50% reduction in both insulin and glucagon concentrations and a transient decline in SGO which returned to baseline values by 86±ll min at which point the glucose infusion was no longer necessary to maintain euglycemia. Arterial concentrations of FFA and β-OH-butyrate and splanchnic β-OH-butyrate production rose 2.5-fold, 6-fold and 7.5-fold, respectively, in response to somatostatin infusion. In the 60-h fasted state, basal SGO (0.29±0.03 mmoymin) was 60% lower than after an overnight fast and basal splanchnic uptake of glucose precursors could account for 85% of SGO, indicating primarily gluconeogenesis. Somatostatin administration suppressed the arterial glucagon and insulin concentrations to values comparable to those observed during the infusion in the overnight fasted state. SGO fell promptly in response to the somatostatin infusion and in contrast to the overnight fasted state, remained inhibited by 50–100% for 5 h. Infusion of glucose was consequently necessary to maintain euglycemia throughout the 5-h infusion of somatostatin. Splanchnic uptake of gluconeogenic precursors was unchanged during somatostatin despite the sustained suppression of SGO. Basal arterial concentration and splanchnic exchange of β-OH-butyrate were respectively 22-fold and 6- to 7-fold elevated and basal FFA concentration was 70% increased as compared to the corresponding values in the overnight fasted state. Somatostatin infusion resulted in a rise in arterial FFA concentration (25–50% in all subjects) while the arterial concentrations and splanchnic release of ketone acids (acetoacetate +β-OH-butyrate) showed a variable response, rising in three subjects and declining in two. Nevertheless, splanchnic ketone acid production in the basal state and during the somatostatin infusion correlated directly with splanchnic inflow of FFA (arterial FFA concentration × hepatic plasma flow). The variable responses in ketogenesis could thus be ascribed to variable reductions in splanchnic blood flow induced by somatostatin and as a consequence, its varying effects on splanchnic inflow of FFA. These data thus demonstrate that combined hypoglucagonemia and hypoinsulinemia induced in humans by somatostatin (a) causes a persistent rather than transient inhibition of splanchnic glucose output when liver glycogen stores have been depleted by 60-h fasting and hepatic glucose production is dependent primarily on gluconeogenesis; and (b) fails to interfere with hepatic ketogenesis so long as FFA delivery to the splanchnic bed is maintained. These findings indicate that in the face of insulin deficiency, basal glucagon levels may not be necessary to maintain hepatic glycogenolysis or ketogenesis but may be essential to maintain gluconeogenesis.     

The forearm and leg perfusion techniques in man do not give the same metabolic information

Summary. The present study evaluates whether forearm and leg perfusion techniques give the same metabolic information. Seven patients hospitalized for operation of uncomplicated disease were investigated pre-operatively in the fasted state, while seven other patients who were on intravenous nutrition were studied in the fed state. Blood flow and the extremity exchange of glucose, lactate, glycerol, free fatty acids and amino acids were measured simultaneously across the forearm and the leg in all individuals. In the fasted state the arteriovenous difference (a-v) of glucose uptake was statistically significant across the forearm while it was statistically insignificant across the. leg (0·27 ± 0·06 vs. -0·04±0·13 mmol l¹). The a-v differences of glycerol (0·025 ± 0·028 vs. -0·043 ± 0·013 mmol l¹) and free fatty acids (0·10 ± 0·03 vs. -0·10 ± 0·04 mmol l¹) were positive across the forearm while they were negative across the leg (P < 0·01). In the fasted state the a-v difference of oxygen uptake (3·93 ± 0·67 vs. 3·21 ± 0·44 mmol l¹) and blood flow (4·1 ± 1·0 vs. 4·0 ± 0·7 ml min¹ 100 g¹) did not differ between the arm and the leg, but the a-v difference in carbon dioxide production was significantly higher (P<0.05) across the forearm (2·43 ± 0·37 vs. 1·29 ± 0·29 mmol l¹) compared to the leg. In the fed state all the above-mentioned differences between forearm and leg became statistically insignificant. In the fed state the a-v difference of the sum of all amino acids was not significantly different from zero balance across the forearm (-146 ± 103 mmol l¹) while there was a significant release from the leg (-175 ± 6 mmol l¹, P<0.05). In the fed state the flux of the sum of all amino acids became significantly positive across the arm while it was not significantly different from zero balance across the leg. In the fed state, forearm blood flow was significantly higher than leg blood flow (6·2 ± 0·5 vs. 4·0 ± 0·2 ml min¹ 100 g¹, P<0.001). The results in the present study demonstrate that the metabolic balance across regions of peripheral tissues may simultaneously differ considerably, i.e. being positive across the forearm and negative across the leg. This fact may imply that some previous claims may need reconsideration about ‘peripheral tissue metabolism’ associated with a certain clinical condition.     

Normalization of blood glucose in diabetic rats with phlorizin treatment reverses insulin-resistant glucose transport in adipose cells without restoring glucose transporter gene expression.

Insulin secretion and insulin sensitivity were evaluated in eight clinically stable cirrhotic patients and in 12 controls. OGTT was normal in cirrhotics but plasma insulin response was increased approximately twofold compared with controls. Subjects received a three-step (0.1, 0.5, 1.0 mU/kg.min) euglycemic insulin clamp with indirect calorimetry, [6-3H]-glucose, and [1-14C]-palmitate. During the two highest insulin infusion steps glucose uptake was impaired (3.33 +/- 0.31 vs. 5.06 +/- 0.40 mg/kg.min, P less than 0.01, and 6.09 +/- 0.50 vs. 7.95 +/- 0.52 mg/kg.min, P less than 0.01). Stimulation of glucose oxidation by insulin was normal; in contrast, nonoxidative glucose disposal (i.e., glycogen synthesis) was markedly reduced. Fasting (r = -0.553, P less than 0.01) and glucose-stimulated (r = -0.592, P less than 0.01) plasma insulin concentration correlated inversely with the severity of insulin resistance. Basal hepatic glucose production was normal in cirrhotics and suppressed normally with insulin. In postabsorptive state, plasma FFA conc (933 +/- 42 vs. 711 +/- 44 mumol/liter, P less than 0.01) and FFA turnover (9.08 +/- 1.20 vs. 6.03 +/- 0.53 mumol/kg.min, P less than 0.01) were elevated in cirrhotics despite basal hyperinsulinemia; basal FFA oxidation was similar in cirrhotic and control subjects. With low-dose insulin infusion, plasma FFA oxidation and turnover failed to suppress normally in cirrhotics. During the two higher insulin infusion steps, all parameters of FFA metabolism suppressed normally. In summary, stable cirrhotic patients with normal glucose tolerance exhibit marked insulin resistance secondary to the impaired nonoxidative glucose disposal. Our results suggest that chronic hyperinsulinism may be responsible for the insulin resistance observed in cirrhosis.     

No effect of carbohydrate feeding on glycogen synthase in human muscle during exercise

Summary. The effect of carbohydrate (CHO) feedings on exercise-mediated changes in glycogen synthase fractional (GSF) activity has been investigated. Subjects cycled at -70% of maximal oxygen uptake on two occasions: the first to fatigue (135±17 min; meanæ) (control, CON), and the second at the same workload and duration as the first, but with the addition of frequent ingestion of CHO during exercise (0.27 g kg^-1 body weight every 15 min). Biopsies were taken from the quadriceps femoris muscle before and immediately after exercise. Plasma glucose and insulin decreased during CON exercise, but remained elevated throughout CHO exercise (end of exercise: glucose = 4.4±0.2 mM CON vs. 5.8±0.2 CHO, P < 0.01; insulin = 9±l mU ml^-1 CON vs. 19±3 CHO, P < 0.05). Glycogen decreased to - 10% of the basal value during CON and to -20% during CHO, and there was no significant difference in net glycogenosis between treatments. GSF activity averaged 0.25±0.03 and 0.22±0.05 at rest, and increased to 0.51 ±0.08 and 0.48±0.09 after exercise in CON and CHO, respectively (P > 0.05 between treatments). It is concluded that under the present conditions CHO feedings do not alter the exercise-mediated changes in GSF activity. The increase in GSF during exercise is attributed at least in part to the decrease in muscle glycogen (which increases the suitability of GS as substrate for GS phosphatase).     

Surgical removal of insulinoma restores glucose recovery from hypoglycaemia but does not normalize insulin action

Abstract. In the present study we have evaluated the effects of chronic hyperinsulinaemia secondary to insulinoma, on insulin sensitivity and on counter-regulatory responses to hypoglycaemia. We studied six patients (M/F = 3/3; age = 40 ± years), before and 6–9 months after surgical ablation of the neoplasia, by means of an euglycaemic-hyperinsulinaemic clamp (1 mUkg^-1min^-1). Seven normal subjects (M/F = 4/ 3; age = 38 ± 6 years) underwent the same experimental study as the control subjects. In insulinoma patients after 100 min of the euglycaemic-hyperinsulinaemic clamp, glycaemia was allowed to drop to a minimum value of l.9mmol L^-1, and recovery evaluated after interrupting insulin infusion. During the entire study, 3-³H-glucose was infused to determine hepatic glucose production and glucose utilization. Surgical removal of the pancreatic adenoma was followed by a reduction in body weight (BMI=25.7 ±l.9vs. 23.0 ± 1.6 kgm^-2; P?0.005), normalization of fasting plasma levels of glucose (2.94 ±0.16 vs. 4.83± 0.11 mmol L^-1), insulin (162 ± 24 vs. 48 ±12 pmol L^-1) and of basal hepatic glucose production (7.6 ± 0.7 vs. 12.2 ± 1.11μmol kg^-1min^-1). Before the operation, insulin-mediated glucose disposal was significantly lower than in the controls (30.8 ±3.1 vs. 4.91± 3.1 μmol kg^-1min^-1). Six to nine months after surgical removal of the adenoma, glucose utilization was unchanged (30.5 ±3.3 μmol kg^-1min^-1) and still significantly lower than in controls (P<0.0). After the euglycaemic phase, the plasma glucose level dropped to the same hypoglycaemic nadir (2.0±0.1 vs. 2.2 ±0.2 mmol L^-1) in both studies. Upon withdrawal of insulin infusion, recovery from hypoglycaemia was much slower before than after removal of the insulinoma (0.66±0.16vs. 2.50 ± 0.38 μmol min^-1; P<0.01). The impaired recovery from hypoglycaemia was associated with a sluggish rise in plasma glucagon concentration (+ 49 ± 15vs. +95 ±27 ng L^-1), growth hormone (+16±6vs.+ 30±3*mu;g L^-1), and cortisol (+156 ±41 vs. +361 ±62nmol L^-1; all P<0.05–0.005). In contrast to that found after adenoma removal, hepatic glucose production in insulinoma patients remained suppressed even after induction of hypoglycaemia. Our data suggest that in hyperinsulinaemic insulinoma patients restoration of normal insulin levels (a) ameliorates the response of some parameters of the counter-regulation to acute hypoglycaemia; but (b) is not able to restore normal insulin sensitivity.     

Cardiovascular and metabolic response to adrenaline infusion in weight-losing patients with and without cancer

Summary. Fasting is generally accompanied by a decrease in energy metabolism and hormones. On the other hand, indirect evidence has suggested that the response to adrenergic agonists may be maintained or even increased in malnutrition. The present study evaluated whether weight-losing patients with and without cancer have increased plasma concentrations of catecholamines and different responses to intravenously infused adrenaline compared to weight-stable individuals. Eight malnourished cancer and 10 non-cancer patients (11% weight loss) were compared to seven well-nourished and weight-stable patients. Adrenaline was infused i.v. at a rate of 0·005 μg min^-1 kg^-1 body weight during 40 min followed by a 40 min rest period (without infusion) and then a final 40 min period with i.v. adrenaline infusion (0·02 μg min^-1 kg^-1 body weight). Plasma glycerol concentration at fast was higher in weight-losing patients compared to weight-stable individuals. Whole body oxygen uptake, carbon dioxide production, heart rate and plasma concentrations of free fatty acids (FFA) increased while the mean arterial pressure decreased significantly in response to adrenaline infusion at 0·02 μg kg^-1 min^-1 in both weight-losing and weight-stable patients. Adrenaline at 0·005 μg kg^-1 min^-1 increased plasma FFA levels by 19% (P<0·05) in weight-losing patients while no significant alteration was observed in well-nourished patients. Adrenaline infusion at 0·02 μg kg^-1 min^-1 decreased the mean arterial blood pressure and stimulated respiratory gas exchange and heart rate significantly more in weight-losing than in weight-stable patients. The slopes for oxygen uptake, carbon dioxide production, heart rate, plasma FFA and plasma glycerol vs. plasma adrenaline and noradrenaline were all significantly steeper (P<0·05–0·01) in malnourished patients than in well-nourished controls. The present study suggests an increased sensitivity to adrenaline in weight-losing patients compared to matched controls with normal nutritional state and stable weight.     

Diet-induced thermogenesis in patients with liver cirrhosis

Summary. Diet-induced thermogenesis after ingestion of a mixed meal was investigated in eight patients with documented liver cirrhosis and in eight age- and sex-matched healthy controls. Respiratory gas exchange was measured continuously for one hour in the basal state and for three hours after ingestion of a mixed liquid meal, consisting of 17% kJ protein, 28% kJ lipids and 55% kJ carbohydrates and dispensed to correspond to 60% of the individually computed energy expenditure. Arterial substrate and hormone concentrations were determined before and at timed intervals for three hours after the meal. Urine was collected for determination of nitrogen excretion. The patients' oxygen uptake, energy expenditure and respiratory quotient were similar to those of the controls in the basal state. After the meal, pulmonary oxygen uptake and energy expenditure rose markedly in both groups during the first hour and were subsequently stable. The average increase in oxygen uptake above basal during the whole study period was 21·2 ± 1·8% and 22·3 ± 1·2% (NS) in patients and controls, respectively. The corresponding increase in energy expenditure was 24·8 ± 2·0% in the patients and 24·9 ± 1·4% in the controls (NS). The respiratory quotient was elevated throughout the postprandial period in both groups but the quotient was significantly higher in the patients (P<0·05–0·001), suggesting a greater proportion of carbohydrate oxidation. The basal arterial concentrations of insulin and glucagon were significantly higher in the patients. After the meal the insulin level increased 10- to 20–fold in both groups. Glucose concentration rose significantly in both groups to a maximum of 8·82 ± 1·00 and 8·03 ± 0·95 mmol/l in patients and controls, respectively, at 60 min after the meal. This was accompanied by a fall in the levels of glycerol and ketone bodies in both groups, indicating decreased lipolysis. It is concluded that both the basal energy expenditure and the thermogenic response to a mixed meal are similar in patients with liver cirrhosis and in healthy controls. The patients' carbohydrate oxidation rose to a greater extent after the meal, probably as a consequence of excessive increases in insulin concentration, demonstrating that insulin resistance in these patients may be compensated for by postprandial hyperinsulinaemia.     

Insulin resistance is not exhibited by advanced chronic obstructive pulmonary disease patients

Summary. We have previously reported increased blood glucose concentrations and skeletal muscle glycogen depletion in severe COPD patients with chronic respiratory failure. In order to see if insulin resistance exists in severe COPD, we investigated nine patients with advanced COPD with chronic hypoxaemia and seven healthy control subjects of similar age, using the euglycaemic hyperinsulinaemic glucose clamp technique. We could not demonstrate a subnormal intravenous glucose requirement in response to insulin when maintaining euglycaemia in the COPD patients with chronic hypoxaemia. This indicates that the net metabolism of glucose in COPD patients with chronic hypoxaemia is not resistant to insulin.