The direct effects of catecholamines on hepatic glucose production occur via alpha(1)- and beta(2)-receptors in the dog

Hepatic noradrenergic innervation acts via CREB/CRTC2 to activate gluconeogenesis during cold

BACKGROUND AND AIM

Although it is well established that hormones like glucagon stimulates gluconeogenesis via the PKA-mediated phosphorylation of CREB and dephosphorylation of the cAMP-regulated CREB coactivators CRTC2, the role of neural signals in the regulation of gluconeogenesis remains uncertain.

METHODS AND RESULTS

Here, we characterize the noradrenergic bundle architecture in mouse liver; we show that the sympathoexcitation induced by acute cold exposure promotes hyperglycemia and upregulation of gluconeogenesis via triggering of the CREB/CRTC2 pathway. Following its induction by dephosphorylation, CRTC2 translocates to the nucleus and drives the transcription of key gluconeogenic genes. Rodents submitted to different models of sympathectomy or knockout of CRTC2 do not activate gluconeogenesis in response to cold. Norepinephrine directly acts in hepatocytes mainly through a Ca2+-dependent pathway that stimulates CREB/CRTC2, leading to activation of the gluconeogenic program.

CONCLUSION

Our data demonstrate the importance of the CREB/CRTC2 pathway in mediating effects of hepatic sympathetic inputs on glucose homeostasis, providing new insights into the role of norepinephrine in health and disease.

Hepatic GRK2 is dispensable for glucose homeostasis and other key metabolic parameters in mice

OBJECTIVE

G-protein-coupled receptor (GPCR) kinases (GRKs) abrogate GPCR signaling by promoting receptor desensitization and internalization. Accumulating evidence suggests that GRK2 represents an important regulator of GPCR-mediated effects on systemic glucose metabolism, obesity, and insulin resistance. Despite the key role of the liver in maintaining euglycemia, the potential metabolic relevance of hepatic GRK2 has yet to be examined. Thus, the goal of this study was to explore the potential role of hepatic GRK2 in maintaining glucose homeostasis and other key metabolic functions.

METHODS

To address this question, we generated mice that showed a ∼90% reduction in GRK2 protein expression selectively in hepatocytes (Hep-GRK2-KO mice) and subjected these mice, together with their control littermates, to systematic metabolic phenotyping studies.

RESULTS

We found that Hep-GRK2-KO mice maintained on regular chow did not differ significantly from their control littermates in glycemia, glucose tolerance, insulin sensitivity, in vivo gluconeogenesis, and glucagon-induced hyperglycemia. We obtained similar findings when we analyzed Hep-GRK2-KO mice and control littermates consuming an obesogenic high-fat diet. Likewise, plasma levels of insulin, glucagon, free fatty acids, and ketone bodies remained unaffected by the lack of hepatocyte GRK2. The same was true when we examined the expression levels of key genes regulating hepatic glucose and fatty acid metabolism.

CONCLUSION

In summary, our data suggest that hepatocyte GRK2 is dispensable for systemic glucose homeostasis and other key metabolic functions in both lean and obese mice. This finding suggests that drug development efforts aimed at inhibiting GRK2 to improve impaired glucose homeostasis and insulin sensitivity need to focus on other metabolically important tissues.

Characterization of Chicken α2A-Adrenoceptor: Molecular Cloning, Functional Analysis, and Its Involvement in Ovarian Follicular Development

Adrenoceptors are suggested to mediate the functions of norepinephrine (NE) and epinephrine (EPI) in the central nervous system (CNS) and peripheral tissues in vertebrates. Compared to mammals, the functionality and expression of adrenoceptors have not been well characterized in birds. Here, we reported the structure, expression, and functionality of chicken functional α_2A-adrenoceptor, named ADRA2A. The cloned chicken ADRA2A cDNA is 1335 bp in length, encoding the receptor with 444 amino acids (a.a.), which shows high amino acid sequence identity (63.4%) with its corresponding ortholog in humans. Using cell-based luciferase reporter assays and Western blot, we demonstrated that the ADRA2A could be activated by both NE and EPI through multiple signaling pathways, including MAPK/ERK signaling cascade. In addition, the mRNA expression of ADRA2A is found to be expressed abundantly in adult chicken tissues including thyroid, lung, ovary and adipose from the reported RNA-Seq data sets. Moreover, the mRNA expression of ADRA2A is also found to be highly expressed in the granulosa cells of 6–8 mm and F5 chicken ovarian follicles, which thus supports that ADRA2A signaling may play a role in ovarian follicular growth and differentiation. Taken together, our data provide the first proof that the α_2A-adrenoceptor is functional in birds involving avian ovarian follicular development.

The Role of Catecholamines in Pathophysiological Liver Processes

Over the last few years, the number of research publications about the role of catecholamines (epinephrine, norepinephrine, and dopamine) in the development of liver diseases such as liver fibrosis, fatty liver diseases, or liver cancers is constantly increasing. However, the mechanisms involved in these effects are not well understood. In this review, we first recapitulate the way the liver is in contact with catecholamines and consider liver implications in their metabolism. A focus on the expression of the adrenergic and dopaminergic receptors by the liver cells is also discussed. Involvement of catecholamines in physiological (glucose metabolism, lipids metabolism, and liver regeneration) and pathophysiological (impact on drug-metabolizing enzymes expression, liver dysfunction during sepsis, fibrosis development, or liver fatty diseases and liver cancers) processes are then discussed. This review highlights the importance of understanding the mechanisms through which catecholamines influence liver functions in order to draw benefit from the adrenergic and dopaminergic antagonists currently marketed. Indeed, as these molecules are well-known drugs, their use as therapies or adjuvant treatments in several liver diseases could be facilitated.

Current Developments on the Role of α1-Adrenergic Receptors in Cognition, Cardioprotection, and Metabolism

The α₁-adrenergic receptors (ARs) are G-protein coupled receptors that bind the endogenous catecholamines, norepinephrine, and epinephrine. They play a key role in the regulation of the sympathetic nervous system along with β and α₂-AR family members. While all of the adrenergic receptors bind with similar affinity to the catecholamines, they can regulate different physiologies and pathophysiologies in the body because they couple to different G-proteins and signal transduction pathways, commonly in opposition to one another. While α₁-AR subtypes (α_1A, α_1B, α_1C) have long been known to be primary regulators of vascular smooth muscle contraction, blood pressure, and cardiac hypertrophy, their role in neurotransmission, improving cognition, protecting the heart during ischemia and failure, and regulating whole body and organ metabolism are not well known and are more recent developments. These advancements have been made possible through the development of transgenic and knockout mouse models and more selective ligands to advance their research. Here, we will review the recent literature to provide new insights into these physiological functions and possible use as a therapeutic target.

Regulation of systemic metabolism by the autonomic nervous system consisting of afferent and efferent innervation

Autonomic nerves, sympathetic and parasympathetic, innervate organs and modulate their functions. It has become evident that afferent and efferent signals of the autonomic nervous system play important roles in regulating systemic metabolism, thereby maintaining homeostasis at the whole-body level. Vagal afferent nerves receive signals, such as nutrients and hormones, from the peripheral organs/tissues including the gastrointestinal tract and adipose tissue then transmit these signals to the hypothalamus, thereby regulating feeding behavior. In addition to roles in controlling appetite, areas in the hypothalamus serves as regulatory centers of both sympathetic and parasympathetic efferent fibers. These efferent innervations regulate the functions of peripheral organs/tissues, such as pancreatic islets, adipose tissues and the liver, which play roles in metabolic regulation. Furthermore, recent evidence has unraveled the metabolic regulatory systems governed by autonomic nerve circuits. In these systems, afferent nerves transmit metabolic information from peripheral organs to the central nervous system (CNS) and the CNS thereby regulates the organ functions through the efferent fibers of autonomic nerves. Thus, the autonomic nervous system regulates the homeostasis of systemic metabolism, and both afferent and efferent fibers play critical roles in its regulation. In addition, several lines of evidence demonstrate the roles of the autonomic nervous system in regulating and dysregulating the immune system. This review introduces variety of neuron-mediated inter-organ cross-talk systems and organizes the current knowledge of autonomic control/coordination of systemic metabolism, focusing especially on a liver-brain-pancreatic β-cell autonomic nerve circuit, as well as highlighting the potential importance of connections with the neuronal and immune systems.

Sepsis as a Pan-Endocrine Illness-Endocrine Disorders in Septic Patients

Sepsis is defined as "life-threatening organ dysfunction caused by a dysregulated host response to infection". One of the elements of dysregulated host response is an endocrine system disorder. Changes in its functioning in the course of sepsis affect almost all hormonal axes. In sepsis, a function disturbance of the hypothalamic-pituitary-adrenal axis has been described, in the range of which the most important seems to be hypercortisolemia in the acute phase. Imbalance in the hypothalamic-pituitary-thyroid axis is also described. The most typical manifestation is a triiodothyronine concentration decrease and reverse triiodothyronine concentration increase. In the somatotropic axis, a change in the secretion pattern of growth hormone and peripheral resistance to this hormone has been described. In the hypothalamic-pituitary-gonadal axis, the reduction in testosterone concentration in men and the stress-induced "hypothalamic amenorrhea" in women have been described. Catecholamine and β-adrenergic stimulation disorders have also been reported. Disorders in the endocrine system are part of the "dysregulated host response to infection". They may also affect other components of this dysregulated response, such as metabolism. Hormonal changes occurring in the course of sepsis require further research, not only in order to explore their potential significance in therapy, but also due to their promising prognostic value.

GPCRs and Insulin Receptor Signaling in Conversation: Novel Avenues for Drug Discovery

Type 2 diabetes is a major health issue worldwide with complex metabolic and endocrine abnormalities. Hyperglycemia, defects in insulin secretion and insulin resistance are classic features of type 2 diabetes. Insulin signaling regulates metabolic homeostasis by regulating glucose and lipid turnover in the liver, skeletal muscle and adipose tissue. Major treatment modalities for diabetes include the drugs from the class of sulfonyl urea, Insulin, GLP-1 agonists, SGLT2 inhibitors, DPP-IV inhibitors and Thiazolidinediones. Emerging antidiabetic therapeutics also include classes of drugs targeting GPCRs in the liver, adipose tissue and skeletal muscle. Interestingly, recent research highlights several shared intermediates between insulin and GPCR signaling cascades opening potential novel avenues for diabetic drug discovery.

Intra-islet glucagon signaling is critical for maintaining glucose homeostasis

Glucagon, a hormone released from pancreatic alpha-cells, plays a key role in maintaining proper glucose homeostasis and has been implicated in the pathophysiology of diabetes. In vitro studies suggest that intra-islet glucagon can modulate the function of pancreatic beta-cells. However, because of the lack of suitable experimental tools, the in vivo physiological role of this intra-islet cross-talk has remained elusive. To address this issue, we generated a novel mouse model that selectively expressed an inhibitory designer G protein-coupled receptor (Gi DREADD) in α-cells only. Drug-induced activation of this inhibitory designer receptor almost completely shut off glucagon secretion in vivo, resulting in significantly impaired insulin secretion, hyperglycemia, and glucose intolerance. Additional studies with mouse and human islets indicated that intra-islet glucagon stimulates insulin release primarily by activating β-cell GLP-1 receptors. These new findings strongly suggest that intra-islet glucagon signaling is essential for maintaining proper glucose homeostasis in vivo. Our work may pave the way toward the development of novel classes of antidiabetic drugs that act by modulating intra-islet cross-talk between α- and β-cells.

Continuous Glucose Monitoring for Hypoglycemia Avoidance and Glucose Counterregulation in Long-Standing Type 1 Diabetes

CONTEXT

Patients with long-standing type 1 diabetes (T1D) are at increased risk for severe hypoglycemia because of defects in glucose counterregulation and recognition of hypoglycemia symptoms, in part mediated through exposure to hypoglycemia.

OBJECTIVE

To determine whether implementation of real-time continuous glucose monitoring (CGM) as a strategy for hypoglycemia avoidance could improve glucose counterregulation in patients with long-standing T1D and hypoglycemia unawareness.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTION

Eleven patients with T1D disease duration of ∼31 years were studied longitudinally in the Clinical & Translational Research Center of the University of Pennsylvania before and 6 and 18 months after initiation of CGM and were compared with 12 nondiabetic control participants.

MAIN OUTCOME MEASURE

Endogenous glucose production response derived from paired hyperinsulinemic stepped-hypoglycemic and euglycemic clamps with infusion of 6,6-2H2-glucose.

RESULTS

In patients with T1D, hypoglycemia awareness (Clarke score) and severity (HYPO score and severe events) improved (P < 0.01 for all) without change in hemoglobin A1c (baseline, 7.2% ± 0.2%). In response to insulin-induced hypoglycemia, endogenous glucose production did not change from before to 6 months (0.42 ± 0.08 vs 0.54 ± 0.07 mg·kg-1·min-1) but improved after 18 months (0.84 ± 0.15 mg·kg-1·min-1; P < 0.05 vs before CGM), albeit remaining less than in controls (1.39 ± 0.11 mg·kg-1·min-1; P ≤ 0.01 vs all).

CONCLUSIONS

Real-time CGM can improve awareness and reduce the burden of problematic hypoglycemia in patients with long-standing T1D, but with only modest improvement in the endogenous glucose production response that is required to prevent or correct low blood glucose.

Glucose autoregulation is the dominant component of the hormone-independent counterregulatory response to hypoglycemia in the conscious dog

The contribution of hormone-independent counterregulatory signals in defense of insulin-induced hypoglycemia was determined in adrenalectomized, overnight-fasted conscious dogs receiving hepatic portal vein insulin infusions at a rate 20-fold basal. Either euglycemia was maintained (group 1) or hypoglycemia (≈45 mg/dl) was allowed to occur. There were three hypoglycemic groups: one in which hepatic autoregulation against hypoglycemia occurred in the absence of sympathetic nervous system input (group 2), one in which autoregulation occurred in the presence of norepinephrine (NE) signaling to fat and muscle (group 3), and one in which autoregulation occurred in the presence of NE signaling to fat, muscle, and liver (group 4). Average net hepatic glucose balance (NHGB) during the last hour for groups 1-4 was -0.7 ± 0.1, 0.3 ± 0.1 (P < 0.01 vs. group 1), 0.7 ± 0.1 (P = 0.01 vs. group 2), and 0.8 ± 0.1 (P = 0.7 vs. group 3) mg·kg^-1·min^-1, respectively. Hypoglycemia per se (group 2) increased NHGB by causing an inhibition of net hepatic glycogen synthesis. NE signaling to fat and muscle (group 3) increased NHGB further by mobilizing gluconeogenic precursors resulting in a rise in gluconeogenesis. Lowering glucose per se decreased nonhepatic glucose uptake by 8.9 mg·kg^-1·min^-1, and the addition of increased neural efferent signaling to muscle and fat blocked glucose uptake further by 3.2 mg·kg^-1·min^-1 The addition of increased neural efferent input to liver did not affect NHGB or nonhepatic glucose uptake significantly. In conclusion, even in the absence of increases in counterregulatory hormones, the body can defend itself against hypoglycemia using glucose autoregulation and increased neural efferent signaling, both of which stimulate hepatic glucose production and limit glucose utilization.

Cannabinoid CB1 receptor inverse agonist MJ08 stimulates glucose production via hepatic sympathetic innervation in rats

As a key insulin target tissue for maintaining systemic glucose homeostasis, the liver plays important roles in improving obesity-associated insulin intolerance via selective cannabinoid CB₁ receptor antagonism/inverse agonism. However, it is unclear whether this receptor inverse agonism affects hepatic glucose metabolism. MJ08 is a novel cannabinoid CB₁ receptor antagonist/inverse agonist that has superior inverse agonism over the well-known antagonist/inverse agonist, SR141716 (rimonabant). MJ08 remarkably elevates fasting blood glucose independent of inhibition of insulin release in mice. In the current study, MJ08 was used to investigate the mechanism by which liver cannabinoid CB₁ receptor inverse activation regulates hepatic glucose metabolism. MJ08 stimulated hepatic glucose production (HGP) in a dose-dependent manner and promoted gluconeogenic gene expression in perfused rat liver. SR141716 exhibited similar but weaker effects. The cannabinoid CB₁ receptor agonist (WIN 55,212-2), Gs protein-cyclic AMP (cAMP)-dependent pathway inhibitors (NF449 and H89), β-adrenoceptor antagonist (propranolol), and peripheral sympathetic inhibitor (reserpine) could antagonize MJ08-induced HGP. Furthermore, MJ08 and SR141716 induced monoamine neurotransmitter (noradrenaline) release and increased cAMP content significantly in perfused liver, although only a slight increase was observed in primary cultured hepatocytes. These results indicate that local liver cannabinoid CB₁ receptor inverse agonism via hepatic sympathetic innervation is responsible for the HGP induced by MJ08. Thus, high inverse agonistic activity could increase fasting blood glucose levels and should be avoided in the development of peripheral cannabinoid CB₁ receptor-targeted weight-loss drugs.

Metabolism, Metabolomics, and Nutritional Support of Patients with Sepsis

Sepsis is characterized by profound changes in systemic and cellular metabolism that disrupt normal metabolic homeostasis. These metabolic changes can serve as biomarkers for disease severity. Lactate, a metabolite of anaerobic metabolism, is the most widely used ICU biomarker and it is incorporated into multiple management algorithms. Technological advances now make broader metabolic profiling possible, with early studies identifying metabolic changes associated with sepsis mortality. Finally, given the marked changes in metabolism in sepsis and the association of worse prognosis in patients with severe metabolic derangements, we summarize the seminal trials conducted to optimize nutrition in the ICU.

Impaired hepatic counterregulatory response to insulin-induced hypoglycemia in hepatic denervated pigs

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Hepatic denervation results in a blunted counterregulatory response during insulin-induced hypoglycemia.

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Fasting glucose concentration, glucose production and uptake are unaffected by hepatic denervation.

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Insulin action and extrahepatic glucose uptake are unaffected by hepatic denervation.

Objective

The liver reacts to hypoglycemia by increasing its glucose output. This response is assumed to depend both on glucose sensing at the liver and the brain, as well as efferent impulses from the brain to the liver. We tested the importance of this signaling pathway by studying the hepatic response to insulin-induced hypoglycemia in hepatic complete denervated pigs.

Materials/methods

Two weeks prior to the metabolic study, 36-kg pigs underwent either total hepatic denervation (DN; n = 12) or sham operation (sham; n = 12). On the metabolic study day, measurements were performed at baseline conditions and during a hypoglycemic hyperinsulinemic (5 mU/kg/min) clamp. Endogenous insulin and glucagon secretions were inhibited by somatostatin, and glucagon was replaced at baseline levels. Endogenous glucose production (EGP) and glucose utilization (Rd) were determined by [3-³H] glucose infusion.

Results

Baseline plasma concentrations of glucose, insulin, EGP and Rd did not differ significantly between the two groups of animals. During insulin infusion, the plasma glucose concentration was clamped at ~3 mmol/L in both groups of animals resulting in an increase in plasma concentrations of epinephrine and norepinephrine in sham pigs (both P < 0.05), while this effect was abolished in DN pigs. While insulin action (P = 0.09) and glucose utilization (P = 0.44) were similar, EGP was markedly decreased in the DN pigs (P < 0.05).

Conclusion

The findings indicate a blunted hepatic counterregulatory response to hypoglycemia following complete hepatic denervation. This implies that intact neural impulses to and from the liver are necessary to maintain the increase in EGP that protects the organism against hypoglycemia.

Beta-blockers in septic shock: a review

In septic shock, high adrenergic stress is associated with cardiovascular and systemic adverse effects, which can negatively affect the results. Beta-adrenergic receptor block has been shown to be effective in controlling the disproportionate increase in heart rate, maintaining a favorable hemodynamic profile and apparently improving the efficiency of the cardiovascular system in order to maintain tissue perfusion. They have also been shown to modulate favorably catecholamine-induced immunosuppression and to decrease insulin resistance, protein catabolism, and proinflammatory cytokine expression associated with cardiovascular dysfunction. Selective beta-1 blockers appear to provide better results than non-selective blockers, even suggesting a positive impact on mortality. Future clinical trials are still needed to confirm these findings and define the scope of their benefits.

Beta-blocker use in severe sepsis and septic shock: a systematic review

OBJECTIVE

Recent growing evidence suggests that beta-blocker treatment could improve cardiovascular dynamics and possibly the outcome of patients admitted to intensive care with severe sepsis or septic shock.

DESIGN

Systematic review.

DATA SOURCES

MEDLINE and EMBASE healthcare databases.

REVIEW METHODS

To investigate this topic, we conducted a systematic review of the above databases up to 31 May 2015. Due to the clinical novelty of the subject, we also included non-randomized clinical studies. We focused on the impact of beta-blocker treatment on mortality, also investigating its effects on cardiovascular, immune and metabolic function. Evidence from experimental studies was reviewed as well.

RESULTS

From the initial search we selected 10 relevant clinical studies. Five prospective studies (two randomized) assessed the hemodynamic effects of the beta1-blocker esmolol. Heart rate decreased significantly in all, but the impact on other parameters differed. The imbalance between prospective studies' size (10 to 144 patients) and the differences in their design disfavor a meta-analysis. One retrospective study showed improved hemodynamics combining metoprolol and milrinone in septic patients, and another retrospective study found no association between beta-blocker administration and mortality. We also found three case series. Twenty-one experimental studies evaluated the hemodynamic, immune and/or metabolic effects of selective and/or non-selective beta-blockers in animal models of sepsis (dogs, mice, pigs, rats, sheep), yielding conflicting results.

CONCLUSIONS

Whilst there is not enough prospective data to conduct a meta-analysis, the available clinical data are promising. We discuss the ability of beta blockade to modulate sepsis-induced alterations at cardiovascular, metabolic, immunologic and coagulation levels.

Nicotinic acetylcholine receptors in glucose homeostasis: the acute hyperglycemic and chronic insulin-sensitive effects of nicotine suggest dual opposing roles of the receptors in male mice

Cigarette smoking causes insulin resistance. However, nicotine induces anti-inflammation and improves glucose tolerance in insulin-resistant animal models. Here, we determined the effects of nicotine on glucose metabolism in insulin-sensitive C57BL/J6 mice. Acute nicotine administration (30 min) caused fasting hyperglycemia and lowered insulin sensitivity acutely, which depended on the activation of nicotinic-acetylcholine receptors (nAChRs) and correlated with increased catecholamine secretion, nitric oxide (NO) production, and glycogenolysis. Chlorisondamine, an inhibitor of nAChRs, reduced acute nicotine-induced hyperglycemia. qRT-PCR analysis revealed that the liver and muscle express predominantly β4 > α10 > α3 > α7 and β4 > α10 > β1 > α1 mRNA for nAChR subunits respectively, whereas the adrenal gland expresses β4 > α3 > α7 > α10 mRNA. Chronic nicotine treatment significantly suppressed expression of α3-nAChR (predominant peripheral α-subunit) in liver. Whereas acute nicotine treatment raised plasma norepinephrine (NE) and epinephrine (Epi) levels, chronic nicotine exposure raised only Epi. Acute nicotine treatment raised both basal and glucose-stimulated insulin secretion (GSIS). After chronic nicotine treatment, basal insulin level was elevated, but GSIS after acute saline or nicotine treatment was blunted. Chronic nicotine exposure caused an increased buildup of NO in plasma and liver, leading to decreased glycogen storage, along with a concomitant suppression of Pepck and G6Pase mRNA, thus preventing hyperglycemia. The insulin-sensitizing effect of chronic nicotine was independent of weight loss. Chronic nicotine treatment enhanced PI-3-kinase activities and increased Akt and glycogen synthase kinase (GSK)-3β phosphorylation in an nAChR-dependent manner coupled with decreased cAMP response element-binding protein (CREB) phosphorylation. The latter effects caused suppression of Pepck and G6Pase gene expression. Thus, nicotine causes both insulin resistance and insulin sensitivity depending on the duration of the treatment.

Seasonal changes in the activity of the adrenal medulla of Viscacha (Lagostomus maximus maximus)

Animals living in nontropical climates modify their physiology and behavior to adapt to seasonal environmental changes. Part of this adaptation involves the release of catecholamine from sympathetic nerve endings and the adrenal medulla, which play a major role in regulating energy balance. The aim of this work was to investigate whether adult male viscachas in their natural habitat exhibits structural changes in the adrenal medulla during the annual seasonal cycle. In August-September, chromaffin granules revealed ultrastructural changes suggestive of piecemeal degranulation. Quantitative morphometric analysis by transmission electron microscopy showed a significantly lower percentage of resting chromaffin granules and a higher percentage of altered granules and empty containers in August-September (late winter) compared to February-March (late summer), suggesting an increased secretory process of catecholamines in August-September. The mechanism of piecemeal degranulation might amplify this process, encouraging the adaptive response to winter environmental conditions. Tissue levels of epinephrine, norepinephrine, and dopamine (analyzed by high-performance liquid chromatography) changed throughout the year, reaching maximum values in February-March and minimum values in August-September. These results demonstrate morphological and biochemical seasonal variations of the adrenal medulla, suggesting that epinephrine might promote energy mobilization, which allow the Lagostomus to cope with adverse environmental conditions and thus to survive during winter season.

Peripheral adrenoceptors: the impetus behind glucose dysregulation and insulin resistance

It is now accepted that several pharmacological drug treatments trigger clinical manifestations of glucose dysregulation, such as hyperglycaemia, glucose intolerance and insulin resistance, in part through poorly understood mechanisms. Persistent sympathoadrenal activation is linked to glucose dysregulation and insulin resistance, both of which significantly increase the risk of emergent endocrinological disorders, including metabolic syndrome and type 2 diabetes mellitus. Through the use of targeted mutagenesis and pharmacological methods, preclinical and clinical research has confirmed physiological glucoregulatory roles for several peripheral α- and β-adrenoceptor subtypes. Adrenoceptor isoforms in the pancreas (α(2A) and β(2) ), skeletal muscle (α(1A) and β(2) ), liver (α(1A & B) and β(2) ) and adipose tissue (α(1A) and β(1 & 3) ) are convincing aetiological targets that account for both immediate and long-lasting alterations in blood glucose homeostasis. Because significant overlap exists between the therapeutic applications of numerous classes of drugs and their associated adverse side-effects, a better understanding of peripheral adrenoceptor-mediated glucose metabolism is thus warranted. Therefore, at the same time as providing a brief review of glucose homeostasis in the periphery, the present review addresses both functional and pathophysiological roles of the mammalian α(1) , α(2) , and β-adrenoceptor isoforms in whole-body glucose turnover. We highlight evidence relating to the clinical use of common adrenergic drugs and their impacts on glucose metabolism.

Plasma glucose, insulin, free fatty acids, lactate and cortisol concentrations in dexmedetomidine-sedated dogs with or without MK-467: a peripheral α-2 adrenoceptor antagonist

Six healthy laboratory Beagles were treated IV with 10 μg/kg dexmedetomidine (DEX) or 10 μg/kg dexmedetomidine combined with 500 μg/kg MK-467 in the same syringe (DMK) in a randomised cross-over design with a 14 day washout. Blood was collected immediately before treatment and 35, 60 and 120 min post-injection through a central venous catheter. The plasma concentrations of glucose, insulin, non-esterified free fatty acids (NEFAs), lactate and cortisol were determined. A repeated-measures ANOVA test was used to compare treatments and effects for each sample time point. Significant differences between treatments were found for plasma glucose (P=0.037) and insulin (P=0.009). DEX significantly increased plasma glucose at 120 min, but reduced plasma insulin at 35 and 60 min. NEFA decreased for both treatments at 35 min. This reduction was transient for DMK, whereas it persisted during the follow up period for DEX. Plasma lactate concentrations increased at 35 and 60 min with DEX. Neither treatment altered plasma cortisol concentrations. The addition of MK-467 to dexmedetomidine prevented or abolished most metabolic changes in healthy Beagles.

The melanocortin system is involved in regulating autonomic nerve activity through central pituitary adenylate cyclase-activating polypeptide

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a peptidergic neurotransmitter that is highly expressed in the nervous system. We have previously reported that a central injection of PACAP leads to changes in the autonomic nervous system tones including sympathetic excitation and parasympathetic inhibition. An anatomical study revealed that melanocortin and PACAP are colocalized in some hypothalamic nuclei. Here, we investigated the possible role of the melanocortin system in autonomic control by PACAP using SHU9119, an antagonist of the melanocortin receptors (MC3-R/MC4-R). Pretreatment with SHU-9119 did not affect the activating neural responses of adrenal, renal, and lumbar sympathetic nerves following a PACAP injection However, SHU9119 significantly eliminated the suppressing effect of a PACAP injection on gastric vagal nerve activity and excitation effects on liver and brown adipose tissue sympathetic nerve activities. These results suggest that the brain melanocortin system might play a key role in the control of thermogenic sympathetic outflows and digestive parasympathetic outflow by PACAP, but this system does not participate in the central effects of PACAP on cardiovascular function and neural activities of renal, adrenal, and lumbar sympathetic nerves.

Pulsatile changes in free fatty acids augment hepatic glucose production and preserves peripheral glucose homeostasis

Recent studies in animal and human models have revealed that free fatty acid (FFA) release from adipose tissue is oscillatory. We have shown in our laboratory that these oscillations are controlled by the sympathetic nervous system (SNS). Although FFAs have been shown to directly stimulate glucose production [endogenous glucose production (EGP)] by the liver and to reduce peripheral glucose utilization, whether the specific pattern of FFA release affects glucose metabolism is unknown. The aim of this study was to examine the effects of pulsatile vs. constant infusion of FFA on glucose homeostasis in the canine model. Euglycemic clamps with basal insulin replacement (0.1 mU.kg(-1).min(-1) insulin) were performed in dogs (n = 8) during infusion of saline (SAL) or the medium-chain fatty acid octanoate, which was given by either pulsatile infusion (PUL: 10 mmol over 2 min every 10 min) or continuous infusion (C-INF: 1 mmol/min) designed to achieve equivalent total FFA mass. Endogenous lipolytic pulses were suppressed with the beta(3)-specific adrenergic receptor antagonist bupranolol. PUL infusion elicited a pulsatile pattern of FFA in circulation with average maximum pulse height of 0.82 +/- 0.04 mM, whereas C-INF FFA levels reached 0.47 +/- 0.03 mM (fasting levels) and were maintained throughout. Glucose uptake was not affected by PUL; however, C-INF significantly reduced glucose uptake compared with both SAL and PUL. Steady-state EGP increased by >90% from basal steady state during PUL but did not change during either SAL or C-INF. Thus, pulsatile FFA infusion led to an increase in EGP while preserving glucose disposal. These data suggest that the pattern of FFA may have a role in regulation of glucose homeostasis, which may have consequences in the obese or insulin-resistant state where the SNS is known to be altered.

Greater systemic lipolysis in women compared with men during moderate-dose infusion of epinephrine and/or norepinephrine

Women have lower circulating catecholamine levels during metabolic perturbations, such as exercise or hypoglycemia, but similar rates of systemic lipolysis. This suggests women may be more sensitive to the lipolytic action of catecholamines, while maintaining similar glucoregulatory effects. The aim of the present study, therefore, was to determine whether women have higher rates of systemic lipolysis compared with men in response to matched peripheral infusion of catecholamines, but similar rates of glucose turnover. Healthy, nonobese women (n = 11) and men (n = 10) were recruited and studied on 3 separate days with the following infusions: epinephrine (Epi), norepinephrine (NE), or the two combined. Tracer infusions of glycerol and glucose were used to determine systemic lipolysis and glucose turnover, respectively. Following basal measurements of substrate kinetics, the catecholamine infusion commenced, and measures of substrate kinetics continued for 60 min. Catecholamine concentrations were similarly elevated in women and men during each infusion: Epi, 182-197 pg/ml and NE, 417-507 pg/ml. There was a significant sex difference in glycerol rate of appearance and rate of disappearance with the catecholamine infusions (P < 0.0001), mainly due to a significantly greater glycerol turnover during the first 30 min of each infusion: glycerol rate of appearance during Epi was only 268 +/- 18 vs. 206 +/- 21 micromol/min in women and men, respectively; during NE, only 173 +/- 13 vs. 153 +/- 17 micromol/min, and during Epi+NE, 303 +/- 24 vs. 257 +/- 21 micromol/min. No sex differences were observed in glucose kinetics under any condition. In conclusion, these data suggest that women are more sensitive to the lipolytic action of catecholamines, but have no difference in their glucoregulatory response. Thus the lower catcholamine levels observed in women vs. men during exercise and other metabolic perturbations may allow women to maintain a similar or greater level of lipid mobilization while minimizing changes in glucose turnover.

alpha2A-adrenoceptor antagonism increases insulin secretion and synergistically augments the insulinotropic effect of glibenclamide in mice

BACKGROUND AND PURPOSE

The imidazoline-type alpha2-adrenoceptor antagonists (+/-)-efaroxan and phentolamine increase insulin secretion and reduce blood glucose levels. It is not known whether they act by antagonizing pancreatic beta-cell alpha2-adrenoceptors or by alpha2-adrenoceptor-independent mechanisms. Many imidazolines inhibit the pancreatic beta-cell KATP channel, which is the molecular target of sulphonylurea drugs used in the treatment of type II diabetes. To investigate the mechanisms of action of (+/-)-efaroxan and phentolamine, alpha2A-adrenoceptor knockout (alpha2A-KO) mice were used.

EXPERIMENTAL APPROACH

Effects of (+/-)-efaroxan, 5 mg kg(-1), and phentolamine, 1 mg kg(-1), on blood glucose and insulin levels were compared with those of the non-imidazoline alpha2-adrenoceptor antagonist [8aR,12aS,13aS]-5,8,8a,9,10,11,12,12a,13,13a-decahydro-3-methoxy-12-(ethylsulphonyl)-6H-isoquino[2,1-g][1,6]naphthyridine (RS79948-197), 1 mg kg(-1), and the sulphonylurea glibenclamide, in alpha2A-KO and control (wild type (WT)) mice.

KEY RESULTS

In fed WT mice, (+/-)-efaroxan, phentolamine and RS79948-197 reduced blood glucose and increased insulin levels. Fasting abolished these effects. In fed alpha2A-KO mice, (+/-)-efaroxan, phentolamine and RS79948-197 did not alter blood glucose or insulin levels, and in fasted alpha2A-KO mice, blood glucose levels were increased. Glibenclamide, at a dose only moderately efficacious in WT mice (5 mg kg(-1)), caused severe hyperinsulinaemia and hypoglycaemia in alpha2A-KO mice. This was mimicked in WT mice by co-administration of RS79948-197 with glibenclamide.

CONCLUSIONS AND IMPLICATIONS

These results suggest that (+/-)-efaroxan and phentolamine increase insulin secretion by inhibition of beta-cell alpha2A-adrenoceptors, and demonstrate a critical role for alpha2A-adrenoceptors in limiting sulphonylurea-induced hyperinsulinaemia and hypoglycaemia.

Doxazosin in metabolically complicated hypertension

Metabolic syndrome, a cluster of metabolic abnormalities with visceral obesity and insulin resistance as its central component, is highly prevalent among hypertensive patients. Hypertension complicated by metabolic syndrome is associated with an increased risk of cardiovascular disease and new-onset Type II diabetes mellitus that further aggravates the prognostic outlook. Such a complex condition requires a multifactorial intervention including blood pressure lowering, improvement of the adverse metabolic profile and delayed onset of new diabetes. In this respect, doxazosin and other alpha-1 adrenoceptor blocking agents are of interest given their effect on the lipid profile in dyslipidemic, obese hypertensive patients, either diabetic or not. Doxazosin improves insulin sensitivity, apparently by accelerating insulin and glucose disposal through vasodilatation of skeletal muscle vascular beds. Whether long-term treatment with the drug might delay, or possibly prevent, incident Type II diabetes in hypertension complicated by metabolic syndrome is an intriguing possibility to be tested in appropriately designed clinical trials.

Increased insulin sensitivity and maintenance of glucose utilization rates in fetal sheep with placental insufficiency and intrauterine growth restriction

In this study we determined body weight-specific fetal (umbilical) glucose uptake (UGU), utilization (GUR), and production rates (GPR) and insulin action in intrauterine growth-restricted (IUGR) fetal sheep. During basal conditions, UGU from the placenta was 33% lower in IUGR fetuses, but GUR was not different between IUGR and control fetuses. The difference between glucose utilization and UGU rates in the IUGR fetuses demonstrated the presence and rate of fetal GPR (41% of GUR). The mRNA concentrations of the gluconeogenic enzymes glucose-6-phophatase and PEPCK were higher in the livers of IUGR fetuses, perhaps in response to CREB activation, as phosphorylated CREB/total CREB was increased 4.2-fold. A hyperglycemic clamp resulted in similar rates of glucose uptake and utilization in IUGR and control fetuses. The nearly identical GURs in IUGR and control fetuses at both basal and high glucose concentrations occurred at mean plasma insulin concentrations in the IUGR fetuses that were approximately 70% lower than controls, indicating increased insulin sensitivity. Furthermore, under basal conditions, hepatic glycogen content was similar, skeletal muscle glycogen was increased 2.2-fold, the fraction of fetal GUR that was oxidized was 32% lower, and GLUT1 and GLUT4 concentrations in liver and skeletal muscle were the same in IUGR fetuses compared with controls. These results indicate that insulin-responsive fetal tissues (liver and skeletal muscle) adapt to the hypoglycemic-hypoinsulinemic IUGR environment with mechanisms that promote glucose utilization, particularly for glucose storage, including increased insulin action, glucose production, shunting of glucose utilization to glycogen production, and maintenance of glucose transporter concentrations.

Glucose metabolism and catecholamines

Until now, catecholamines were the drugs of choice to treat hypotension during shock states. Catecholamines, however, also have marked metabolic effects, particularly on glucose metabolism, and the degree of this metabolic response is directly related to the beta2-adrenoceptor activity of the individual compound used. Under physiologic conditions, infusing catecholamine is associated with enhanced rates of aerobic glycolysis (resulting in adenosine triphosphate production), glucose release (both from glycogenolysis and gluconeogenesis), and inhibition of insulin-mediated glycogenesis. Consequently, hyperglycemia and hyperlactatemia are the hallmarks of this metabolic response. Under pathophysiologic conditions, the metabolic effects of catecholamines are less predictable because of changes in receptor affinity and density and in drug kinetics and the metabolic capacity of the major gluconeogenic organs, both resulting from the disease per se and the ongoing treatment. It is also well-established that shock states are characterized by a hypermetabolic condition with insulin resistance and increased oxygen demands, which coincide with both compromised tissue microcirculatory perfusion and mitochondrial dysfunction. This, in turn, causes impaired glucose utilization and may lead to inadequate glucose supply and, ultimately, metabolic failure. Based on the landmark studies on intensive insulin use, a crucial role is currently attributed to glucose homeostasis. This article reviews the effects of the various catecholamines on glucose utilization, both under physiologic conditions, as well as during shock states. Because, to date (to our knowledge), no patient data are available, results from relevant animal experiments are discussed. In addition, potential strategies are outlined to influence the catecholamine-induced effects on glucose homeostasis.

Reduced blood glucose levels, increased insulin levels and improved glucose tolerance in alpha2A-adrenoceptor knockout mice

Alpha(2)-Adrenoceptors regulate insulin secretion and sympathetic output. In the present study, alpha(2A)-adrenoceptor knockout (alpha(2A)-KO) mice and their C57BL/6J wild-type (WT) controls were used to assess the glucoregulatory role of the alpha(2A)-adrenoceptor subtype in vivo. Fasting and glucose-stimulated blood glucose and plasma insulin levels were determined with or without (+/-)-propranolol (5 mg/kg) or atropine (10 mg/kg) pre-treatment. Intraperitoneal glucose (1 g/kg) and insulin (0.5 and 1.0 IU/kg) tolerance tests were performed. Fasting plasma glucagon and corticosterone levels were measured. Blood glucose levels (mean+/-S.E.M.) were lower in alpha(2A)-KO males (7.2+/-0.6 mM) and females (7.2+/-0.2 mM) than in WT males (9.8+/-0.3 mM) and females (9.1+/-0.3 mM). Plasma insulin levels were higher in alpha(2A)-KO males (2.2+/-0.5 microg/l) and females (1.7+/-0.3 microg/l) than in WT males (0.7+/-0.1 microg/l) and females (0.8+/-0.2 microg/l). These differences remained after pharmacological beta-adrenoceptor and muscarinic acetylcholine receptor inhibition. In spite of a tendency for slightly decreased insulin sensitivity in alpha(2A)-KO mice, glucose tolerance in alpha(2A)-KO mice was significantly better than in WT mice. However, glucose-stimulated insulin secretion was not increased in alpha(2A)-KO mice compared to WT controls. Plasma glucagon levels, but not corticosterone levels, were elevated in alpha(2A)-KO mice. These results suggest that lack of inhibitory pancreatic beta-cell alpha(2A)-adrenoceptor function results in hyperinsulinaemia, reduced blood glucose levels and improved glucose tolerance in alpha(2A)-KO mice, and demonstrate a key role for the alpha(2A)-adrenoceptor in adrenergic regulation of blood glucose and insulin homeostasis.

Metabolism modulators in sepsis: Propranolol

Sepsis is accompanied by an enormous increase in catecholamine expression, leading to metabolism of lipids and glucose, changes in cardiovascular output, immunomodulatory effects, and changes in protein metabolism, all of which push the body into a catabolic state. Deleterious beta-adrenoceptor controlled responses to stress and sepsis are well documented; therefore, it would seem appropriate to use propranolol under such circumstances. There are arguments both for and against the use of beta-adrenoceptor blockade during episodes of stress and infection. The definition of sepsis itself is a clinical one in most cases. There are guidelines concerning the diagnosis of sepsis (systemic inflammatory response syndrome [SIRS] in the presence of significant infection). However, when the cause of SIRS is not infection, for example, in burn patients, is it not possible, and indeed preferable, to tackle the stress response in a more aggressive fashion? The effects of SIRS on the body are myriad and have been defined and illustrated in many fine reviews. The effects of sepsis on the body, as well, have been discussed in the world literature and are beyond the scope of this article. In this article we attempt to demonstrate the effects of sepsis (SIRS plus infection) on whole body metabolism, outline the mediators of these changes, and then show the ability of propranolol to attenuate the changes seen.

Effect of alpha1-adrenergic receptors in cardiac pathophysiology

Compelling evidence now exists that proves adrenergic blockade is at the center of neurohormonal antagonism in heart failure (HF). Catecholamines are well known to act through both beta- and alpha-adrenergic receptors (ARs), which mediate their effects through distinct receptor pathways. Beta-AR blockers are commonly used in the treatment of HF and have distinct receptor affinity profiles. The recent COMET trial comparing 2 important beta-blocking drugs showed a distinct advantage for carvedilol in decreasing the risk of mortality from HF. The mechanism of action for carvedilol differs from metoprolol tartrate in its ability to block both alpha- and beta-ARs, leading to renewed interest in the potential role of alpha-ARs in the progression of HF. In contrast, however, the ALLHAT study discontinued use of doxazosin, an alpha1-receptor blocker because of an increase in cardiovascular events among patients using this drug. The results of these studies appear to be in contrast with respect to the role of alpha-ARs in regards to cardiovascular pathophysiology. Further study of the alpha-receptor and understanding the role of alpha-ARs in HF is necessary to understand the therapeutic effect of alpha-blockade. This article reviews our understanding of the alpha-AR in HF.

The effect of an acute elevation of NEFA concentrations on glucagon-stimulated hepatic glucose output

To determine the effect of nonesterified fatty acids (NEFA) on glucagon action, glucagon was infused intraportally (1.65 ng.min(-1).kg(-1)) for 3 h into 18-h-fasted, pancreatic-clamped conscious dogs in the presence [NEFA + glucagon (GGN)] or absence (GGN) of peripheral Intralipid plus heparin infusion. Additionally, hyperglycemic (HG), hyperglycemic-hyperlipidemic (NEFA + HG), and glycerol plus glucagon (GLYC + GGN) controls were studied. Arterial plasma glucagon concentrations rose equally in GGN, NEFA + GGN, and GLYC + GGN but remained basal in hyperglycemic controls. Peripheral infusions of Intralipid and heparin increased arterial plasma NEFA concentrations equally in NEFA + GGN and NEFA + HG and did not change in other protocols. After 15 min, glucagon infusion resulted in a rapid, brief increase in net hepatic glycogenolysis (NHGLY, mg.min(-1).kg(-1)) of approximately 6.0 in GGN and GLYC + GGN but only increased by 3.8 +/- 1.3 in NEFA + GGN. Thus increases in NHGLY, and consequently net hepatic glucose output (NHGO), were blunted by 40%, with no difference between the groups in the last 2.5 h of the study. NHGO and NHGLY did not significantly change in HG and NEFA + HG. Net hepatic gluconeogenic flux did not change in GGN, GLYC + GGN, or HG. However, Intralipid and heparin infusion resulted in similar increases in net hepatic gluconeogenic flux in NEFA + GGN and NEFA + HG. Thus elevated NEFA limit the initial increase in glucagon-stimulated HGO by blunting glycogenolysis, without having any effect on the gluconeogenic or glycogenolytic contributions or NHGO thereafter.

Metabolic effects of antihypertensive agents: role of sympathoadrenal and renin-angiotensin systems

Reports of beneficial, neutral and adverse impacts of antihypertensive drug classes on glucose and lipid metabolism can be found in human data. Furthermore, mechanisms for these diverse effects are often speculative and controversial. Clinical trial data on the metabolic effects of antihypertensive agents are highly contradictory. Comparisons of clinical trials involving different agents are complicated by differences in the spectrum of metabolic disturbances that accompany hypertension in different groups of patients. Two physiological systems are predominant at the interface between metabolic and cardiovascular regulation: the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). These two systems are major targets of antihypertensive drug actions, and also mediate many of the beneficial and adverse effects of antihypertensive agents on glucose and lipid metabolism. Thiazides and beta-adrenergic antagonists can adversely affect glucose and lipid metabolism, which are frequently compromised in human essential hypertension, and increase the incidence of new cases of diabetes. Laboratory studies confirm these effects, and suggest that compensatory activation of the SNS and RAS may be one mechanism. Other antihypertensives directly targeting the SNS and RAS may have beneficial effects on glucose and lipid metabolism, and may prevent diabetes. Resolution of the controversies surrounding the metabolic effects of antihypertensive agents can only be resolved by further laboratory studies, in addition to controlled clinical trials.

Ontogenesis of mRNA levels and binding sites of hepatic alpha-adrenoceptors in young cattle

Catecholamines affect hepatic glucose production through (alpha- and beta2-) adrenoceptors (AR). We studied mRNA abundance and binding of hepatic alpha-AR in pre-term (P0) calves and in full-term calves at day 0 (F0), day 5 (F5) and day 159 (F159) to test the hypothesis that gene expression and numbers of hepatic alpha-AR in calves are influenced by age and associated with beta2-AR and selected traits of glucose metabolism. mRNA levels of alpha1- and alpha2-AR were measured by real time RT-PCR. alpha1- and alpha2-AR numbers (maximal binding, Bmax) were determined by saturation binding of (3H)-prazosin and (3H)-RX821002, respectively. alpha1- and alpha2-AR subtypes were evaluated by competitive binding. alpha1A-AR mRNA levels were lower in P0 than in F0, F5 and F159 and alpha(2AD)-AR mRNA levels were lower in F159 than in P0, F0 and F5, while alpha2C-AR mRNA levels increased from P0 and F0 to F5 and F159. Bmax of alpha1-AR increased from P0 to F5, then decreased in F159. Bmax of alpha2-AR decreased from F0 to F159. Bmax of alpha1-AR was positively associated with mRNA levels of alpha1A-AR (r = 0.7), Bmax of beta2-AR (r = 0.5) and negatively with hepatic glycogen content (r = -0.6). Bmax of alpha2-AR was negatively associated with Bmax of beta2-AR (r = -0.4). In conclusion, mRNA levels and binding sites of alpha1- and alpha2-AR in calves exhibited developmental changes and were negatively associated with hepatic glycogen content.

Role of the hepatic sympathetic nerves in the regulation of net hepatic glucose uptake and the mediation of the portal glucose signal

Portal glucose delivery enhances net hepatic glucose uptake (NHGU) relative to peripheral glucose delivery. We hypothesize that the sympathetic nervous system normally restrains NHGU, and portal glucose delivery relieves the inhibition. Two groups of 42-h-fasted conscious dogs were studied using arteriovenous difference techniques. Denervated dogs (DEN; n=10) underwent selective sympathetic denervation by cutting the nerves at the celiac nerve bundle near the common hepatic artery; control dogs (CON; n=10) underwent a sham procedure. After a 140-min basal period, somatostatin was given along with basal intraportal infusions of insulin and glucagon. Glucose was infused peripherally to double the hepatic glucose load (HGL) for 90 min (P1). In P2, glucose was infused intraportally (3-4 mg.kg(-1).min(-1)), and the peripheral glucose infusion was reduced to maintain the HGL for 90 min. This was followed by 90 min (P3) in which portal glucose infusion was terminated and peripheral glucose infusion was increased to maintain the HGL. P1 and P3 were averaged as the peripheral glucose infusion period (PE). The average HGLs (mg.kg(-1).min(-1)) in CON and DEN were 55+/-3 and 54+/-4 in the peripheral periods and 55+/-3 and 55+/-4 in P2, respectively. The arterial insulin and glucagon levels remained basal in both groups. NHGU (mg.kg(-1).min(-1)) in CON averaged 1.7+/-0.3 during PE and increased to 2.9+/-0.3 during P2. NHGU (mg.kg(-1).min(-1)) was greater in DEN than CON (P<0.05) during PE (2.9+/-0.4) and failed to increase significantly (3.2+/-0.2) during P2 (not significant vs. CON). Selective sympathetic denervation increased NHGU during hyperglycemia but significantly blunted the response to portal glucose delivery.

Stress-mediated modulation of B(α)P-induced hepatic CYP1A1: role of catecholamines

The present study investigated the involvement of catecholamines in stress-mediated alterations in CYP1A1 induction by benzo(alpha)pyrene (B(alpha)P) in Wistar rats. This was achieved by measuring EROD activity and CYP1A1 mRNA levels in liver tissue from rats exposed to restraint stress and B(alpha)P coupled with pharmacological modulation of peripheral and central catecholamine levels and different adrenoceptors. In a state of reserpine-induced central and peripheral catecholamine depletion, stress strongly suppressed EROD induction. Peripheral catecholamines do not appear to play a critical role in the stress-mediated modulation of EROD inducibility by B(alpha)P. Stress did not alter EROD inducibility by B(alpha)P when peripheral catecholamines were either depleted by guanethidine or supplemented by peripheral adrenaline administration. On the other hand, central noradrenergic systems appear to have a role in the stress-mediated changes in B(alpha)P-induced EROD activity and Cyp1A1 gene expression. Stimulation or blockade of noradrenaline release with atipamezole and dexmedetomidine, respectively, significantly modified the up-regulating effect of stress. Alpha1 adrenoceptors also appear to participate in the effect of stress on EROD inducibility. Alpha1-blockade with prazosin potentiated the up-regulating effect of stress, possibly preventing the down-regulating effect of noradrenaline. Beta adrenoceptors also seem to be involved directly or indirectly in the stress-mediated modulation of Cyp1A1, as propranolol (beta-antagonist) blocked the down-regulating effect of stress on B(alpha)P-induced Cyp1A1 gene expression. Plasma corticosterone alterations after stress were not related to alterations in the B(alpha)P-induced EROD activity and Cyp1A1 gene expression. In conclusion, stress appears to interfere in the regulation of B(alpha)P-induced hepatic CYP1A1 in an unpredictable manner and via signalling pathways not always directly related to catecholamines. In particular, whenever drug treatment disrupts noradrenergic neurotransmission, other stress-stimulated factors appear to modify the induction of CYP1A1. In summary, regulation of induction of hepatic CYP1A1 during stress appears to involve various components of the stress system, including central and peripheral catecholamines, which interact in a complex manner, yet to be elucidated.

Metabolic effects of norepinephrine and dobutamine in healthy volunteers

The objective of the present study was to evaluate the effects of norepinephrine (n = 9) and dobutamine (n = 7) on carbohydrate and protein metabolism in healthy volunteers in comparison with a control group (n = 9). Norepinephrine (0.1 microg/kg min), dobutamine (5 microg/kg min), or placebo was infused for 240 min. The plasma concentration of glucose, lactate, epinephrine, norepinephrine, insulin, and glucagon were determined. Glucose and urea production and leucine flux were measured using a tracer technique. Norepinephrine caused a persisting rise in plasma glucose concentration, whereas the increase in glucose production was only transient. A minor increase in plasma lactate concentration was observed, but it did not exceed the physiological range. No change in leucine flux, urea production, or plasma concentration of insulin, glucagon, or epinephrine was found. Dobutamine slightly decreased glucose production, whereas the plasma concentration of glucose and lactate did not change. The reduction in leucine flux was paralleled by a decrease in urea production. No change in the plasma concentration of insulin, glucagon, or the catecholamines was observed. In conclusion, both norepinephrine and dobutamine have only minor metabolic effects. Because glucose production is enhanced by alpha1- and beta2-adrenoceptor stimulation, we conclude that dobutamine is only a weak agonist at these adrenoceptors. These minor metabolic actions may make both compounds suitable for critically ill patients because no further increase in metabolic rate should be caused.