The effects of acute elevations in plasma cortisol levels on alanine metabolism in the conscious dog

Social context affects tissue-specific copper distribution and behaviour of threespine stickleback (Gasterosteus aculeatus)

Many species exhibit social living which offers ecological advantages such as increased foraging opportunities, more efficient locomotion and reduced predation risk. Additionally, exposure to multiple individuals of the same species can decrease an individual's stress and metabolic demand, termed social buffering. If disruption to an animal's social structure occurs and prevents social buffering, an elevated metabolic rate and thus ventilation frequency and gill permeability are likely. A potential consequence of this physiological response could be the increased accumulation of toxicants. The objective of this study was to investigate whether inducing social stress in marine threespine stickleback (Gasterosteus aculeatus) through social isolation during a sublethal water-borne copper (Cu) exposure would affect Cu uptake and whether that would translate to differences in behaviour and biochemical functioning. We hypothesized that isolating threespine stickleback during a Cu exposure would increase Cu uptake and sublethal toxicity compared to a grouped exposure. Wild-caught fish were exposed to control, low Cu or high Cu conditions (0 - 150 µg/L of Cu, nominally), either in isolation or groups of six for 96 h. Isolated stickleback travelled three times less distance, took six times longer to consume food and exhibited moderately increased gill sodium-potassium ATPase activity than group exposed fish, with no effect of Cu. Isolated stickleback also demonstrated significantly higher Cu levels in their gill and liver tissue compared to the group exposed fish. However, this Cu distribution was also present within the control fish, which had not been exposed to Cu, suggesting that the social context affects endogenous Cu distribution under stressful conditions. Our results illustrate the differences in physiology and behaviour that can arise when social contexts are manipulated and stress the importance of considering sociality when conducting toxicity tests with social organisms.

Influence of Stress on Liver Circadian Physiology. A Study in Rainbow Trout, Oncorhynchus mykiss, as Fish Model

In vertebrates stress negatively affects body homeostasis and triggers a battery of metabolic responses, with liver playing a key role. This organ responds with altered metabolism, leading the animal to cope with the stress situation, which involves carbohydrate and lipid mobilization. However, metabolism among other physiological functions is under circadian control within the liver. Then, metabolic homeostasis at system level involves circadian timing systems within tissues and cells, and collaborate with each other. During chronic stress, cortisol maintains the liver metabolic response by modulating carbohydrate- and lipid-related metabolism. Stress also disrupts the circadian oscillator within the liver in mammals, whereas little information is available in other vertebrates, such as fish. To raise the complexity of this process, other candidates may mediate in such effect of stress. In fact, sirtuin1, a link between cellular sensing of energy status and circadian clocks, participates in the response to stress in mammals, but no information is available in fish. Considering the role played by liver in providing energy for the animal to deal with an adverse situation, and the existence of a circadian oscillator within this tissue, jeopardized liver circadian physiology during stress exposure might be expected. Whether the physiological response to stress is a well conserved process through the phylogeny and the mechanisms involved in such response is a question that remains to be elucidated. Then, we provide information at this respect in mammals and show comparable results in rainbow trout as fish animal model. Similar to that in mammals, stress triggers a series of responses in fish that leads the animal to cope with the adverse situation. Stress influences liver physiology in fish, affecting carbohydrate and lipid metabolism-related parameters, and the circadian oscillator as well. In a similar way than that of mammals different mediators participate in the response of liver circadian physiology to stress in fish. Among them, we confirm for the teleost rainbow trout a role of nuclear receptors (rev-erbβ), cortisol, and sirt1. However, further research is needed to evaluate the independent effect of each one, or the existence of any interaction among them.

Actions of glucocorticoids at a seasonal baseline as compared to stress-related levels in the regulation of periodic life processes

For decades, demands associated with the predictable life-history cycle have been considered stressful and have not been distinguished from stress that occurs in association with unpredictable and life-threatening perturbations in the environment. The recent emergence of the concept of allostasis distinguishes behavioral and physiological responses to predictable routines as opposed to unpredictable perturbations, and allows for their comparison within one theoretical framework. Glucocorticosteroids (GCs) have been proposed as important mediators of allostasis, as they allow for rapid readjustment and support of behavior and physiology in response to predictable and unpredictable demands (allostatic load). Much work has already been done in defining GC action at the high concentrations that accompany life-threatening perturbations. However, less is known about the role of GCs in relation to daily and seasonal life processes. In this review, we summarize the known behavioral and physiological effects of GCs relating to the predictable life-history cycle, paying particular attention to feeding behavior, locomotor activity and energy metabolism. Although we utilize a comparative approach, emphasis is placed on birds. In addition, we briefly review effects of GCs at stress-related concentrations to test the hypothesis that different levels of GCs play specific and distinct roles in the regulation of life processes and, thus, participate in the promotion of different physiological states. We also examine the receptor types through which GC action may be mediated and suggest mechanisms whereby different GC concentrations may exert their actions. In conclusion, we argue that biological actions of GCs at "non-stress" seasonal concentrations play a critical role in the adjustment of responses that accompany predictable variability in the environment and demand more careful consideration in future studies.

Portal 5-hydroxytryptophan infusion enhances glucose disposal in conscious dogs

Intraportal serotonin infusion enhances net hepatic glucose uptake (NHGU) during glucose infusion but blunts nonhepatic glucose uptake and can cause gastrointestinal discomfort and diarrhea at high doses. Whether the serotonin precursor 5-hydroxytryptophan (5-HTP) could enhance NHGU without gastrointestinal side effects during glucose infusion was examined in conscious 42-h-fasted dogs, using arteriovenous difference and tracer ([3-3H]glucose) techniques. Experiments consisted of equilibration (-120 to -30 min), basal (-30 to 0 min), and experimental (EXP; 0-270 min) periods. During EXP, somatostatin, fourfold basal intraportal insulin, basal intraportal glucagon, and peripheral glucose (to double the hepatic glucose load) were infused. In one group of dogs (HTP, n = 6), saline was infused intraportally from 0 to 90 min (P1), and 5-HTP was infused intraportally at 10, 20, and 40 microg x kg(-1) x min(-1) from 90 to 150 (P2), 150 to 210 (P3), and 210 to 270 (P4) min, respectively. In the other group (SAL, n = 7), saline was infused intraportally from 0 to 270 min. NHGU in SAL was 14.8 +/- 1.9, 18.5 +/- 2.3, 16.3 +/- 1.4, and 19.7 +/- 1.6 micromol x kg(-1) x min(-1) in P1-P4, whereas NHGU in 5-HTP averaged 16.4 +/- 2.6, 18.5 +/- 1.4, 20.8 +/- 2.0, and 27.6 +/- 2.6 micromol x kg(-1) x min(-1) (P < 0.05 vs. SAL). Nonhepatic glucose uptake (micromol x kg(-1) x min(-1)) in SAL was 30.2 +/- 4.3, 36.8 +/- 5.8, 44.3 +/- 5.8, and 54.6 +/- 11.8 during P1-P4, respectively, whereas in HTP the corresponding values were 26.3 +/- 6.8, 44.9 +/- 10.1, 47.5 +/- 11.7, and 51.4 +/- 13.2 (not significant between groups). Intraportal 5-HTP enhances NHGU without significantly altering nonhepatic glucose uptake or causing gastrointestinal side effects, raising the possibility that a related agent might have a role in reducing postprandial hyperglycemia.

Diurnal rhythms in plasma cortisol, insulin, glucose, lactate and urea in pigs fed identical meals at 12-hourly intervals

Diurnal rhythms in plasma cortisol, insulin, glucose, lactate and urea concentrations were investigated in eight catheterized pigs of approximately 35 kg BW. Pigs were fed isoenergetic/isoproteinic diets at a restricted level (2.5 x maintenance requirement for energy) in two daily rations (06:00 and 18:00 hours) in order to obtain equal intervals between feed intake. Preprandial plasma cortisol concentration was 22+/-3 ng/mL in the morning and 14+/-2 ng/mL in the evening (p<0.025), whereas the concentrations of insulin, glucose, lactate, and urea were similar. In the postprandial period in the morning (06:00-09:00 hours) plasma cortisol, insulin and lactate concentrations (expressed as the total area under the curve) were greater (p<0.001) compared to the evening (18:00-21:00 hours) by 100%, 42%, and 24%, respectively, while postprandial plasma glucose and urea concentrations were not affected by time of the meal. When postprandial plasma concentrations were expressed as a response over preprandial concentrations (decremental or incremental area under the curve), the diurnal rhythm was not observed for cortisol and glucose, persisted for insulin and lactate, and appeared for urea with a smaller postprandial urea response (p<0.05) in the morning compared to the evening. We conclude that the diurnal rhythm in plasma cortisol is independent of feeding whereas the diurnal rhythms in plasma insulin, lactate and urea are unveiled by the morning/evening meals in pigs. At equal 12-h intervals between meals, the postprandial responses of lactate and urea show diurnal variations, each in a specific manner, which suggest decreased postprandial efficiency of carbohydrate metabolism and increased postprandial efficiency of protein metabolism in the morning compared to the evening.

Portal infusion of a selective serotonin reuptake inhibitor enhances hepatic glucose disposal in conscious dogs

Intraportal delivery of serotonin enhanced net hepatic glucose uptake (NHGU) during a hyperinsulinemic hyperglycemic clamp, but serotonin elevated catecholamines and can cause gastrointestinal distress. We hypothesized that the selective serotonin reuptake inhibitor (SSRI) fluvoxamine would enhance NHGU without side effects. Arteriovenous difference and tracer ([3-(3)H]glucose) techniques were used in conscious 42-h-fasted dogs. Experiments consisted of equilibration (-120 to -30 min), basal (-30 to 0 min), and experimental (EXP; 0-270 min) periods. During EXP, somatostatin, fourfold basal intraportal insulin, basal intraportal glucagon, and peripheral glucose (to double the hepatic glucose load) were infused. Saline (SAL) was infused intraportally during 0-90 min (P1), and fluvoxamine was infused intraportally at 0.5, 1, and 2 mug.kg(-1).min(-1) from 90 to 150 (P2), 150 to 210 (P3), and 210 to 270 (P4) min, respectively, in the FLUV group (n = 8). The SAL group (n = 9) received intraportal saline during 0-270 min. NHGU in SAL was 13.9 +/- 1.7 and 17.0 +/- 2.0 mumol.kg(-1).min(-1) in P3-P4, respectively, while NHGU in FLUV averaged 19.7 +/- 2.8 and 26.6 +/- 3.0 mumol.kg(-1).min(-1) (P < 0.05 vs. SAL). Net hepatic carbon retention was greater (P < 0.05) in FLUV than in SAL (17.6 +/- 2.6 vs. 13.9 +/- 2.7 and 23.8 +/- 3.0 vs. 14.4 +/- 3.3 mumol.kg(-1).min(-1) in P3-P4, respectively), and final hepatic glycogen concentrations were 50% greater in FLUV (P < 0.005). Nonhepatic glucose uptake was greater in SAL than in FLUV at 270 min (P < 0.05). Catecholamine concentrations remained basal, and the animals evidenced no distress. Thus fluvoxamine enhanced NHGU and hepatic carbon storage without raising circulating serotonin concentrations or causing stress, suggesting that hepatic-targeted SSRIs might be effective in reducing postprandial hyperglycemia in individuals with diabetes or impaired glucose tolerance.

Impaired basal glucose effectiveness but unaltered fasting glucose release and gluconeogenesis during short-term hypercortisolemia in healthy subjects

Excess cortisol has been demonstrated to impair hepatic and extrahepatic insulin action. To determine whether glucose effectiveness and, in terms of endogenous glucose release (EGR), gluconeogenesis, also are altered by hypercortisolemia, eight healthy subjects were studied after overnight infusion with hydrocortisone or saline. Glucose effectiveness was assessed by a combined somatostatin and insulin infusion protocol to maintain insulin concentration at basal level in the presence of prandial glucose infusions. Despite elevated insulin concentrations (P < 0.05), hypercortisolemia resulted in higher glucose (P < 0.05) and free fatty acid concentrations (P < 0.05). Furthermore, basal insulin concentrations were higher during hydrocortisone than during saline infusion (P < 0.01), indicating the presence of steroid-induced insulin resistance. Postabsorptive glucose production (P = 0.64) and the fractional contribution of gluconeogenesis to EGR (P = 0.33) did not differ on the two study days. During the prandial glucose infusion, the integrated glycemic response above baseline was higher in the presence of hydrocortisone than during saline infusion (P < 0.05), implying a decrease in net glucose effectiveness (4.42 +/- 0.52 vs. 6.65 +/- 0.83 ml.kg-1.min-1; P < 0.05). To determine whether this defect is attributable to an impaired ability of glucose to suppress glucose production, to stimulate its own uptake, or both, glucose turnover and "hot" (labeled) indexes of glucose effectiveness (GE) were calculated. Hepatic GE was lower during cortisol than during saline infusion (2.39 +/- 0.24 vs. 3.82 +/- 0.51 ml.kg-1.min-1; P < 0.05), indicating a defect in the ability of glucose to restrain its own production. In addition, in the presence of excess cortisol, glucose disappearance was inappropriate for the prevailing glucose concentration, implying a decrease in glucose clearance (P < 0.05). The decrease in glucose clearance was confirmed by the higher increment in [3-3H]glucose during hydrocortisone than during saline infusion (P < 0.05), despite the administration of identical tracer infusion rates. In conclusion, short-term hypercortisolemia in healthy individuals with normal beta-cell function decreases insulin action but does not alter rates of EGR and gluconeogenesis. In addition, cortisol impairs the ability of glucose to suppress its own production, which due to accumulation of glucose in the glucose space results in impaired peripheral glucose clearance. These results suggest that cortisol excess impairs glucose tolerance by decreasing both insulin action and glucose effectiveness.

Acute glucocorticoid treatment increases urinary biotin excretion and serum biotin

Previous studies have demonstrated that glucocorticoids alter biotin metabolism. To extend these studies, the effect of dexamethasone on biotin pools was analyzed in rats consuming a purified diet containing a more physiological level of dietary biotin intake (0.06 mg/kg). Acute (5 h) dexamethasone administration (0.5 mg/kg) elicited elevated urinary glucose output as well as elevated urinary biotin excretion and serum biotin. Renal and hepatic free biotin was also significantly elevated by acute dexamethasone administration. Chow-fed rats treated with an acute administration of dexamethasone demonstrated significantly elevated urinary glucose excretion, urinary biotin excretion, and serum biotin, but no change in tissue associated biotin was detected. Chronic administration of dexamethasone (0.5 mg/kg ip) over 4 days significantly elevated urinary glucose excretion 42% but had no effect on urinary biotin excretion, serum biotin, or hepatic- or renal-associated free biotin. These results demonstrate the existence of potentially novel regulatory pathways for total biotin pools and the possibility that experimental models with high initial biotin status may mask potentially important regulatory mechanisms.

Insulin- and glucagon-independent effects of calcitonin gene-related peptide in the conscious dog

Calcitonin gene-related peptide (CGRP) causes vasodilation in many vascular beds, resulting in hypotension and tachycardia. The current studies were conducted in overnight-fasted conscious dogs to determine the effect of different CGRP dosages on carbohydrate metabolism and catecholamine release resulting from hemodynamic changes. During a pancreatic clamp, dogs received intraportal infusions of CGRP at 13, 26, and 52 (n = 3) or 52, 105, and 210 pmol x kg(-1) x min(-1) (n = 4; 60 minutes at each rate). Blood pressure decreased (P < .05) and the heart rate and hepatic blood flow (HBF) increased a maximum of 100% and 30%, respectively (P < .05). For the five CGRP infusion rates, arterial plasma epinephrine increased approximately 1.3-, 2.4-, 7.4-, 12-fold, and eightfold basal, respectively; norepinephrine increased about 2.3-, 3.3-, 4.1-, 4.6-, and 4.8-fold basal, respectively; and cortisol increased about twofold, 3.4-fold, fivefold, sixfold, and 6.2-fold basal, respectively. At CGRP infusion rates of 52 pmol x kg(-1) x min(-1) or higher, increases (P < .05) occurred for plasma glucose, endogenous glucose production (EndoRa), and net hepatic uptake of gluconeogenic substrates (maximum change, 24 mg/dL, 1.3 mg x kg(-1) x min(-1), and 9.9 micromol x kg(-1) x min(-1), respectively). Arterial blood glycerol concentrations increased only a maximum of 30%. At the two highest CGRP infusion rates, glycerol returned to basal concentrations and arterial plasma nonesterified fatty acids (NEFAs) decreased. The increased net hepatic uptake of gluconeogenic substrates during CGRP infusion was sufficient to account for 49% to 58% of the increase in EndoRa. CGRP has no apparent direct effects on hepatic carbohydrate metabolism, but the catecholamines, at levels similar to those observed during CGRP infusion, stimulate hepatic glycogenolysis. Therefore, some factor(s) other than CGRP, probably an increase in circulating catecholamine concentrations, would appear to be responsible for at least 42% to 51% of the increase in EndoRa.

Role of hepatic alpha- and beta-adrenergic receptor stimulation on hepatic glucose production during heavy exercise

The role of catecholamines in the control of hepatic glucose production was studied during heavy exercise in dogs, using a technique to selectively block hepatic alpha- and beta-adrenergic receptors. Surgery was done > 16 days before the study, at which time catheters were implanted in the carotid artery, portal vein, and hepatic vein for sampling and the portal vein and vena cava for infusions. In addition, flow probes were implanted on the portal vein and hepatic artery. Each study consisted of a 100-min equilibration, a 30-min basal, a 20-min heavy exercise (approximately 85% of maximum heart rate), a 30-min recovery, and a 30-min adrenergic blockade test period. Either saline (control; n = 7) or alpha (phentolamine)- and beta (propranolol)-adrenergic blockers (Blk; n = 6) were infused in the portal vein. In both groups, epinephrine (Epi) and norepinephrine (NE) were infused in the portal vein during the blockade test period to create supraphysiological levels at the liver. Isotope ([3-3H]glucose) dilution and arteriovenous differences were used to assess hepatic function. Arterial Epi, NE, glucagon, and insulin levels were similar during exercise in both groups. Endogenous glucose production (Ra) rose similarly during exercise to 7.9 +/- 1.2 and 7.5 +/- 2.0 mg.kg-1.min-1 in control and Blk groups at time = 20 min. Net hepatic glucose output also rose to a similar rate in control and Blk groups with exercise. During the blockade test period, arterial plasma glucose and Ra rose to 164 +/- 5 mg/dl and 12.0 +/- 1.4 mg.kg-1.min-1, respectively, but were essentially unchanged in Blk. The attenuated response to catecholamine infusion in Blk substantiates the effectiveness of the hepatic adrenergic blockade. In conclusion, these results show that direct hepatic adrenergic stimulation does not participate in the increase in Ra, even during the exaggerated sympathetic response to heavy exercise.

Effects of dexamethasone on hepatic glucose production and fructose metabolism in healthy humans

This study was designed to determine whether glucocorticoids alter autoregulation of glucose production and fructose metabolism. Two protocols with either dexamethasone (DEX) or placebo (Placebo) were performed in six healthy men during hourly ingestion of[13C]fructose (1.33 mmol.kg-1.h-1) for 3 h. In both protocols, endogenous glucose production (EGP) increased by 8 (Placebo) and 7% (DEX) after fructose, whereas gluconeogenesis from fructose represented 82 (Placebo) and 72% (DEX) of EGP. Fructose oxidation measured from breath 13CO2 was similar in both protocols [9.3 +/- 0.7 (Placebo) and 9.6 +/- 0.5 mumol.kg-1.min-1 (DEX)]. Nonoxidative carbohydrate disposal, calculated as fructose administration rate minus net carbohydrate oxidation rate after fructose ingestion measured by indirect calorimetry, was also similar in both protocols [5.8 +/- 0.8 (Placebo) and 5.9 +/- 2.0 mumol.kg-1.min-1 (DEX)]. We concluded that dexamethasone 1) does not alter the autoregulatory process that prevents a fructose-induced increase in gluconeogenesis from increasing total glucose production and 2) does not affect oxidative and nonoxidative pathways of fructose. This indicates that the insulin-regulated enzymes involved in these pathways are not affected in a major way by dexamethasone.

Role of cortisol in the metabolic response to stress hormone infusion in the conscious dog

The role of cortisol in directing the metabolic response to a combined infusion of glucagon, epinephrine, norepinephrine, and cortisol (stress hormones) was investigated. Chronically catheterized, conscious fasted dogs were studied before hormone infusion and after a 70-hour stress hormone infusion containing glucagon, epinephrine, norepinephrine, and cortisol (n = 11) or containing all these hormones except cortisol (n = 5). Combined stress hormone infusion increased arterial plasma glucagon, cortisol, epinephrine, and norepinephrine approximately sixfold. Whole-body glucose production (Ra), glycogenolysis, and gluconeogenesis were assessed using tracer and arteriovenous-difference techniques. The absence of an increase in cortisol during stress hormone infusion attenuated the increase in arterial plasma glucose concentration and Ra (delta 81 +/- 16 v 24 +/- 3 mg/dL and 1.7 +/- 0.3 v 0.8 +/- 0.4 mg/ kg/min, respectively). However, it did not alter the increase in net hepatic glucose output (delta 0.7 +/- 0.3 v 0.8 +/- 0.4 mg/kg/min). When the increase in cortisol was absent, the increase in net hepatic gluconeogenic precursor uptake was attenuated (delta 0.7 +/- 0.3 v 0.1 +/- 0.3 mg glucose/kg/min) due to a decrease in gluconeogenic precursor levels. The efficiency of gluconeogenesis increased to a greater extent (delta 0.19 +/- 0.07 v 0.31 +/- 0.11) when cortisol was not infused. The absence of an increase in cortisol also led to marked glycogen depletion in the liver (10 +/- 4 v 55 +/- 10 mg/g liver). Cortisol thus plays a pivotal role in the metabolic response to stress hormone infusion by sustaining gluconeogenesis through a stimulatory effect on hepatic gluconeogenic precursor supply and by maintaining hepatic glycogen availability.

Evidence that the brain of the conscious dog is insulin sensitive

The aim of this study was to determine whether a selective increase in the level of insulin in the blood perfusing the brain is a determinant of the counterregulatory response to hypoglycemia. Experiments were carried out on 15 conscious 18-h-fasted dogs. Insulin was infused (2 mU/kg per min) in separate, randomized studies into a peripheral vein (n = 7) or both carotid and vertebral arteries (n = 8). This resulted in equivalent systemic insulinemia (84 +/- 6 vs. 86 +/- 6 microU/ml) but differing insulin levels in the head (84 +/- 6 vs. 195 +/- 5 microU/ml, respectively). Glucose was infused during peripheral insulin infusion to maintain the glucose level (56 +/- 2 mg/dl) at a value similar to that seen during head insulin infusion (58 +/- 2 mg/dl). Despite equivalent peripheral insulin levels and similar hypoglycemia; steady state plasma epinephrine (792 +/- 198 vs. 2394 +/- 312 pg/ml), norepinephrine (404 +/- 33 vs. 778 +/- 93 pg/ml), cortisol (6.8 +/- 1.8 vs. 9.8 +/- 1.6 micrograms/dl) and pancreatic polypeptide (722 +/- 273 vs. 1061 +/- 255 pg/ml) levels were all increased to a greater extent during head insulin infusion (P < 0.05). Hepatic glucose production, measured with [3-3H]glucose, rose from 2.6 +/- 0.2 to 4.3 +/- 0.4 mg/kg per min (P < 0.01) in response to head insulin infusion but remained unchanged (2.6 +/- 0.5 mg/kg per min) during peripheral insulin infusion. Similarly, gluconeogenesis, lipolysis, and ketogenesis were increased twofold (P < 0.001) during head compared with peripheral insulin infusion. Cardiovascular parameters were also significantly higher (P < 0.05) during head compared with peripheral insulin infusion. We conclude that during hypoglycemia in the conscious dog (a) the brain is directly responsive to physiologic elevations of insulin and (b) the response includes a profound stimulation of the autonomic nervous system with accompanying metabolic and cardiovascular changes.

Inhibition of central GABAA receptors enhances hepatic glucose production and peripheral glucose uptake

Previous studies have demonstrated that intracerebroventricular (ICV) injection of bicuculline methiodide (BMI), a gamma-aminobutyric acid receptor antagonist, increases plasma glucose concentrations. The purpose of the present study was to determine whether the hyperglycemic response was due to an increased rate of hepatic glucose production (HGP) or a change in the rate of glucose utilization. In vivo glucose flux was assessed in catheterized, conscious overnight fasted rats using [3-3H]glucose. ICV injection of BMI (10 nmol) increased glucose levels 60% after 30 min. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of glucose utilization. No alteration in the glucose metabolic clearance rate, an index of the avidity of the body's tissues for glucose, was detected in BMI-injected rats. BMI enhanced both hepatic gluconeogenesis and glycogenolysis, since the reduction in liver glycogen (19 mumol/g liver) could not totally account for all of the increased HGP. These metabolic alterations were associated with sustained increases in circulating concentrations of corticosterone, glucagon and catecholamines. Prior adrenalectomy completely abolished the BMI-induced increase in glucose flux and the reduction in tissue glycogen, despite the persistent hyperglucagonemia. These data indicate that, in the fasted condition, the hyperglycemia produced by central administration of BMI results from an increased rate of HGP (both gluconeogenesis and glycogenolysis) and not a reduction in the ability of tissues to use glucose. The concomitant elevation in glucose disposal was the result of an increased mass action effect. The enhanced glucose metabolic response to BMI appears mediated exclusively by an increased secretion of epinephrine from the adrenal medulla.

Contribution of central and peripheral adrenergic stimulation to IL-1 alpha-mediated glucoregulation

The present study determined the contribution of central adrenoceptors and the peripheral sympathetic nervous system in regulating the hormonal and glucose metabolic response to intracerebroventricular injection of interleukin (IL)-1 alpha. After an overnight fast, hepatic glucose production (HGP) and peripheral glucose uptake (GU) were assessed in catheterized conscious unrestrained rats using [3-3H]glucose. Intracerebroventricular injection of IL-1 alpha (100 ng) produced a hyperglycemia that resulted from an early increase in HGP (108%) that exceeded a smaller elevation (82%) in GU. Intracerebroventricular injection of the alpha- and beta-adrenergic antagonists phentolamine and propranolol before IL-1 alpha blunted the glucose metabolic response 30-50%. This attenuated response was associated with normalization of the IL-1 alpha-induced hyperglucagonemia and hyperinsulinemia and a 50-60% reduction in the incremental increase in plasma catecholamines. In contrast to central administration, systemic infusion of adrenergic blockers completely prevented the IL-1 alpha-induced increases in plasma glucose, as well as HGP and GU. In these rats, the elevated plasma levels of insulin, glucagon, and corticosterone produced by intracerebroventricular injection of IL-1 alpha were still present. The results indicate that 1) the enhanced whole body glucose metabolism seen after central administration of IL-1 alpha is mediated by increased sympathoadrenal activity and 2) the IL-1 alpha-induced increase in pancreatic insulin and glucagon secretion as well as part of the peripheral catecholamine release is mediated by central adrenoreceptors.

Differential control of glucoregulatory hormone response and glucose metabolism by NMDA and kainate

The aim of the present study was to elucidate the effect of kainate and N-methyl-D-aspartate (NMDA), two different excitatory amino acid (EAA) agonists, on glucoregulatory hormone production and whole body glucose metabolism. Rates of hepatic glucose production (HGP) and peripheral glucose utilization (GU) were assessed in overnight fasted, catheterized, conscious rats using [3-3H]glucose. At the highest dose of kainate examined (16 mg/kg), glucose levels increased 97% after 1 h; thereafter, glucose fell towards basal values but was still elevated 25% at the end of the 3 h experiment. This hyperglycemia resulted from a rapid increase in HGP that exceeded an increased rate of GU. Both HGP and GU were elevated 86% throughout the final 2 h of the experiment. NMDA induced changes in glucose flux that were qualitatively similar, yet of smaller magnitude and of shorter duration, than those produced by kainate. Kainate-induced increases in glucose metabolism were associated with an early transient hyperinsulinemia followed by a period of insulinopenia, and sustained increases in the plasma concentrations of glucagon, corticosterone, epinephrine and norepinephrine. In contrast, sustained increases in glucagon and catecholamines, as well as the late hypoinsulinemia were not detected in NMDA-treated rats. Adrenergic blockade attenuated the kainate- but not the NMDA-induced increase in glucose metabolism. These results indicate that EAA agonists that bind preferentially to different receptor subtypes produce qualitatively similar changes in glucose metabolism. Whereas the increased HGP in kainate-injected rats was associated with sustained elevations in glucagon, catecholamines and corticosterone, NMDA only transiently elevated circulating glucocorticoid levels, suggesting a different mechanism of action. These data, support the involvement of EAA in various aspects of glucoregulation.