GABA agonists differentially modify blood glucose levels of diabetic rats

Impact of processing techniques on the glycemic index of rice

Rice is an important starchy staple food and generally, rice varieties are known to have a higher glycemic index (GI). Over the years, the significance of GI on human health is being better understood and is known to be associated with several lifestyle disorders. Apart from the intrinsic characteristics of rice, different food processing techniques are known to have implications on the GI of rice. This work details the effect of domestic and industrial-level processing techniques on the GI of rice by providing an understanding of the resulting physicochemical changes. An attempt has been made to relate the process-dependent digestion behavior, which in turn reflects on the GI. The role of food constituents is elaborated and the various in vitro and in vivo approaches that have been used to determine the GI of foods are summarized. Considering the broader perspective, the effect of cooking methods and additives is explained. Given the significance of the cereal grain, this work concludes with the challenges and key thrust areas for future research.

Cystathionine-β-Synthase: Molecular Regulation and Pharmacological Inhibition

Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used "CBS inhibitors" (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.

Dietary GABA enhances hypoxia tolerance of a bottom-dwelling carp, Cirrhinus mrigala by modulating HIF-1α, thyroid hormones and metabolic responses

The Indian major carp, mrigal (Cirrhinus mrigala), is a bottom-dwelling fish that can survive hypoxic episodes in its natural environment. We hypothesise that it can better survive hypoxic conditions by altering metabolic responses through GABA (Gamma-aminobutyric acid) supplementation. In the first experiment, the hypoxia tolerance time of the fishes was evaluated under extreme anoxic conditions after feeding with GABA, which showed that GABA had improved survival time under hypoxia. To study the response of dietary GABA in hypoxia-exposed fish, the branchial HIF-1α expression levels, serum thyroid hormone levels and hepatic metabolic responses were assessed in the subsequent experiment. The treatment groups were fed for 60 days with experimental diets containing 4 levels of GABA (0.00% G, 0.50% G, 0.75% G and 1.0%G) and were subjected to 72-h hypoxia exposure (0.5 ± 0.02 mg L^-1 dissolved oxygen (DO)) whereas a control group was maintained under normoxic conditions (6.0 ± 0.21 mg L^-1 DO). The five treatment groups with three replicates were C0 (0% G + normoxia), H0 (0% G + hypoxia), H0.5 (0.50% G + hypoxia), H0.75 (0.75% G + hypoxia) and H1.0 (1.00% G + hypoxia). The results indicated that GABA supplementation triggered downregulation of HIF 1 alpha expression. When compared with the control group, decreased thyroxine (T4) and triiodothyronine (T3) levels were observed in the GABA-fed hypoxic groups. However, TSH (thyroid stimulating hormone) level remained unchanged in all the treatments. The LDH (lactate dehydrogenase) level in hypoxia-exposed groups was decreased by GABA supplementation. Our study demonstrated that GABA supplementation restores acute hypoxia-induced HIF-1α expression, thyroid hormone levels and LDH activities. On the other hand, it enhanced the citrate synthase (CS) activities at 0.5-1.00%, which showed a sharp decline in hypoxia. Hypoxia caused increase in the serum metabolites such as glucose, lactate, cholesterol and triglycerides. However, GABA supplementation was partially effective in reducing glucose and lactate level while triglycerides and cholesterol values remained unchanged. Overall, our results suggested a potential role of GABA in suppressing metabolism during hypoxia exposure, which can increase the chances of survival of the species Cirrhinus mrigala during hypoxia.

Comparison of Toxicity of Taurine and GABA in Combination with Alcohol in 7-Day-Old Mice

Previously, we described the combined toxicity of taurine and alcohol, and assumed hypoglycemia to be one reason of this toxicity. To understand whether taurine-ethanol combined toxicity is exclusively connected to taurine or whether other inhibitory amino acids may have similar effects when combined with ethanol, we tested different doses of gamma-aminobutyric acid (GABA) in combination with ethanol in 7-day-old mice. The minimal dose of GABA in combination with 5 g/kg ethanol which could kill a mouse was 2 g/kg. GABA combined with ethanol at doses of 3 g/kg, 4 g/kg, 6 g/kg induced lethality of 30%, 90% and 100%, correspondingly. Taurine at the doses of 4 and 6 g/kg combined with ethanol induced death in 60 and 100% of mice. Ethanol (5 g/kg), taurine (6 g/kg), GABA (4 g/kg) administered alone and the combination of ethanol (5 g/kg) with taurine (3 g/kg) have no lethal effects. GABA (6 g/kg) applied alone induced 90% lethality. Taurine or GABA alone decreased blood glucose in a dose-depending manner. Ethanol potentiated GABA- and taurine-induced decrease in blood glucose and in some animals it dropped from 8.8 (intact) to a hypoglycemic level 3.1-3.3 mmol/L (GABA 4 g/kg, taurine 6 g/kg), but this may not be considered a single reason of death. We conclude that the combination of GABA and ethanol has a lethal effect and this is stronger than the combined toxicity of ethanol and taurine.

Sleep Control, GPCRs, and Glucose Metabolism

Modern lifestyles prolong daily activities into the nighttime, disrupting circadian rhythms, which may cause sleep disturbances. Sleep disturbances have been implicated in the dysregulation of blood glucose levels and reported to increase the risk of type 2 diabetes (T2D) and diabetic complications. Sleep disorders are treated using anti-insomnia drugs that target ionotropic and G protein-coupled receptors (GPCRs), including γ-aminobutyric acid (GABA) agonists, melatonin agonists, and orexin receptor antagonists. A deeper understanding of the effects of these medications on glucose metabolism and their underlying mechanisms of action is crucial for the treatment of diabetic patients with sleep disorders. In this review we focus on the beneficial impact of sleep on glucose metabolism and suggest a possible strategy for therapeutic intervention against sleep-related metabolic disorders.

Antidiabetic properties of germinated brown rice: a systematic review

Diet is an important variable in the course of type 2 diabetes, which has generated interest in dietary options like germinated brown rice (GBR) for effective management of the disease among rice-consuming populations. In vitro data and animal experiments show that GBR has potentials as a functional diet for managing this disease, and short-term clinical studies indicate encouraging results. Mechanisms for antidiabetic effects of GBR due to bioactive compounds like γ-aminobutyric acid (GABA), γ-oryzanol, dietary fibre, phenolics, vitamins, acylated steryl β-glucoside, and minerals include antihyperglycemia, low insulin index, antioxidative effect, antithrombosis, antihypertensive effect, hypocholesterolemia, and neuroprotective effects. The evidence so far suggests that there may be enormous benefits for diabetics in rice-consuming populations if white rice is replaced with GBR. However, long-term clinical studies are still needed to verify these findings on antidiabetic effects of GBR. Thus, we present a review on the antidiabetic properties of GBR from relevant preclinical and clinical studies, in order to provide detailed information on this subject for researchers to review the potential of GBR in combating this disease.

Prophylactic effects of swimming exercise on autophagy-induced muscle atrophy in diabetic rats

Diabetes decreases skeletal muscle mass and induces atrophy. However, the mechanisms by which hyperglycemia and insulin deficiency modify muscle mass are not well defined. In this study, we evaluated the effects of swimming exercise on muscle mass and intracellular protein degradation in diabetic rats, and proposed that autophagy inhibition induced by swimming exercise serves as a hypercatabolic mechanism in the skeletal muscles of diabetic rats, supporting a notion that swimming exercise could efficiently reverse the reduced skeletal muscle mass caused by diabetes. Adult male Sprague-Dawley rats were injected intraperitoneally with streptozotocin (60 mg/kg body weight) to induce diabetes and then submitted to 1 hr per day of forced swimming exercise, 5 days per week for 4 weeks. We conducted an intraperitoneal glucose tolerance test on the animals and measured body weight, skeletal muscle mass, and protein degradation and examined the level of autophagy in the isolated extensor digitorum longus, plantaris, and soleus muscles. Body weight and muscle tissue mass were higher in the exercising diabetic rats than in control diabetic rats that remained sedentary. Compared to control rats, exercising diabetic rats had lower blood glucose levels, increased intracellular contractile protein expression, and decreased autophagic protein expression. We conclude that swimming exercise improves muscle mass in diabetes-induced skeletal muscle atrophy, suggesting the activation of autophagy in diabetes contributes to muscle atrophy through hypercatabolic metabolism and that aerobic exercise, by suppressing autophagy, may modify or reverse skeletal muscle wasting in diabetic patients.

Paracrine interactions within islets of Langerhans

Glucose supply fluctuates between meal and fasting periods and its consumption by the body varies greatly depending on bodily metabolism. Pancreatic islets of Langerhans secrete various endocrine hormones including insulin and glucagon to keep blood glucose level relatively constant. Additionally, islet hormones regulate activity of neighboring cells as local autocrine or paracrine modulators. Moreover, islet cells release neurotransmitters such as glutamate and γ-aminobutyric acid (GABA) to gain more precise regulation of hormones release kinetics. Excitatory glutamate is co-released with glucagon from α-cells and activates glutamate receptors in the neighboring cells. GABA released from β-cells was shown to inhibit α-cells but to activate β-cells by acting GABA(A) receptors. This review summarizes the recent progress in understanding the paracrine/autocrine interactions in islets.

Effects of GABAB receptor agonists and antagonists on glycemia regulation in mice

γ-Aminobutyric acid (GABA) inhibits insulin secretion through GABA(B) receptors in pancreatic β-cells. We investigated whether GABA(B) receptors participated in the regulation of glucose homeostasis in vivo. BALB/c mice acutely pre-injected with the GABA(B) receptor agonist baclofen (7.5mg/kg, i.p.) presented glucose intolerance and diminished insulin secretion during a glucose tolerance test (GTT, 2g/kg body weight, i.p.). The GABA(B) receptor antagonist 2-hydroxysaclofen (15 mg/kg, i.p.) improved the GTT and reversed the baclofen effect. Also a slight increase in insulin secretion was observed with 2-hydroxysaclofen. In incubated islets 1.10(-5)M baclofen inhibited 20mM glucose-induced insulin secretion and this effect was reversed by coincubation with 1.10(-5)M 2-hydroxysaclofen. In chronically-treated animals (18 days) both the receptor agonist (5mg/kg/day i.p.) and the receptor antagonist (10mg/kg/day i.p.) induced impaired GTTs; the receptor antagonist, but not the agonist, also induced a decrease in insulin secretion. No alterations in insulin tolerance tests, body weight and food intake were observed with the treatments. In addition glucagon, insulin-like growth factor I, prolactin, corticosterone and growth hormone, other hormones involved in glucose metabolism regulation, were not affected by chronic baclofen or 2-hydroxysaclofen. In islets obtained from chronically injected animals with baclofen, 2-hydroxysaclofen or saline (as above), GABA(B2) mRNA expression was not altered. Results demonstrate that GABA(B) receptors are involved in the regulation of glucose homeostasis in vivo. Treatment with receptor agonists or antagonists, given acutely or chronically, altered glucose homeostasis and insulin secretion alerting to the need to evaluate glucose metabolism during the clinical use of these drugs.

Topiramate and type 2 diabetes: an old wine in a new bottle

Topiramate, a marketed antiepileptic drug, has been used to treat seizures and allied neurological problems since 1999. Recently, a series of newer findings for the use of topiramate have cropped up, which include Type 2 diabetes and obesity. In a series of clinical studies, a subset of neurological patients with Type 2 diabetes mellitus (T2DM) serendipitously showed better glycaemic control when treated with topiramate. It has since been demonstrated that topiramate can act both as an insulin secretagogue and sensitiser in T2DM animal models. Pathogenesis of Type 2 diabetes involves both beta-cell dysfunction and insulin resistance. Therefore, an agent that has dual action (insulin secretagougue and sensitisation) is preferred for T2DM. Topiramate seems to act through multiple mechanisms to ameliorate diabetic symptoms, some of them unknown. Hence, it becomes imperative to discuss its probable modes of action. Topiramate raises new hope as an antidiabetic agent or a potential new chemotype with a better safety profile for the treatment of T2DM.

GABAB receptors and glucose homeostasis: evaluation in GABAB receptor knockout mice

GABA has been proposed to inhibit insulin secretion through GABAB receptors (GABABRs) in pancreatic beta-cells. We investigated whether GABABRs participated in the regulation of glucose homeostasis in vivo. The animals used in this study were adult male and female BALB/C mice, mice deficient in the GABAB1 subunit of the GABABR (GABAB(-/-)), and wild types (WT). Blood glucose was measured under fasting/fed conditions and in glucose tolerance tests (GTTs) with a Lifescan Glucose meter, and serum insulin was measured by ELISA. Pancreatic insulin content and islet insulin were released by RIA. Western blots for the GABAB1 subunit in islet membranes and immunohistochemistry for insulin and GABAB1 were performed in both genotypes. BALB/C mice preinjected with Baclofen (GABABR agonist, 7.5 mg/kg ip) presented impaired GTTs and decreased insulin secretion compared with saline-preinjected controls. GABAB(-/-) mice showed fasting and fed glucose levels similar to WT. GABAB(-/-) mice showed improved GTTs at moderate glucose overloads (2 g/kg). Baclofen pretreatment did not modify GTTs in GABAB(-/-) mice, whereas it impaired normal glycemia reinstatement in WT. Baclofen inhibited glucose-stimulated insulin secretion in WT isolated islets but was without effect in GABAB(-/-) islets. In GABAB(-/-) males, pancreatic insulin content was increased, basal and glucose-stimulated insulin secretion were augmented, and impaired insulin tolerance test and increased homeostatic model assessment of insulin resistance index were determined. Immunohistochemistry for insulin demonstrated an increase of very large islets in GABAB(-/-) males. Results demonstrate that GABABRs are involved in the regulation of glucose homeostasis in vivo and that the constitutive absence of GABABRs induces alterations in pancreatic histology, physiology, and insulin resistance.

Oxidative stress parameters in diabetic rats submitted to forced swimming test: the clonazepam effect

Diabetes-associated depression may occur due to changes in the quality of life imposed by treatment, or may be a consequence of the biochemical changes accompanying the disease. We evaluated the oxidative stress from diabetic animals submitted to an experimental model of depression and the effects of clonazepam. Male Wistar rats were induced to diabetes with streptozotocin and submitted to forced swimming test. Clonazepam was administered 24, 5 and 1 h before test. The animals were sacrificed by decapitation, and plasma and erythrocytes were separated, as well as hippocampus, cortex and striatum. Reactive species of thiobarbituric acid (TBARS) and total antioxidant reactivity (TAR) as well as antioxidant enzyme activities catalase (CAT) and superoxide dismutase (SOD) were evaluated. Results showed a significant increase of TBARS and a significant decrease of TAR in plasma from diabetic animals, which was altered by clonazepam. There were no effects of CAT and SOD activities in erythrocytes from tested animals. The results observed in hippocampus showed a significant increase of TBARS from diabetic rats, altered by clonazepam, and no one alteration was verified in TAR. The significant increase of TBARS and the significant decrease of TAR in cortex from diabetic rats were not altered by clonazepam administration. There were no alterations of TBARS and TAR in striatum from tested animals. Besides, clonazepam reverses the immobility in diabetic rats. Considering the action of clonazepam, it is suggested that it could be an alternative therapeutic for depression to diabetic patients, once it could give a protection against free radicals.

Gamma-aminobutyric acid up- and downregulates insulin secretion from beta cells in concert with changes in glucose concentration

AIMS/HYPOTHESIS

The role of gamma-aminobutyric acid (GABA) and A-type GABA receptors (GABA(A)Rs) in modulating islet endocrine function has been actively investigated since the identification of GABA and GABA(A)Rs in the pancreatic islets. However, the reported effects of GABA(A)R activation on insulin secretion from islet beta cells have been controversial.

METHODS

This study examined the hypothesis that the effect of GABA on beta cell insulin secretion is dependent on glucose concentration.

RESULTS

Perforated patch-clamp recordings in INS-1 cells demonstrated that GABA, at concentrations ranging from 1 to 1,000 micromol/l, induced a transmembrane current (I(GABA)) which was sensitive to the GABA(A)R antagonist bicuculline. The current-voltage relationship revealed that I(GABA) reversed at -42+/-2.2 mV, independently of glucose concentration. Nevertheless, the glucose concentration critically controlled the membrane potential (V (M)), i.e., at low glucose (0 or 2.8 mmol/l) the endogenous V (M) of INS-1 cells was below the I(GABA) reversal potential and at high glucose (16.7 or 28 mmol/l), the endogenous V (M) of INS-1 cells was above the I(GABA) reversal potential. Therefore, GABA dose-dependently induced membrane depolarisation at a low glucose concentration, but hyperpolarisation at a high glucose concentration. Consistent with electrophysiological findings, insulin secretion assays demonstrated that at 2.8 mmol/l glucose, GABA increased insulin secretion in a dose-dependent fashion (p<0.05, n=7). This enhancement was blocked by bicuculline (p<0.05, n=4). In contrast, in the presence of 28 mmol/l glucose, GABA suppressed the secretion of insulin (p<0.05, n=5).

CONCLUSIONS/INTERPRETATION

These findings indicate that activation of GABA(A)Rs in beta cells regulates insulin secretion in concert with changes in glucose levels.

The peripheral GABAergic system as a target in endocrine disorders

In addition to its well-recognized function as a cerebral inhibitory transmitter, less well established is the role of GABA in peripheral nervous and endocrine systems. We summarize current evidence that GABA serves as a neurotransmitter or neuromodulator in the autonomic nervous system and as a hormone or trophic factor in non-neuronal peripheral tissue as well. GABA is widely distributed in endocrine tissues including the pituitary, pancreas, adrenal glands, uterus, ovaries, placenta and testis. Moreover, GABA is involved in the pathophysiology of endocrine disorders such as diabetes mellitus, diseases of adrenal glands and reproductive tracts. Current literature indicates that the peripheral GABA system in the autonomic nervous system, endocrine and immune systems is as yet nearly an unexplored target for diagnosis and drug treatment.

Postprandial blood glucose and insulin responses to pre-germinated brown rice in healthy subjects

Effects of pre-germinated brown rice (PGBR) on postprandial blood glucose and insulin concentrations were compared with brown rice (BR) and white rice (WR) in two studies. In the first study, we investigated the time course of postprandial blood glucose and insulin concentrations after ingesting 25% (W/V) glucose solution, PGBR, BR or WR in 19 healthy young subjects. In the second study, dose-dependent effect of PGBR on the time course of postprandial blood glucose concentrations was compared among 4 different mixtures of PGBR and WR in 13 healthy young subjects. They were solely PGBR, 2/3 PGBR (PGBR: WR = 2 : 1), 1/3 PGBR (PGBR : WR = 1 : 2) and solely WR. Each sample was studied on a different day. The samples were selected randomly by the subjects. All the rice samples contained 50 g of available carbohydrates. The previous day the subjects ate the assigned dinner by 9:00 pm and then were allowed only water until the examination. The next morning, they ingested each test rice sample with 150 ml of water in 5-10 min. Blood was collected into capillary tubes from finger at 0, 30, 60, 90 and 120 min after the ingestion. The incremental areas under the curve (IAUC) of blood glucose concentrations (IAUC-Glc) for 120 min after the administration of PGBR and BR were lower than those after WR. In contrast the IAUC-Glc of BR and PGBR were not different (Study 1). The higher the ratio of PGBR/WR, the lower the glycemic index became (Study 2). These results suggest that intake of PGBR instead of WR is effective for the control of postprandial blood glucose concentration without increasing the insulin secretion.

The dietary flavonoids apigenin and (-)-epigallocatechin gallate enhance the positive modulation by diazepam of the activation by GABA of recombinant GABA(A) receptors

The dietary flavonoids apigenin, genistein and (-)-epigallocatechin gallate (EGCG) inhibited the activation by GABA (40 microM) of recombinant human alpha1beta2gamma2L GABA(A) receptors expressed in Xenopus laevis oocytes with IC(50) values of 8, 30 and 15 microM, respectively. Apigenin and genistein also acted as GABA antagonists at flumazenil-insensitive alpha1beta2 GABA(A) receptors, indicating that they were not acting as negative modulators through flumazenil-sensitive benzodiazepine sites on GABA(A) receptors. In addition to these GABA(A) antagonist effects, a novel second order modulatory action was found for apigenin and EGCG on the first order enhancement of GABA responses by diazepam. Apigenin (1 microM) and EGCG (0.1 microM) enhanced the modulatory action of diazepam (3 microM) on the activation by GABA (5 microM) of recombinant human alpha1beta2gamma2L GABA(A) receptors by up to 22% and 52%, respectively. This was not found with genistein, nor was it observed with enhancement by allopregnanolone or pentobarbitone.

Insoluble Fiber Is a Major Constituent Responsible for Lowering the Post-Prandial Blood Glucose Concentration in the Pre-Germinated Brown Rice

The intake of pre-germinated brown rice (PR) instead of white rice (WR) ameliorates the hyperglycemia. To clarify the mechanism(s) to decrease the post-prandial blood glucose concentration, the effect of water-soluble/oil-soluble fraction-depleted PR bran (termed as "DB"; which is destarched and defatted PR bran) on post-prandial blood glucose was compared with that of full-fat PR bran (PB) or WR. The test diets, WR diet, PB diet and DB diet which are containing identical amount of available carbohydrate (1.5 g) were fed to Wistar strain rats. Post-prandial blood glucose concentration and incremental area under the curve (IAUC) for DB diet were lower than those for WR diet, and there was no difference between the DB diet and PB diet. Changes in plasma insulin concentration and the IAUC obtained also revealed the same tendency as those observed in blood glucose concentration. These results indicate that the blood glucose-lowering effect of PB diet may be derived from the properties of PB involving substantially higher content of dietary fiber than WR, and that the potential benefit of intake of PR instead of WR in the prevention of diabetic vascular complications.

Clonazepam increases in vivo striatal extracellular glucose in diabetic rats after glucose overload

Hyperglycemia modulates brain function, including neuronal excitability, neurotransmitter release and behavioral changes. There may be connections between the GABAergic system, glucose sensing neurons and glucose in the neuronal environment that shed light on the mechanism by which GABA(A) agents influence depressive behavior in diabetic rats submitted to the forced swimming test. We aimed to investigate whether clonazepam (CNZ), a GABA(A) receptor positive modulator, modifies in vivo striatal extracellular glucose levels in diabetic rats under fasting condition or after oral glucose overload. Streptozotocin diabetic and nondiabetic rats were submitted to in vivo striatal microdialysis. Perfusate samples were collected at baseline, during fasting and following administration of CNZ (0.25 mg/kg) and oral glucose overload. Blood glucose and striatal extracellular glucose were measured simultaneously at several time points. Fasting striatal glucose levels were higher in diabetic than in nondiabetic rats and the differences between these animals were maintained after glucose overload. The increases in extracellular striatal glucose after glucose overload were around 40% and blood to brain transference was decreased in diabetics. CNZ treatment paradoxically increased striatal glucose after glucose overload in diabetic rats, which may mark the dysfunction in brain glucose homeostasis.

Valproic acid modulates islet cell insulin secretion: a possible mechanism of weight gain in epilepsy patients

A significant weight gain in the course of treatment of epilepsy with valproic acid (VPA) was described in several clinical studies. We recently demonstrated that postprandial insulin levels are increased in patients with VPA therapy. This possible modulation of pancreatic insulin secretion by VPA could be due to the structure of VPA as a fatty acid derivative and thus to direct stimulation of pancreatic insulin secretion or competition with free fatty acids (FFA) for albumin binding. In order to investigate the effect of VPA on insulin secretion in pancreatic islet cells we performed in vitro experiments with islets from pancreases of multiorgan donors. After preparation, the incubation with valproate caused a time and dose-dependent increase of insulin concentration in the cell supernatant. This could also be demonstrated with the control drug, lorazepam, a benzodiazepine, but not with mirtazepin and phenytoin. It can be speculated that an increase in pancreatic insulin secretion under chronic VPA treatment enhances appetite and energy storage and is related to the observed weight gain.

A reappraisal of the blood glucose homeostat which comprehensively explains the type 2 diabetes mellitus-syndrome X complex

Blood glucose concentrations are unaffected by exercise despite very high rates of glucose flux. The plasma ionised calcium levels are even more tightly controlled after meals and during lactation. This implies 'integral control'. However, pairs of integral counterregulatory controllers (e.g. insulin and glucagon, or calcitonin and parathyroid hormone) cannot operate on the same controlled variable, unless there is some form of mutual inhibition. Flip-flop functional coupling between pancreatic alpha- and beta-cells via gap junctions may provide such a mechanism. Secretion of a common inhibitory chromogranin by the parathyroids and the thyroidal C-cells provides another. Here we describe how the insulin:glucagon flip-flop controller can be complemented by growth hormone, despite both being integral controllers. Homeostatic conflict is prevented by somatostatin-28 secretion from both the hypothalamus and the pancreatic islets. Our synthesis of the information pertaining to the glucose homeostat that has accumulated in the literature predicts that disruption of the flip-flop mechanism by the accumulation of amyloid in the pancreatic islets in type 2 diabetes mellitus will lead to hyperglucagonaemia, hyperinsulinaemia, insulin resistance, glucose intolerance and impaired insulin responsiveness to elevated blood glucose levels. It explains syndrome X (or metabolic syndrome) as incipient type 2 diabetes in which the glucose control system, while impaired, can still maintain blood glucose at the desired level. It also explains why it is characterised by high plasma insulin levels and low plasma growth hormone levels, despite normoglycaemia, and how this leads to central obesity, dyslipidaemia and cardiovascular disease in both syndrome X and type 2 diabetes.

GABA in the endocrine pancreas: cellular localization and function in normal and diabetic rats

Gamma amino butyric acid (GABA) and its related enzymes have been demonstrated in pancreatic beta cells of normal rat. Antibodies against GABA-synthesizing enzymes have been implicated in the pathogenesis of Type I diabetes. In spite of the importance of GABA in the aetiology of diabetes mellitus, detailed morphological data on the pattern of distribution of GABA in the pancreas of normal and diabetic rats are lacking. Diabetes mellitus (DM) was induced by a single dose of streptozotocin (STZ) given intraperitoneally (60 mg kg body weight(-1)). Four weeks after the induction of DM, normal (n = 6) and diabetic (n = 6) rats were anesthetized with chloral hydrate and their pancreata were removed and processed for the localization and effect of GABA on insulin secretion using immunohistochemistry and radioimmunoassay techniques. The number of GABA-like immunoreactive (GABA-LIR) cells in the pancreatic islets of STZ-diabetic rats decreased significantly (P<0.0001) when compared to non-diabetic control rats. The pattern and percentage distribution of GABA in the islet of Langerhans of normal and diabetic rat was similar to that of insulin. GABA induced a significant (P<0.0007) increase in insulin secretion from the pancreas of normal rats. In diabetic pancreas, GABA evoked a higher but not significant (P<0.1) increase in insulin secretion. These findings showed that the number of GABA-LIR cells is reduced significantly in diabetes. Moreover, GABA is a strong secretagogue of insulin from the pancreas of normal rat.

Acute effect of different antidepressants on glycemia in diabetic and non-diabetic rats

Diabetic patients have a 20% higher risk of depression than the general population. Treatment with antidepressant drugs can directly interfere with blood glucose levels or may interact with hypoglycemic agents. The treatment of depression in diabetic patients must take into account variations of glycemic levels at different times and a comparison of the available antidepressant agents is important. In the present study we evaluated the interference of antidepressants with blood glucose levels of diabetic and non-diabetic rats. In a first experiment, male adult Wistar rats were fasted for 12 h. Imipramine (5 mg/kg), moclobemide (30 mg/kg), clonazepam (0.25 mg/kg), fluoxetine (20 mg/kg) sertraline (30 mg/kg) or vehicle was administered. After 30 min, fasting glycemia was measured. An oral glucose overload of 1 ml of a 50% glucose solution was given to rats and blood glucose was determined after 30, 60 and 90 min. Imipramine and clonazepam did not change fasting or overload glycemia. Fluoxetine and moclobemide increased blood glucose at different times after the glucose overload. Sertraline neutralized the increase of glycemia induced by oral glucose overload. In the second experiment, non-diabetic and streptozotocin-induced diabetic rats were fasted, and the same procedures were followed for estimation of glucose tolerance 30 min after glucose overload. Again, sertraline neutralized the increase in glycemia after glucose overload both in diabetic and non-diabetic rats. These data raise the question of whether sertraline is the best choice for prolonged use for diabetic individuals, because of its antihyperglycemic effects. Clonazepam would be useful in cases with potential risk of hypoglycemia.