M Miola

Forearm Nitric Oxide Balance, Vascular Relaxation, and Glucose Metabolism in NIDDM Patients

Endothelium-dependent and -independent vascular responses were assessed in 10 NIDDM patients and 6 normal subjects with no evidence of atherosclerotic disease. Changes in forearm blood flow and arteriovenous (AV) serum nitrite/nitrate (NO2−/NO3-) concentrations were measured in response to intra-arterial infusion of acetylcholine (ACh) (7.5, 15, 30 μg/min, endothelium-dependent response) and sodium nitroprusside (SNP) (0.3, 3, 10 μg/min, endothelium-independent response). Insulin sensitivity (determined by minimal model intravenous glucose tolerance test) was lower in NIDDM patients (0.82 ± 0.20 vs. 2.97 ± 0.29 104 min · μU−1 · ml−1; P < 0.01). Baseline forearm blood flow (4.8 ± 0.3 vs. 4.4 ± 0.3 ml · 100 ml−1 tissue · min−1; NS), mean blood pressure (100 ± 4 vs. 92 ± 4 mmHg; NS), and vascular resistance (21 ± 1 vs. 21 ± 1 units; NS), as well as their increments during ACh and SNP, infusion were similar in both groups. No difference existed in baseline NO2−/NO3− concentrations (4.09 ± 0.33 ]NIDDM patients] vs. 5.00 ± 0.48 μmol/1 ]control subjects]; NS), their forearm net balance (0.31 ± 0.08 ]NIDDM patients] vs. 0.26 ± 0.08 μmol/1 · 100 ml−1 tissue · min−1; NS), and baseline forearm glucose uptake. During ACh infusion, both NO2− and NO3− concentrations and net balance significantly increased in both groups, whereas glucose uptake increased only in control subjects. When data from NIDDM and control groups were pooled together, a correlation was found between the forearm AV NO2− and NO3− differences and blood flow (r = 0.494, P = 0.024). On the contrary, no correlation was evident between NO2− and NO3− concentrations or net balance and insulin sensitivity. In summary, 1) no difference existed in basal and ACh-stimulated NO generation and endothelium-dependent relaxation between uncomplicated NIDDM patients and control subjects; 2) in both NIDDM and control groups, forearm NO2− and NO3− net balance following ACh stimulation was related to changes in the forearm blood flow; and 3) ACh-induced increase in forearm blood flow was associated with an increase in glucose uptake only in control subjects but not in NIDDM patients. In conclusion, our results argue against a role of impaired NO generation and blood flow regulation in determining the insulin resistance of uncomplicated NIDDM patients; rather, it supports an independent insulin regulation of hemodynamic and metabolic effects.

Gemfibrozil improves insulin sensitivity and flow-mediated vasodilatation in type 2 diabetic patients

Background Endothelial dysfunction is an early feature of atherosclerosis. The relationship between insulin action and hypertriglyceridaemia on endothelial function is still debated.

Intracellular lactate- and pyruvate-interconversion rates are increased in muscle tissue of non-insulin-dependent diabetic individuals.

The contribution of muscle tissues of non-insulin-dependent diabetes mellitus (NIDDM) patients to blood lactate appearance remains undefined. To gain insight on intracellular pyruvate/lactate metabolism, the postabsorptive forearm metabolism of glucose, lactate, FFA, and ketone bodies (KB) was assessed in seven obese non-insulin-dependent diabetic patients (BMI = 28.0 +/- 0.5 kg/m2) and seven control individuals (BMI = 24.8 +/- 0.5 kg/m2) by using arteriovenous balance across forearm tissues along with continuous infusion of [3-13C1]-lactate and indirect calorimetry. Fasting plasma concentrations of glucose (10.0 +/- 0.3 vs. 4.7 +/- 0.2 mmol/liter), insulin (68 +/- 5 vs. 43 +/- 6 pmol/liter), FFA (0.57 +/- 0.02 vs. 0.51 +/- 0.02 mmol/liter), and blood levels of lactate (1.05 +/- 0.04 vs. 0.60 +/- 0.06 mmol/liter), and KB (0.48 +/- 0.04 vs. 0.29 +/- 0.02 mmol/liter) were higher in NIDDM patients (P < 0.01). Forearm glucose uptake was similar in the two groups (10.3 +/- 1.4 vs. 9.6 +/ 1.1 micromol/min/liter of forearm tissue), while KB uptake was twice as much in NIDDM patients as compared to control subjects. Lactate balance was only slightly increased in NIDDM patients (5.6 +/- 1.4 vs. 3.3 +/- 1.0 micromol/min/liter; P = NS). A two-compartment model of lactate and pyruvate kinetics in the forearm tissue was used to dissect out the rates of lactate to pyruvate and pyruvate to lactate interconversions. In spite of minor differences in the lactate balance, a fourfold increase in both lactate- (44.8 +/- 9.0 vs. 12.6 +/- 4.6 micromol/min/liter) and pyruvate-(50.4 +/- 9.8 vs. 16.0 +/- 5.0 micromol/min/liter) interconversion rates (both P < 0.01) were found. Whole body lactate turnover, assessed by using the classic isotope dilution principle, was higher in NIDDM individuals (46 +/- 9 vs. 21 +/- 3 micromol/min/kg; P < 0.01). Insights into the physiological meaning of this parameter were obtained by using a whole body noncompartmental model of lactate/pyruvate kinetics which provides a lower and upper bound for total lactate and pyruvate turnover (NIDDM = 46 +/- 9 vs. 108 +/- 31; controls = 21 +/- 3 - 50 +/-13 micromol/min/kg). In conclusion, in the postabsorptive state, despite a trivial lactate release by muscle, lactate- and pyruvate-interconversion rates are greatly enhanced in NIDDM patients, possibly due to concomitant impairment in the oxidative pathway of glucose metabolism. This finding strongly suggest a major disturbance in intracellular lactate/pyruvate metabolism in NIDDM.

An Unidentified Pancreatic Cancer Cell Product Alters Some Intracellular Pathways of Glucose Metabolism in Isolated Rat Hepatocytes

In this study we assessed whether conditioned media from a human pancreatic cancer cell line (MIA PaCa 2) can interfere with some intracellular pathways involved in glucose metabolism in isolated rat hepatocytes. The hepatocytes, isolated from Male Wistar rats, were incubated with MIA PaCa 2-conditioned or nonconditioned media. Conditioned and nonconditioned hepatocytes were run for 120 min in the presence or absence of insulin (100 mM) and were sampled at fixed time intervals. Supernatant glucose levels decreased to a similar extent over time in both conditioned and nonconditioned hepatocytes, while lactate levels significantly increased in nonconditioned hepatocytes with respect to conditioned hepatocytes. A pyruvate kinase activity increase was observed only in nonconditioned hepatocytes and was biphasic in nature, since this increased activity was detected both after a few and after 30 min following insulin stimulation. The cyclic AMP level increase was significantly higher in conditioned than in non-conditioned hepatocytes. It appears that MIA PaCa 2 cells produce a factor(s) that may interfere with one of the insulin-mediated intracellular pathways of glucose metabolism, namely, glycolysis. This detrimental effect on glycolysis is supported by the blunted rise in lactate concentration in the medium after the glucose challenge. This substance(s) probably transfers its signal inside the target cells, activating the adenylate cyclase pathway. These results support the hypothesis that pancreatic cancer is the cause rather than the consequence of diabetes mellitus.

High blood ketone body concentration in Type 2 non-insulin dependent diabetic patients

To assess the metabolic disturbances, and, in particular, the occurrence of high blood ketone body concentration in post-absorptive Type 2 (non-insulin-dependent) diabetic patients as compared to a matched normal population, a study was carried out in a group of 78 Type 2 diabetic outpatients matched for age and sex and in 78 normal individuals. In all subjects we measured HbA1c, and fasting levels of glucose, FFA, lactate, pyruvate, glycerol, alanine, 3-hydroxybutyrate, acetoacetate, uric acid, total cholesterol, triglycerides, creatinine, growth hormone, Cortisol, glucagon, free insulin, and C-peptide. Multistix strips were used for urine ketone determination. As expected HbA1c, and plasma glucose were higher in Type 2 diabetics. This was associated with multiple metabolic disturbances as shown by higher circulating concentrations of FFA, glycerol and gluconeogenic precursors. Similarly, blood levels of ketones (351 ± 29 vs 159 ± 15 umol/I; p<0.0001) were increased, in spite of higher plasma free-insulin (77 ± 7 vs. 49 ± 14 pmol/I; p<0.0001) and C-peptide concentration (0.63 ± 0.03 vs. 0.46 ± 0.07 nmol/I; p<0.05) and no differences in plasma levels of Cortisol, and growth hormone. Plasma glucagon levels were higher in Type 2 diabetics. Blood ketone body levels were directly correlated with both plasma glucose and FFA concentrations. These observations clearly show that Type 2 diabetes is a pathologic condition characterised by multiple metabolic disturbances which are fully apparent in the basal state. Furthermore, we emphasise that Type 2 diabetic patients, though not insulin deficient, may present a significant increase in their fasting levels of ketone bodies.

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

SummaryThis 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 μU/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<0.05) in Type 1 diabetic patients and from 4.94±0.20 to 7.11±0.38 mmol/l (p<0.05) in normal subjects, respectively). At intermediate insulin levels (35 μU/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<0.05) in Type 1 diabetic patients, and from 5.05±0.13 to 6.61±0.22 mmol/l (p<0.05) in normal subjects. At high insulin levels (70 μU/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.

The effect of gemfibrozil on lipid profile and glucose metabolism in hypertriglyceridaemic well-controlled non-insulin-dependent diabetic patients

Abstract We assessed the efficacy of gemfibrozil therapy on lipid profile and glucose metabolism in a large cohort of (type 2) non-insulin-dependent diabetic patients. We enrolled 217 type 2 diabetic patients with plasma triglyceride concentrations equal to or above 2 mmol/l: 110 were randomized to gemfibrozil (600 mg twice daily) and 107 to placebo treatment in a double blind fashion. Each treatment was followed for 20 weeks. To assess postprandial glucose metabolism and insulin secretion, at time 0 and 20 weeks, a standard meal containing 12.5 g of proteins, 40.1 g of carbohydrate, 10 g of lipids was given. No differences in demographic characteristics were observed between patients randomized either to gemfibrozil or to placebo therapy. No differences were observed in total cholesterol and LDL-cholesterol concentration changes between the baseline observations and week 20 of both treatments. At variance, both treatments significantly increased HDL cholesterol. Gemfibrozil treatment significantly decreased plasma triglyceride concentration from 316±84 to 214±82 mg/dl (P < 0.001), whereas with placebo triglyceride levels increased from 318 + 93 to 380 + 217 mg/dl. No changes were observed in non-esterified fatty acid concentrations or in fasting plasma glucose concentrations, in HbA1C values, insulin and C-peptide concentrations. Gemfibrozil treatment: 1) significantly reduces circulating triglyceride concentration; 2) does not significantly affect cholesterol concentration; 3) does not worsen glucose metabolism.