Minireview. The hypothalamus and blood glucose regulation

The Role of the Human Hypothalamus in Food Intake Networks: An MRI Perspective

Hypothalamus (HT), this small structure often perceived through the prism of neuroimaging as morphologically and functionally homogeneous, plays a key role in the primitive act of feeding. The current paper aims at reviewing the contribution of magnetic resonance imaging (MRI) in the study of the role of the HT in food intake regulation. It focuses on the different MRI techniques that have been used to describe structurally and functionally the Human HT. The latest advances in HT parcellation as well as perspectives in this field are presented. The value of MRI in the study of eating disorders such as anorexia nervosa (AN) and obesity are also highlighted.

Factors affecting the buccal delivery of deformable nanovesicles based on insulin-phospholipid complex: an in vivo investigation

Deformable nanovesicles (DNVs) have been used in the buccal delivery of biomacromolecules due to their ability to enhance drug penetration. However, no breakthroughs have been made until now due to limited understanding of the factors affecting in vivo buccal delivery. In this study, we designed a series of DNVs, based on an insulin-phospholipid complex (IPC-DNVs), to investigate the influence of drug dose, buccal administration methods, and key quality characteristics of IPC-DNVs for buccal delivery. IPC-DNVs showed a non-linear dose-response relationship between 8 and 12 IU. There was no significant effect of drug delivery site (sublingual mucosa/buccal mucosa) or ligation time (15 or 30 min) on buccal absorption of IPC-DNVs. However, the area above the curve of reduction in blood glucose level overtime (AAC0-6h) for oral mucosa administration was significantly higher than that for buccal mucosa administration. Increasing the drug concentration in IPC-DNVs led to a decrease in AAC0-6h. This might be due to local leakage of DNVs, while squeezing through biological barriers with high concentration of insulin, thus hindering the subsequent delivery of DNVs. IPC-DNVs, measuring 80-220 nm in size, did not significantly affect AAC0-6h. However, when the size was increased to approximately 400 nm, AAC0-6h decreased, thus suggesting that IPC-DNVs with reasonable size were more effective. Additionally, increased deformability of IPC-DNVs might cause drugs to leak easily, thus reducing the promoting effect of buccal absorption. Our results clarified the effect of characteristics of IPC-DNVs on buccal delivery in vivo and provided meaningful support for the design of dosage form of DNVs.

Acute Metabolic Effects of Olanzapine Depend on Dose and Injection Site

Atypical antipsychotics (AAPs), such as olanzapine (OLZ), are associated with metabolic side effects, including hyperglycemia. Although a central mechanism of action for the acute effects on glycemia has been suggested, evidence for peripheral versus central effects of AAPs has been mixed and has not been explored for an effect of OLZ on the respiratory exchange ratio (RER). Here, we tested the hypothesis that some inconsistencies in the glycemic responses are likely a result of different doses and central sites of injection. We also compared the effects of central versus peripherally administered OLZ on the RER of unsedated rats. Third ventricle infusion of OLZ at 0.3 mg/kg caused hyperglycemia within 30 minutes, with a higher dose (1.8 mg/kg) needed to elicit a similar response in the lateral ventricles. In contrast, 3 mg/kg of OLZ was needed to raise blood glucose within 30 minutes when given intragastrically, and 10 mg/kg resulted in a prolonged hyperglycemia lasting at least 60 minutes. Third ventricle injection of OLZ significantly decreased RER after 75 minutes, whereas intragastric OLZ resulted in a faster drop in RER after 30 minutes. Since changes in glycemia were most sensitive when OLZ was infused into the third ventricle, but effects on RER were more rapidly and efficaciously observed when the drug was given peripherally, these results raise the likelihood of a dual mechanism of action involving hypothalamic and peripheral mechanisms. Some discrepancies in the literature arising from central administration appear to result from the injection site and dose.

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.

Repaglinide, but not nateglinide administered supraspinally and spinally exerts an anti-diabetic action in d-glucose fed and streptozotocin-treated mouse models

We have recently demonstrated that some anti-diabetic drugs such as biguanide and thizolidinediones administered centrally modulate the blood glucose level, suggesting that orally administered anti-diabetic drugs may modulate the blood glucose level by acting on central nervous system. The present study was designed to explore the possible action of another class of anti-diabetic drugs, glinidies, administered centrally on the blood glucose level in ICR mice. Mice were administered intracerebroventricularly (i.c.v.) or intrathecally (i.t.) with 5 to 30 µg of repaglinide or nateglinide in D-glucose-fed and streptozotocin (STZ)-treated models. We found that i.c.v. or i.t. injection with repaglinide dose-dependently attenuated the blood glucose level in D-glucose-fed model, whereas i.c.v. or i.t. injection with nateglinide showed no modulatory action on the blood glucose level in D-glucose-fed model. Furthermore, the effect of repaglinide administered i.c.v. or i.t. on the blood glucose level in STZ-treated model was studied. We found that repaglinide administered i.c.v. slightly enhanced the blood glucose level in STZ-treated model. On the other hand, i.t. injection with repaglinide attenuated the blood glucose level in STZ-treated model. The plasma insulin level was enhanced by repaglinide in D-glucose-fed model, but repaglinide did not affect the plasma insulin level in STZ-treated model. In addition, nateglinide did not alter the plasma insulin level in both D-glucose-fed and STZ-treated models. These results suggest that the anti-diabetic action of repaglinide appears to be, at least, mediated via the brain and the spinal cord as revealed in both D-glucose fed and STZ-treated models.

Central anti-diabetic action of biguanide and thizolidinediones in D-glucose fed and streptozotocin-treated mouse models

BACKGROUND

In the present study, the possible anti-diabetic action of biguanide and thiazolidinediones administered supraspinally or spinally was studied in ICR mice.

METHODS

Mice were intracerebroventricular (i.c.v.) or intrathecal (i.t.) treated with 20 or 30 μg metformin, pioglitazone and rosiglitazone in d-glucose fed and streptozotocin-treated models, and blood glucose levels was measured at 30, 60 and 120 min after i.c.v. or i.t. administration.

RESULTS

We found that i.c.v. injection with metformin or rosiglitazone slightly attenuated the blood glucose level in d-glucose fed model, whereas pioglitazone showed no effect on the blood glucose level in d-glucose fed model. The i.t. administration with metformin, pioglitazone or rosiglitazone did not alter the blood glucose level in d-glucose fed model. We also assessed the possible roles of biguanide and thiazolidinedione in the regulation of the blood glucose level in streptozotocin-treated model. We found in the present study that i.c.v. or i.t. administration with metformin caused a pronounced attenuation of the blood glucose level in streptozotocin-treated model. However, rosiglitazone administered i.c.v. did not affect the blood glucose level in streptozotocin-treated model.

CONCLUSIONS

Our results suggest that the anti-diabetic actions of metformin and rosiglitazone appear to be mediated via the brain regions as revealed in d-glucose fed animal model. Furthermore, metformin administered supraspinally or spinally may be effective for treating type I diabetes mellitus as revealed in streptozotocin-treated mouse model.

Effects of acute insulin-induced hypoglycaemia on psychomotor function: people with type 1 diabetes are less affected than non-diabetic adults

AIMS/HYPOTHESIS

We examined the effects of acute insulin-induced hypoglycaemia on psychomotor function in non-diabetic volunteers and in adults with type 1 diabetes.

METHODS

Non-diabetic adults (n = 20) and adults with type 1 diabetes mellitus (n = 16) each underwent a euglycaemic-hyperinsulinaemic glucose clamp on two separate occasions. Arterialised blood glucose was maintained for 1 h at either 4.5 mmol/l (euglycaemia) or 2.5 mmol/l (hypoglycaemia). During this time participants underwent neuropsychological tests to assess psychomotor function.

RESULTS

During hypoglycaemia the non-diabetic participants showed a significant deterioration in the following: (1) four-choice reaction time (p = 0.008); (2) grooved pegboard (a test of manual dexterity; p = 0.004); (3) hand steadiness (p = 0.003); (4) pursuit rotor (a test of fine motor function, attention and coordination; p = 0.018); and (5) test of total body coordination (p = 0.004). No significant differences were observed between euglycaemia and hypoglycaemia in hand-grip (p = 0.897) and line tracing time (p = 0.480) tests. In type 1 diabetes mellitus patients, only four-choice reaction time (p = 0.023) and pursuit rotor (p = 0.045) were impaired significantly during hypoglycaemia.

CONCLUSIONS/INTERPRETATION

Although acute hypoglycaemia caused significant impairment of several psychomotor functions in non-diabetic adults, a lower magnitude of impairment was observed in those with type 1 diabetes. The mechanism underlying this discrepant effect of hypoglycaemia on psychomotor function remains unknown, but may be related to the difference in sympathoadrenal activation observed between the groups. People with type 1 diabetes may also have had a behavioural advantage of over non-diabetic participants derived from their previous exposure to hypoglycaemia or potentially the disparate results arose from hypoglycaemia-induced cerebral adaptation.

Oral glucose intake inhibits hypothalamic neuronal activity more effectively than glucose infusion

We previously showed that hypothalamic neuronal activity, as measured by the blood oxygen level-dependent (BOLD) functional MRI signal, declines in response to oral glucose intake. To further explore the mechanism driving changes in hypothalamic neuronal activity in response to an oral glucose load, we here compare hypothalamic BOLD signal changes subsequent to an oral vs. an intravenous (iv) glucose challenge in healthy humans. Seven healthy, normal-weight men received four interventions in random order after an overnight fast: 1) ingestion of glucose solution (75 g in 300 ml) or 2) water (300 ml), and 3) iv infusion of 40% glucose solution (0.5 g/kg body wt, maximum 35 g) or 4) infusion of saline (0.9% NaCl, equal volume). The BOLD signal was recorded as of 8 min prior to intervention (baseline) until 30 min after. Glucose infusion was associated with a modest and transient signal decline in the hypothalamus. In contrast, glucose ingestion was followed by a profound and persistent signal decrease despite the fact that plasma glucose levels were almost threefold lower than in response to iv administration. Accordingly, glucose ingestion tended to suppress hunger more than iv infusion (P < 0.1). We infer that neural and endocrine signals emanating from the gastrointestinal tract are critical for the hypothalamic response to nutrient ingestion.

Glucocorticoid responses to stress in castrate and testosterone-replaced rams

Stress is an important contributor to cardiovascular disease and to reduced immunity and fertility. As the role of androgens in stress is uncertain, we investigated the effects of testosterone (T) on hormonal responses to stress in conscious Romney Marsh wethers. Six T-treated sheep and six control sheep were stressed by exposure to a psychological and a metabolic stimulus. Baseline glucose levels were significantly lower in the treated animals compared with controls (p=0.002). T treatment significantly attenuated ACTH (p<0.01) and cortisol (p<0.05) responses to metabolic stress. Following psychological stress, ACTH responses were significantly lower in treated sheep compared with controls (p<0.05), but differences in mean cortisol responses did not reach significance. There were no significant differences in epinephrine or norepinephrine responses following either stressor. We conclude that T replacement in wethers lowers glucose and attenuates responses to metabolic and psychological stress. While the implications of these results for human physiology require further studies, they suggest that male hypogonadism may play a role in determining the risk of cardiovascular disease and diabetes.

Blood glucose is correlated with cerebrospinal fluid neurotransmitter metabolites

Medications which influence monoaminergic neurotransmission can also have an effect on glucose regulation. In order to better understand the role of central monoaminergic neurotransmission in blood glucose homeostasis, we explored the relation between blood glucose and cerebrospinal fluid metabolite concentrations of monoaminergic neurotransmitters. Under stringently controlled resting conditions, we measured fasting blood glucose and performed lumbar punctures on 41 healthy participants. Peripheral blood glucose concentrations were significantly correlated with the cerebrospinal fluid concentrations of the dopamine metabolite, homovanillic acid and the noradrenaline metabolite, 3-methoxy-4-hydroxyphenylglycol. These correlations may represent a homeostatic relation between brain neurotransmitter activity and blood glucose.

Cerebral insulin increases brain response to glucose

The hypothalamus participates in the regulation of carbohydrate metabolism involving a feedback loop between the brain and the periphery in which glucose-sensitive hypothalamic areas appear to be involved. We have previously shown that a glucose injection (9 mg/kg) in the carotid artery toward the brain, in an amount that did not modify glycaemia, caused a rapid and transient increase in plasma insulin concentrations. To determine whether central insulin could influence this response, we investigated the change in central glucose-induced insulin secretion in intracerebroventricular (i.c.v) insulin-injected rats and in hyperinsulinaemic obese Zucker rats. Central glucose-induced insulin secretion was increased by 50% in i.c.v. insulin-injected rats compared to control rats. When a similar test was performed at a lower dose of glucose (3 mg/kg), a significant insulin secretion was observed only in rats submitted to a prior central insulin injection. These data indicate an increase in the brain response to glucose after insulin treatment. Using an identical lower glucose dose, we also demonstrated an enhanced brain glucose sensitivity in hyperinsulinaemic and insulin-resistant obese Zucker rats. Together, these results indicate that acute i.c.v. insulin or pathological hyperinsulinaemic state (i.e. obese Zucker rat) modulates the nervous control of insulin secretion by increasing the brain response to glucose.

Octreotide-induced suppression of the hyperglycemic response to neostigmine or bombesin: relationship to hypothalamic noradrenergic drive

Neostigmine (cholinesterase inhibitor) or bombesin, when injected into the third cerebral ventricle of awake rat, dose-dependently increased serum glucose with the simultaneous rise in hypothalamic noradrenergic neuronal activity (NAA). Co-administration of octreotide with neostigmine or bombesin suppressed the hypothalamic NNA response with the simultaneous inhibition of the hyperglycemic response. There was a close relationship between hypothalamic NNA and serum glucose in these studies. On the basis of the concept that hypothalamic noradrenergic drive plays an important role in mediating the hyperglycemic response to stressful stimuli, the present findings suggest that the hyperglycemic response to neostigmine or bombesin is mediated via the interaction with hypothalamic noradrenergic neurons.

Central suppressive effect of octreotide on the hyperglycemic response to 2-deoxy-D-glucose injection or cold-swim stress in awake rats: possible mediation role of hypothalamic noradrenergic drive

Somatostatin (SRIH) and its analog have been reported to act within the central nervous system to suppress the hyperglycemic response to a variety of neural stimuli. On the other hand, the hyperglycemic response to 2-deoxy-D-glucose (2-DG) injection or cold-swim stress is well demonstrated to be closely associated with an increase in hypothalamic noradrenergic neuronal activity (NNA). To evaluate whether the suppression of the hypothalamic NNA response could be involved in the central mechanism whereby a SRIH analog inhibits the hyperglycemic response, octreotide, a clinically used long-acting octapeptide SRIH analog, was administered into the third cerebral ventricle of awake rats prior to the intraperitoneal injection of 2-DG or cold-swim stress. Hypothalamic noradrenaline (NA) and its neuronal metabolite, 3,4-dihydroxyphenylethyleneglycol (DHPG), were analyzed, and the ratio of DHPG to NA was used as an index of NNA. Intracerebroventricular (i.c.v.) pretreatment with octreotide suppressed the 2-DG-induced increase in hypothalamic NNA, accompanied by the inhibition of the serum glucose, NA and adrenaline responses. This suppressive effect of octreotide was dose-dependent. Similarly, i.c.v. pretreatment with octreotide prevented the hypothalamic NNA response to cold-swim stress, accompanied by a blockade of the increases in serum glucose, NA and adrenaline. A close relationship between hypothalamic NNA and serum glucose emerged from these studies. Intraperitoneal pretreatment with octreotide had no significant effect on the hyperglycemic or hypothalamic NNA response to 2-DG injection. These findings suggest that the inhibitory effect of octreotide on the hypothalamic NNA response to 2-DG injection or cold-swim stress is associated with the simultaneous suppression of the hyperglycemic response. Supporting the concept that hypothalamic NNA contributes to the modulation of blood glucose in stressful conditions, it is suggested that the suppression of the hypothalamic NNA response is, at least in part, involved in the central mechanism by which octreotide inhibits the hyperglycemic response to 2-DG injection or cold-swim stress.

Oral glucose augments the counterregulatory hormone response during insulin-induced hypoglycemia in humans

It has been suggested that the counterregulatory hormone (CRH) response to acute hypoglycemia is triggered via glucose sensors situated in either the hypothalamus or the portohepatic area. If the latter were critical during hypoglycemia, one would anticipate that ingestion of glucose, by raising glucose levels in the portal circulation, should attenuate CRH responses previously described in animal studies. To evaluate the effect of raising portal, but not peripheral, glucose levels during insulin-induced hypoglycemia, we performed hypoglycemic clamp studies in five healthy adult males on two occasions. On one occasion, subjects received oral glucose (OG) (25 g) during hypoglycemia; and on one occasion, noncarbohydrate-containing drink of equal volume, while maintaining plasma glucose at 55 +/- 2 mg/dL (3.08 mmol/L). As a result, there were no significant differences in systemic plasma glucose levels between the two hypoglycemic clamp studies, and basal CRH concentrations were also similar. As expected, there was a brisk rise in all CRH during the control (hypoglycemia+noncarbohydrate drink) study. In the experimental study, administration of OG (hypoglycemia+OG), to raise intraportal glucose levels during systemic hypoglycemia, did not attenuate CRH responses. Indeed, OG enhanced the rise in epinephrine, glucagon, and GH. Increases in cortisol and norepinephrine did not differ between the two studies. Therefore, our data suggest that increasing the level of glucose in the portal vein above that in the systemic circulation, during hypoglycemia, enhances (rather than suppresses) CRH responses. Thus, ingestion of glucose may reverse hypoglycemia directly by provision of substrate, as well as indirectly by stimulating counteregulatory mechanisms.

The temporal response of the brain after eating revealed by functional MRI

After eating, the human brain senses a biochemical change and then signals satiation, but precisely when this occurs is unknown. Even for well-established physiological systems like glucose-insulin regulation, the timing of interaction between hormonal processes and neural events is inferred mostly from blood sampling. Recently, neuroimaging studies have provided in vivo information about the neuroanatomical correlates of the regulation of energy intake. Temporal orchestration of such systems, however, is crucial to the integration of neuronal and hormonal signals that control eating behaviour. The challenge of this functional magnetic resonance imaging study is to map not only where but also when the brain will respond after food ingestion. Here we use a temporal clustering analysis technique to demonstrate that eating-related neural activity peaks at two different times with distinct localization. Importantly, the differentiated responses are interacting with an internal signal, the plasma insulin. These results support the concept of temporal parcellation of brain activity, which reflects the different natures of stimuli and responses. Moreover, this study provides a neuroimaging basis for detecting dynamic processes without prior knowledge of their timing, such as the acute effects of medication and nutrition in the brain.

Chronic ventromedial hypothalamic infusion of norepinephrine and serotonin promotes insulin resistance and glucose intolerance

The ventromedial hypothalamus (VMH) is involved in the regulation of peripheral metabolism. We and others have shown that activities, or extracellular metabolites of norepinephrine (NE) and serotonin (5-HT) are elevated in the VMH of both genetically and seasonally insulin-resistant and glucose-intolerant animals. This study examined whether chronic increases in VMH NE and 5-HT concentration of normal animals might lead to insulin-resistant and glucose-intolerant conditions in hamsters. Euinsulinemic, glucose-tolerant hamsters were infused continuously for 5 weeks into the right VMH with either vehicle, NE (5 or 25 nmol/h), 5-HT (2.5 nmol/h), or NE (5 or 25 nmol/h) plus 5-HT (2.5 nmol/h) through osmotic minipumps. Compared to vehicle, NE (25 nmol/h) significantly increased the glucose total area under the curve (TAUC) by 32% during glucose tolerance tests (GTT) conducted after 5 weeks' infusion. 5-HT alone significantly increased the GTT insulin TAUC (131%) and basal plasma insulin level (116%) but not glucose TAUC. NE (5 nmol/h) plus 5-HT infusion significantly increased insulin TAUC (129%) and basal plasma insulin (120%), whereas NE (25 nmol/h) plus 5-HT infusion significantly increased both the GTT glucose and insulin TAUC (43 and 113%, respectively), as well as basal plasma insulin level (158%), relative to vehicle infusion. Our findings demonstrate for the first time the differential and, more importantly, interactive effects of increased VMH NE and 5-HT in producing hyperinsulinemia, insulin resistance and glucose intolerance.

Bromocriptine improves glycaemic control and serum lipid profile in obese Type 2 diabetic subjects: a new approach in the treatment of diabetes

Bromocriptine, a potent dopamine D(2) receptor agonist, has been shown to reduce insulin resistance, glucose intolerance and hyperlipidaemia in both numerous animal studies and in Phase II studies. Bromocriptine has been used worldwide for over 20 years to treat Parkinson's disease, macroprolactinoma and other disorders; it has been found to be generally safe. We therefore investigated the possible beneficial effects of Ergoset(R) (Ergo Science Corp.), a new quick release formulation of bromocriptine, on glycaemic control and serum lipid profile in obese Type 2 diabetic subjects in two large Phase III studies. A large, randomised, double-blind placebo-controlled study was conducted in which Ergoset was given once daily at 8 am. (4.8 mg maximum dose) for 24 weeks as adjunctive therapy to sulphonylurea (485 subjects) to obese Type 2 diabetics held on a weight- maintaining diet. Treatment efficacy parameters included change from baseline in glycated haemoglobin A(1c) (HbA(1c)), fasting and post-prandial serum glucose, insulin, triglyceride and free fatty acid levels. Baseline glycated haemoglobin, fasting glucose, insulin, triglyceride and free fatty acid levels did not differ between treatment groups. and on average were 9.4 +/- 0.05%, 222 +/- 2 mg/dl, 24 +/- 1 µU/ml, 248 +/- 11 mg/dl, and 850 +/- 32 µEq/l, respectively. A similarly designed study of Ergoset as monotherapy in Type 2 diabetics (154 subjects) with similar baseline clinical characteristics was conducted. Addition of Ergoset treatment to sulphonylurea reduced percent glycated HbA(1c) by 0.55 (P < 0.0001) (approximately 1.0 for responders, 65% of population), fasting and post-prandial glucose by 23 and 26 mg/dl (P < 0.0002), fasting and post-prandial triglycerides by 72 and 63 mg/dl (P < 0.005) and fasting and post-prandial free fatty acids by 150 and 165 µEq/l (P < 0.05), relative to placebo. Twelve percent of all Ergoset subjects, compared to 3% of placebo subjects, withdrew from the study due to adverse events. The most common events causing withdrawal were nausea, dizziness, asthenia, and rhinitis (representing 4.5, 3.3, 2.0, and 0.8% of the total Ergoset populations, respectively). The incidence of serious adverse events did not differ between Ergoset- (3.4%) and placebo- (4.3%) treated subjects. Ergoset as monotherapy also improved glycaemic control (0.56 HbA(1c) decrease relative to placebo after 24 weeks of treatment; P < 0.02). Once daily Ergoset treatment improves glycaemic control and serum lipid profile and is well-tolerated in obese Type 2 diabetics.

Estrogenic stimulation of hypothalamic-limbic system metabolism in ageing diabetic C57BL/KsJ mice

The therapeutic influences of estrogen treatment on age- and diabetes-related declines in regional brain glucose utilization (RBGU) rates were evaluated in 8- to 20-week-old female C57BL/KsJ normal (+/?) and diabetic (db/db) mice. Following either oil vehicle (oil: 0.1 ml) or estradiol (E: 1 microgram/3.5 days) treatments starting at 3 weeks of age, RBGU rates were subsequently determined at 8, 12, 16 and 20 weeks of age. A gradual decline in the basal rate of brain glucose utilization was observed in all control (oil- and E-treated) groups between 8 and 20 weeks. Expression of the hyperglycemic-obese diabetes syndrome in db/db mice resulted in a significant reduction in RBGU rates between 8 and 20 weeks relative to control values. In estrogen-sensitive hypothalamic, septal and amygdaloid regions, E therapy modulated RBGU rates in db/db mice relative to oil-treated diabetics, but did not significantly alter utilization rates in +/? mice. In cortical samples, E therapy had no significant influence on glucose utilization rates in either control or diabetic groups. A noticeable pattern of maturation-associated decline in CNS glucose utilization rates in all brain regions resulted in comparable regional metabolic indices being exhibited by all groups at 20 weeks of age, with the exception of the diabetes-associated exacerbation of RBGU rates in the oil-treated db/db group. These data demonstrate that the normal development-related decline in regional brain carbohydrate metabolism is accelerated by the diabetes syndrome, and that E therapy can modulate the syndrome-associated suppression of glucose utilization in steroid-sensitive CNS loci. These data suggest that the depressive influences of the diabetes syndrome on brain carbohydrate utilization rates may be therapeutically modified in recognized CNS regions possessing steroid-sequestering, metabolically responsive neurons.

Bromocriptine reduces obesity, glucose intolerance and extracellular monoamine metabolite levels in the ventromedial hypothalamus of Syrian hamsters

We examined whether reductions in body fat stores and insulin resistance in Syrian hamsters induced by bromocriptine are associated with reductions in daily norepinephrine (NE) and serotonin activities as indicated by their extracellular metabolite levels in the ventromedial hypothalamus (VMH). High levels of these monoamines within the VMH have been suspected to induce obesity and insulin resistance. Microdialysate samples from the VMH of freely moving obese male hamsters (BW: 208 +/- 5 g) were collected hourly over a 25-hour period before bromocriptine treatment, during the first day of and after 2 weeks of bromocriptine treatment (800 microg/animal daily, i.p.), and body composition and glucose tolerance analyses were conducted before and after 2 weeks of treatments. The microdialysate samples were analyzed by HPLC for metabolites of serotonin: 5-hydroxy-indoleacetic acid (5-HIAA), NE: 3-methoxy-4-hydroxy-phenylglycol (MHPG), and dopamine: homovanillic acid (HVA). Bromocriptine treatment for 14 days significantly reduced body fat by 60% and areas under the glucose and insulin curves during a glucose tolerance test by 50 and 46%, respectively. Concurrently, extracellular VMH contents of 5-HIAA, MHPG, and HVA were reduced by 50, 29 and 66%, respectively (p < 0.05). Similarly, VMH 5-HIAA and MHPG contents were 48 and 44% less, respectively (p < 0.05), in naturally glucose-tolerant hamsters compared with naturally glucose-intolerant hamsters. Bromocriptine induced reductions of body fat, and improvements in glucose intolerance may result in part from its ability to decrease serotonin and NE activities in the VMH.

Regulation of glucose homeostasis in humans with denervated livers

The liver plays a major role in regulating glucose metabolism, and since its function is influenced by sympathetic/ parasympathetic innervation, we used liver graft as a model of denervation to study the role of CNS in modulating hepatic glucose metabolism in humans. 22 liver transplant subjects were randomly studied by means of the hyperglycemic/ hyperinsulinemic (study 1), hyperglycemic/isoinsulinemic (study 2), euglycemic/hyperinsulinemic (study 3) as well as insulin-induced hypoglycemic (study 4) clamp, combined with bolus-continuous infusion of [3-3H]glucose and indirect calorimetry to determine the effect of different glycemic/insulinemic levels on endogenous glucose production and on peripheral glucose uptake. In addition, postabsorptive glucose homeostasis was cross-sectionally related to the transplant age (range = 40 d-35 mo) in 4 subgroups of patients 2, 6, 15, and 28 mo after transplantation. 22 subjects with chronic uveitis (CU) undergoing a similar immunosuppressive therapy and 35 normal healthy subjects served as controls. The results showed that successful transplantation was associated with fasting glucose concentration and endogenous glucose production in the lower physiological range within a few weeks after transplantation, and this pattern was maintained throughout the 28-mo follow-up period. Fasting glucose (4. 55+/-0.06 vs. 4.75+/-0.06 mM; P = 0.038) and endogenous glucose production (11.3+/-0.4 vs. 12.9+/-0.5 micromol/[kg.min]; P = 0.029) were lower when compared to CU and normal patients. At different combinations of glycemic/insulinemic levels, liver transplant (LTx) patients showed a comparable inhibition of endogenous glucose production. In contrast, in hypoglycemia, after a temporary fall endogenous glucose production rose to values comparable to those of the basal condition in CU and normal subjects (83+/-5 and 92+/-5% of basal), but it did not in LTx subjects (66+/-7%; P < 0.05 vs. CU and normal subjects). Fasting insulin and C-peptide levels were increased up to 6 mo after transplantation, indicating insulin resistance partially induced by prednisone. In addition, greater C-peptide but similar insulin levels during the hyperglycemic clamp (study 1) suggested an increased hepatic insulin clearance in LTx as compared to normal subjects. Fasting glucagon concentration was higher 6 mo after transplantation and thereafter. During euglycemia/hyperinsulinemia (study 3), the insulin-induced glucagon suppression detectable in CU and normal subjects was lacking in LTx subjects; furthermore, the counterregulatory response during hypoglycemia was blunted. In summary, liver transplant subjects have normal postabsorptive glucose metabolism, and glucose and insulin challenge elicit normal response at both hepatic and peripheral sites. Nevertheless, (a) minimal alteration of endogenous glucose production, (b) increased concentration of insulin and glucagon, and (c) defective counterregulation during hypoglycemia may reflect an alteration of the liver-CNS-islet circuit which is due to denervation of the transplanted graft.

Intracarotid glucose selectively increases Fos-like immunoreactivity in paraventricular, ventromedial and dorsomedial nuclei neurons

Perfusion of the forebrain with glucose at concentrations which alter neither plasma insulin nor glucose levels leads to sympathetic activation in some rats. We used the expression of Fos-like immunoreactivity (FLI) as an index of neuronal activation to examine the anatomic substrate underlying this phenomenon. Male Sprague-Dawley rats were infused via the right internal carotid artery with glucose (4 mg/kg/min) or equiosmolar mannitol for 60 min. They were killed 3 h after infusion onset and their brains reacted for FLI. As compared to mannitol-infused controls, 105% and 117% more neurons in hypothalamic ventromedial nucleus (VMN) and parvocellular portion of the paraventricular nuclei (PVN) of glucose-infused rats showed FLI, respectively. Importantly, only about half the glucose-infused rats showed increased FLI cells in these areas when compared to controls. In these same animals, glucose also significantly activated cells in the dorsomedial n. There was little FLI expressed in the magnocellular neurons of the PVN. This selective glucose response was bilateral in keeping with the bilateral distribution of India ink to midline hypothalamic structures following unilateral carotid infusions. Retrograde transport of cholera toxin B from medullary and thoracic spinal cord sympathetic outflow areas showed labeling of about 10% of PVN neurons with FLI activated by intracarotid glucose. There was no double labeling of VMN neurons. This supports the presence of anatomic pathways by which a subpopulation of glucose responsive PVN neurons might activate the sympathetic outflow areas in the medulla and spinal cord. The apparent bimodal distribution of glucose-induced activation of VMN and PVN neurons is in keeping with a similar bimodal pattern of sympathetic activation which obesity-prone but not obesity-resistant rats show following glucose infusions. Taken together, these data support a role for glucose-sensitive VMN and parvocellular PVN neurons in the weight gain phenotype specific sympathetic activation to glucose.

Central beta-adrenoceptor involvement in neural control of blood glucose in pigeons

The effects of ICV injections of adrenaline (30 nmol in 1 microL of saline) on blood glucose levels were investigated in conscious adult pigeons. This procedure increased blood glucose levels at 15-45 min after treatment. Previous ICV injection of propranolol (50 nmol) suppressed the increase observed at 15 min. The higher propranolol dose (100 nmol) was more effective than the lower dose (50 nmol) at blocking adrenaline-induced hyperglycemia. On the other hand, the ICV pretreatment with an alpha-adrenergic antagonist, phentolamine, slightly potentiated the hyperglycemia caused by ICV injection of adrenaline. The IP administration of propranolol (100 nmol) or phentolamine (100 nmol) before adrenaline ICV failed to induce change in the hyperglycemic response induced by this catecholamine. Both IP and ICV injections of these adrenergic blockers, before ICV injections of saline, evoked no changes in baseline glycemic levels. Therefore, elevation of blood glucose concentration by ICV adrenaline and blockade of the response by propranolol suggest the involvement of a central beta-adrenergic mechanism in the neural control of glycemia in pigeons.

Developmental and regional changes in brain norepinephrine levels in diabetic C57BL/KsJ mice: effects of estradiol and progesterone

Developmental and diabetes-associated changes in regional brain norepinephrine (NE) concentrations, and the influence of estradiol (E) and progesterone (P) on NE levels, were correlated with changes in blood glucose levels and body weight (obesity) in developing 4-16-week-old C57BL/KsJ (db/db) mice relative to corresponding age-matched control (+/?) parameters. Regional brain (i.e. amygdala, hypothalamus and medulla) NE levels were determined by high performance liquid chromatography. The (db/db) mice exhibited overt hyperglycemia and obesity relative to controls between 4 and 16 weeks of age. Hypothalamic NE levels in diabetics were chronically elevated as compared to those of age-matched controls by 8 weeks of age, and remained elevated through 16 weeks of age. Regional amygdaloid and medullary NE concentrations were comparable in (+/?) and (db/db) groups by 16 weeks. E-treatments normalized (db/db) hypothalamic NE concentrations to control levels between 8 and 16 weeks of age, but had no effect on amygdaloid or medullary values. In contrast, in 16 week old (db/db) mice, P-treatments elevated hypothalamic and medullary NE levels compared to controls and expected diabetic levels. These data demonstrate that a marked modification in regional brain NE concentrations occurs in association with the overt expression of the diabetes mutation during development in this species. Observed changes in adrenergic influences in specific CNS loci may be therapeutically modulated by ovarian steroid hormones, especially in the hypothalamic locus which is recognized to possess steroid-concentrating neurons. The observed normalization of regional brain NE concentrations by E-therapy may be causally related to the ovarian steroid-modulation of overt hyperglycemia and diabetes-associated neuronal degeneration in (db/db) mice.

Normalization of blood glucose in insulin-dependent diabetic pregnancies and the risks of hypoglycemia: a therapeutic dilemma

Intensive insulin therapy delays the onset and progression of microvascular complications in insulin-dependent diabetes mellitus (IDDM). Such therapy, however, is associated with an increased risk of potentially life-threatening hypoglycemia due to the loss of normal counterregulatory hormonal responses to hypoglycemia and to the syndrome of hypoglycemia unawareness. Current standards for glycemic control during pregnancy in IDDM women require intensive insulin therapy to optimize pregnancy outcome. Therefore, obstetricians and gynecologists providing prenatal care for women with IDDM should be aware that intensive insulin therapy predisposes these patients to the significant risks of severe hypoglycemia. It often becomes necessary to individualize the optimal balance between glycemic control during pregnancy and the risks of hypoglycemia.

Recovery of hypoglycaemia-associated compromised cerebral function after a short interval of euglycaemia in insulin-dependent diabetic patients

To test the hypothesis that compromised cerebral function, induced by recurrent hypoglycaemic episodes, may recover after a short interval of euglycaemia, we examined electrophysiological activity and symptom awareness during two sequential euglycaemic-hypoglycaemic clamp studies in 11 insulin-dependent diabetic patients without any signs of peripheral or autonomic neuropathy. Neurophysiological testing and evaluation of hypoglycaemic symptoms were performed at stable glycaemic plateaus of 5.6, 3.3, 2.2, and 1.7 mmol/l. The first clamp study was preceded by 3 short-term hypoglycaemic episodes, whereas the second clamp study followed a 2 day interval of strict euglycaemia. The latter caused a recovery of electrophysiological activity, which was demonstrated by recovery of delays of the middle latency auditory evoked potentials (latency shift of the P(a) component, MANOVA, P < 0.01). Reversal of hypoglycaemic symptom unawareness involved the overall symptom perception (MANOVA, P < 0.04), as well as the autonomic symptoms of heart pounding (P < 0.05) and sweating (P < 0.05). We conclude that the previously reported impaired cerebral function, occurring as a consequence of repetitive hypoglycaemic episodes, may recover after a single euglycaemic interval.

Ventromedial hypothalamic lesions in rats suppress counterregulatory responses to hypoglycemia

The central nervous system has been implicated in the activation of counterregulatory hormone release during hypoglycemia. However, the precise loci involved are not established. To determine the role of the ventromedial hypoglycemia, we performed hypoglycemic clamp studies in conscious Sprague-Dawley rats with bilateral VMH lesions produced by local ibotenic acid injection 2 wk earlier. Rats with lesions in the lateral hypothalamic area, frontal lobe, sham operated (stereotaxic needle placement into hypothalamus without injection), and naive animals served as control groups. The clamp study had two phases. For the first hour plasma glucose was fixed by a variable glucose infusion at euglycemia (approximately 5.9 mM). Thereafter, for an additional 90 min, glucose was either allowed to fall to (a) mild hypoglycemia (approximately 3.0 mM) or (b) more severe hypoglycemia (approximately 2.5 mM). Glucagon and catecholamine responses of lateral hypothalamic area-, frontal lobe-lesioned, sham operated, and naive animals were virtually identical at each hypoglycemic plateau. In contrast, glucagon, epinephrine, and norepinephrine responses in the VMH-lesioned rats were markedly inhibited; hormones were diminished by 50-60% during mild and by 75-80% during severe hypoglycemia as compared with the other groups. We conclude that the VMH plays a crucial role in triggering the release of glucagon and catecholamines during hypoglycemia.

Primacy of liver glucosensors in the sympathetic response to progressive hypoglycemia

The impact of hepatic glucose concentration on the sympathetic response to progressive hypoglycemia was examined in chronically cannulated conscious male dogs (n = 6). Graded hypoglycemia was induced via peripheral insulin infusion (30 pmol.kg-1.min-1) with either peripheral (PER) or portal (POR) glucose infusion. Over the 260-min experimental period, arterial glycemia was adjusted from 5.2 +/- 0.1 to 2.5 +/- 0.1 mM in decrements of approximately 0.5 mM every 40 min. Arterial glycemias were not significantly different between PER and POR at any measured level. However, hepatic glycemia was significantly elevated at all times during POR (8.4 +/- 0.8 to 3.4 +/- 0.2 mM) when compared to PER (5.2 +/- 0.2 to 2.5 +/- 0.1 mM). Plasma epinephrine values were significantly greater during PER vs. POR at all arterial glycemias below 4.0 mM. At the lowest level of arterial glycemia studied (2.5 +/- 0.2 mM) the epinephrine response above basal was 3-fold greater for PER (8.7 +/- 1.7 nM) when compared to POR (2.6 +/- 0.6 nM) (P < 0.01). Plasma norepinephrine results were similar for the two protocols, with PER demonstrating a 3-fold greater response above basal when compared to POR at 2.5 mM arterial glycemia (P < 0.05). While the sympathetic response was markedly different between protocols when expressed as a function of arterial glycemia, when expressed as a function of hepatic glycemia this discrepancy was largely eliminated. This latter observation supports the liver as the primary locus for glycemic detection relevant to the sympathoadrenal response when hypoglycemia develops slowly--i.e., over a period of 2-3 h. A comparison of the current findings with our previous observations suggests that the hepatic glucosensors may play a greater role in hypoglycemic counterregulation as the rate of fall in glycemia is less.

The role of the central nervous system in modulating glucose and protein metabolism during insulin-induced hypoglycemia

We previously established that insulin-induced hypoglycemia is associated with enhanced proteolysis with the GI tract being the major contributor to this response. In the present study we examined whether brain hypoglycemia modulates the changes in amino acid and glucose kinetics during insulin-induced hypoglycemia. Studies were performed in 24 h faster conscious dogs chronically fitted with catheters in the femoral artery, portal vein, hepatic vein, femoral vein and in both carotid and vertebral arteries, and that were also fitted with permanent tracheostomies. Following a 30 min basal period insulin was infused i.v. at 300 mU/kg.h to achieve systemic hypoglycemia averaging 42 +/- 2 mg/dl. In group I (n = 6) both central and systemic (global) hypoglycemia was allowed to develop. The rate of net hepatic glucose output (NHGO) increased by 50% above basal. Plasma leucine increased from 120 +/- 12 mumol/l basally to 154 +/- 30 mumol/l during the last hour of hypoglycemia. The rate of leucine appearance into the plasma compartment (R(a)) increased from 154 +/- 30 to 200 +/- 36 mumol/kg.h and its rate of oxidation increased from 22 +/- 5 to 51 +/- 8 mumol/kg.h, while its non-oxidative rate of disposal (141 +/- 12 mumol/kg.h) did not change. Net leucine balance across the gut was neutral (6 +/- 5 mumol/kg.h) and switched to net output of 96 +/- 24 mumol/kg.h. In group II (n = 5) 10% dextrose in water was infused into both carotid and vertebral arteries to prevent profound CNS glucopenia. This was associated with a drop in NHGO.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pancreas transplantation on glucose counterregulation in insulin-dependent diabetic patients prone to severe hypoglycaemia

Pancreatic transplantation was performed in three patients with insulin-dependent diabetes mellitus in whom recurrent and severe episodes of hypoglycaemia had been found to be due to defective glucose counterregulation. Thus in these patients the spontaneous blood glucose recovery after insulin-induced hypoglycaemia (0.1 U kg-1 h-1 i.v. insulin until blood glucose levels fell below 2.8 mmol l-1) was delayed, and the responses of glucagon, epinephrine and growth hormone (GH) were absent or diminished. After pancreas transplantation the patients exhibited essentially normal blood glucose control. When the insulin infusion test was repeated 3 months after the transplantation, the blood glucose level recovered rapidly after insulin withdrawal. The glucagon response was restored, and the responses of epinephrine and GH were improved. Plasma C-peptide was suppressed by approximately 50%, which is less than is observed in normal subjects. It is concluded that glucose counterregulation improves after pancreas transplantation. This appears to be mainly due to an improvement in the hypoglycaemia-induced glucagon response, but an amelioration of sympatho-adrenal and hypothalamic-pituitary regulatory mechanisms may also be involved. The apparent failure to suppress completely the insulin release from the denervated pancreas transplant indicates that inhibition of beta-cell secretion during insulin-induced hypoglycaemia may be partly under neural control.

Glucose-induced excitation in molluscan central neurons producing insulin-related peptides

The light green cells (LGCs) are a group of identified central neurons in the pond snail, Lymnaea stagnalis, that produce a number of insulin-related peptides. Freshly dissociated LGCs are activated by physiological concentrations of extracellular glucose. The response to glucose consists of a slow depolarization, which, at concentrations of 1 mM or more, rapidly induces regular spiking activity. The response persists during prolonged application of glucose but is completely reversed upon washing. The threshold concentration is 0.2 mM; the maximal effect occurs at 5 mM. In LGCs in central nervous system preparations kept in organ culture for 16-24 h, glucose causes a similar depolarization, which may lead to spiking activity. In freshly isolated preparations, which have very inexcitable LGCs, no direct response to glucose was seen. The response is specific to the LGCs; no other central neurons in Lymnaea showed consistent responses. The glucose response is evoked by D-glucose and the non-metabolized analogue 2-deoxy-D-glucose, but not by related hexoses, including L-glucose, nor pentoses or disaccharides. The response is not affected by interfering with the glucose metabolism, nor is the response mimicked by the metabolite D-glyceraldehyde or by injection of glucose. This suggests that glucose metabolites are not involved in the response. The glucose response depends on the presence of extracellular Na+ and is blocked by phlorizin, which specifically inhibits Na(+)-coupled glucose transport. This suggests that the response is due to activation of an electrogenic Na(+)-coupled glucose transporter.

Fluoxetine, a selective inhibitor of serotonin uptake

In summary, fluoxetine is a highly selective serotonin uptake inhibitor in vitro and in vivo. The conformation of fluoxetine, which resembles that of sertraline and other serotonin uptake inhibitors, appears to be a key feature that enables its high affinity and selective interaction with the serotonin transporter. The para-trifluoromethyl substituent, however, is also a pivotal structural element. The molecular pharmacology of fluoxetine has been well-defined, and its in vivo pharmacological effects appear to be mediated almost exclusively by serotonin uptake inhibition. Its selectivity for the serotonin transporter, lack of affinity for neurotransmitter receptors, and retention of selectivity following metabolism to norfluoxetine make fluoxetine a useful tool to explore pharmacologically induced increases in serotonin neurotransmission. Fluoxetine has found a variety of therapeutic application. Its use in treating depression has been most extensively studied, but controlled clinical studies also suggest the drug may have a role in treating obesity and bulimia. Moreover, a variety of other psychiatric disorders may be treatable with this drug. Regardless of the outcome of these clinical trials, it is apparent that fluoxetine has found a useful niche in therapy, and can be used as a probe to determine the role of serotonin in modulating human pathophysiologies.

Search for the hypoglycemia receptor using the local irrigation approach

To elucidate the loci for the putative glucoreceptors responding to hypoglycemia we introduced 'brain' and 'liver' clamps. Systemic hypoglycemia was induced by insulin infusion while the area of interest (ie. forebrain, hindbrain, portal-hepatic region) was maintained euglycemic via local glucose irrigation. Utilizing this approach, there appear to be no glucoreceptors residing exclusively in either the forebrain or hindbrain which are essential for the sympathoadrenal response to hypoglycemia. This is true for both moderate and severe hypoglycemic conditions. The possibility of a redundant glucoreceptor system within the brain, as suggested by a subsequent study, remains to be confirmed. The portal-hepatic glucoreceptors appear essential to engendering the full counterregulatory response. Establishing euglycemia across the portal-hepatic region inhibits the sympathoadrenal response to moderate hypoglycemia by over 40%. Further, despite prevailing hypoglycemia and significant elevations in counter-regulatory hormones, the liver demonstrated net glucose extraction during the liver clamp, suggestive of overriding neural input to the liver. Thus, the hepatic afferents appear to be very important for the counterregulatory response to hypoglycemia.

Age- and diabetes-associated alterations in regional brain norepinephrine concentrations and adrenergic receptor populations in C57BL/KsJ mice

The diabetes-associated changes in regional brain norepinephrine (NE) concentrations and related adrenergic receptor types were correlated with changes in blood glucose levels and body weight (obesity) in 4-16-week-old C57BL/KsJ (db/db) mice relative to corresponding age-matched control (+/?) parameters. Regional brain (i.e. frontal cortex, septal area, amygdala, hypothalamus and medulla) NE levels were determined by high performance liquid chromatography and compared to the associated changes in tissue alpha-1,2 and beta-adrenergic membrane receptor populations. All db/db mice exhibited overt hyperglycemia and obesity relative to controls between 4 and 16 weeks of age. Regional brain NE levels in diabetics were chronically elevated as compared to those of age-matched controls. All of the alpha 1 and alpha 2 adrenergic receptor populations were elevated in the regional brain samples of diabetics relative to controls. In contrast, beta-adrenergic receptor populations were depressed in diabetics as compared with age-matched controls. These data demonstrate that a marked modification in regional brain adrenergic parameters occurs in association with the overt expression of the diabetes mutation in this species. The observed changes in adrenergic influences in specific CNS loci may be causally related to the recognized diabetes-associated alterations in regional brain structure, function and metabolism in C57BL/KsJ (db/db) mice.

2-deoxy-D-glucose-induced hyperglycemia: role for direct sympathetic nervous system activation of liver glucose output

The hypothalamus plays an important integrative role in the control of peripheral metabolism, achieved by modulation of autonomic outflow to the endocrine pancreas, the liver and the adrenal medulla. This study examines the role of direct sympathetic nervous system control of hepatic glucose output during neuroglycopenia induced by the non-metabolizable glucose analogue 2-deoxy-D-glucose (2-DG). Steady-state tracer methodology was used to directly measure hepatic glucose output (Ra) in pentobarbitone-anesthetised male Wistar rats (220-320 g). Administration of 500 mg/kg 2-DG i.p. produced an increase in Ra from a control value of 7.3 +/- 0.3 mg/kg.min (n = 4) to 15.2 +/- 2.2 mg/kg.min-1 (n = 8), corresponding to an increase in plasma glucose (PG) from 6.4 +/- 0.1 mmol/l to 10.1 +/- 0.4 mmol/l. This rise was countered by the sympathetic noradrenergic blocker guanethidine (100 mg/kg i.p.), reducing Ra to 10.4 +/- 0.9 mg/kg.min-1 and PG to 6.1 +/- 0.3 mmol/l (n = 8), despite markedly lower plasma insulin (PI) levels (2-DG: PI = 94.7 +/- 18.6 mU/l (n = 7), 2-DG + guanethidine: PI = 41.4 +/- 3.3 mU/l (n = 8). Hyperglycemia and elevated liver glucose output were maintained in ADX animals treated with 2-DG, indicating an absence of adrenal-medullary influence (2-DG: Ra = 15.2 +/- 2.2 mg/kg.min-1, 2-DG + ADX = 15.6 +/- 1.0 mg/kg.min-1). Elevated Ra in the 2-DG + ADX was maintained despite markedly elevated insulin levels 349.3 +/- 72.6 mU/l (n = 7)).(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric analysis of obesity (ob/ob)- and diabetes (db/db)-associated hypothalamic neuronal degeneration in C57BL/KsJ mice

The influence of the obese (ob/ob) and diabetes (db/db) genetic mutations on hypothalamic structure was investigated in C57BL/KsJ and C57BL/6J mice strains by morphometric analysis of medial basal nuclei which are recognized to possess glucoregulatory neurons. Brains were collected and prepared for histomorphometric analysis at selected times following the development of expressed obesity and diabetes (Type II, non-insulin dependent) syndromes in order to compare both the strain and genomic influences on neuronal viability in the hypothalamic ventromedial (VMH) and arcuate (ARC) nuclei of mutant and age-matched control mice. The severity of each syndrome was determined by monitoring the concomitant changes in body weight and blood glucose levels in all groups. Both (db/db) and (ob/ob) mutant C57BL/KsJ mice exhibited an increase in the number and distribution of degenerated neurons in the VMH and ARC nuclei relative to corresponding controls. The mutation-associated exacerbation of the normal age-related neuronal loss, as observed in control MBH nuclei, was temporally associated with the overt expression of the hyperglycemic component of the obese and diabetes syndromes in aging C57BL/KsJ mice. No temporal or causal relationships were noted between the enhanced rate of premature neuronal degeneration, and either body weight or blood glucose levels, in either (db/db) or (ob/ob) C57BL/6J mice relative to controls. These data suggest that the hyperglycemic condition which characterizes the (ob/ob) and (db/db) mutant C57BL/KsJ mice is causally associated with the pronounced, premature MBH neuronal degeneration in these mouse strains. Neuronal changes were not pronounced when the genetic mutations were expressed in C57BL/6J mice. The accompanying alterations in brain glucose metabolism, hormone sensitivity, bioamine content and function which are recognized to occur in these mutant C57BL/KsJ mice may be causally associated consequences of the observed changes in MBH structural integrity and neuronal competence, with the severity of the mutation-associated changes being related to genetic background of the murine strain.

Response to deep hypoglycemia does not involve glucoreceptors in carotid perfused tissue

In the present study we examined whether the magnified hormonal counter-regulatory response seen during deep hypoglycemia (40 mg/dl) could be attenuated by supplying the forebrain with glucose furnished through carotid infusion. Two protocols were performed in conscious dogs. In the first protocol we infused glucose bilaterally into the carotid circulation to produce a forebrain glycemia of 55 +/- 1 mg/dl (as reflected in the jugular vein), whereas systemic glycemia declined to 39 +/- 2 mg/dl. In the second protocol as a control we infused glucose into the systemic circulation at a rate matched to protocol 1 so that both systemic and jugular plasma glucose concentrations were equivalent to the systemic glucose concentrations in protocol 1 (jugular, 41 +/- 3 mg/dl; systemic, 40 +/- 2 mg/dl; P greater than 0.9). In spite of a substantial difference in forebrain glycemia (55 mg/dl compared with 41 mg/dl) there were no differences in the counter-regulatory responses of catecholamines or glucagon. In addition, through the use of radiolabeled microspheres, we defined the precise regions of the forebrain irrigated during bilateral intracarotid glucose infusions. The concentration of microspheres was high in the forebrain but very low in the hindbrain. Our results indicate that glucoreceptor cells in tissues perfused by carotid arteries may play a tautological role in the sympathetic response to hypoglycemia and imply that glucose-sensitive receptors must also be located elsewhere in the central nervous system or in the periphery.

Immunological blockade of endogenous thyrotropin-releasing hormone impairs recovery from hyperglycemia in mice

Administration of antiserum to thyrotropin-releasing hormone (TRH) into the lateral cerebral ventricle of mice significantly attenuated recovery from hyperglycemia induced by treatment with 2-deoxyglucose but had no effect on the plasma glucose of saline-treated mice. TRH, injected centrally together with the anti-TRH antibody, reversed the effect of the antiserum and blocked the development of hyperglycemia. These findings suggest that activation of TRH neurons in the central nervous system may be a physiological event influencing recovery from hyperglycemia.

Intrahypothalamic microinfusion of corticotropin-releasing factor elevates blood glucose and free fatty acids in rats

Three experiments examined whether intrahypothalamic microinfusions of corticotropin releasing factor (CRF) can affect circulating levels of the metabolic fuels, glucose and free fatty acids. Infusions of CRF into the paraventricular nucleus dose-dependently increased serum glucose levels; greater increases were seen in acute than in chronic preparations. The greater effectiveness could not be accounted for by anesthetization per se. CRF infusion into the ventromedial nucleus did not affect serum glucose. Infusions into both sites, however, significantly increased serum free fatty acids. Neither glucose nor free fatty acids were altered by infusions into the lateral hypothalamus or the caudate-putamen. These data suggest that the previously identified CRF binding sites and CRF neuronal terminals in the paraventricular and ventromedial nuclei may be involved in the central regulation of metabolic fuel release. Additionally, it appears that the importance of CRF in the paraventricular nucleus in regulating serum glucose may be greater under some conditions than others.

Counterregulatory hormonal responses to hypoglycaemia in type 1 (insulin-dependent) diabetes: evidence for diminished hypothalamic-pituitary hormonal secretion

Acute insulin-induced hypoglycaemia in humans provokes autonomic neural activation and counterregulatory hormonal secretion mediated in part via hypothalamic stimulation. Many patients with Type 1 (insulin-dependent) diabetes have acquired deficiencies of counterregulatory hormonal release following hypoglycaemia. To study the integrity of the hypothalamic-pituitary and the sympatho-adrenal systems, the responses of pituitary hormones, beta-endorphin, glucagon and adrenaline to acute insulin-induced hypoglycaemia (0.2 units/kg) were examined in 16 patients with Type 1 diabetes who did not have autonomic neuropathy. To examine the effect of duration of diabetes these patients were subdivided into two groups (Group 1: 8 patients less than 5 years duration; Group 2: 8 patients greater than 15 years duration) and were compared with 8 normal volunteers (Group 3). The severity and time of onset of hypoglycaemia were similar in all 3 groups, but mean blood glucose recovery was slower in the diabetic groups (p less than 0.01). The mean responses of glucagon, adrenaline, adrenocorticotrophic hormone, prolactin and beta-endorphin were similar in all 3 groups, but the mean responses of growth hormone were lower in both diabetic groups than in the normal group (p less than 0.05). The mean increments of glucagon and adrenaline in the diabetic groups were lower than the normal group, but these differences did not achieve significance; glucagon secretion was preserved in several diabetic patients irrespective of duration of disease. Various hormonal responses to hypoglycaemia were absent or diminished in individual diabetic patients, and multiple hormonal deficiencies could be implicated in delaying blood glucose recovery.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian hormone effects on activity, glucoregulation and thyroid hormones in the rat

Ovarian hormonal influences on the range of physiological and behavioral variables which combine to affect overall energy balance are poorly delineated. In the present study 4 groups of virgin, female rats (intact, ovariectomized, ovariectomized with estrogen replacement and ovariectomized with estrogen plus progesterone) were allowed access to running wheels and activity; food intake and weight gain were measured initially under food restricted, then under ad lib conditions. Serum insulin, glucose, thyroxine (T4) and triiodothyronine (T3) were determined on trunk blood samples obtained at the end of the experiment. Ovariectomy resulted in an increased rate of weight gain through reduced activity and T3 but food intake was unchanged. Insulin levels were greatly reduced. Estrogen replacement restored activity to the intact group's level and normalized weight gain. Insulin and T3 were also raised to control levels but T4 was reduced as was serum glucose. Estrogen plus progesterone replacement reduced weight gain markedly and increased T3 with normal T4. Despite the lower body weight this group was hyperglycemic and hyperinsulinemic suggesting insulin resistance. The results have important implications for the glucoregulatory and energy balance perturbations of ovarian hormone fluctuations and focus particularly on progesterone.

Vasopressin excites ventromedial hypothalamic glucose-responsive neurons in vitro

Effects of vasopressin (AVP), oxytocin (OXY), norepinephrine (NE), and glucose on the single-unit activity of hypothalamic ventromedial nucleus (VMN) in tissue slices were studied. While AVP was exclusively excitatory on 58% of the neurons, OXY could be excitatory or inhibitory and affected only 42% of the neurons. There was no correlation between the responses to these two peptides. Each of these two peptides could desensitize neuronal response to itself, but did not cross-desensitize responses to each other. These results indicate that AVP and OXY do not act on the same population of VMN neurons through the same cellular mechanism. Furthermore, only the responses to AVP were correlated to responses to glucose and NE, two agents relevant to central regulation of feeding. This correlation with responses to feeding-relevant agents and the exclusively excitatory action on the VMN, which is involved in the regulation of feeding, suggest that AVP can play a role in the regulation of feeding, particularly the feeding induced by the injection of NE into the paraventricular nucleus, that is known to alter AVP release.

Central glucagon-induced hyperglycemia is mediated by combined activation of the adrenal medulla and sympathetic nerve endings

Intracerebroventricular (ICV) microinjection of glucagon (0.0025-2.5 micrograms) produced significant dose-dependent hyperglycemia in mice. This hyperglycemic effect was prevented by pretreatment with the sympathetic ganglionic blocker chlorisondamine chloride or bilateral adrenalectomy plus chemical sympathectomy with 6-hydroxydopamine. Similar pretreatments had no effect on the plasma glucose responses to systemic glucagon administration. Pretreatment with somatostatin, which blocks pancreatic glucagon secretion had no effect on the hyperglycemic response to central glucagon administration. The results suggest that the increase in plasma glucose following central glucagon administration is mediated by combined action of adrenal and sympathetic amines to stimulate hepatic glucose production, or additionally to inhibit insulin release from the pancreas. The possible involvement of glucagon in the central nervous system in systemic glucoregulation is discussed.

Similarities in feeding behavior of chronic methamphetamine treated and withdrawn rats to VMH lesioned rats

During chronic methamphetamine (M) administration and after drug withdrawal, total daily food intake, water consumption and body weight increase was measured. Additionally, food intake in the early light phase provided an index of normal circadian rhythmicity. A parallel development of tolerance to the anorexic effect of M and increased feeding in the early light phase occurred. A further abnormal behavior of both chronic M-treated and withdrawn rats was the lack of preference reversal when given free access to concentrated vs. diluted glucose solutions. Both disturbed circadian feeding rhythmicity and inhibition of the glucose preference reversal are found in rats with ventromedial hypothalamic (VMH) lesions. Reduced food intake and diminished body weight increase is a characteristic of lateral hypothalamic lesions. By analogy, chronic M-treatment could be considered to induce a functional state similar to lesions of the medial and lateral hypothalamus, each with a different time course.