Response of insulin, glucagon, lactate, and nonesterified fatty acids to glucose in visceral obesity with and without NIDDM: relationship to hypertension

Glucose and protein metabolic responses to an energy- but not protein- restricted diet in type 2 diabetes

AIMS

To test the effect of energy restriction with maintained protein intake on body composition and on insulin sensitivity of glucose and protein metabolism in adults with type 2 diabetes (T2D).

MATERIALS AND METHODS

After 3 days of an isoenergetic diet with 1.2 g/kg/d protein, obese adults with T2D (three women, two men) followed a 5-week diet providing 60% of energy requirements with 45% carbohydrate, and with protein maintained at pre-intervention level. Isotopic tracers were used to quantify whole-body glucose (3-³ H-glucose) and protein (¹³ C-leucine) metabolism pre- (day 4) and post-intervention (day 39), in the postabsorptive state and during a hyperinsulinaemic, isoglycaemic, isoaminoacidaemic clamp. Body composition was measured using dual-energy x-ray absorptiometry.

RESULTS

After energy restriction, 6% weight loss occurred via total body (11%) and visceral fat losses (25%), but lean mass was preserved. Fasting glucose level, serum insulin level, homeostatic model assessment of insulin resistance index and C-peptide level decreased significantly (29%, 38%, 54% and 38%, respectively) as did other cardiometabolic risk factors. Between clamp studies, postabsorptive protein turnover and oxidation rates decreased (12% and 32%), resulting in less negative net balance, consistent with protein conservation. The rates of glucose turnover decreased, and glucose metabolic clearance rate improved (24%). During the clamp, protein flux was lower (9%) and breakdown suppressed (12%), and net balance became less negative but not different. Although glucose turnover did not differ, metabolic clearance improved by 47%.

CONCLUSIONS

In obese adults with T2D, an energy-restricted diet with maintained protein intake of ~1.2 g/kg/d improved the kinetics of protein metabolism (particularly in the postabsorptive state), and preserved lean body mass and increased glucose metabolic clearance rate.

Acute activation of pyruvate dehydrogenase increases glucose oxidation in muscle without changing glucose uptake

Pyruvate dehydrogenase (PDH) activity is a key component of the glucose/fatty acid cycle hypothesis for the regulation of glucose uptake and metabolism. We have investigated whether acute activation of PDH in muscle can alleviate the insulin resistance caused by feeding animals a high-fat diet (HFD). The importance of PDH activity in muscle glucose disposal under insulin-stimulated conditions was determined by infusing the PDH kinase inhibitor dichloroacetate (DCA) into HFD-fed Wistar rats during a hyperinsulinemic-euglycemic clamp. Acute DCA infusion did not alter glucose infusion rate, glucose disappearance, or hepatic glucose production but did decrease plasma lactate levels. DCA substantially increased muscle PDH activity; however, this did not improve insulin-stimulated glucose uptake in insulin-resistant muscle of HFD rats. DCA infusion increased the flux of pyruvate to acetyl-CoA and reduced glucose incorporation into glycogen and alanine in muscle. Similarly, in isolated muscle, DCA treatment increased glucose oxidation and decreased glycogen synthesis without changing glucose uptake. These results suggest that, although PDH activity controls the conversion of pyruvate to acetyl-CoA for oxidation, this has little effect on glucose uptake into muscle under insulin-stimulated conditions.

Plasma lactate and incident hypertension in the atherosclerosis risk in communities study

BACKGROUND

Recent evidence suggests that insufficient oxidative capacity or mitochondrial dysfunction may play a causal role in the development of high blood pressure. However, this hypothesis has not been tested in the general population. We hypothesized that lactate, a measure of oxidative capacity, would be positively associated with incident hypertension even after accounting for traditional hypertension risk factors.

METHODS

Plasma lactate was measured in 5,554 participants from the Atherosclerosis Risk in Communities (ARIC) Study with no subclinical or diagnosed hypertension at baseline (1996-1998). Incident hypertension was defined by self-report or hypertension medication use. Analyses were performed with Cox proportional hazards models.

RESULTS

The mean age was 61.9 years, and the mean lactate was 0.8 mmol/L. During a median follow-up period of 11.9 years (range = 26.9 days to 13.4 years), there were 3,849 new cases of hypertension. The fourth quartile of lactate (compared with the first quartile) was associated with an elevated risk of hypertension (hazard ratio (HR) = 1.18; 95% confidence interval (CI) = 1.07-1.31) even after adjustment for traditional risk factors, including baseline systolic and diastolic blood pressure. This association was stronger when the population was restricted to participants with normal blood pressure (<120mm Hg/<80mm Hg; HR = 1.42; 95% CI = 1.23-1.63). In strata of sex, the association was strong in women vs. null in men (P interaction = 0.01).

CONCLUSIONS

Plasma lactate is associated with incident hypertension in women, especially with a normal blood pressure (<120mm Hg/<80mm Hg). Future studies should elucidate the mechanisms underlying these observations.

The extracellular cAMP-adenosine pathway regulates expression of renal D1 dopamine receptors in diabetic rats

Activation of D1 dopamine receptors expressed in the kidneys promotes the excretion of sodium and regulates sodium levels during increases in dietary sodium intake. A decrease in the expression or function of D1 receptors results in increased sodium retention which can potentially lead to the development of hypertension. Studies have shown that in the absence of functional D1 receptors, in null mice, the systolic, diastolic, and mean arterial pressures are higher. Previous studies have shown that the expression and function of D1 receptors in the kidneys are decreased in animal models of diabetes. The mechanisms that down-regulate the expression of renal D1 receptor gene in diabetes are not well understood. Using primary renal cells and acutely isolated kidneys from the streptozotocin-induced rat diabetic model, we demonstrate that the renal D1 receptor expression is down-regulated by the extracellular cAMP-adenosine pathway in vitro and in vivo. In cultures of primary renal cells, a 3 mm, 60-h cAMP treatment down-regulated the expression of D1 receptors. In vivo, we determined that the plasma and urine cAMP levels as well as the expression of 5'-ectonucleotidase, tissue-nonspecific alkaline phosphatase, and adenosine A2a receptors are significantly increased in diabetic rats. Inhibitors of 5'-ectonucleotidase and tissue-nonspecific alkaline phosphatase, α,β-methyleneadenosine 5'-diphosphate, and levamisole, respectively, blocked the down-regulation of D1 receptors in the primary renal cells and in the kidney of diabetic animals. The results suggest that inhibitors of the extracellular cAMP-adenosine pathway reverse the down-regulation of renal D1 receptor in diabetes.

Association of lactate with blood pressure before and after rapid weight loss

BACKGROUND

The mechanism linking obesity with its downstream complications is poorly understood. Accumulating evidence suggests that insufficient oxidative capacity plays a central role in the development of insulin resistance and, perhaps, hypertension.

METHODS

To investigate this hypothesis, we measured lactate, a marker of the gap between energy expenditure and oxidative capacity, in 40 obese subjects with the metabolic syndrome (Ob-MS), 40 obese subjects without the metabolic syndrome (Ob), and 20 lean controls (LCs). The 40 Ob-MS participants were then entered into a 12-20 week very low-calorie diet (VLCD) intervention. The change in lactate and a number of other metabolic factors including blood pressure were subsequently assessed.

RESULTS

At baseline, median lactate levels were significantly higher in both the Ob (36.4 mg/dl) and Ob-MS (34.7 mg/dl) groups when compared to LCs (17.4 mg/dl; P < 0.001). After the VLCD intervention, Ob-MS subjects lost 14.7 kg on average, corresponding to a 5.0 kg/m(2) decrease in body mass index (BMI). Lactate levels fell from 41.3 to 28.7 mg/dl, a 31% reduction (P = 0.006). Even after adjustment for BMI change, change in lactate was strongly associated with change in diastolic blood pressure (DBP) (P = 0.007) and mean arterial pressure (P = 0.014), but not with systolic blood pressure (SBP) (P = 0.20) or other obesity-related traits.

CONCLUSIONS

Baseline and longitudinal associations between lactate and DBP suggest that insufficient oxidative capacity may play a role in obesity-related hypertension.

Animal and human tissue Na,K-ATPase in normal and insulin-resistant states: regulation, behaviour and interpretative hypothesis on NEFA effects

The sodium(Na)- and potassium(K)-activated adenosine-triphosphatase (Na,K-ATPase) is a membrane enzyme that energizes the Na-pump by hydrolysing adenosine triphosphate and wasting energy as heat, so playing a role in thermogenesis and energy balance. Na,K-ATPase regulation by insulin is controversial; in tissue of hyperglycemic-hyperinsulinemic ob/ob mice, we reported a reduction, whereas in streptozotocin-treated hypoinsulinemic-diabetic Swiss and ob/ob mice we found an increased activity, which is against a genetic defect and suggests a regulation by hyperinsulinemia. In human adipose tissue from obese patients, Na,K-ATPase activity was reduced and negatively correlated with body mass index, oral glucose tolerance test-insulinemic area and blood pressure. We hypothesized that obesity is associated with tissue Na,K-ATPase reduction, apparently linked to hyperinsulinemia, which may repress or inactivate the enzyme, thus opposing thyroid hormones and influencing thermogenesis and obesity development. Insulin action on Na,K-ATPase, in vivo, might be mediated by the high level of non-esterified fatty acids, which are circulating enzyme inhibitors and increase in obesity, diabetes and hypertension. In this paper, we analyse animal and human tissue Na,K-ATPase, its level, and its regulation and behaviour in some hyperinsulinemic and insulin-resistant states; moreover, we discuss the link of the enzyme with non-esterified fatty acids and attempt to interpret and organize in a coherent view the whole body of the exhaustive literature on this complicated topic.

The pancreatohepatorenal cAMP-adenosine mechanism

Stimulation of adenylyl cyclase causes cellular efflux of cAMP, and cAMP (unlike adenosine) is stable in blood. Therefore, it is conceivable that cAMP could function as a circulating adenosine prohormone by local target-organ conversion of distally released cAMP to adenosine via the sequential actions of ectophosphodiesterase and ecto-5'-nucleotidase (cAMP==> AMP==> adenosine; called the cAMP-adenosine pathway). A possible specific representation of this general concept is the pancreatohepatorenal cAMP-adenosine mechanism. The pancreas secretes glucagon into the portal circulation, and glucagon is a stimulant of hepatic adenylyl cyclase. Therefore, we hypothesize that the pancreas, via glucagon, stimulates hepatic cAMP production, which provides circulating cAMP for conversion to adenosine in the kidney via the cAMP-adenosine pathway. In normal rats, intravenous cAMP increased urinary and renal interstitial (assessed by renal microdialysis) cAMP and adenosine. Intraportal infusions of glucagon increased plasma cAMP 10-fold, it did not affect plasma adenosine, and it increased urinary and renal interstitial cAMP and adenosine. Local renal interstitial blockade (by adding inhibitors directly to the microdialysis perfusate) of ectophosphodiesterase (using 3-isobutyl-1-methylxanthine or 1,3-dipropyl-8-p-sulfophenylxanthine) or ecto-5'-nucleotidase (using alpha,beta-methyleneadenosine-5'-diphosphate) prevented the cAMP-induced and glucagon-induced increases in renal interstitial adenosine, but not cAMP. In ZSF1 rats with the metabolic syndrome, an oral glucose load increased plasma glucagon and urinary cAMP and adenosine excretion. We conclude that circulating cAMP is a substrate for local conversion to adenosine via the cAMP-adenosine pathway. A specific manifestation of this is the pancreatohepatorenal cAMP-adenosine mechanism (pancreas==> portal glucagon==> liver==> circulating cAMP==> kidney==> local cAMP-adenosine pathway).

Animal and Human Tissue Na,K-ATPase in Obesity and Diabetes: A New Proposed Enzyme Regulation

BACKGROUND

Na,K-ATPase is a membrane enzyme that energizes the Na-pump, hydrolyzing ATP and wasting energy as heat. It may play a role in thermogenesis, energy balance, and obesity development. Regulation of the enzyme by insulin is controversial.

METHODS

In animal and human obesity, tissue Na,K-ATPase was assayed by colorimetric measurement of released Pi.

RESULTS

Na,K-ATPase of hyperglycemic-hyperinsulinemic ob/ob mice (compared with lean control animals) was reduced in liver (-63%) and in kidney (-47%) (P < 0.001 in both instances). In contrast, in streptozotocin-treated hypoinsulinemic-diabetic Swiss mice, versus untreated animals, we found an increase of liver (+54%, P < 0.01) and kidney (+94%, P < 0.001) Na,K-ATPase. The enzyme was also increased (+99%, P < 0.05) in kidney from ob/ob mice made diabetic-hypoinsulinemic with streptozotocin (versus untreated obese animals). This is contrary to the occurrence of a genetic enzymatic defect and suggests regulation by hyperinsulinemia, present in ob/ob mice. A positive correlation between tissue enzyme activity and glycemia existed in both ob/ob and Swiss mice. In adipose tissue from obese patients (compared with lean subjects), Na,K-ATPase was reduced (-65%, P < 0.001) and negatively correlated with body mass index, oral glucose tolerance test-insulinemic area, and mean blood pressure. In vitro, in human liver tissue, 3 mug/mL glucagon exerted a statistically inhibitory effect on Na,K-ATPase (-44%).

CONCLUSION

We hypothesize that animal and human obesity is associated with reduction of tissue Na,K-ATPase, linked to hyperinsulinemia, which may repress or inactivate the enzyme, influencing thermogenesis and energy balance.

Impact of glucagon response on postprandial hyperglycemia in men with impaired glucose tolerance and type 2 diabetes mellitus

Glucagon is the physiological antagonist of insulin. Postprandial (pp) hyperglycemia in impaired glucose tolerance (IGT) and in type 2 diabetes mellitus (T2DM) may also depend on irregularities in glucagon secretion. This study investigated the glucagon excursion after a lipid-glucose-protein tolerance test in subjects with different stages of glucose intolerance. We also analyzed the relationship between pp glucagon secretion and hyperglycemias. A total of 64 men (27 healthy subjects with normal glucose tolerance [NGT], 15 with IGT, and 22 with T2DM) were examined. Plasma glucose (PG), insulin, proinsulin, free fatty acids, and triglycerides were measured in the fasting state and at 30 minutes and 2, 3, 4, and 6 hours after the intake of the test meal, which contained 126 g carbohydrates, 92 g fat, and 17 g protein. Postprandial concentrations of metabolic parameters were calculated as area under the curve (AUC). Glucagon was measured in the fasting state and at 30 minutes and 2 and 4 hours pp. Early glucagon increment was defined as glucagon at 30 minutes minus fasting glucagon. The insulin response was quantified as insulin increment divided by PG increment in the corresponding time. Insulin resistance was calculated using lomeostasis model assessment (HOMA). Fasting glucagon was significantly increased in IGT vs NGT (P<.05), and early glucagon increment was significantly higher in T2DM vs NGT and IGT (P<.05). The 2-hour glucagon concentration after the load (AUC) was increased in IGT and T2DM vs NGT (P<.05). Early glucagon increment and the 2-hour AUC of glucagon were strongly correlated to pp glycemia (r=0.494 and P=.001, and r=0.439 and P=.003, respectively). An inverse correlation was observed between early glucagon increment and insulin response at 30 minutes and 2 hours after the meal load (r=-0.287 and P=.026, and r=-0.435 and P=.001, respectively). The 2-hour AUC of glucagon was significantly associated with insulin resistance (r=0.354, P=.020). Multivariate analysis revealed 2-hour insulin response and early glucagon increment as significant independent determinants of the AUC of PG in IGT (R=0.787). In T2DM, 2-hour insulin response, insulin resistance, and early glucagon increment were significant determinants of the AUC of PG (R=0.867). Our study suggests an important role for the irregularities in glucagon response in the pp glucose excursion after a standardized oral mixed meal in IGT and in T2DM. According to our data, a bihormonal imbalance starts before diabetes is diagnosed. Prospective studies are needed to evaluate the impact of glucagon on the progression of glucose intolerance and the possible effects of medicinal suppression of glucagon increment to prevent the progression of glucose tolerance.

Comparison of Hormone and Glucose Responses of Overweight Women to Barley and Oats

OBJECTIVE

To determine the effect of particle size (flour vs. flakes) on glycemic responses after oats and barley (Prowashonupana cultivar), which contain high amounts of soluble fiber, are consumed by overweight women.

DESIGN

Ten women, average age 50 years and body mass index 30, consumed glucose (1 g/kg body weight) and four test meals (1 g carbohydrate/kg body weight; 2/3 of the carbohydrate from oat flour, oatmeal, barley flour, or barley flakes and 1/3 from pudding) in a Latin square design after consuming controlled diets for 2 days. Blood samples were collected at fasting and periodically after each meal.

RESULTS

Peak glucose and insulin levels after barley were significantly lower than those after glucose or oats. Glucose areas under the curve (AUCs) after test meals compared with AUCs after glucose were reduced after both oats and barley (29-36% by oats and 59-65% by barley) (p < 0.002). Insulin AUCs after test meals compared with glucose AUCs were significantly reduced only by barley (44-56%) (p < 0.005). Indexes for insulin resistance (HOMA, MFFM, Cederholm) after the oat and barley meals were not different from indexes after the glucose meal. Glucagon and leptin responses did not significantly differ for the carbohydrates tested.

CONCLUSIONS

Particle size of the oats or barley had little effect on the glycemic responses. Both oat and barley meals reduced glycemic responses; the high soluble fiber content of this barley appeared to be a factor in the greater reduction observed.

A mild form of Alstrom disease associated with metabolic syndrome and very high fasting serum free fatty acids: two cases diagnosed in adult age

Alstrom syndrome (ALMS) is a very rare genetic autosomal recessive disease, characterized by early-onset severe abdominal obesity, impaired glucose tolerance or type 2 diabetes with insulin resistance, acanthosis nigricans, hyperlipidemia, childhood progressive retinal degeneration or retinitis pigmentosa and neurosensory hearing loss or deafness, cardiomyopathy, and other endocrine disorders. Genetic studies locate the ALMS gene on chromosome 2p12-13. The aim of this paper is to describe and discuss two unrelated cases of a mild ALMS form diagnosed after the age of 40 and 60, respectively, in adult fertile female patients. These cases showed several features of the disease plus other alterations characteristic of the classic "metabolic syndrome," including hypertension, hyperfibrinogenemia, and thrombotic states. Moreover, the patients had very high fasting serum free fatty acid (FFA) levels (2150 and 1919 micromol/L, respectively), which proved to be sensitive to inhibition by oral glucose tolerance test (OGTT)-induced hyperinsulinemia as well as to caloric restriction. ALMS may have an adverse prognosis and is often underdiagnosed. Its mild form, which allows a long survival, may also be associated with the late complications of the metabolic syndrome, leading to increased vascular risk.

The extracellular cyclic AMP-adenosine pathway in renal physiology

Many cell types in the kidney express adenosine receptors, and adenosine has multiple effects on renal function. Although adenosine is produced within the kidney by several biochemical reactions, recent studies support a novel mechanism for renal adenosine production, the extracellular cAMP-adenosine pathway. This extracellular cAMP-adenosine pathway is initiated by efflux of cAMP from cells following activation of adenylyl cyclase. Extracellular cAMP is then converted to adenosine by the serial actions of ecto-phosphodiesterase and ecto-5'-nucleotidase. When extracellular cAMP is converted to adenosine near the biophase of cAMP production and efflux, this local extracellular cAMP-adenosine pathway permits tight coupling of the site of adenosine production to the site of adenosine receptors. cAMP in renal compartments may also be formed by tissues/organs remote from the kidney. For example, stimulation of hepatic adenylyl cyclase by the pancreatic hormone glucagon increases circulating cAMP, which is filtered at the glomerulus and concentrated in the tubular lumen as water is extracted from the ultrafiltrate. Conversion of hepatic-derived cAMP to adenosine in the kidney completes a pancreatohepatorenal cAMP-adenosine pathway that may serve as an endocrine link between the pancreas, liver, and kidney.

Effects of short-term metformin treatment on insulin sensitivity of blood glucose and free fatty acids

AIM

Based on the known effect of metformin (MET) in improving insulin sensitivity in type 2 diabetes, with the scope to focus the effects on glycaemic and free fatty acids (FFA) levels, we studied the effects of a short-term treatment with this drug in obese subjects and obese patients with diabetes or family history of diabetes (FHD). We used a method to allow us to evaluate the possible difference of insulin sensibility with regard to the insulin action on glycaemia and blood FFA, both in the basal state and during oral glucose tolerance test (OGTT).

METHODS

Insulin sensitivity was investigated before and after MET treatment (850 mg bid for 10 days) in seven obese subjects with normal glucose tolerance and without FHD and 13 obese patients with diabetes (n=7) or FHD (n=6). By using specifically designed formulae, we calculated four insulin-sensitivity indices (ISI) from basal level (b) and area values (a) (during OGTT) of insulinaemia, glycaemia (gly) or FFA (ffa), namely: ISI (gly)-b, ISI (gly)-a, ISI (ffa)-b and ISI (ffa)-a.

RESULTS

In patients with diabetes or FHD, MET improved ISI (gly)-b (0.79 +/- 0.06 vs. 0.59 +/- 0.07, p<0.001) and ISI (gly)-a (0.69 +/- 0.09 vs. 0.51 +/- 0.07, p<0.05), whereas only minor changes occurred for ISI (ffa)-b and ISI (ffa)-a. In contrast, in simple obese subjects, MET induced further deterioration of both ISI (gly)-a (0.47 +/- 0.07 vs. 0.64 +/- 0.10, p<0.01) and ISI (ffa)-a (0.43 +/- 0.07 vs. 0.55 +/- 0.08, p<0.05). Fasting level and total area of lactate were high in the obese patients and were not affected by MET. A statistically significant increase (p<0.01), however, was observed for the 'decremental' area of lactate in obese subjects with diabetes or FHD, which might probably contribute to the reduction of insulin resistance induced by the drug in these patients.

CONCLUSIONS

Although the low number of subjects studied precludes absolute conclusions, data would suggest that MET improved ISI towards glucose but not towards FFA, in the diabetic and 'prediabetic' obese patients, whereas worsened it in the obese subjects without FHD. Therefore, the effects of MET would not be secondary to changes of FFA but rather to a primary action of MET on glucose metabolism. Thus, utilization of MET to treat the insulin resistance in obesity is indicated only in the presence of alterations of glucose metabolism or FHD.

Glucose and insulin responses to a new zero-energy fiber source

OBJECTIVE

Consumption of a number of soluble fiber sources reduces glucose and insulin responses in humans. These fibers provide some available energy. Z-trim, a completely insoluble, noncaloric fiber/fat replacer produced from grain, was developed by ARS scientist George Inglett but until this report had not been tested in humans. The objective was to test the effects of consumption of various doses of this new fiber on glucose and insulin responses in humans.

DESIGN

Men and women (12 each) matched for age and body mass index (41 years, BMI 27) were given glucose or glucose with three levels of fiber in a Latin-square design. Blood samples were obtained before and 30, 60, 120 and 180 minutes after solutions containing glucose alone (1 g/kg body weight) and glucose plus 0.08, 0.17 and 0.33 g/kg body weight of Z-trim were consumed. Plasma glucose, insulin and glucagon were determined by enzyme or radioimmunoassays. A repeated-measures analysis of variance was conducted.

RESULTS

Glucose responses were lower for women than for men (p = 0.02) regardless of the test solution. At 30 minutes, glucose levels of men were 0.7-1.1 mmol/L lower after the two higher levels of fiber than after glucose alone. Insulin peak responses were delayed by high amounts of Z-trim. Fasting and response levels of glucagon were higher (p < 0.002) in women than in men. The decline in glucagon usually seen after a glucose load was moderated by the addition of fiber.

CONCLUSION

Although high levels of this new fiber may beneficially affect glucose metabolism of middle-aged people, it is less effective than soluble fiber.

A review of the literature of Bardet-Biedl disease and report of three cases associated with metabolic syndrome and diagnosed after the age of fifty

Bardet-Biedl syndrome (BBS) is a genetic autosomal-recessive disease (formerly grouped with Laurence-Moon-Biedl syndrome but considered today as a separate entity) characterized by abdominal obesity, mental retardation, dysphormic extremities (syndactyly, brachydactyly or polydactyly), retinal dystrophy or pigmentary retinopathy, hypogonadism or hypogenitalism (limited to male patients) and kidney structural abnormalities or functional impairment. The expression and severity of the various clinical BBS features show inter- and intrafamilial variability. This study focuses on three cases of familial BBS--two sisters and one brother (66, 64 and 51 years of age, respectively)--with the main cardinal findings of the disease plus a classic 'metabolic syndrome' (characterized by abdominal obesity, atherogenic dyslipidaemia, raised blood pressure, insulin resistance with or without glucose intolerance, and prothrombotic risk and proinflammatory states). One female patient (not affected by reproductive dysfunction) had three healthy offspring, while the other two patients were unmarried. Another severely affected brother died at 70 years of age; two other brothers are lean but affected by nephropathy, retinopathy, slight mental retardation, polydactyly, hypertension and thrombotic diseases, and had healthy offspring. BBS is a rather rare but severe syndrome that is often mis- or undiagnosed. Ophthalmologists, endocrinologists and nephrologists should be aware of BBS because of its adverse prognosis--early onset of blindness, associated findings of metabolic syndrome and increased vascular risk, and severe renal impairment (the most frequent cause of reduced survival and death early in life).

Plasma glucagon and free fatty acid responses to a glucose load in the obese spontaneous hypertensive rat (SHROB) model of metabolic syndrome X

Metabolic Syndrome X is a cluster of abnormalities including insulin resistance, hyperlipidemia, hypertension, and obesity. We sought to determine if excess plasma glucagon and free fatty acids (FFA) might contribute to the insulin resistance in the obese spontaneous hypertensive rat (SHROB), a unique animal model of leptin resistance and metabolic Syndrome X. SHROB were extremely hyperinsulinemic and mildly glucose intolerant compared with lean SHR. SHROB had elevated fasting plasma glucagon and FFA, and showed paradoxical responses to an oral glucose challenge, with increased glucagon at 30 and 60 min postchallenge (200% plus minus 45% and 91% plus minus 13%, respectively; n = 9). In lean SHR, glucagon was nearly unchanged by glucose loading (<30% increase, P > 0.05; n = 5). Plasma FFA were not affected by a glucose load in SHROB, whereas SHR showed a decrease of 40% plus minus 6% (n = 5--9). The I/G molar ratio changed in opposite directions in the two genotypes, with a decrease in SHROB at 30 and 60 min, in contrast to the appropriate increase at 30 and 60 min postchallenge in the lean SHR (P < 0.01; n = 5--9). Administration of 500 ng/kg exogenous glucagon to SHR raised glucagon 56% plus minus 5% to a level that was similar to fasting SHROB. This level of circulating glucagon was sufficient to elevate glucose and insulin during the 7 hr of observation (n = 9). Based on these results, we suggest that fasting hyperglucagonemia and impaired suppression of glucagon secretion and FFA in response to an oral glucose load may contribute to insulin resistance and glucose intolerance in the SHROB model of metabolic Syndrome X.

The relationship between metformin therapy and the fasting plasma lactate in type 2 diabetes: The Fremantle Diabetes Study

AIMS

To determine (i) which factors, including metformin, are associated with the fasting plasma lactate concentration in type 2 diabetes, and (ii) whether plasma lactate is associated with haemodynamic and metabolic effects.

METHODS

We measured fasting plasma lactate in 272 well-characterized diabetic patients from a community-based sample, 181 (67%) of whom were taking metformin with or without other therapies. Linear regression analysis was used to identify predictors, including metformin therapy, of the plasma lactate, and to investigate associations between plasma lactate and resting pulse rate and serum bicarbonate. Factor analysis assessed independent relationships between groups of cosegregating variables.

RESULTS

Metformin-treated patients had higher plasma lactate concentrations than nonmetformin-treated subjects (geometric mean [s.d. range] 1.86 [1.34-2.59] vs 1.58 [1.09-2.30] mmol x l(-1), respectively; P < 0.001). In a linear regression model, plasma glucose, BMI and metformin use (but not dose) were independently associated with plasma lactate (P < or = 0.028); after adjustment for the former two variables, metformin-treated patients had a mean plasma lactate 0.16 mmol l-1 greater than in subjects not taking the drug. Factor analysis revealed that plasma lactate, plasma glucose, BMI and pulse rate cosegregated but serum bicarbonate was not in this grouping.

CONCLUSIONS

The present results show that metformin therapy increases the fasting plasma lactate in ambulant patients with type 2 diabetes from a community-based cohort. From associations in the data we hypothesize that this increase reflects (i) increased sympathetic activity in patients with the metabolic syndrome (ii) increased substrate (glucose) availability and (iii) a direct metformin effect.

Estimations of muscle interstitial insulin, glucose, and lactate in type 2 diabetic subjects

Previous measurement of insulin in human muscle has shown that interstitial muscle insulin and glucose concentrations are approximately 30-50% lower than in plasma during hyperinsulinemia in normal subjects. The aims of this study were to measure interstitial muscle insulin and glucose in patients with type 2 diabetes to evaluate whether transcapillary transport is part of the peripheral insulin resistance. Ten patients with type 2 diabetes and ten healthy controls matched for sex, age, and body mass index were investigated. Plasma and interstitial insulin, glucose, and lactate (measured by intramuscular in situ-calibrated microdialysis) in the medial quadriceps femoris muscle were analyzed during a hyperinsulinemic euglycemic clamp. Blood flow in the contralateral calf was measured by vein plethysmography. At steady-state clamping, at 60-120 min, the interstitial insulin concentration was significantly lower than arterial insulin in both groups (409 +/- 86 vs. 1,071 +/- 99 pmol/l, P < 0.05, in controls and 584 +/- 165 vs. 1, 253 +/- 82 pmol/l, P < 0.05, in diabetic subjects, respectively). Interstitial insulin concentrations did not differ significantly between diabetic subjects and controls. Leg blood flow was significantly higher in controls (8.1 +/- 1.2 vs. 4.4 +/- 0.7 ml. 100 g(-1).min(-1) in diabetics, P < 0.05). Calculated glucose uptake was less in diabetic patients compared with controls (7.0 +/- 1.2 vs. 10.8 +/- 1.2 micromol. 100 g(-1).min(-1), P < 0.05, respectively). Arterial and interstitial lactate concentrations were both higher in the control group (1.7 +/- 0.1 vs. 1.2 +/- 0.1, P < 0. 01, and 1.8 +/- 0.1 vs. 1.2 +/- 0.2 mmol/l, P < 0.05, in controls and diabetics, respectively). We conclude that, during hyperinsulinemia, muscle interstitial insulin and glucose concentrations did not differ between patients with type 2 diabetes and healthy controls despite a significantly lower leg blood flow in diabetic subjects. It is suggested that decreased glucose uptake in type 2 diabetes is caused by insulin resistance at the cellular level rather than by a deficient access of insulin and glucose surrounding the muscle cell.

Metabolic complications of obesity. Pathophysiologic considerations

Given a specific research interest in human fatty acid metabolism, this article focuses primarily on the evidence surrounding the hypothesis that dysregulation of the fuel release function of fat cells (lipolysis) is an important contributing factor to the health hazards of obesity.