Biomedical subjects

R S Sherwin

Publications and source records attributed to R S Sherwin.

At least 19 recordsLinked to original sources

PubMed1997

Local ventromedial hypothalamus glucose perfusion blocks counterregulation during systemic hypoglycemia in awake rats.

The ventromedial hypothalamic nucleus (VMH) is necessary for the integrated hormonal response to hypoglycemia. To determine the role of the VMH as a glucose sensor, we performed experiments designed to specifically prevent glucopenia in the VMH, while producing hypoglycemia elsewhere. We used awake chronically catheterized rats, in which local VMH glucose perfusion (100 mM or 15 mM of D-glucose) was combined with a sequential euglycemic-hypoglycemic clamp. In two control groups the VMH was perfused either with (a) an iso-osmotic solution lacking glucose, or with (b) nonmetabolizable L-glucose (100 mM). During systemic hypoglycemia glucagon and catecholamine concentrations promptly increased in the control animals perfused with either 100 mM L-glucose or the iso-osmotic solution lacking glucose. In contrast, glucagon, epinephrine and norepinephrine release was inhibited in the animals in which the VMH was perfused with D-glucose; hormonal secretion was partially suppressed by the VMH perfusion with 15 mM D-glucose and suppressed by approximately 85% when the VMH was perfused with 100 mM D-glucose, as compared with the control groups. We conclude that the VMH must sense hypoglycemia for full activation of catecholamine and glucagon secretion and that it is a key glucose sensor for hypoglycemic counterregulation.

Animals↗

PubMed1997

Acute incretin response to oral glucose is associated with stimulation of gastric inhibitory polypeptide, not glucagon-like peptide in young subjects.

Oral glucose induces a greater insulin response than i.v. glucose, a difference apparently due to the secretion of gut factors ("incretins"). Studies examining the mechanisms of this finding in human subjects are limited, however, because of differences in glucose profiles. To overcome this obstacle, we studied eight young nonobese subjects using the hyperglycemic clamp with and without superimposed ingestion of oral glucose. In both studies, glucose was acutely raised by 12.5 mg/dL above fasting values by the infusion of i.v. glucose and maintained at this level for 180 min. During the experimental study, but not the control, each subject ingested oral glucose (30 g) at 120 min, and the glucose infusion was adjusted to maintain the plasma glucose plateau. Plasma insulin responses were nearly identical during both studies until oral glucose was added. After oral glucose, both plasma insulin and C-peptide levels sharply increased by 45-55% above control values (p < 0.001), indicating a potentiation of insulin secretion rather than decreased hepatic extraction of insulin. Plasma gastric inhibitory polypeptide (GIP) levels increased significantly in response to oral glucose, whereas plasma levels of glucagon-like peptide-1 (7-37) were not affected. The time course of the rise in plasma GIP and insulin was nearly identical. We conclude that the GIP response to a modest oral glucose load may play an important physiologic role in glucose-stimulated insulin secretion in healthy young subjects.

Administration, Oral↗

PubMed1997

Resistance to neuroglycopenia: an adaptive response during intensive insulin treatment of diabetes.

Counterregulation and awareness of hypoglycemia begins at lower plasma glucose levels in insulin-dependent diabetes mellitus (IDDM) subjects given intensive insulin treatment. To determine whether these changes are associated with an alteration in the susceptibility of the brain to mild hypoglycemia, we compared central nervous system responses to hypoglycemia in 8 intensively treated (hemoglobin A1, 8.3 +/- 0.2%; normal, <8%) and 11 conventionally treated IDDM patients (hemoglobin A1, 14.6 +/- 1.3%) with those in 10 healthy subjects. Plasma glucose was lowered from approximately 4.6 mmol/L in 0.5-0.6 steps using the clamp technique. Glucose levels triggering hormonal responses and perception of hypoglycemic symptoms were significantly lower in intensively treated patients compared to their poorly controlled counterparts (P < 0.05), and hormonal responses were suppressed compared to those in healthy controls. Similarly directed changes occurred in the level of circulating glucose required to alter cortical evoked potentials during hypoglycemia. A greater reduction in plasma glucose was required to alter P300 event-related potentials in the intensively treated patients (2.2 mmol/L) compared to those in the conventionally treated and nondiabetic groups (approximately 3.5 and approximately 3.0 mmol/L, respectively). We conclude that intensively treated IDDM patients are resistant to changes in cortical evoked potentials induced by mild hypoglycemia. This may explain why intensively treated IDDM counterregulate and experience hypoglycemic symptoms at a lower glucose level than conventionally treated patients.

Adaptation, Physiological↗

PubMed1997

The effect of leptin is enhanced by microinjection into the ventromedial hypothalamus.

To determine whether changes in food intake produced by leptin involve targeting the hormone to distinct central nervous system regions, guide cannulas were positioned stereotaxically into three brain regions--the ventromedial hypothalamus (VMH) (bilaterally, n = 6), the dorsal raphe nucleus (n = 3), and the lateral ventricle (n = 3)--of nonobese male rats (400-500 g). Daily food intake and body weight changes were measured during twice-daily injections of saline (0.1 microl) followed by recombinant human leptin (0.05 microg) for 3 days via the brain cannulas. VMH-injected rats also were followed during a postleptin saline recovery interval. This small dose of leptin did not change food intake or body weight from that during the preceding saline injection period in ventricle-injected or dorsal raphe-injected rats. In sharp contrast, VMH-injected rats ate much less food (56 +/- 8% basal) and lost 9 +/- 3 g/day or 5% of their body weight during 3 days of leptin administration. VMH-injected animals fully recovered from leptin-induced effects within 3 days. We conclude that small doses of leptin that do not effect eating behavior when delivered to the ventricle or the dorsal raphe (another brain region believed to regulate feeding), suppress food intake when injected into the VMH. These data suggest that the VMH or a brain region in close proximity to it is a key target for the biological actions of leptin.

Animals↗

PubMed1997

Counterregulation in peripheral tissues: effect of systemic hypoglycemia on levels of substrates and catecholamines in human skeletal muscle and adipose tissue.

We used microdialysis to distinguish the effects of hyperinsulinemia and hypoglycemia on glucose, gluconeogenic substrate, and catecholamine levels in adipose and muscle extracellular fluid (ECF). Ten lean humans (six males and four females) were studied during baseline and hyperinsulinemic (3 mU x kg-1 x min-1 for 3 h) euglycemia (5.0 mmol/l) and hypoglycemia (2.8 mmol/l). In muscle and adipose, basal ECF glucose was lower (muscle, 3.5 +/- 0.2 mmol/l; adipose tissue, 3.3 +/- 0.2 mmol/l) and lactate was higher (muscle, 2.2 +/- 0.2 mmol/l; adipose, 1.5 +/- 0.3 mmol/l) than respective plasma values (glucose, 4.9 +/- 0.1 mmol/l; lactate, 0.7 +/- 0.1 mmol/l), whereas alanine was higher in muscle ECF (379 +/- 22 micromol/l) than adipose tissue (306 +/- 22 micromol/l) and plasma (273 +/- 33 micromol/l). Plasma catecholamines (unchanged during euglycemia) rose during hypoglycemia with epinephrine, increasing approximately fivefold more than norepinephrine. In contrast, the hypoglycemia-induced increments in muscle dialysate norepinephrine and epinephrine were similar, suggesting local generation of norepinephrine. Compared with euglycemia, hypoglycemia produced a greater increase in lactate and a smaller reduction in alanine in muscle ECF, whereas hypoglycemia caused a greater relative fall in ECF glucose concentrations in muscle (72 +/- 16%) and adipose tissue (69 +/- 9%) than in plasma (42 +/- 3%) (P < 0.05). We conclude that hypoglycemia increases the generation of norepinephrine and gluconeogenic substrates in key target tissues, while increasing the plasma-tissue concentration gradient for glucose. These changes suggest the stimulation of glucose extraction by peripheral tissues, despite systemic counterregulatory hormone release and local sympathetic activation.

Adipose Tissue↗

PubMed1997

Importance of cerebral blood flow to the recognition of and physiological responses to hypoglycemia.

During hypoglycemia, cerebral blood flow (CBF) does not increase significantly until peripheral glucose levels are very low (2.0 mmol/l), that is, well below the blood glucose threshold for impairment of cognitive function (3.0 mmol/l). Because increased rates of cerebral blood flow will increase glucose transport, a failure of flow to rise earlier, before brain function is threatened, might be considered maladaptive. To examine the influence of inducing an earlier rise in CBF during hypoglycemia, eight healthy volunteers participated in three studies using a randomized, placebo-controlled design. In all three studies, a hyperinsulinemic (60 mU x m2 x min(-1)) clamp was used to maintain blood glucose levels at 4.5 mmol/l for 60 min. Thereafter, for EUG-ACZ, blood glucose was maintained at 4.5 mmol/l from 60 to 170 min and at 90 min from the start of this study, and 1-g acetazolamide i.v. was given to induce an early rise in CBF; for HYPO-ACZ, glucose was lowered over 20 min to 2.8 mmol/l and kept at that level for 90 min, and acetazolamide was given 90 min from the start of this study; and for HYPO-CON, glucose was treated as in HYPO-ACZ, and matching placebo was given in place of acetazolamide. Injection of acetazolamide was associated with a 30% rise in right (95% CI 24-34%) and left (20-32%) middle cerebral artery velocity (an index of CBF) during euglycemia without any change in hypoglycemia awareness or counterregulatory hormone levels. When glucose was lowered to 2.8 mmol/l, acetazolamide caused a similar rise in middle cerebral artery velocity in the HYPO-ACZ study. However, all subjects were less "aware" of hypoglycemia, had fewer adrenergic symptoms (sweating, palpitations, tremors; all P < 0.05), and had lower plasma epinephrine levels (1,026 vs. 1,790 pmol/l; -764 [437 to 1,097] pmol/l, point estimate of difference [95% CI]; P < 0.001), compared with the HYPO-CON study, whereas levels of other counter-regulatory hormones and norepinephrine were similar. Cognitive function (latency of the P300 evoked response) was unaffected by increasing CBF. In conclusion, enhanced rates of cerebral blood flow at the onset of systemic hypoglycemia are associated with diminished perception of low blood glucose levels and attenuation of the epinephrine counterregulatory response. These findings suggest that augmenting cerebral blood flow leads to an enhanced rate of substrate delivery to the central nervous system.

Acetazolamide↗

PubMed1996

High density insulin receptor-positive T lymphocytes from nonobese diabetic mice transfer insulitis and diabetes.

In the nonobese diabetic mouse, insulin-dependent diabetes is an autoimmune disease characterized by T cell-mediated invasion and destruction of pancreatic islet beta cells. The importance of insulin receptor (IR) expression in the pathogenesis of diabetes was examined, since it has been shown that the IR is a chemotactic receptor capable of directing cell movement in response to insulin. Using polyclonal antisera to the IR, phenotypic analysis of purified splenic T cells from diabetic mice showed that about 15% of T cells expressed high density IR (IRhigh). In addition, IRhigh T cells were already a dominant phenotype in the insulitis of young prediabetic mice. To determine the ability of IRhigh T cells to transfer diabetes, cells were sorted by flow cytometry before adoptive transfer into young (6- to 8-wk-old) nondiabetic irradiated nonobese mice. Transfer of as few as 3 x 10(6) purified IRhigh T cells alone resulted in rapid onset of insulitis and diabetes, and IRhigh-depleted T cells were essentially unable to passage either insulitis or diabetes. The adoptive transfer of disease was not due to the transfer of activated cells, since removal of IL-2R+ or transferrin R+ cells did not alter diabetes transfer. Therefore, IRhigh T cells are aggressively diabetogenic, suggesting that increased IR expression may provide a mechanism for delivering potentially autoreactive T cells to the islet, regardless of their activation state.

Animals↗

PubMed1996

Effect of caffeine on recognition of and physiological responses to hypoglycaemia in insulin-dependent diabetes.

BACKGROUND: For the patient with diabetes, hypoglycaemia unawareness--ie, the warning signs of falling blood glucose are missing--is potentially dangerous. One study has suggested that, in healthy volunteers, caffeine might be a helpful treatment. Our study looked at two effects of caffeine ingestion (250 mg) on the brain--namely, a decrease in cerebral blood flow and an increase in brain glucose use--to see if the recognition of and physiological responses to hypoglycaemia were altered in patients with insulin-dependent diabetes mellitus (IDDM). METHODS: 12 patients were studied twice. A hyperinsulinaemic glucose clamp was used to maintain plasma glucose at 5 mmol/L for 90 min, followed by 60 min at 3.8 mmol/L, and then 2.8 mmol/L for a further hour. After 30 min at 5 mmol/L, patients consumed, in a double-blind, crossover design, 250 mg caffeine or matched placebo. We recorded middle cerebral artery velocity (VMCA), counterregulatory hormone levels, and cognitive function, and patients recorded hypoglycaemia symptoms on a visual analogue scale. RESULTS: Caffeine caused an immediate and sustained fall in VMCA of 10 cm/s, from 60 to 50 cm/s (95% CI -5 to -15 cm/s; p < 0.001). At a blood glucose of 3.8 mmol/L, plasma adrenaline levels were twice as high after caffeine than after placebo (difference 524 pmol/L). When glucose was lowered to 2.8 mmol/L, caffeine ingestion was associated with: greater awareness of hypoglycaemia in 9 patients, significantly more intense autonomic and neuroglycopenic symptoms, and higher levels of adrenaline, cortisol, and growth hormone. Cognitive function (latency of P300 evoked potentials) deteriorated to the same extent in both studies at this glucose level. INTERPRETATION: The sustained fall in VMCA and augmented sympathoadrenal and symptomatic responses during moderate hypoglycaemia suggest caffeine as a potentially useful treatment for diabetic patients who have difficulty recognising the onset of hypoglycaemia.

Adult↗

PubMed1996

Co-existence of severe insulin resistance and hyperinsulinaemia in pre-adolescent obese children.

To determine the time course of changes in insulin action and secretion that occur early during the development of obesity, we studied children before the onset of puberty. The reason for choosing the prepubertal stage of development is that it is metabolically characterized by both a high sensitivity to insulin and low glucose stimulated insulin responses. Fifteen obese preadolescents (8 male/7 female, age 10 +/- 0.4 years, body mass index (BMI) 31 +/- 1.2 kg/m2 Tanner Stage I) with a duration of obesity of less than 5 years and 10 non-obese preadolescents (6 male/4 female, age 10 +/- 0.4 years, BMI 18 +/- 0.9 kg/m2) matched for gender were studied. In a cross-sectional analysis, we compared responses in obese preadolescents, with those in obese adolescents and obese adults with a longer duration of obesity. The euglycaemic hyperinsulinaemic clamp with 1-13C-glucose (Hot Ginf) and indirect calorimetry were used to quantitate insulin action and the hyperglycaemic clamp used to assess beta-cell function. Insulin-stimulated glucose uptake measured at two physiological levels of hyperinsulinaemia (approximately 180 and 480 pmol) was reduced by 20 and 45% in all three groups of obese compared to non-obese subjects (p < 0.01). Defects in oxidative and non-oxidative glucose metabolism were observed in all three groups of obese subjects at the higher insulin infusion rate. The ability of insulin to inhibit lipid oxidation was impaired in all three obese groups at both levels of hyperinsulinaemia. Increases in basal and glucose-stimulated insulin levels during the hyperglycaemic clamp mirrored the reductions in glucose uptake during the insulin clamp in all obese groups. These results indicate that insulin resistance and hyperinsulinaemia co-exist in preadolescent children with moderate to severe obesity.

Adolescent↗

PubMed1996

Time course of the defective alpha-cell response to hypoglycemia in diabetic BB rats.

Although it is understood that patients with insulin-dependent diabetes mellitus (IDDM) lose the ability to release glucagon during a hypoglycemic challenge, the relationship of this defect to the disease onset and loss of beta-cell function is not well defined. To address this issue, we measured the counterregulatory response in three groups of BB/wor rats during sequential 90-minute euglycemic (7 mmol/L) and hypoglycemic (3 mmol/L) insulin clamps (180 pmol/kg.min). Group 1 (n = 8) consisted of nondiabetic BB rats (aged 84 +/- 3 days), and groups 2 and 3 were rats studied 1 day (n = 7) or 7 days (n = 6) after diabetes onset. Plasma glucagon concentrations were similar in all groups during euglycemia (244 +/- 47 ng/L for nondiabetic, 308 +/- 38 for 1 day of diabetes, and 277 +/- 30 for 7 days of diabetes). Moreover, after 1 day of diabetes, the increase in plasma glucagon during hypoglycemia was similar to that seen in controls (to 581 +/- 94 and 650 +/- 118 ng/L, respectively) even though insulin production by the pancreas was virtually absent. However, after 7 days of diabetes, plasma glucagon only increased to 339 +/- 59 ng/L during hypoglycemia (P = nonsignificant v basal), despite normal pancreatic glucagon content (11.5 +/- 1.2 v 10.8 +/- 0.6 micrograms/g in nondiabetic controls). In conclusion, the hypoglycemia-associated defect in glucagon release occurs early in the course of diabetes in BB rats and is not associated with decreased baseline plasma or pancreatic glucagon levels. This impairment, although not immediately linked to the decrease in pancreatic insulin content, occurs soon afterward, implying that the two events are related.

Animals↗

PubMed1996

IGF-I stimulation of muscle protein synthesis in the awake rat: permissive role of insulin and amino acids.

Infusion of insulin-like growth factor I (IGF-I) lowers plasma amino acid and insulin concentrations, which may limit the capacity of IGF-I to promote muscle protein synthesis in vivo. We measured heart and skeletal muscle incorporation of continuously infused L-[ring-2,6-3H]phenylalanine in awake postabsorptive rats receiving 4-h intravenous infusions of saline (n = 11), IGF-I (1 microgram.kg-1.min-1) with (n = 10) or without (n = 11) amino acid replacement, or IGF-I with insulin replacement (n = 8). There were no significant increases in muscle protein synthesis during the infusion of IGF-I alone, which was associated with decreases in both plasma insulin (52 +/- 5%, P < 0.001) and amino acids (25 +/- 5%, P < 0.05). When IGF-I was given together with amino acids, protein synthesis was significantly increased in gastrocnemius (4.7 +/- 0.4 vs. 2.5 +/- 0.3%/day, P < 0.001), oblique (4.5 +/- 0.4 vs. 2.8 +/- 0.4%/day, P < 0.05), and soleus (8.8 +/- 0.7 vs. 6.4 +/- 0.3%/day, P < 0.01) and tended to be higher than saline control values in heart (10.9 +/- 0.9 vs. 8.8 +/- 0.7%/day, P = 0.08). Amino acid replacement prevented plasma concentrations from falling and also blunted the decline in plasma insulin (22 +/- 5%, P < 0.01 vs. IGF-I alone). When IGF-I and insulin replacement were given, protein synthesis was increased in heart (13.0 +/- 0.6%/day), gastrocnemius (4.7 +/- 0.4%/day), and oblique (4.5 +/- 0.4%/day) (P < 0.001 for each, compared with saline). We conclude that the action of IGF-I to acutely stimulate muscle protein synthesis in the awake rat is limited by the fall in circulating insulin and/or amino acid concentrations that accompanies IGF-I infusion in vivo and is prevented by co-infusion of insulin or amino acids.

Amino Acids↗

PubMed1996

Hyperleptinemia: an early sign of juvenile obesity. Relations to body fat depots and insulin concentrations.

Leptin, the OB gene product, is an adipocyte-derived circulating protein. In several rodent models of obesity, such as the db/db mice, fa/fa rats, and ventromedial hypothalamus-lesioned mice, as well as adult obese subjects, leptin mRNA expression and the circulating levels are elevated, suggesting resistance to its action. However, it is unknown whether the rise in leptin concentration occurs early in the natural evolution of human obesity or is a chronic adaptation to the obese state. Moreover, whether the distribution of body fat (i.e., visceral vs. subcutaneous abdominal fat) influences circulating leptin levels has not been assessed. We have determined in a group of obese and nonobese children and young adults whether leptin levels 1) are increased early in the development of obesity, 2) are related to a specific fat depot measured by magnetic resonance imaging, 3) vary during hyperinsulinemic, euglycemic, and hyperglycemic clamp studies, and 4) are different in males vs. females. In the basal state, leptin levels were elevated in obese children. Children and adults demonstrated a strong positive correlation between leptin concentrations and the subcutaneous fat depot (r = 0.84, P < 0.001). Surprisingly, a weaker correlation was found with visceral fat mass (r = 0.59, P = 0.001). Leptin levels remained unchanged under both euglycemic and hyperglycemic hyperinsulinemic conditions in both obese and nonobese subjects. A pronounced effect of gender on leptin levels was also observed. We conclude that, early in the development of juvenile obesity, leptin concentrations are elevated and are more closely linked to subcutaneous than visceral fat mass. Acute increases in insulin concentrations do not affect circulating leptin levels.

Adipose Tissue↗

PubMed1995

Targeting of the 67-kDa isoform of glutamic acid decarboxylase to intracellular organelles is mediated by its interaction with the NH2-terminal region of the 65-kDa isoform of glutamic acid decarboxylase.

The two isoforms of glutamic acid decarboxylase (GAD), GAD67 and GAD65, synthesize the neurotransmitter gamma-aminobutyric acid in neurons and pancreatic beta-cells. Previous studies suggest that GAD67 is a soluble cytosolic protein, whereas GAD65 is membrane-associated. Here, we study the intracellular distribution of GAD67 in neurons, pancreatic beta-cells, and fibroblasts transfected either with GAD65 and GAD67 together or with GAD67 alone. Neuronal GAD67 is partially recovered with GAD65 in membrane-containing pellet fractions and Triton X-114 detergent phases. The two proteins co-immunoprecipitate from extracts of brain and GAD65-GAD67 co-transfected fibroblasts, but not when extracts of GAD65 and GAD67 transfected fibroblasts were mixed and used as a starting material for immunoprecipitation. GAD67 is concentrated in the Golgi complex region in GAD65-GAD67 co-transfected fibroblasts, but not in fibroblasts transfected with GAD67 alone. A pool of neuronal GAD67 co-localizes with GAD65 in the Golgi complex region and in many synapses. The two proteins also co-localize in the perinuclear region of some pancreatic beta-cells. GAD67 interacts with the NH2-terminal region of GAD65, even in the absence of palmitoylation of this region of GAD65. Taken together, our results indicate that GAD65-GAD67 association occurs in vivo and is required for the targeting of GAD67 to membranes.

Animals↗

PubMed1995

Enhanced adrenomedullary response and increased susceptibility to neuroglycopenia: mechanisms underlying the adverse effects of sugar ingestion in healthy children.

OBJECTIVE: Eating simple sugars has been suggested as having adverse behavioral and cognitive effects in children, but a physiologic mechanism has not been established. This study was performed to address this issue. DESIGN: Metabolic, hormonal, and symptomatic responses to a standard oral glucose load (1.75 gm/kg; maximum, 120 gm) were compared in 25 healthy children and 23 young adults, and the hypoglycemic clamp, together with measurements of P300 auditory evoked potentials, was used to assess whether children are more vulnerable than adults to neuroglycopenia. SETTING: Children's Clinical Research Center, Yale University School of Medicine. RESULTS: Baseline and oral glucose-stimulated plasma glucose and insulin levels were similar in both groups, including the nadir glucose level 3 to 5 hours after oral administration of glucose (3.4 +/- 0.1 mmol/L (61 +/- 1.8 mg/dl) in children and 3.5 +/- 0.1 mmol/L (63 +/- 1.8 mg/dl) in adults). The late glucose decrease stimulated a rise in plasma epinephrine levels that was twofold higher in children than in adults (2260 +/- 289 vs 1031 +/- 147 pmol/L (407 +/- 52 vs 186 +/- 26 pg/ml), p < 0.01) and a significant increase in hypoglycemic symptom scores in children (p < 0.01), but not in adults. During control experiments, in which six of the healthy children ingested a sugar-free drink, there were no significant changes in plasma glucose levels, hormone concentrations, or hypoglycemic symptom scores. During the hypoglycemic clamp, P300 potentials did not change in any of eight adult subjects until the plasma glucose concentration was lowered to 3.0 mmol/L (54 mg/dl), whereas similar changes in P300 potentials were observed in six of seven children at glucose levels 3.6 to 4.2 mmol/L (65 to 75 mg/dl). CONCLUSION: Enhanced adrenomedullary responses to modest reductions in plasma glucose concentration and increased susceptibility to neuroglycopenia may be important contributing factors to adverse behavioral and cognitive effects after sugar ingestion in healthy children.

Adolescent↗

PubMed1995

Effects of epinephrine on human muscle glucose and protein metabolism.

Systemic epinephrine infusion causes hypoaminoacidemia and inhibits whole body leucine flux (proteolysis) in humans. Its specific action on muscle protein is not known and is difficult to assess during systemic epinephrine infusions, which affect plasma insulin, amino acid, and free fatty acid concentrations. During a steady-state infusion of L-[ring-2,6-3H]phenylalanine, we examined the effect of locally infused epinephrine on the metabolism of protein and glucose in forearm muscle of 10 healthy human volunteers. During local epinephrine infusion, systemic concentrations of glucose, phenylalanine, insulin, and epinephrine were unchanged and lactate declined (P < 0.02). Compared with baseline, epinephrine induced significant increases in forearm blood flow (P < 0.01) and net lactate release (P < 0.001) and a decrease in glucose uptake (P < 0.01) at both 2 and 4 h. At 2 and 4 h phenylalanine release from muscle proteolysis was suppressed (P < 0.01), and at 4 h the net phenylalanine balance was less negative than baseline (P < 0.02), indicating an anticatabolic effect on muscle protein. We conclude that in human forearm muscle epinephrine, at physiological concentrations, has a catabolic effect on muscle glycogen but an anticatabolic action on muscle protein. The mechanism of this latter effect is not known.

Adult↗

PubMed1995

Central adiposity and its metabolic correlates in obese adolescent girls.

To establish whether alterations in insulin action and secretion and their relationship to body fat distribution occur early in the course of developing obesity, we studied 14 obese adolescent girls [13.2 +/- 0.7 yr, body mass index (BMI) 32 +/- 1.4], 16 nonobese young women (24.0 +/- 0.6 yr, BMI 21.0 +/- 0.9). Insulin action was assessed by a sequential two-step (8 and 40 mU,m-2.min-1) euglycemic insulin clamp in combination with [1-13C]glucose and indirect calorimetry. Insulin secretion was determined by the hyperglycemic clamp technique (6.9 mmol/l). Magnetic resonance imaging was used to quantify visceral and subcutaneous abdominal fat depots. In obese girls, an impairment in glucose disposal was present with both insulin doses; at the higher dose, rates of glucose uptake were reduced by 30% in nonobese girls (240 +/- 30 vs. 340 +/- 19 mg.m-2.min-1, P < 0.05) and by an additional 29% (170 +/- 17 mg.m-2.min-1, P < 0.05) in obese girls. Insulin infusion failed to stimulate glucose oxidation and to suppress lipid oxidation only in obese girls. Suppression of free fatty acid levels, but not hepatic glucose production, was decreased in obese girls compared with controls. Fasting and glucose-stimulated insulin responses were greater in obese than in nonobese adolescents, who, in turn, had greater responses than lean women. In obese girls, visceral fat, but neither waist-to-hip circumference ratio nor subcutaneous fat, was highly correlated with basal insulin secretion (r = 0.89, P < 0.001), stimulated insulin secretion (r = 0.61, P < 0.05), and insulin resistance (r = -0.87, P < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗

PubMed1995

Glucose modulates rat substantia nigra GABA release in vivo via ATP-sensitive potassium channels.

Glucose modulates beta cell insulin secretion via effects on ATP-sensitive potassium (KATP) channels. To test the hypothesis that glucose exerts a similar effect on neuronal function, local glucose availability was varied in awake rats using microdialysis in the substantia nigra, the brain region with the highest density of KATP channels. 10 mM glucose perfusion increased GABA release by 111 +/- 42%, whereas the sulfonylurea, glipizide, increased GABA release by 84 +/- 20%. In contrast, perfusion of the KATP channel activator, lemakalim, or depletion of ATP by perfusion of 2-deoxyglucose with oligomycin inhibited GABA release by 44 +/- 8 and 45 +/- 11%, respectively. Moreover, the inhibition of GABA release by 2-deoxyglucose and oligomycin was blocked by glipizide. During systemic insulin-induced hypoglycemia (1.8 +/- 0.3 mM), nigral dialysate GABA concentrations decreased by 49 +/- 4% whereas levels of dopamine in striatal dialysates increased by 119 +/- 18%. We conclude that both local and systemic glucose availability influences nigral GABA release via an effect on KATP channels and that inhibition of GABA release may in part mediate the hyperexcitability associated with hypoglycemia. These data support the hypothesis that glucose acts as a signaling molecule, and not simply as an energy-yielding fuel, for neurons.

Adenosine Triphosphate↗

PubMed1995

Interstitial fluid concentrations of glycerol, glucose, and amino acids in human quadricep muscle and adipose tissue. Evidence for significant lipolysis in skeletal muscle.

To determine the relationship between circulating metabolic fuels and their local concentrations in peripheral tissues we measured glycerol, glucose, and amino acids by microdialysis in muscle and adipose interstitium of 10 fasted, nonobese human subjects during (a) baseline, (b) euglycemic hyperinsulinemia (3 mU/kg per min for 3 h) and, (c) local norepinephrine reuptake blockade (NOR). At baseline, interstitial glycerol was strikingly higher (P < 0.0001) in muscle (3710 microM) and adipose tissue (2760 microM) compared with plasma (87 microM), whereas interstitial glucose (muscle 3.3, fat 3.6 mM) was lower (P < 0.01) than plasma levels (4.8 mM). Taurine, glutamine, and alanine levels were higher in muscle than in adipose or plasma (P < 0.05). Euglycemic hyperinsulinemia did not affect interstitial glucose, but induced a fall in plasma glycerol and amino acids paralleled by similar changes in the interstitium of both tissues. Local NOR provoked a fivefold increase in glycerol (P < 0.001) and twofold increase in norepinephrine (P < 0.01) in both muscle and adipose tissues. To conclude, interstitial substrate levels in human skeletal muscle and adipose tissue differ substantially from those in the circulation and this disparity is most pronounced for glycerol which is raised in muscle as well as adipose tissue. In muscle, insulin suppressed and NOR increased interstitial glycerol concentrations. Our data suggest unexpectedly high rates of intramuscular lipolysis in humans that may play an important role in fuel metabolism.

Adipose Tissue↗