Surgical Sympathetic Denervation Research Articles

PO-698-06 NEUROMODULATION FOR THE TREATMENT OF REFRACTORY VENTRICULAR ARRHYTHMIAS

Neuromodulation of sympathetic tone is increasingly recognized as a therapeutic strategy for patients with refractory ventricular arrhythmias (VA). Percutaneous stellate ganglion blockade (SGB), transcutaneous magnetic stimulation (TcMS), and surgical sympathetic denervation (SD) have all been utilized in this setting. To describe our experience with autonomic neuromodulation for the treatment of refractory VA. This retrospective cohort study included all patients at the Hospital of the University of Pennsylvania with antiarrhythmic drug (AAD) refractory VA from 2019-2021 who were treated with SGB, TcMS, or SD. A total of 33 patients (age 60±14 years, 25 (76%) male, 14 (42%) polymorphic VA) met inclusion criteria. VA were refractory to 1.8±0.8 AAD. SGB was performed on 11 patients (33%), TcMS on 19 (56%), and SD on 6 (18%). Two patients underwent both SGB and SD, and one patient underwent both SGB and TcMS. Two patients who underwent SGB had the procedure repeated after 1 and 5 days respectively due to recurrent VA. SGB was performed on the left-side in 5 (46%) and was bilateral in 6 (54%) patients. SGB was guided by ultrasound in 9 (82%), fluoroscopy in 3 (27%), or anatomic landmarks with no imaging in 1 (9%). Lidocaine was the most common agent used (n=9). SD was performed on the left-side in 1 (17%) and was bilateral in 5 (83%). SD was performed via thoracotomy in 1 (17%) due to body habitus and via video-assisted thoracoscopic surgery in 5 (83%). There were no complications of any neuromodulation approach. Neuromodulation was associated with a reduction in the number of episodes of sustained VA from 10.4±11.3 episodes in the 24-hours prior to the initial neuromodulation strategy to 1.3±3.1 episodes in the subsequent 24-hours (p<0.001) with no decrease in 5 patients (15%). During 602±250 days of follow-up, 18 (55%) experienced recurrent ventricular arrhythmias and among those patients, the time to recurrence was 22±44 days. Recurrence was similar in patient in monomorphic (58%) vs polymorphic VA (50%). Autonomic neuromodulation with SGB, TcMS, or SD in patients with AAD refractory VT is safe and results in substantial acute reduction of VA burden in the majority although recurrent arrhythmias are common and not all patients experience a reduction in arrhythmia burden.

B-PO05-168 BEDSIDE PERCUTANEOUS SYMPATHETIC BLOCK IS SAFE AND EFFECTIVE IN REFRACTORY ELECTRICAL STORM AS A BRIDGE TO ADVANCED THERAPIES

Patients with electrical storm (ES) who fail standard medical and interventional therapies have a high mortality rate and are difficult to bridge to definitive therapies. Bedside, ultrasound-guided percutaneous sympathetic block (PSB) can stabilize these patients in the acute setting. To describe the outcomes of patients with electrical storm (ES), in whom PSB was used to bridge them to advanced therapies. Retrospective study of consecutive ES patients undergoing bedside ultrasound-guided PSB between 1/2017-3/2020 at our institution. Of the 19 PSB patients in ES, the majority were male (89.5%) with average age of 66.5±6.0 years and left ventricular ejection fraction (LVEF) 28± 10%. There was underlying ischemic cardiomyopathy in 52%. Catheter ablation was performed in 47.3% prior to PSB with average 1.1±1.4 ablations with 2.5±0.48 adjunctive anti-arrhythmia medications. The ventricular arrhythmia (VA) was monomorphic in 70% with cycle length 250-490ms. Despite intubation and mechanical ventilation in 47% of these patients, the majority were in ES (94%) the day of procedure. After PSB, no ventricular arrhythmia recurred in eight patients (42%). There was a significant decrease in amount of VA (4.4±2.5 vs. 2.2± 3.5 episodes P= 0.019) and number of patients with ES the day before and after procedure 18 vs. 16 patients P=0.00001. Minor reversible side effects were noted in 21% and no significant bleeding was reported despite all patients being on anticoagulants or antiplatelet agents. Follow up was 4.5±5 months: 5 patients died, one referred to hospice, 5 had heart transplant and 3 underwent surgical sympathetic denervation. Four patients underwent coronary revascularization, 2 were treated with immunosuppression, 2 underwent stereotactic body radiation therapy, 1 surgical cryoablation, one AAI pacing, 2 LVAD and 1 needle catheter ablation. Fifteen patients survived admission and 13 (86%) were free of any arrhythmia during follow up. PSB with continue infusion is a safe and effective beside procedure in patients who have exhausted conventional therapy and can offer a rescue bridge to facilitate advanced treatments.

Sympathetic Denervation of the Common Hepatic Artery Lessens Glucose Intolerance in the Fat- and Fructose-Fed Dog.

This study assessed the effectiveness of surgical sympathetic denervation of the common hepatic artery (CHADN) in improving glucose tolerance. CHADN eliminated norepinephrine content in the liver and partially decreased it in the pancreas and the upper gut. We assessed oral glucose tolerance at baseline and after 4 weeks of high-fat high-fructose (HFHF) feeding. Dogs were then randomized to sham surgery (SHAM) (n = 9) or CHADN surgery (n = 11) and retested 2.5 or 3.5 weeks later while still on the HFHF diet. CHADN improved glucose tolerance by ∼60% in part because of enhanced insulin secretion, as indicated by an increase in the insulinogenic index. In a subset of dogs (SHAM, n = 5; CHADN, n = 6), a hyperinsulinemic-hyperglycemic clamp was used to assess whether CHADN could improve hepatic glucose metabolism independent of a change in insulin release. CHADN reduced the diet-induced defect in net hepatic glucose balance by 37%. In another subset of dogs (SHAM, n = 4; CHADN, n = 5) the HFHF diet was continued for 3 months postsurgery and the improvement in glucose tolerance caused by CHADN continued. In conclusion, CHADN has the potential to enhance postprandial glucose clearance in states of diet-induced glucose intolerance.

Activating cAMP/PKA signaling in skeletal muscle suppresses the ubiquitin-proteasome-dependent proteolysis: implications for sympathetic regulation.

Although we have recently demonstrated that plasma catecholamines induce antiproteolytic effects on skeletal muscle (Graça FA, Gonçalves DAP, Silveira WA, Lira EC, Chaves VE, Zanon NM, Garófalo MAR, Kettelhut IC, Navegantes LCC. Am J Physiol Endocrinol Metab. 305: E1483-E1494, 2013), the role of the muscle sympathetic innervation and, more specifically, norepinephrine (NE) in regulating the ubiquitin (Ub)-proteasome system (UPS) remains unknown. Based on previous findings that chemical sympathectomy acutely reduces UPS activity, we hypothesized that muscle NE depletion induces adrenergic supersensitivity in rat skeletal muscles. We report that surgical sympathetic denervation (SDEN), a condition in which only muscle NE from both hindlimbs is depleted, transiently reduced the overall proteolysis and the UPS activity (∼25%) in both soleus and extensor digitorum longus muscles. This antiproteolytic response was accompanied by increased activity of adenylyl cyclase (112%), levels of cyclic adenosine monophosphate (cAMP; 191%), and the serine phosphorylation of cAMP response element-binding protein (32%). In extensor digitorum longus from normal rats, NE (10(-4) M) in vitro increased the levels of cAMP (115%) and the serine phosphorylation of both cAMP response element-binding protein (2.7-fold) and forkhead box class O1 transcription factor. Similar effects were observed in C2C12 cells incubated with forskolin (10 μM). In parallel, NE significantly reduced the basal UPS (21%) activity and the mRNA levels of atrophy-related Ub-ligases. Similar responses were observed in isolated muscles exposed to 6-BNZ-cAMP (500 μM), a specific PKA activator. The phosphorylation levels of Akt were not altered by SDEN, NE, forskolin or 6-BNZ-cAMP. Our results demonstrate that SDEN induces muscle adrenergic supersensitivity for cAMP leading to the suppression of UPS, and that the suppressive effects of NE on UPS activity and expression of Ub-ligases can be mediated by the activation of cAMP/PKA signaling, with the inhibition of forkhead box class O1 transcription factor.

Activation of brown adipose tissue thermogenesis by electrical stimulation to the dorsal surface of the tissue in rats

Brown adipose tissue (BAT) is a heat-producing organ that plays an important role in maintenance of energy homeostasis. The purpose of this study was to test a novel method for stimulating BAT thermogenesis in rats. Application of electrical field stimulation to the dorsal surface of interscapular BAT caused a substantial rise in tissue temperature without affecting rectal temperature. The electrical stimulation failed to raise BAT temperature on the 2nd day after surgical sympathetic denervation. This is unlikely to be due to loss of thermogenic capacity, since neither UCP1 contents nor norepinephrine-induced thermogenesis were diminished 2 days after the denervation. A pharmacological experiment revealed that the BAT thermogenesis induced after electrical stimulation is mediated through β-adrenoceptors. The present study demonstrates that electrical stimulation applied to the dorsal surface of BAT is able to activate thermogenesis of BAT through mediation of norepinephrine released from sympathetic nerves. Our findings may provide a basis for developing a novel therapeutic procedure for obesity and related disorders.

Exercise attenuates alpha-adrenergic-receptor responsiveness in skeletal muscle vasculature.

Attenuation of sympathetic vasoconstriction (sympatholysis) in working muscles during dynamic exercise is controversial. A potential mechanism is a reduction in alpha-adrenergic-receptor responsiveness. The purpose of this study was to examine alpha(1)- and alpha(2)-adrenergic-receptor-mediated vasoconstriction in resting and exercising skeletal muscle using intra-arterial infusions of selective agonists. Thirteen mongrel dogs were instrumented chronically with flow probes on the external iliac arteries of both hindlimbs and a catheter in one femoral artery. The selective alpha(1)-adrenergic agonist (phenylephrine) or the selective alpha(2)-adrenergic agonist (clonidine) was infused as a bolus into the femoral artery catheter at rest and during mild and heavy exercise. Intra-arterial infusions of phenylephrine elicited reductions in vascular conductance of 76 +/- 4, 71 +/- 5, and 31 +/- 2% at rest, 3 miles/h, and 6 miles/h and 10% grade, respectively. Intra-arterial clonidine reduced vascular conductance by 81 +/- 5, 49 +/- 4, and 14 +/- 2%, respectively. The response to intra-arterial infusion of clonidine was unaffected by surgical sympathetic denervation. Agonist infusion did not affect either systemic blood pressure, heart rate, or blood flow in the contralateral iliac artery. alpha(1)-Adrenergic-receptor responsiveness was attenuated during heavy exercise. In contrast, alpha(2)-adrenergic-receptor responsiveness was attenuated even at a mild exercise intensity. These results suggest that the mechanism of exercise sympatholysis may involve reductions in postsynaptic alpha-adrenergic-receptor responsiveness.

Role of the sympathetic nervous system and insulin in enhancing glucose uptake in peripheral tissues after intrahypothalamic injection of leptin in rats.

Our previous study demonstrated that microinjection of leptin into the ventromedial hypothalamus (VMH) dramatically increased glucose uptake in the heart, brown adipose tissue (BAT), and skeletal muscles, but not in white adipose tissue (WAT) in conscious unrestrained rats, as assessed in vivo by the 2-[3H]deoxyglucose method. Here we examined the role of the sympathetic nervous system and insulin in enhanced glucose uptake by tissues after hypothalamic leptin injection. Pretreatment with guanethidine significantly suppressed the increased glucose uptake by the tissues in response to leptin injected into the VMH, whereas bilateral adrenal demedullation had no significant effect. Treatment with propranolol but not phenoxybenzamine also decreased significantly enhanced glucose uptake by the tissues. We further examined the interaction of the effects of hypothalamic leptin and insulin administered peripherally by clamping the glucose concentrations at a constant level. When leptin was injected into the VMH and a maximal dose of insulin was administered intravenously, the rates of glucose uptake by the heart, BAT, and skeletal muscles, but not by WAT, markedly increased beyond the values reached by insulin stimulation alone. Surgical sympathetic denervation of BAT abolished the enhancement of glucose uptake in this tissue, decreasing to the level stimulated by insulin alone. These results appear to indicate that leptin in the hypothalamus enhances glucose uptake in certain peripheral tissues through mediation of a beta-adrenergic mechanism for the sympathetic nerves innervating the tissues and that central leptin and peripheral insulin have a synergistic role in augmenting tissue glucose uptake.

Differential regulation of uncoupling protein-1, -2 and -3 gene expression by sympathetic innervation in brown adipose tissue of thermoneutral or cold-exposed rats

The control of uncoupling protein-1, -2 and -3 (UCP-1, UCP-2, UCP-3) mRNA levels by sympathetic innervation in rats was investigated by specific and sensitive RT-PCR assays. In rats reared at thermoneutrality (25°C), unilateral surgical sympathetic denervation of interscapular brown adipose tissue (BAT) markedly reduced the UCP-1 mRNA level (−38%) as compared with the contralateral innervated BAT pad, but was without significant effect on UCP-2 and -3 mRNA levels. Cold exposure (7 days, 4°C) markedly increased UCP-1 (+180%), UCP-2 (+115%) and UCP-3 (+195%) mRNA levels in interscapular BAT. Unilateral sympathetic denervation prevented the cold-induced rise in BAT UCP-1 and UCP-2 mRNAs, but not that in BAT UCP-3 mRNA. Results were confirmed by Northern blot analysis. These data indicate a differential endocrine control of UCP-1, UCP-2 and UCP-3 gene expression in rat BAT both at thermoneutrality and during prolonged cold exposure.

Microinjection of leptin into the ventromedial hypothalamus increases glucose uptake in peripheral tissues in rats.

We studied the effects of microinjection of leptin into the ventromedial hypothalamus (VMH) and lateral hypothalamus (LH) on glucose uptake in peripheral tissues in unanesthetized rats. The rate of glucose uptake was assessed in vivo by 2-[3H]deoxyglucose incorporation. Single injection of leptin into VMH increased glucose uptake in brown adipose tissue (BAT), heart, skeletal muscles, and spleen but not in white adipose tissue or skin. On the other hand, microinjection of leptin into LH had little effect on glucose uptake in those tissues. The plasma concentrations of glucose and insulin were unaltered by intrahypothalamic injection of leptin into either VMH or LH. Among skeletal muscles, the increase in glucose uptake induced by intrahypothalamic injection of leptin was greater in the soleus than in the extensor digitorum longus. Likewise, the increased glucose uptake in the gastrocnemius in response to leptin was more prominent in the red part than in the white part of the tissue. When surgical sympathetic denervation of the interscapular BAT was performed, the enhanced glucose uptake by BAT in response to intrahypothalamic leptin was completely suppressed. These findings suggest that intrahypothalamic injection of leptin preferentially increases glucose uptake by some peripheral tissues through activation of the VMH-sympathetic (or its neighboring medial hypothalamus-sympathetic) nervous system, thereby contributing to the maintenance of energy balance.

Microinjection of leptin into the ventromedial hypothalamus increases glucose uptake in peripheral tissues in rats

We studied the effects of microinjection of leptin into the ventromedial hypothalamus (VMH) and lateral hypothalamus (LH) on glucose uptake in peripheral tissues in unanesthetized rats. The rate of glucose uptake was assessed in vivo by 2-[3H]deoxyglucose incorporation. Single injection of leptin into VMH increased glucose uptake in brown adipose tissue (BAT), heart, skeletal muscles, and spleen but not in white adipose tissue or skin. On the other hand, microinjection of leptin into LH had little effect on glucose uptake in those tissues. The plasma concentrations of glucose and insulin were unaltered by intrahypothalamic injection of leptin into either VMH or LH. Among skeletal muscles, the increase in glucose uptake induced by intrahypothalamic injection of leptin was greater in the soleus than in the extensor digitorum longus. Likewise, the increased glucose uptake in the gastrocnemius in response to leptin was more prominent in the red part than in the white part of the tissue. When surgical sympathetic denervation of the interscapular BAT was performed, the enhanced glucose uptake by BAT in response to intrahypothalamic leptin was completely suppressed. These findings suggest that intrahypothalamic injection of leptin preferentially increases glucose uptake by some peripheral tissues through activation of the VMH-sympathetic (or its neighboring medial hypothalamus-sympathetic) nervous system, thereby contributing to the maintenance of energy balance.

Adrenergic activation of vascular endothelial growth factor mRNA expression in rat brown adipose tissue: implication in cold-induced angiogenesis.

Cold exposure produces adaptive hyperplasia and growth of brown adipose tissue (BAT), the major site of non-shivering thermogenesis in rodents, associated with increased angiogenesis in this tissue. Vascular endothelial growth factor (VEGF), one of the most potent angiogenic factors, was found to be expressed abundantly in BAT of the rat. When rats were exposed to cold at 4 degrees C, the VEGF mRNA level in BAT was increased by 2-3-fold in 1-4 h, but returned to the basal level within 24 h. VEGF expression in other tissues such as heart, kidney and lung did not change after cold exposure. The cold-induced increase in VEGF mRNA was abolished by surgical sympathetic denervation, but mimicked by administration of noradrenaline or a beta3-adrenoceptor agonist CL316,243, indicating the critical role of the beta-adrenergic pathway in VEGF expression in BAT. Among three isoforms of VEGF, the mRNA of a short form (VEGF120) lacking heparin-binding activity was preferentially increased after cold exposure and treatment with the adrenergic agonists. These results suggest that cold exposure activates the sympathetic nerves and leads to a rapid increase in synthesis of VEGF in BAT, which in turn stimulates the proliferation of surrounding vascular endothelial cells.

Activation of mitogen-activated protein kinase by norepinephrine in brown adipocytes from rats.

We have investigated the adrenergic control of mitogen-activated protein kinase (MAPK) activity in brown adipocytes. Cold exposure in rats led to an activation of MAPK in brown adipose tissue, as determined by the gel mobility shift assay and in-gel kinase assay. In contrast, no activation was seen after surgical sympathetic denervation of the tissue. The neurotransmitter, norepinephrine (NE), directly activated MAPK of brown adipocytes in primary cultures in the absence of insulin and serum. NE-induced activation of MAPK was mimicked by beta-adrenergic agonists, including a beta 3-agonist, BRL37344. Activation of MAPK also was observed by an alpha-agonist, phenylephrine, the extent of which being much lower than that by beta-agonists. The effect of NE was attenuated by the beta-adrenergic antagonist, propranolol. Dibutyryl cAMP also mimicked the effect of NE. The phorbol ester, phorbol-12-myristate, 13-acetate(PMA), could induce activation of MAPK, but pretreatment of the cultured cells with PMA to down-regulate protein kinase C did not abolish the ability of NE in activating MAPK. Furthermore, a selective inhibitor of phosphatidylinositol-3 kinase, wortmannin, did not inhibit the effect of NE, whereas insulin-induced activation of MAPK was totally suppressed. These results demonstrate that NE activates MAPK directly in brown adipocytes and that the effect of NE is not mediated by PMA-sensitive protein kinase C or wortmannin-sensitive phosphatidylinositol-3 kinase but rather is likely to be dependent on beta-receptor-mediated increase in cAMP with a minor contribution of alpha-receptor-mediated signals.

Electrodermal Response in Nonglabrous Skin of Freely Moving Rats: Mediation by the Sympathetic Nervous System and Evaluation in an Animal Model of Depression

Electrodermal responses in the facial region of freely moving rats were recorded bilaterally. After a nociceptive stimulus (ammonia vapor exposure), the response (a transient negative potential followed by a longer-lasting positive potential) attained a similar amplitude on both sides. Surgical sympathetic denervation of facial skin by ipsilateral superior cervical ganglionectomy (SCGx) significantly decreased the electrodermal response. When an inferior cervical ganglionectomy was performed in addition to SCGx, a further decrease in electrodermal response was observed. Pretreatment of unilaterally SCGx rats with atropine blunted the electrical response in the control side to levels similar to those found in the SCGx side. Treatment with phenoxybenzamine or propranolol was ineffective. Skin potential responses were measured in adult rats administered with clomipramine from the 8th to the 21st day of life and exhibiting a long-lasting syndrome resembling human depression. Clomipramine-injected rats developed larger skin potential responses to sound stimulation than controls while responses to ammonia vapor were similar in both groups, as well as the habituation rate after repetitive exposure to ammonia vapor. The results indicate that some of the altered electrodermal responses found in depressed patients are detectable in the clomipramine animal model of endogenous depression.

Chronic Administration of β-Adrenergic Agonists Can Mimic the Stimulative Effect of Cold Exposure on Protein Synthesis in Rat Brown Adipose Tissue

When mammals are exposed to a cold environment for a long time, the capacity of nonshivering thermogenesis by brown adipose tissue (BAT) increases in association with the stimulation of synthesis of some specific proteins and tissue hyperplasia, which are totally dependent on sympathetic innervation to this tissue. To clarify the roles of the adrenergic mechanisms for the cold-induced protein synthesis and hyperplasia in BAT, in this study, the effects of chronic treatment with adrenergic agonists using an osmotic mini-pump were examined in rats. Continuous administration of noradrenaline or isoproterenol (beta-agonist) for 10 days resulted in increased synthesis of the mitochondrial uncoupling protein and an isoform of glucose transporter (GLUT4), and tissue hyperplasia, in the same way as after cold exposure of the same duration. Phenylephrine (alpha-agonist) administration did not have any significant effect. Surgical sympathetic denervation completely abolished the effects of cold exposure, whereas it did not influence those of adrenergic agonists at all. These results indicate that the stimulative effects of cold exposure on protein synthesis and hyperplasia of BAT are attributable solely to the beta-adrenergic action of noradrenaline secreted from the sympathetic nerves in this tissue.

Effects of surgical sympathetic denervation on G-protein levels, alpha and beta-adrenergic receptors, cAMP production and adenylate cyclase activity in the smooth muscles of rabbit iris.

The relative densities of a number of G protein subunits were quantified in membranes prepared from iris sphincter and dilator muscles of rabbits that have undergone sympathetic denervation and from contralateral innervated controls by immunoblotting with specific polyclonal antibodies against Gs alpha, Gi alpha and Gq alpha protein subunits. In addition, alpha and beta-adrenergic receptor densities, basal and isoproterenol (ISO)-stimulated cAMP production, and basal and ISO+GTP gamma S-stimulated adenylate cyclase (AC) activities were measured in the same tissues. Densitometric analysis of the immunoblot data revealed a 32% reduction in the level of Gi alpha in the denervated sphincter, a 26% increase in the level of Gi alpha in the denervated dilator, and no changes due to denervation were found in the levels of Gs alpha and Gq alpha. Sympathetic denervation had no effect on the densities of alpha- and beta-adrenergic receptors in these tissues, however, it did induce a significant decrease in the KD values of alpha-adrenergic receptors in both dilator and sphincter, and in beta-adrenergic receptors in the sphincter. The basal- and ISO-stimulated cAMP production in the sphincter was 4-fold as high as that of the dilator, and at 0.05 microM ISO the denervation supersensitivity for cAMP production in the sphincter increased by 118% as compared to 36% in the dilator. Sympathetic denervation increased by 19-47% the basal- and ISO-stimulated activity of AC in these tissues, however, it had no effect on the phospholipase C activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased expression of glucose transporter GLUT-4 in brown adipose tissue of fasted rats after cold exposure.

Cold exposure has been shown to increase glucose uptake specifically in brown adipose tissue (BAT), the major site for sympathetically controlled metabolic heat production. In this study, the relationship between glucose uptake and glucose transporters (GLUT) was examined in rats exposed to cold for various periods. To minimize the stimulatory effect of circulating insulin, all animals were starved for 20-24 h before the measurements. Acute (4 h) cold exposure had no effect on protein and mRNA levels of GLUT-4, the predominant isoform of GLUT in BAT, despite a significant increase in cellular glucose uptake. Prolonged (1-10 days) cold exposure produced a parallel increase in GLUT-4 expression and glucose uptake in BAT. In contrast, cold exposure had no noticeable effect on GLUT-1, another isoform of GLUT in BAT, and on GLUT-4 in other insulin-sensitive tissues such as white adipose tissue and muscles. The increased glucose uptake and GLUT-4 expression were completely abolished after surgical sympathetic denervation. These findings suggest that cold exposure increases glucose uptake in BAT by at least two distinct mechanisms, both of which are dependent on sympathetic nerve: 1) an increase in the amount of GLUT-4 due to the stimulation of its de novo synthesis, and 2) an increase without stimulation of GLUT synthesis, probably due to the change in the transport activity of GLUT-4 and/or its translocation from an intracellular pool to the plasma membrane.

Ventromedial hypothalamic stimulation enhances peripheral glucose uptake in anesthetized rats

Effects of electrical and chemical stimulation of the ventromedial (VMH) and lateral hypothalamic (LH) nuclei on glucose uptake in peripheral tissues were studied by the 2-deoxy-D-[3H]glucose (2-[3H]DG) method in anesthetized rats. Electrical stimulation of the VMH increased the rate constant of glucose uptake in brown adipose tissue (BAT; 8 times), heart (3 times), and skeletal muscles (1.5 times) but not in white adipose tissue, diaphragm, and brain, without detectable changes in plasma insulin levels. Chemical stimulation of the VMH by microinjection of L-glutamate also enhanced the rate constant of glucose uptake in BAT, heart, and skeletal muscles preferentially, which indicates that the enhancement of glucose uptake in these tissues is derived from activation of VMH neurons. The increased rate of glucose uptake in BAT in response to VMH stimulation was effectively suppressed by surgical sympathetic denervation, suggesting a mediation of the sympathetic nerve in this effect. On the other hand, electrical stimulation of the LH had no appreciable effect on 2-[3H]DG uptake in any tissues. It is concluded that glucose uptake in certain peripheral tissues is accelerated selectively by activation of VMH neurons, the action of which is independent of plasma insulin but which is probably via the sympathetic nervous system.

Activation of brown adipose tissue thermogenesis in recovery from anesthetic hypothermia in rats

Changes of brown adipose tissue (BAT) thermogenesis in the recovery from anesthetic hypothermia were studied by measuring the temperatures of the interscapular BAT and rectum or the tissue uptake of 2-deoxyglucose (2-DG) in rats. After intraperitoneal injection of pentobarbital sodium (50 mg/kg), rectal temperature decreased to reach a steady level of approximately 33 degrees C (steady phase) and then increased gradually (recovery phase). The temperature of the interscapular BAT was significantly higher than rectal temperature in the recovery phase. The uptake of 2-DG in vivo in BAT was low in the steady phase but increased greatly in the recovery phase. The increase in 2-DG uptake was suppressed after surgical sympathetic denervation or when rectal temperature was maintained at approximately 37.5 degrees C. In the heart, skeletal muscle, and white adipose tissue, there was no appreciable change in 2-DG uptake except a slight increase in the heart. beta-Adrenergic blockade attenuated the changes in BAT temperature and 2-DG uptake seen during the recovery phase. It was concluded that BAT significantly contributes to heat production in recovery from anesthetic hypothermia.

Effects of Surgical Sympathetic Denervation on myo-Inositol Trisphosphate Production and Contraction in the Dilator and Sphincter Smooth Muscles of the Rabbit Iris: Evidence for Interaction Between the Cyclic AMP and Calcium Signaling Systems

The effects of norepinephrine (NE), carbachol (CCh), NaF, 3-isobutyl-1-methylxanthine (IBMX), and high K+ concentration (80 mM) depolarization on inositol trisphosphate (IP3) accumulation, cyclic AMP (cAMP) formation, and contraction were investigated in the dilator and sphincter smooth muscles of the sympathetically denervated as well as the normal rabbit eye. (a) In the denervated dilator muscle, NE-stimulated IP3 production and contraction are enhanced. (b) In the sphincter muscle of rabbits that have undergone sympathetic denervation. CCh-stimulated IP3 production and contraction are attenuated. (c) The increase in tension by a maximal effective dose of NaF (209 mM) in the dilator was 12.5 and 18 mg of tension/mg wet weight in normal and denervated tissue, respectively, and in the sphincter was 33.8 and 15.2 mg of tension/mg wet weight in normal and denervated tissue, respectively. NaF had no effect on cAMP formation. (d) Addition of NE had no effect on cAMP formation in both the normal and denervated dilator, whereas basal and IBMX-induced cAMP formation increased. in the denervated sphincter over that of the normal tissue by 15 and 60%, respectively. (e) Isoproterenol (5 microM) increased cAMP formation in the normal and denervated sphincter by 47 and 91%, respectively. (f) Whereas CCh inhibits cAMP formation in the normal sphincter, it lost its inhibitory effect in the sphincter with denervation. (g) IBMX (0.1 mM) attenuated the CCh-stimulated IP3 production and contraction of the sphincter by approximately 30% of their respective controls. (h) High K+ concentration depolarization attenuated contraction in both dilator and sphincter muscles with denervation. These observations suggest that an increase in the level of cAMP in the iris sphincter due to sympathetic denervation could lead to inhibition of phospholipase C (or other target sites, such as phosphorylation of the muscarinic receptor, Gp protein itself, myosin light chain kinase, or the IP3 receptor), IP3 production, and contraction. In conclusion, we suggest that the supersensitivity and subsensitivity observed after surgical sympathetic denervation of the iris dilator and sphincter muscles, respectively, are caused by alterations in the efficiency of coupling, probably through the Gp proteins, between their respective receptors and the breakdown of polyphosphoinositides by phospholipase C. In addition, we propose that the sympathetic nervous system can regulate, through alterations in cAMP levels, the muscarinic stimulation of IP3 accumulation and contraction in the iris sphincter. These findings add further support to the hypothesis that there are reciprocal interactions between the cAMP and IP3-Ca2+ signaling systems and the contractile response in the iris smooth muscle.

Distribution of peptidergic nerves in the choroid plexus, focusing on coexistence of neuropeptide Y, vasoactive intestinal polypeptide and peptide histidine isoleucine

Choroid plexus from rat, guinea-pig, rabbit and pig was investigated by light-microscopic immunohistochemistry and by radioimmunoassay for the presence of neuropeptides. A moderately dense supply of nerve fibers containing neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP), respectively, was found around blood vessels and in close relation to the secretory epithelium in both pig and rabbit, while lower densities of nerve fibers were found in rat and guinea-pig. Peptide concentrations ranged from 10–40 pmolequivalents/g (pmoleqv/g) for NPY and 0.5–6 pmoleqv/g for VIP in all four species. Peptide histidine isoleucine (PHI) immunoreactive nerve fibers were present in pig choroid plexus at a lower density than NPY and VIP but with a similar distribution. Low concentrations of substance P (0.3–3 pmoleqv/g) and calcitonin gene-related peptide (0.1–3 pmoleqv/g) were found to a varying degree in choroid plexus tissue from the different species, while immunohistochemical investigation was unable to detect any immunoreactive nerve fibers. NPY was often found to coexist with VIP and PHI in pig choroid plexus, while a lesser amount of nerve fibers showed coexistence of NPY and the noradrenaline synthetizing enzyme, dopamine-β-hydroxylase. Surgical sympathetic denervation by excision of the superior cervical ganglion in the rabbit abolished NPY-containing nerve fibers, as revealed by immunohistochemistry, but only decreased NPY levels by one third, which may be due to different identity of the peptide being detected by the two techniques. It is concluded that NPY-containing nerve fibers have a dual origin in the choroid plexus and coexist with either noradrenaline or VIP/PHI.