Effects of a selective serotonin reuptake inhibitor, fluoxetine, on counterregulatory responses to hypoglycemia in healthy individuals

Current and future therapies to treat impaired awareness of hypoglycemia

In order to achieve optimal glycemic control, intensive insulin regimes are needed for individuals with Type 1 Diabetes (T1D) and insulin-dependent Type 2 Diabetes (T2D). Unfortunately, intensive glycemic control often results in insulin-induced hypoglycemia. Moreover, recurrent episodes of hypoglycemia result in both the loss of the characteristic warning symptoms associated with hypoglycemia and an attenuated counterregulatory hormone responses. The blunting of warning symptoms is known as impaired awareness of hypoglycemia (IAH). Together, IAH and the loss of the hormonal response is termed hypoglycemia associated autonomic failure (HAAF). IAH is prevalent in up to 25% in people with T1D and up to 10% in people with T2D. IAH and HAAF increase the risk of severe hypoglycemia 6-fold and 25-fold, respectively. To reduce this risk for severe hypoglycemia, multiple different therapeutic approaches are being explored that could improve awareness of hypoglycemia. Current therapies to improve awareness of hypoglycemia include patient education and psychoeducation, the use of novel glycemic control technology, pancreas/islet transplantation, and drug therapy. This review examines both existing therapies and potential therapies that are in pre-clinical testing. Novel treatments that improve awareness of hypoglycemia, via improving the counterregulatory hormone responses or improving hypoglycemic symptom recognition, would also shed light on the possible neurological mechanisms that lead to the development of IAH. To reduce the risk of severe hypoglycemia in people with diabetes, elucidating the mechanism behind IAH, as well as developing targeted therapies is currently an unmet need for those that suffer from IAH.

Antidepressants and type 2 diabetes: highways to knowns and unknowns

Type 2 diabetes (T2D) is a metabolic disease caused by the development of insulin resistance (IR), relative insulin deficiency, and hyperglycemia. Hyperglycemia-induced neurochemical dysregulation activates the progression of depression in T2D patients. Therefore, management of depression by antidepressant agents improves glucose homeostasis and insulin sensitivity. However, prolong use of antidepressant drugs may increase the risk for the development of T2D. However, there is strong controversy concerning the use of antidepressant drugs in T2D. Therefore, this review try to elucidate the potential effects of antidepressant drugs in T2D regarding their detrimental and beneficial effects.

Serotonin and the serotonin transporter in the adrenal gland

The adrenal glands are key components of the mammalian endocrine system, helping maintain physiological homeostasis and the coordinated response to stress. Each adrenal gland has two morphologically and functionally distinct regions, the outer cortex and inner medulla. The cortex is organized into three concentric zones which secrete steroid hormones, including aldosterone and cortisol. Neural crest-derived chromaffin cells in the medulla are innervated by preganglionic sympathetic neurons and secrete catecholamines (epinephrine, norepinephrine) and neuropeptides into the bloodstream, thereby functioning as the neuroendocrine arm of the sympathetic nervous system. In this article we review serotonin (5-HT) and the serotonin transporter (SERT; SLC6A4) in the adrenal gland. In the adrenal cortex, 5-HT, primarily sourced from resident mast cells, acts as a paracrine signal to stimulate aldosterone and cortisol secretion through 5-HT4/5-HT7 receptors. Medullary chromaffin cells contain a small amount of 5-HT due to SERT-mediated uptake and express 5-HT1A receptors which inhibit secretion. The atypical mechanism of the 5-HT1A receptors and interaction with SERT fine tune this autocrine pathway to control stress-evoked catecholamine secretion. Receptor-independent signaling by SERT/intracellular 5-HT modulates the amount and kinetics of transmitter release from single vesicle fusion events. SERT might also influence stress-evoked upregulation of tyrosine hydroxylase transcription. Transient signaling via 5-HT3 receptors during embryonic development can limit the number of chromaffin cells found in the mature adrenal gland. Together, this emerging evidence suggests that the adrenal medulla is a peripheral hub for serotonergic control of the sympathoadrenal stress response.

Impact of antidepressant use on the autonomic nervous system: A meta-analysis and systematic review

Changes in cardiac autonomic nervous system (ANS) regulation observed in psychiatric disorders may be mitigated by antidepressants. We meta-analyzed and systematically reviewed studies examining antidepressants' effects on ANS outcomes, including heart rate variability (HRV). We conducted a PRISMA/MOOSE-compliant search of PubMed and Scopus until March 28th, 2022. We included randomized placebo-controlled trials (RCTs) and pre-post studies, regardless of diagnosis. We pooled results in random-effects meta-analyses, pooling homogeneous study designs and outcomes. We conducted sensitivity analyses and assessed quality of included studies. Thirty studies could be meta-analyzed. Selective serotonin reuptake inhibitors (SSRIs) were significantly associated with a reduction in the square root of the mean-squared difference between successive R-R intervals (RMSSD) (SMD= -0.48) and skin conductance response (SMD= -0.55) in RCTs and with a significant increase in RMSSD in pre-post studies (SMD=0.27). In pre-post studies, tricyclic antidepressants (TCAs) were associated with a significant decrease in several HRV outcomes while agomelatine was associated with a significant increase in high frequency power (SMD= 0.14). In conclusion, SSRIs reduce skin conductance response but have no or inconclusive effects on other ANS outcomes, depending on study design. TCAs reduce markers of parasympathetic function while agomelatine might have the opposite effect. Studies are needed to investigate the impact of SSRIs on the recovery of cardiac ANS regulation after acute myocardial infarction, and the effects of newer antidepressants.

The serotonergic system dysfunction in diabetes mellitus

Most peripheral serotonin (5-HT) is synthesized in enterochromaffin cells, and most circulating 5-HT is stored in platelets. As a monoamine, 5-HT has several functions in various non-neuronal and neuronal systems. In the central nervous system, it functions as a neurotransmitter to modulate feeding behavior and mood. Numerous clinical trials have focused on increasing 5-HT activation in the central nervous system, including those involving anti-obesity drugs currently in the market, although severe side effects on peripheral system can lead to the withdrawal of certain drugs. Recent studies have revealed that both the peripheral and central serotonergic systems play a vital role in diabetes and its complications. This review summarizes the roles of the serotonergic system in blood glucose regulation, diabetic macroangiopathy, diabetic peripheral neuropathy, and diabetic encephalopathy, indicating its potential clinical significance as a therapeutic target for the treatment of diabetes and its complications.

Effects of the selective serotonin reuptake inhibitor fluoxetine on glucose metabolism: A systematic review

OBJECTIVES

The metabolic effects of antidepressants should be considered when prescribing antidepressants due to the increasing risk of diabetes, obesity and cardiovascular disease. This study aims to explore the effects of fluoxetine on glucose and lipid metabolism in human body.

METHODS

Studies of the effects of fluoxetine on glucose and lipid metabolism were collected from the PubMed, MEDLINE and Embase databases without limiting the research design. The retrieval spanned between inception and January 2021. The main outcome measures were fasting blood glucose, glycosylated hemoglobin (mainly HbA1c) and body weight.

RESULTS

A total of 24 studies were retrieved, including 20 randomized controlled trials (RCTs), 1 prospective study and 3 case reports. The meta-analysis showed that FBG and HbA_1c levels were moderately decreased(MD-0.85[-1.75, -0.13], P = 0.02 and MD-0.55[-1.23, 0.13], P = 0.11 respectively) and body weight was significantly decreased (MD-3.01[-5.58, -0.44], P < 0.00001) with fluoxetine treatment compared with placebo. Both plasma triglyceride (TG) and total cholesterol (TC) levels decreased significantly (P < 0.00001).

CONCLUSION

Fluoxetine had a positive effect on improving blood glucose control in patients with disorders of glucose metabolism and was good for weight management in obese people despite significant heterogeneity between studies.

N-Hydroxyethyl-1-Deoxynojirimycin (Miglitol) Restores the Counterregulatory Response to Hypoglycemia Following Antecedent Hypoglycemia

Antecedent hypoglycemia suppresses the counterregulatory responses to subsequent hypoglycemic episodes, which can be prevented by normalizing portal-mesenteric vein (PMV) glycemia alone during the antecedent bout. Since the sodium-glucose transporter 3 receptor has been implicated in PMV glucosensing, we hypothesized that PMV infusion of the sodium-glucose cotransporter 3 receptor agonist N-hydroxyethyl-1-deoxynojirimycin (miglitol) would rescue the sympathoadrenal response to subsequent hypoglycemia. Rats underwent hyperinsulinemic-hypoglycemic clamps on 2 consecutive days without miglitol infusion (antecedent hypoglycemia without miglitol [HYPO]) or with miglitol infused upstream in the PMV, perfusing the glucosensors, or adjacent to the liver, bypassing PMV glucosensors, on day 1 or day 2. Control animals underwent day 1 euglycemic clamps, followed by hypoglycemic clamps on day 2. Peak epinephrine (EPI) responses for HYPO on day 2 were significantly blunted when compared with controls. Miglitol infusion on day 1 proved ineffective in restoring the EPI response following antecedent hypoglycemia, but day 2 miglitol infusion restored EPI responses to control levels. As norepinephrine and glucagon demonstrated similar responses, day 2 administration of miglitol effectively restored the counterregulatory response following antecedent hypoglycemia. In subsequent experiments, we demonstrate similar results with reduced miglitol infusion doses, approaching those currently prescribed for type 2 diabetes (correcting for rodent size), as well as the efficacy of oral miglitol administration in restoring the counterregulatory responses following antecedent hypoglycemia.

Impact of Fluoxetine Treatment and Folic Acid Supplementation on the Mammary Gland Transcriptome During Peak Lactation

Serotonin is a key regulator of mammary gland homeostasis during lactation. Selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat peripartum depression, but also modulates mammary gland serotonin concentrations and signaling in part through DNA methylation. The objective of this study was to determine mouse mammary transcriptome changes in response to the SSRI fluoxetine and how methyl donor supplementation, achieved by folic acid supplementation, affected the transcriptome. Female C57BL/6J mice were fed either breeder diet (containing 4 mg/kg folic acid) or supplemented diet (containing 24 mg/kg folic acid) beginning 2 weeks prior to mating, then on embryonic day 13 mice were injected daily with either saline or 20 mg/kg fluoxetine. Mammary glands were harvested at peak lactation, lactation day 10, for transcriptomic analysis. Fluoxetine but not folic acid altered circulating serotonin and calcium concentrations, and folic acid reduced mammary serotonin concentrations, however only fluoxetine altered genes in the mammary transcriptome. Fluoxetine treatment altered fifty-six genes. Elovl6 was the most significantly altered gene by fluoxetine treatment along with gene pathways involving fatty acid homeostasis, PPARγ, and adipogenesis, which are critical for milk fat synthesis. Enriched pathways in the mammary gland by fluoxetine revealed pathways including calcium signaling, serotonin receptors, milk proteins, and cellular response to cytokine stimulus which are important for lactation. Although folic acid did not impact specific genes, a less stringent pathway analysis revealed more diffuse effects where folic acid enriched pathways involving negative regulation of gene expression as expected, but additionally enriched pathways involving serotonin, glycolysis, and lactalbumin which are critical for lactation. In conclusion, peripartal SSRI use and folic acid supplementation altered critical genes related to milk synthesis and mammary gland function that are important to a successful lactation. However, folic acid supplementation did not reverse changes in the mammary gland transcriptome altered by peripartal SSRI treatment.

Hypoglycemia-associated autonomic failure, counterregulatory responses, and therapeutic options in type 1 diabetes

Hypoglycemia remains a major barrier to the achievement of target levels of glycemic control for most individuals with insulin-dependent type 1 diabetes (T1D). Both the loss of β cells and an accompanying defect in the α cell response to hypoglycemia predispose patients with T1D to the development of low blood glucose. Increased glucose variability, exposure to hypoglycemia, and impaired awareness of hypoglycemia all contribute to increased risk of experiencing severe hypoglycemia, which is explained by progressive impairment in epinephrine secretion and autonomic symptom generation in response to hypoglycemia leading to defective glucose counterregulation and hypoglycemia unawareness that characterize hypoglycemia-associated autonomic failure (HAAF). Interruption of HAAF requires interfering with the mechanisms of brain adaptation to low blood glucose that affect central glucose sensing and the autonomic response to hypoglycemia, or avoidance of hypoglycemia that may allow for eventual recovery of counterregulatory and autonomic symptom responses. Strategies for hypoglycemia avoidance that include continuous glucose monitoring may reduce, but do not eliminate, clinically significant hypoglycemia, with ongoing counterregulatory defects and impaired awareness of hypoglycemia. Complete avoidance of hypoglycemia can be achieved following pancreatic islet transplantation and allows for the restoration of counterregulatory and autonomic symptom responses that evidences the potential for reversing HAAF in T1D.

Detection of Human Plasma Glucose Using a Self-Powered Glucose Biosensor

This work presents the characterization of a self-powered glucose biosensor using individual sequential assays of human plasma glucose obtained from diabetic patients. The self-powered glucose biosensor is exploited to optimize the assay parameters for sensing plasma glucose levels. In particular, the biofuel cell component of the system at pH 7.4, 37 °C generates a power density directly proportional to plasma glucose and exhibited a maximum power density of 0.462 mW·cm−2 at a cell voltage of 0.213 V in 5 mM plasma glucose. Plasma glucose is further sensed by monitoring the charge/discharge frequency (Hz) of the integrated capacitor functioning as the transducer. With this method, the plasma glucose is quantitatively detected in 100 microliters of human plasma with unprecedented sensitivity, as high as 104.51 ± 0.7 Hz·mM−1·cm−2 and a detection limit of 2.31 ± 0.3 mM. The results suggest the possibility to sense human plasma glucose at clinically relevant concentrations without the use of an external power source.

The Effects of Tryptophan Enhancement and Depletion on Plasma Catecholamine Levels in Healthy Individuals

OBJECTIVE

Central nervous system (CNS) serotonin (5-HT) exerts both excitatory and inhibitory effects on the sympathetic nervous system (SNS) in animals. In this study, we examine the effects of tryptophan enhancement and depletion on plasma catecholamine levels in humans.

METHODS

The total sample consisted of 164 healthy men and women who were tested for 2 days. Seventy-nine participants were randomized to a tryptophan enhancement condition and 85 to a tryptophan depletion condition. Both protocols consisted of a "sham day," followed by an "active day." Blood samples for assessment of plasma norepinephrine and epinephrine levels were collected before and after tryptophan enhancement/depletion. Data were analyzed using general linear models. Separate analyses were conducted for each study arm and for each measure.

RESULTS

In the depletion condition, both epinephrine (F(5,330) = 2.69, p = .021) and norepinephrine (F(5,335) = 2.79, p = .018) showed small increases on active versus "sham" depletion days. There were also significant day by time interactions for epinephrine (F(3,171) = 39.32, p < .0001) and norepinephrine (F(3,195) = 31.09, p < .0001) levels in the enhancement arm. Tryptophan infusion resulted in a marked increase in epinephrine (Premean = 23.92 (12.23) versus Postmean = 81.57 (62.36)) and decrease in norepinephrine (Premean = 257.2 (106.11) versus Postmean = 177.04 (87.15)), whereas levels of both catecholamines were stable on the "sham day."

CONCLUSIONS

CNS 5-HT exerts both inhibitory and excitatory effects on SNS activity in humans, potentially due to stimulation of CNS 5-HT receptors that have shown to have inhibitory (5-HT1A) and excitatory (5-HT1A and/or 5-HT2) SNS effects in animal models.

The Impact of Prolonged, Selective, Serotonin Reuptake Inhibitor Treatment on Serum Lipid and Glucose Levels in Children and Adolescents: A Preliminary Prospective Study

OBJECTIVES

Treatment with selective serotonin reuptake inhibitors (SSRIs) is common and is considered safe and effective in the treatment of anxiety and depressive disorders in pediatric populations. SSRI administration, however, is associated with adverse metabolic effects. The aim of this preliminary study was to evaluate the possible influence of a 6-month SSRI treatment on metabolic parameters in children and adolescents with depressive and/or anxiety disorders.

METHODS

Metabolic parameters (glucose, cholesterol, triglycerides, low-density lipoprotein [LDL], and high-density lipoprotein [HDL]) were monitored in 22 children and adolescents (16 boys and 6 girls, aged 8-18 years) at baseline and after 6 months of SSRI treatment for depression and/or anxiety.

RESULTS

Six months of SSRI treatment did not affect serum glucose, cholesterol, or triglycerides significantly, but a tendency (p = 0.06) toward elevation in serum LDL accompanied by a parallel reduction in HDL levels was detected.

CONCLUSION

It appears that the 6-month SSRI treatment is metabolically safe in children and adolescents and does not affect the glucose or lipid profile. Long-term large-scale studies in pediatric populations focusing on the possible impact of long-term SSRI treatment (>6 months) on metabolic parameters are warranted.

Adrenal serotonin derives from accumulation by the antidepressant-sensitive serotonin transporter

Adrenal chromaffin cells comprise the neuroendocrine arm of the sympathetic nervous system and secrete catecholamines to coordinate the appropriate stress response. Deletion of the serotonin (5-HT) transporter (SERT) gene in mice (SERT^-/- mice) or pharmacological block of SERT function in rodents and humans augments this sympathoadrenal stress response (epinephrine secretion). The prevailing assumption is that loss of CNS SERT alters central drive to the peripheral sympathetic nervous system. Adrenal chromaffin cells also prominently express SERT where it might coordinate accumulation of 5-HT for reuse in the autocrine control of stress-evoked catecholamine secretion. To help test this hypothesis, we have generated a novel mouse model with selective excision of SERT in the peripheral sympathetic nervous system (SERT^ΔTH), generated by crossing floxed SERT mice with tyrosine hydroxylase Cre driver mice. SERT expression, assessed by western blot, was abolished in the adrenal gland but not perturbed in the CNS of SERT^ΔTH mice. SERT-mediated [³H] 5-HT uptake was unaltered in midbrain, hindbrain, and spinal cord synaptosomes, confirming transporter function was intact in the CNS. Endogenous midbrain and whole blood 5-HT homeostasis was unperturbed in SERT^ΔTH mice, contrasting with the depleted 5-HT content in SERT^-/- mice. Selective SERT excision reduced adrenal gland 5-HT content by ≈ 50% in SERT^ΔTH mice but had no effect on adrenal catecholamine content. This novel model confirms that SERT expressed in adrenal chromaffin cells is essential for maintaining wild-type levels of 5-HT and provides a powerful tool to help dissect the role of SERT in the sympathetic stress response.

Noradrenergic Activity in the Human Brain: A Mechanism Supporting the Defense Against Hypoglycemia

CONTEXT

Hypoglycemia, one of the major factors limiting optimal glycemic control in insulin-treated patients with diabetes, elicits a brain response to restore normoglycemia by activating counterregulation. Animal data indicate that local release of norepinephrine (NE) in the hypothalamus is important for triggering hypoglycemia-induced counterregulatory (CR) hormonal responses.

OBJECTIVE

To examine the potential role of brain noradrenergic (NA) activation in humans during hypoglycemia.

DESIGN

A hyperinsulinemic-hypoglycemic clamp was performed in conjunction with positron emission tomographic imaging.

PARTICIPANTS

Nine lean healthy volunteers were studied during the hyperinsulinemic-hypoglycemic clamp.

DESIGN

Participants received intravenous injections of (S,S)-[11C]O-methylreboxetine ([11C]MRB), a highly selective NE transporter (NET) ligand, at baseline and during hypoglycemia.

RESULTS

Hypoglycemia increased plasma epinephrine, glucagon, cortisol, and growth hormone and decreased [11C]MRB binding potential (BPND) by 24% ± 12% in the raphe nucleus (P < 0.01). In contrast, changes in [11C]MRB BPND in the hypothalamus positively correlated with increments in epinephrine and glucagon levels and negatively correlated with glucose infusion rate (all P < 0.05). Furthermore, in rat hypothalamus studies, hypoglycemia induced NET translocation from the cytosol to the plasma membrane.

CONCLUSIONS

Insulin-induced hypoglycemia initiated a complex brain NA response in humans. Raphe nuclei, a region involved in regulating autonomic output, motor activity, and hunger, had increased NA activity, whereas the hypothalamus showed a NET-binding pattern that was associated with the individual's CR response magnitude. These findings suggest that NA output most likely is important for modulating brain responses to hypoglycemia in humans.

Potential approaches to prevent hypoglycemia-associated autonomic failure

Clear health benefits are associated with intensive glucose control in type 1 diabetes mellitus (T1DM). However, maintaining near-normal glycemia remains an elusive goal for many patients, in large part owing to the risk of severe hypoglycemia. In fact, recurrent episodes of hypoglycemia lead to 'hypoglycemia-associated autonomic failure' (HAAF), characterized by defective counter-regulatory responses to hypoglycemia. Extensive studies to understand the mechanisms underlying HAAF have revealed multiple potential etiologies, suggesting various approaches to prevent the development of HAAF. In this review, we present an overview of the literature focused on pharmacological approaches that may prevent the development of HAAF. The purported underlying mechanisms of HAAF include: 1) central mechanisms (opioid receptors, ATP-sensitive K+(KATP) channels, adrenergic receptors, serotonin selective receptor inhibitors, γ-aminobuyric acid receptors, N-methyl D-aspartate receptors); 2) hormones (cortisol, estrogen, dehydroepiandrosterone (DHEA) or DHEA sulfate, glucagon-like peptide-1) and 3) nutrients (fructose, free fatty acids, ketones), all of which have been studied vis-à-vis their ability to impact the development of HAAF. A careful review of the current literature reveals many promising therapeutic approaches to treat or reduce this important limitation to optimal glycemic control.

Serotonin and Serotonin Transporters in the Adrenal Medulla: A Potential Hub for Modulation of the Sympathetic Stress Response

Serotonin (5-HT) is an important neurotransmitter in the central nervous system where it modulates circuits involved in mood, cognition, movement, arousal, and autonomic function. The 5-HT transporter (SERT; SLC6A4) is a key regulator of 5-HT signaling, and genetic variations in SERT are associated with various disorders including depression, anxiety, and autism. This review focuses on the role of SERT in the sympathetic nervous system. Autonomic/sympathetic dysfunction is evident in patients with depression, anxiety, and other diseases linked to serotonergic signaling. Experimentally, loss of SERT function (SERT knockout mice or chronic pharmacological block) has been reported to augment the sympathetic stress response. Alterations to serotonergic signaling in the CNS and thus central drive to the peripheral sympathetic nervous system are presumed to underlie this augmentation. Although less widely recognized, SERT is robustly expressed in chromaffin cells of the adrenal medulla, the neuroendocrine arm of the sympathetic nervous system. Adrenal chromaffin cells do not synthesize 5-HT but accumulate small amounts by SERT-mediated uptake. Recent evidence demonstrated that 5-HT1A receptors inhibit catecholamine secretion from adrenal chromaffin cells via an atypical mechanism that does not involve modulation of cellular excitability or voltage-gated Ca2+ channels. This raises the possibility that the adrenal medulla is a previously unrecognized peripheral hub for serotonergic control of the sympathetic stress response. As a framework for future investigation, a model is proposed in which stress-evoked adrenal catecholamine secretion is fine-tuned by SERT-modulated autocrine 5-HT signaling.

Serotonin-mediated modulation of acetylcholine-induced intracellular calcium responses in chromaffin cells isolated from the rat adrenal medulla

We examined serotonin (5-HT)-mediated modulation of acetylcholine (ACh)-induced intracellular Ca²⁺ ([Ca²⁺]_i) responses in rat adrenal chromaffin cells using calcium imaging. 5-HT did not induce any [Ca²⁺]_i response in clustered chromaffin cells. However, the magnitude of ACh-induced [Ca²⁺]_i increases in the same specimens was inhibited in the presence of 5-HT. ACh-induced [Ca²⁺]_i increases in chromaffin cells were also inhibited by the 5-HT1A receptor agonist, 8-hydroxy-2-(dipropylamino) tetralin hydrobromide, but were not changed by the 5-HT1B, 5-HT2, or 5-HT3 receptor agonists, CP93129, α-methyl-5-HT, or 1-(m-chlorophenyl) biguanide, respectively. RT-PCR analysis detected the expression of all 5-HT receptor subtype mRNAs, except for 5-HT5 receptors, in extracts of the adrenal medulla. Immunohistochemistry revealed that immunoreactivity for 5-HT1A receptor was located in the chromaffin cells immunoreactive for the biosynthetic enzyme for noradrenaline, dopamine β-hydroxylase. These results suggest that 5-HT inhibits ACh-induced excitability in adrenal chromaffin cells via the 5-HT1A receptor in order to reduce catecholamine release during preganglionic sympathetic stimuli.

Effects of equivalent sympathetic activation during hypoglycemia on endothelial function and pro-atherothrombotic balance in healthy individuals and obese standard treated type 2 diabetes

OBJECTIVE

Recent studies in type 2 diabetes have reported an association between hypoglycemia and severe cardiovascular adverse events, which are relatively increased in standard versus intensively treated individuals. The aim of this study was to determine the effects of equivalent sympathetic nervous system (SNS) activity during moderate hypoglycemia on in-vivo endothelial function, pro-inflammatory, pro-atherothrombotic, and pro-coagulant responses in healthy and standard treated type 2 diabetes individuals.

RESEARCH DESIGN AND METHODS

Eleven type 2 diabetes and 16 healthy individuals participated in single 2day studies. Day 1 involved a 2h hyperinsulinemic/euglycemic clamp and day 2, a 2h hyperinsulinemic/hypoglycemic clamp of 3.2±1mmol/L in type 2 diabetes and (2.9±0.1mmol/L) in healthy individuals.

RESULTS

ICAM-1, VCAM-1, P-selectin, PAI-1, VEGF and endothelin-1 (ET-1) fell during hyperinsulinemic euglycemia but increased during hypoglycemia in type 2 diabetes and healthy individuals. Epinephrine and norepinephrine levels were equivalent during hypoglycemia in type 2 DM and healthy individuals. However, despite similar SNS drive but milder and hypoglycemia there were greater ICAM-1, VCAM-1, PAI-1, VEGF and ET-1 responses in the type 2 diabetes group. Endogenous and exogenous nitric oxide mediated arterial vasodilation were also impaired only during hypoglycemia in type 2 diabetes.

CONCLUSION

We conclude that, milder hypoglycemia but equivalent SNS activation results in more diffuse endothelial dysfunction and a greater pro-inflammatory, pro-atherothrombotic and pro-coagulant state in standard treated type 2 diabetes as compared to healthy individuals.

HBK-14 and HBK-15 Do Not Influence Blood Pressure, Lipid Profile, Glucose Level, or Liver Enzymes Activity after Chronic Treatment in Rats

Older and even new antidepressants cause adverse effects, such as orthostatic hypotension, hyper- or hypoglycemia, liver injury or lipid disorders. In our previous experiments we showed significant antidepressant- and anxiolytic-like activities of dual 5-HT_1A and 5-HT₇ antagonists with α₁-adrenolitic properties i.e. 1-[(2,6-dimethylphenoxy)ethoxyethyl]-4-(2-methoxyphenyl)piperazine hydrochloride (HBK-14) and 1-[(2-chloro-6-methylphenoxy)ethoxyethyl]-4-(2-methoxyphenyl)piperazine hydrochloride (HBK-15). Here, we evaluated the influence of chronic administration of HBK-14 and HBK-15 on blood pressure (non-invasive blood pressure measurement system for rodents), lipid profile (total cholesterol, low density lipoproteins—LDL, high density lipoproteins—HDL, triglycerides), glucose level, and liver enzymes activity (aspartate aminotransferase, alanine aminotransferase, γ-glutamyl transferase). We determined potential antihistaminic (isolated guinea pig ileum) and antioxidant properties (ferric reducing ability of plasma–FRAP, non-protein thiols–NPSH, stable free radical diphenylpicrylhydrazyl—DPPH) cytotoxicity. Our experiments revealed that HBK-14 and HBK-15 did not influence blood pressure, lipid profile, glucose level or liver enzymes activity in rats after 2-week treatment. We also showed that none of the compounds possessed antioxidant or cytotoxic properties at antidepressant- and anxiolytic-like doses. HBK-14 and HBK-15 very weakly blocked H₁ receptors in guinea pig ileum. Positive results of our preliminary experiments on the safety of HBK-14 and HBK-15 encourage further studies concerning their effectiveness in the treatment of depression and/or anxiety disorders.

Acute Effects of Oral Dehydroepiandrosterone on Counterregulatory Responses During Repeated Hypoglycemia in Healthy Humans

We tested the hypothesis that acute administration of oral dehydroepiandrosterone (DHEA) during episodes of repeated hypoglycemia can prevent the development of hypoglycemia-associated neuroendocrine and autonomic failure in healthy humans. Twenty-seven individuals (16 men, 11 women) participated in two separate randomized, single-blind, 2-day protocols. Day 1 consisted of morning and afternoon 2-h hypoglycemic clamps (2.9 mmol/L) with 800 mg of DHEA or placebo administered before each clamp. Day 2 consisted of a single 2-h hypoglycemic clamp (2.9 mmol/L) following either DHEA (1,600 mg) or placebo. A 3-tritiated glucose was used to determine glucose kinetics during hypoglycemia on day 2. Antecedent hypoglycemia with placebo resulted in significant reductions of epinephrine, norepinephrine, glucagon, growth hormone, cortisol, endogenous glucose production, and lipolytic and symptom responses. During hypoglycemia on day 2, DHEA prevented blunting of all neuroendocrine, autonomic nervous system (ANS), metabolic, and symptom counterregulatory responses following hypoglycemia on day 1. In summary, DHEA can acutely preserve a wide range of key neuroendocrine, ANS, and metabolic counterregulatory homeostatic responses during repeated hypoglycemia. We conclude that DHEA may have acute effects to protect against hypoglycemia-associated neuroendocrine and autonomic failure in healthy humans.

Effects of γ-Aminobutyric Acid A Receptor Activation on Counterregulatory Responses to Subsequent Exercise in Individuals With Type 1 Diabetes

The effects of γ-aminobutyric acid (GABA) A receptor activation on physiologic responses during next-day exercise in type 1 diabetes are unknown. To test the hypothesis that GABA A activation with the benzodiazepine alprazolam would blunt counterregulatory responses during subsequent exercise, 29 (15 male, 14 female) individuals with type 1 diabetes (HbA1c 7.8 ± 1%) were studied during separate 2-day protocols. Day 1 consisted of morning and afternoon 2-h euglycemic or 2.9 mmol/L hypoglycemic clamps with or without 1 mg alprazolam given 30 min before each clamp. Day 2 consisted of a 90-min euglycemic cycling exercise at 50% VO2max Tritiated glucose was used to measure glucose kinetics. Despite equivalent day 2 insulin (93 ± 6 pmol/L) and glucose levels (5.3 ± 0.1 mmol/L), plasma epinephrine, norepinephrine, glucagon, cortisol, and growth hormone responses were similarly reduced after alprazolam or day 1 hypoglycemia compared with euglycemic control. Endogenous glucose production, lipolysis (glycerol, nonesterified fatty acid), and glycogenolysis (lactate) were also reduced during day 2 exercise after day 1 GABA A activation. We conclude that activation of GABA A receptors with alprazolam can result in widespread neuroendocrine, autonomic nervous system, and metabolic counterregulatory failure during subsequent submaximal exercise and may increase the risk of exercise-associated hypoglycemia in individuals with type 1 diabetes.

An interplay between the serotonin transporter (SERT) and 5-HT receptors controls stimulus-secretion coupling in sympathoadrenal chromaffin cells

Adrenal chromaffin cells (ACCs), the neuroendocrine arm of the sympathetic nervous system, secrete catecholamines to mediate the physiological response to stress. Although ACCs do not synthesize 5-HT, they express the serotonin transporter (SERT). Genetic variations in SERT are linked to several CNS disorders but the role(s) of SERT/5-HT in ACCs has remained unclear. Adrenal glands from wild-type mice contained 5-HT at ≈ 750 fold lower abundance than adrenaline, and in SERT(-/-) mice this was reduced by ≈80% with no change in catecholamines. Carbon fibre amperometry showed that SERT modulated the ability of 5-HT1A receptors to inhibit exocytosis. 5-HT reduced the number of amperometric spikes (vesicular fusion events) evoked by KCl in SERT(-/-) cells and wild-type cells treated with escitalopram, a SERT antagonist. The 5-HT1A receptor antagonist WAY100635 blocked the inhibition by 5-HT which was mimicked by the 5-HT1A agonist 8-OH-DPAT but not the 5-HT1B agonist CP93129. There was no effect on voltage-gated Ca(2+) channels, K(+) channels, or intracellular [Ca(2+)] handling, showing the 5-HT receptors recruit an atypical inhibitory mechanism. Spike charge and kinetics were not altered by 5-HT receptors but were reduced in SERT(-/-) cells compared to wild-type cells. Our data reveal a novel role for SERT and suggest that adrenal chromaffin cells might be a previously unrecognized hub for serotonergic control of the sympathetic stress response.

Effects of Acute and Antecedent Hypoglycemia on Endothelial Function and Markers of Atherothrombotic Balance in Healthy Humans

The aim of this study was to determine the effects of single and repeated episodes of clamped hypoglycemia on fibrinolytic balance, proinflammatory biomarkers, proatherothrombotic mechanisms, and endothelial function. Twenty healthy individuals (12 male and 8 female) were studied during separate 2-day randomized protocols. Day 1 consisted of either two 2-h hyperinsulinemic (812 ± 50 pmol/L)-euglycemic (5 ± 0.1 mmol/L) or hyperinsulinemic (812 ± 50 pmol/L)-hypoglycemic (2.9 ± 0.1 mmol/L) clamps. Day 2 consisted of a single 2-h hyperinsulinemic-hypoglycemic clamp. Two-dimensional Doppler ultrasound was used to determine brachial arterial endothelial function. Plasminogen activator inhibitor 1, vascular cell adhesion molecule-1, intracellular adhesion molecule-1, E-selectin, P-selectin, TAT (thrombin/antithrombin complex), tumor necrosis factor-α, and interleukin-6 responses were increased (P < 0.05) during single or repeated hypoglycemia compared with euglycemia. Endogenous and exogenous nitric oxide (NO)-mediated vasodilation were both impaired by repeated hypoglycemia. Neuroendocrine and autonomic nervous system (ANS) responses were also blunted by repeated hypoglycemia (P < 0.05). In summary, acute moderate hypoglycemia impairs fibrinolytic balance; increases proinflammatory responses, platelet activation, and coagulation biomarkers; and reduces NO-mediated endothelial function in healthy individuals. Repeated episodes of hypoglycemia further impair vascular function by additionally reducing exogenously NO-mediated endothelial function and increasing coagulation biomarkers. We conclude that despite reduced neuroendocrine and ANS responses, antecedent hypoglycemia results in greater endothelial dysfunction and an increased proatherothrombotic state compared with a single acute episode of hypoglycemia.

Perifornical hypothalamic orexin and serotonin modulate the counterregulatory response to hypoglycemic and glucoprivic stimuli

Previous reports suggested an important role for serotonin (5-hydroxytryptamine [5-HT]) in enhancing the counterregulatory response (CRR) to hypoglycemia. To elucidate the sites of action mediating this effect, we initially found that insulin-induced hypoglycemia stimulates 5-HT release in widespread forebrain regions, including the perifornical hypothalamus (PFH; 30%), ventromedial hypothalamus (34%), paraventricular hypothalamus (34%), paraventricular thalamic nucleus (64%), and cerebral cortex (63%). Of these, we focused on the PFH because of its known modulation of diverse neurohumoral and behavioral responses. In awake, behaving rats, bilateral PFH glucoprivation with 5-thioglucose stimulated adrenal medullary epinephrine (Epi) release (3,153%) and feeding (400%), while clamping PFH glucose at postprandial brain levels blunted the Epi response to hypoglycemia by 30%. The PFH contained both glucose-excited (GE) and glucose-inhibited (GI) neurons; GE neurons were primarily excited, while GI neurons were equally excited or inhibited by 5-HT at hypoglycemic glucose levels in vitro. Also, 5-HT stimulated lactate production by cultured hypothalamic astrocytes. Depleting PFH 5-HT blunted the Epi (but not feeding) response to focal PFH (69%) and systemic glucoprivation (39%), while increasing PFH 5-HT levels amplified the Epi response to hypoglycemia by 32%. Finally, the orexin 1 receptor antagonist SB334867A attenuated both the Epi (65%) and feeding (47%) responses to focal PFH glucoprivation. Thus we have identified the PFH as a glucoregulatory region where both 5-HT and orexin modulate the CRR and feeding responses to glucoprivation.

Hyperglycemia following recovery from hypoglycemia worsens endothelial damage and thrombosis activation in type 1 diabetes and in healthy controls

BACKGROUND AND AIMS

Hypoglycemia produces thrombosis activation, but little attention has been paid to the effects of hyperglycemia following recovery from hypoglycemia on thrombosis activation.

METHODS AND RESULTS

In both twenty-two healthy subjects and twenty-one matched persons with type 1 diabetes, recovery from a 2-h induced hypoglycemia was obtained by reaching normo-glycemia or hyperglycemia for another 2 h. After this, normal glycemia was maintained for the following 6 h. Hyperglycemia after hypoglycemia was also repeated with the concomitant infusion of vitamin C. In both controls and people with diabetes, the recovery with normo-glycemia was accompanied by a significant improvement of Von Willebrand factor (vWF), prothrombin fragment 1 + 2 (F1 + 2), thrombin-antithrombin III-complexes (TAT), P-selectin, plasminogen activator inhibitor-1 (PAI-1), nitrotyrosine and 8-iso-prostaglandin F2α (8-iso-PGF2α) (p < 0.01 vs hypoglycemia for all the parameters), all directly affected by hypoglycemia itself (p < 0.01 vs baseline for all the parameters). On the contrary, the recovery with hyperglycemia after hypoglycemia worsens all these parameters (p < 0.01 vs normoglycemia for all the parameters), an effect persisting even after the additional 6 h of normo-glycemia. The effect of hyperglycemia following hypoglycemia was partially counterbalanced when vitamin C was infused (p < 0.01 vs hyperglycemia alone for all the parameters), suggesting that hyperglycemia following hypoglycemia may activate thrombosis through the oxidative stress production.

CONCLUSION

This study shows that, in type 1 diabetes as well as in controls, the way in which recovery from hypoglycemia takes place could play an important role in favoring the activation of thrombosis and oxidative stress, widely recognized cardiovascular risk factors.

Mechanisms of hypoglycemia and exercise-associated autonomic dysfunction

It is well established that diabetes can lead to multiple microvascular and macrovascular complications. Several large scale randomized multicenter studies have shown that intensifying glucose control decreases microvascular and, to a certain extent, macrovascular complications of diabetes. However, intensifying glucose control in both type 1 and type 2 diabetes increases the risk of developing hypoglycemia, one of the most feared complications of people with the disease. The mechanisms responsible for intensive therapy causing increased hypoglycemia in patients with diabetes have been extensively investigated. It is now known that a single episode of hypoglycemia can blunt the body's normal counterregulatory defenses against subsequent hypoglycemia or exercise. Similarly, a single bout of exercise can also blunt counterregulatory responses against subsequent hypoglycemia. Both neuroendocrine and autonomic nervous system responses are reduced by prior hypoglycemia and/or exercise. Work from several laboratories has identified multiple physiologic mechanisms involved in the pathogenesis of this hypoglycemia and exercise-associated counterregulatory failure. By continuing to study these mechanisms, some promising approaches to amplify counterregulatory responses to hypoglycemia are being discovered.

Reduced serotonin reuptake transporter (SERT) function causes insulin resistance and hepatic steatosis independent of food intake

Serotonin reuptake transporter (SERT) is a key regulator of serotonin neurotransmission and a major target of antidepressants. Antidepressants, such as selectively serotonin reuptake inhibitors (SSRIs), that block SERT function are known to affect food intake and body weight. Here, we provide genetic evidence that food intake and metabolism are regulated by separable mechanisms of SERT function. SERT-deficient mice ate less during both normal diet and high fat diet feeding. The reduced food intake was accompanied with markedly elevated plasma leptin levels. Despite reduced food intake, SERT-deficient mice exhibited glucose intolerance and insulin resistance, and progressively developed obesity and hepatic steatosis. Several lines of evidence indicate that the metabolic deficits of SERT-deficient mice are attributable to reduced insulin-sensitivity in peripheral tissues. First, SERT-deficient mice exhibited beta-cell hyperplasia and islet-mass expansion. Second, biochemical analyses revealed constitutively elevated JNK activity and diminished insulin-induced AKT activation in the liver of SERT-deficient mice. SERT-deficient mice exhibited hyper-JNK activity and hyperinsulinemia prior to the development of obesity. Third, enhancing AKT signaling by PTEN deficiency corrected glucose tolerance in SERT-deficient mice. These findings have potential implications for designing selective SERT drugs for weight control and the treatment of metabolic syndromes.

The physiology and pathophysiology of the neural control of the counterregulatory response

Despite significant technological and pharmacological advancements, insulin replacement therapy fails to adequately replicate β-cell function, and so glucose control in type 1 diabetes mellitus (T1D) is frequently erratic, leading to periods of hypoglycemia. Moreover, the counterregulatory response (CRR) to falling blood glucose is impaired in diabetes, leading to an increased risk of severe hypoglycemia. It is now clear that the brain plays a significant role in the development of defective glucose counterregulation and impaired hypoglycemia awareness in diabetes. In this review, the basic intracellular glucose-sensing mechanisms are discussed, as well as the neural networks that respond to and coordinate the body's response to a hypoglycemic challenge. Subsequently, we discuss how the body responds to repeated hypoglycemia and how these adaptations may explain, at least in part, the development of impaired glucose counterregulation in diabetes.

Waterborne fluoxetine disrupts feeding and energy metabolism in the goldfish Carassius auratus

Fluoxetine (FLX) is one of the most commonly detected pharmaceuticals in wastewater and bioaccumulates in wild-caught fish, especially in brain, liver and muscle tissues. Previous studies indicated that FLX is pharmacologically active in fish species exerting anorexigenic effects, but it is not clear whether waterborne FLX has any potential effects on regulating food intake and energy metabolism. In this study, we investigated the effect of two doses of FLX, an environmental concentration of 540 ng/L, and 100-times this concentration (54 μg/L), on feeding and key metabolic parameters in goldfish. Fish were exposed for a period of 28 days and changes in food intake and body mass were assessed. Pair-fed groups were maintained to discern primary FLX-induced effects from secondary metabolic responses induced by the decreased food intake. Additionally, an untreated control group and a fasted group were used to further compare physiological changes in the context of nutritional status of the animals. Significant decreases in food intake and weight gain were recorded in goldfish exposed to 54 μg/L FLX. Furthermore a significant decrease occurred in circulating glucose levels in the group exposed to 540 ng/L FLX. To elucidate potential mechanisms, we investigated gene expression of feeding neuropeptides in the neuroendocrine brain of goldfish as well as gene expression and enzymatic activity of glycolytic and gluconeogenetic enzymes in liver and muscle tissues. The results confirm brain gene expression patterns in line with potential anorexigenic effects in the hypothalamus, with increased expression in corticotropin-releasing factor (CRF) and decreased expression of neuropeptide Y (NPY). With respect to glucose metabolism, liver gene expression of the gluconeogenic enzyme fructose-1,6-bisphosphatase decreased and muscle hexokinase activity increased in fish exposed to 540 ng/L FLX. Overall, this study demonstrated anorectic properties of FLX at a dose of 54 μg/L FLX and moderate but significant effects on glucose metabolism in goldfish exposed to 540 ng/L FLX. Future studies investigating the importance of these changes in fish are warranted.

Effects of acute hypoglycemia on inflammatory and pro-atherothrombotic biomarkers in individuals with type 1 diabetes and healthy individuals

OBJECTIVE

Recent large randomized trials have linked adverse cardiovascular and cerebrovascular events with hypoglycemia. However, the integrated physiological and vascular biological mechanisms occurring during hypoglycemia have not been extensively examined. Therefore, the aim of this study was to determine whether 2 h of moderate clamped hypoglycemia could decrease fibrinolytic balance and activate pro-atherothrombotic mechanisms in individuals with type 1 diabetes and healthy individuals.

RESEARCH DESIGN AND METHODS

Thirty-five healthy volunteers (19 male and 16 female subjects age 32 +/- 2 years, BMI 26 +/- 2 kg/m(2), A1C 5.1 +/- 0.1%) and twenty-four with type 1 diabetes (12 male and 12 female subjects age 33 +/- 3 years, BMI 24 +/- 2 kg/m(2), A1C 7.7 +/- 0.2%) were studied during either a 2-h hyperinsulinemic (9 pmol x kg(-1) x min(-1)) euglycemic or hypoglycemic (2.9 +/- 0.1 mmol/l) clamp or both protocols. Plasma glucose levels were normalized overnight in type 1 diabetic subjects prior to each study.

RESULTS

Insulin levels were similar (602 +/- 44 pmol/l) in all four protocols. Glycemia was equivalent in both euglycemic protocols (5.2 +/- 0.1 mmol/l), and the level of hypoglycemia was also equivalent in both type 1 diabetic subjects and healthy control subjects (2.9 +/- 0.1 mmol/l). Using repeated ANOVA, it was determined that plasminogen activator inhibitor (PAI-1), vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), E-selectin, P-selectin, interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), and adiponectin responses were all significantly increased (P < 0.05) during the 2 h of hyperinsulinemic hypoglycemia as compared with euglycemia in healthy control subjects. All measures except PAI-1 were also found to be increased during hypoglycemia compared with euglycemia in type 1 diabetes.

CONCLUSIONS

In summary, moderate hypoglycemia acutely increases circulating levels of PAI-1, VEGF, vascular adhesion molecules (VCAM, ICAM, E-selectin), IL-6, and markers of platelet activation (P-selectin) in individuals with type 1 diabetes and healthy individuals. We conclude that acute hypoglycemia can result in complex vascular effects including activation of prothrombotic, proinflammatory, and pro-atherogenic mechanisms in individuals with type 1 diabetes and healthy individuals.

The effect of selective serotonin reuptake inhibitors in healthy subjects. A systematic review

BACKGROUND

Selective serotonin reuptake inhibitors (SSRIs) show antidepressant properties in many patients with a diagnosis of depression. An understanding of the underlying mechanisms of the effect of SSRIs in healthy patients may lead to an understanding of the yet unclear pathophysiology of depression. Recent reviews of studies investigating the effect of SSRIs in healthy persons conclude that the results are inconsistent and that--in relation to a wide range of outcomes--the effect of SSRIs is limited; however, reasons for the inconsistencies are poorly studied.

AIMS AND METHODS

To investigate whether methodological artefacts can explain the diverging findings, we conducted a systematic review of all randomized multiple-dose, placebo-controlled trials on the effect of treatment by SSRI for at least a week in healthy persons published before January 2009.

RESULTS

We identified 33 trials, investigating six SSRIs and 163 outcome tests. The effect of SSRI showed divergence presumably related to methodological issues. Specifically, it is likely that the majority of studies included a mix of healthy persons with and without a family history of affective disorders. Few presented information on factors that may influence outcomes such as age, gender, family history of psychiatric disorder, drug levels and ethnicity. No study fulfilled principles of conducting and reporting randomized controlled trials, according to the CONSORT Statement guidelines.

CONCLUSIONS

It is unclear whether the effect of SSRIs in healthy persons may lead to an understanding of the pathophysiology of depression, since the present evidence is divergent and may be severely influenced by a number of methodological drawbacks.

Hypoglycemia: still the limiting factor in the glycemic management of diabetes

OBJECTIVE

To review the prevalence of, risk factors for, and prevention of hypoglycemia from the perspective of the pathophysiologic aspects of glucose counterregulation in diabetes.

METHODS

This review is based on personal experience and research and the relevant literature.

RESULTS

Although it can result from insulin excess alone, iatrogenic hypoglycemia is generally the result of the interplay of therapeutic insulin excess and compromised defenses against declining plasma glucose concentrations. Failure of beta-cells of the pancreas -- early in patients with type 1 diabetes mellitus but later in those with type 2 diabetes mellitus (T2DM) -- causes loss of the first 2 physiologic defenses: a decrease in insulin and an increase in glucagon. Such patients are critically dependent on epinephrine, the third physiologic defense, and neurogenic symptoms that prompt the behavioral defense (carbohydrate ingestion). An attenuated sympathoadrenal response to declining glucose levels -- caused by recent antecedent hypoglycemia, prior exercise, or sleep -- causes hypoglycemia-associated autonomic failure (HAAF) and thus a vicious cycle of recurrent hypoglycemia. Accordingly, hypoglycemia is infrequent early in T2DM but becomes increasingly more frequent in advanced (absolutely endogenous insulin-deficient) T2DM, and risk factors for HAAF include absolute endogenous insulin deficiency; a history of severe hypoglycemia, hypoglycemia unawareness, or both; and aggressive glycemic therapy per se.

CONCLUSION

By practicing hypoglycemia risk reduction -- addressing the issue, applying the principles of aggressive glycemic therapy, and considering both the conventional risk factors and those indicative of HAAF -- it is possible both to improve glycemic control and to minimize the risk of hypoglycemia in many patients.

Effects of the selective serotonin reuptake inhibitor fluoxetine on counterregulatory responses to hypoglycemia in individuals with type 1 diabetes

OBJECTIVE

Previous work has demonstrated that chronic administration of the serotonin reuptake inhibitor (SSRI) fluoxetine augments counterregulatory responses to hypoglycemia in healthy humans. However, virtually no information exists regarding the effects of fluoxetine on integrated physiological counterregulatory responses during hypoglycemia in type 1 diabetes. Therefore, the specific aim of this study was to test the hypothesis that 6-week use of the SSRI fluoxetine would amplify autonomic nervous system (ANS) counterregulatory responses to hypoglycemia in individuals with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Eighteen type 1 diabetic patients (14 men/4 women aged 19-48 years with BMI 25 +/- 3 kg/m(2) and A1C 7.0 +/- 0.4%) participated in randomized, double-blind 2-h hyperinsulinemic (9 pmol . kg(-1) . min(-1))-hypoglycemic clamp studies before and after 6 weeks of fluoxetine administration (n = 8) or identical placebo (n = 10). Glucose kinetics was determined by 3-tritiated glucose. Muscle sympathetic nerve activity (MSNA) was determined by microneurography.

RESULTS

Hypoglycemia (2.8 +/- 0.1 mmol/l) and insulinemia (646 +/- 52 pmol/l) were similar during all clamp studies. ANS, neuroendocrine, and metabolic counterregulatory responses remained unchanged in the placebo group. However, fluoxetine administration significantly (P < 0.05) increased key ANS (epinephrine, norepinephrine, and MSNA), metabolic (endogenous glucose production and lipolysis), and cardiovascular (systolic blood pressure) counterregulatory responses during hypoglycemia.

CONCLUSIONS

This study has demonstrated that 6-week administration of the SSRI fluoxetine can amplify ANS and metabolic counterregulatory mechanisms during moderate hypoglycemia in patients with type 1 diabetes. These data also suggest that the use of fluoxetine may be useful in increasing epinephrine responses during hypoglycemia in clinical practice.