Epi Release Research Articles

Sublingual route for the continuous release of epinephrine from chitosan nanoparticles

Administration of Epinephrine (Epi) using an intramuscular autoinjector (EAI) is the primary first aid treatment available for the management of anaphylaxis in the community of many countries. Around 1 in 10 patients require a second EAI within 5–15 min. Previously, we successfully developed rapidly disintegrating sublingual tablets (RDST) containing Epi microcrystals that exhibited comparable in vivo pharmacokinetics to that of EAI to overcome the drawbacks of EAIs. To further advance these RDST, we hypothesized that synthesizing Epi nanoparticles (Epi-NP) for incorporation into our previously developed Epi RDST could prolong Epi release sufficiently to eliminate the need for a second dose. Therefore, the primary objective of this research was to synthesize various Epi-NP with different drug loads and investigate their release profiles and sublingual permeability. In vitro release and ex vivo permeability studies were performed using synthetic dialysis membranes and excised porcine sublingual membranes, receptively. The release and permeation of Epi from both NP with adsorbed Epi (Ads Epi-NP) and NP with encapsulated Epi (Enc Epi-NP) were significantly slowed down and achieved continuous control over 8 h. At 60 % Epi load, Epi release from Enc Epi-NP was significantly lower than from Ads Epi-NP, however, the cumulative permeated Epi was only significantly lower towards the end of the experiment, suggesting similar control over Epi permeability. Finally, visualization of NP permeation across the sublayers of the sublingual mucosa confirmed the formation of a temporary depot for Epi and maintained Epi release for several hours post-administration. The results from this study demonstrate for the first time the short-term sustained-release potential of the sublingual route to overcome the need for a second dose.

Chromaffin Cells of the Adrenal Medulla: Physiology, Pharmacology, and Disease.

Chromaffin cells (CCs) of the adrenal gland and the sympathetic nervous system produce the catecholamines (epinephrine and norepinephrine; EPI and NE) needed to coordinate the bodily "fight-or-flight" response to fear, stress, exercise, or conflict. EPI and NE release from CCs is regulated both neurogenically by splanchnic nerve fibers and nonneurogenically by hormones (histamine, corticosteroids, angiotensin, and others) and paracrine messengers [EPI, NE, adenosine triphosphate, opioids, γ-aminobutyric acid (GABA), etc.]. The "stimulus-secretion" coupling of CCs is a Ca2+ -dependent process regulated by Ca2+ entry through voltage-gated Ca2+ channels, Ca2+ pumps, and exchangers and intracellular organelles (RE and mitochondria) and diffusible buffers that provide both Ca2+ -homeostasis and Ca2+ -signaling that ultimately trigger exocytosis. CCs also express Na+ and K+ channels and ionotropic (nAChR and GABAA ) and metabotropic receptors (mACh, PACAP, β-AR, 5-HT, histamine, angiotensin, and others) that make CCs excitable and responsive to autocrine and paracrine stimuli. To maintain high rates of E/NE secretion during stressful conditions, CCs possess a large number of secretory chromaffin granules (CGs) and members of the soluble NSF-attachment receptor complex protein family that allow docking, fusion, and exocytosis of CGs at the cell membrane, and their recycling. This article attempts to provide an updated account of well-established features of the molecular processes regulating CC function, and a survey of the as-yet-unsolved but important questions relating to CC function and dysfunction that have been the subject of intense research over the past 15 years. Examples of CCs as a model system to understand the molecular mechanisms associated with neurodegenerative diseases are also provided. Published 2019. Compr Physiol 9:1443-1502, 2019.

Smart aptamer-modified calcium carbonate nanoparticles for controlled release and targeted delivery of epirubicin and melittin into cancer cells in vitro and in vivo

To explore the effect of combination therapy of epirubicin (Epi) and melittin (Mel) to cancer cells, calcium carbonate nanoparticles (CCN), as carriers, were developed which were modified with MUC1-Dimer aptamers as targeting agents. Both Epi and Mel were delivered at the same time to cancer cells overexpressing the target of MUC1 aptamer, mucin 1 glycoproteins (MCF7 and C26 cells). CCN were prepared with a water-in-oil emulsion method. Epi and Mel were separately encapsulated in CCN and the nanoparticles were modified with MUC1-Dimer aptamers. In vitro studies, including MTT assay, flow cytometry analysis and fluorescence imaging were applied to investigate the targeting and cell proliferation inhibition capabilities of MUC1-Dimer aptamer-CCN-Mel complex and MUC1-Dimer aptamer-CCN-Epi complex in the target (MCF-7 and C26 cells) and nontarget (HepG2) cells. Also, the function of the developed complexes was analyzed using in vivo tumor growth inhibition. The release of Epi from MUC1-Dimer aptamer-CCN-Epi complex was pH-sensitive. Cellular uptake studies showed more internalization of the MUC1-Dimer aptamer-CCN-Epi complex into MCF-7 and C26 cells (target) compared to HepG2 cells (nontarget). Interestingly, the MUC1-Dimer aptamer-CCN-Mel complex and MUC1-Dimer aptamer-CCN-Epi complex indicated very low toxicity as compared to target cells. Moreover, co-delivery of Epi and Mel using the mixture of MUC1-Dimer aptamer-CCN-Mel complex and MUC1-Dimer aptamer-CCN-Epi complex exhibited strong synergistic cytotoxicity in MCF-7 and C26 cells. Furthermore, the presented complexes had a better function to control tumor growth in vivo compared to free Epi.

Abstract 16720: Exercise-Stimulated Catecholamine Release Enhances Resolution of Acute Inflammation

The mechanisms by which regular exercise prevents the development and progression of chronic inflammatory diseases are largely unknown. We find that exercise (Exe) enhances resolution of acute inflammation by promoting macrophage (MФ) phagocytosis and by augmenting resolvin D1 (RvD1) levels. When compared with sedentary controls (Sed), mice adapted to a 4-week treadmill exercise regimen displayed 1.48-fold higher MФ phagocytotic activity, enhanced RvD1 levels (Sed 28.08±1.5 vs Exe 48.01±8.6 pg/mL, n=6), and earlier neutrophilic clearance (ΔR i ~7 h) during peritonitis. Peritonitis cell extracts from exercise-adapted mice showed elevated expression of Alox15 (48 h: Sed 0.97±0.15 vs Exe 1.5±0.16 relative expression, n=8-9), Alox5 (48 h: Sed 0.77±0.15 vs Exe 1.7±0.27 relative expression, n=4-5), and RvD1 levels (48 h: 29.0±2.1 vs 52.6±8.9 pg/mL, n=5). Because exercise stimulates epinephrine (Epi) release, which has immunomodulatory effects, we questioned if Epi exerts pro-resolving actions on macrophages. Epi-treated macrophages displayed higher 15-lipoxygenase 1 expression and RvD1 levels, which were prevented by incubation with the α1 adrenergic receptor (AR-α1) blocker, Prazosin (Praz). During zymosan-induced peritonitis, Praz abrogated exercise-enhanced neutrophilic clearance (48 h: Exe+Veh 2.07±0.41 vs Exe+Praz 5.2±1.04 x10 6 PMN, n=5), MФ phagocytosis (Exe+Veh 33463.0±2174.0 vs Exe+Praz 8303.0±2748.0 MFI, n=5-7), and RvD1 biosynthesis (Exe+Veh 211.0±55.4 vs Exe+Praz 81.79±11.8 pg/mL, n=6). These results suggest that exercise-stimulated Epi release enhances resolution of acute inflammation in an AR-α1 dependent manner. These findings provide new mechanistic insights into the pro-resolving effects of exercise and may lead to the identification of novel pathways to stimulate resolution biology.

Study of the release kinetics of (−) epicatechin: Effect of its location within the fiber or sphere

ABSTRACTThe (−) epicatechin (Epi) is a flavonoid with antioxidant and regenerative properties for cardiac tissue. In this work, a study of release assays and their corresponding adjustments to models was performed to determine the mechanism of (−) Epi release in the cellulose acetate (CA)–polyvinylpyrrolidone (PVP) system. The morphology of the material was considered, fibers, or spheres, as well as the possible chemical interactions between Epi, PVP, and CA. It was observed that in the systems in which the PVP is present, a high release is observed in comparison with those that only contained CA and (−) Epi, which showed very low release. This difference can be explained considering the possible hydrogen bond interaction between CA and (−) Epi, as well as the insolubility of the CA, in the release medium. The factors that have an important effect on the release of (−) Epi in the different systems are: the morphology, a faster release in morphologies with greater surface area, and the chemical interactions that can be formed among the (−) Epi and the components of the matrix. Another factor is the solubility of the components in the release medium, which allows the diffusion and drag phenomena to be observed simultaneously. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47166.

Polysialic acid-modifying liposomes for efficient delivery of epirubicin, in-vitro characterization and in-vivo evaluation

Polysialic acid (PSA) serves as a hydrophilic polymer and affords conjugated biologically active molecules a longer circulation time in vivo. Furthermore, PSA could potentially target tumor tissues and help achieve better curative effects. In this study, PSA was conjugated with octadecyl dimethyl betaine (BS18) to yield a PSA-BS18 conjugate. The PSA-BS18 modified liposomal epirubicin (EPI-SL), had a particle size of 133.63±0.92nm, a zeta potential of −26.23±1.50mV and an encapsulation efficiency (%EE) of 96.23±1.16%. In vitro release studies showed that PSA-BS18 could delay EPI release from the modified liposomes. The MTT assay suggested that EPI-SL led to stronger cytotoxic activity than that exhibited by common and PEGylated liposomes. The pharmacokinetic study showed that EPI-SL prolonged the residence time of the EPI in the blood compared with that observed from common liposomes. Bio-distribution results obtained from tumor-bearing mice clearly demonstrated that PSA-BS18 increased the accumulation of modified liposomes in tumors compared with that of common liposomes. In the antitumor efficacy study, EPI-SL showed the best antitumor and life-prolonging effects among all of the tested formulations. These findings strongly indicate EPI-SL might have great potential as an effective approach for anticancer therapy.

Targeted Delivery of Epirubicin to Cancer Cells by Polyvalent Aptamer System in vitro and in vivo.

The clinical use of Epirubicin (Epi), as an anthracycline drug, is limited because of its cardiotoxicity. Here, an Epirubicin (Epi)-modified polyvalent aptamer system (MPAS) conjugate was developed for the treatment of both murine colon carcinoma cells (C26) and breast cancer cells (MCF-7). Epi-MPAS conjugate formation was evaluated by fluorometric analysis. Release profiles of Epi from the developed conjugate were analyzed at pHs 5.4 and 7.4. For MTT assay (cytotoxic study) C26 and MCF-7 (target cells) and CHO cells (Chinese hamster ovary cell, nontarget) were treated with Epi, MPAS and Epi-MPAS conjugate. Internalization was assessed by fluorescence imaging and flow cytometry analysis. The designed conjugate was used for prohibition of tumor growth in vivo. Release of Epi from the Epi-MPAS conjugated was pH-dependent (more release at pH 5.5). Flow cytometry analysis and MTT assay showed that Epi-MPAS conjugate could significantly enhance the cellular uptake of Epi and increase its cytotoxicity in target cells as compared with non-targeted cell (CHO). Additionally, this complex could efficiently prohibit the tumor growth in vivo. In conclusion, the developed drug delivery system had the characteristics of efficient Epi loading, pH-dependent drug release and tumor targeting in vitro and in vivo.

Evaluation of Epirubicin in Thermogelling and Bioadhesive Liquid and Solid Suppository Formulations for Rectal Administration

Temperature sensitive Pluronic (Plu) and pH-sensitive polyacrylic acid (PAA) were successfully mixed in different ratios to form in situ gelling formulations for colon cancer therapy. The major formulations were prepared as the liquid and solid suppository dosage forms. Epirubicin (Epi) was chosen as a model anticancer drug. In vitro characterization and in vivo pharmacokinetics and therapeutic efficacy of Epi in six Plu/PAA formulations were evaluated. Our in vitro data indicate that Epi in Plu 14%/PAA 0.75% of both solid and liquid suppositories possess significant cytotoxicity, strong bioadhesive force, long-term appropriate suppository base, sustained release, and high accumulation of Epi in rat rectums. These solid and liquid suppositories were retained in the upper rectum of Sprague-Dawley (SD) rats for at least 12 h. An in vivo pharmacokinetic study using SD rats showed that after rectal administration of solid and liquid suppositories, Epi had greater area under the curve and higher relative bioavailability than in a rectal solution. These solid and liquid suppositories exhibited remarkable inhibition on the tumor growth of CT26 bearing Balb/c mice in vivo. Our findings suggest that in situ thermogelling and mucoadhesive suppositories demonstrate a great potential as colon anticancer delivery systems for protracted release of chemotherapeutic agents.

Effects of intravenous magnesium infusion on in vivo release of acetylcholine and catecholamine in rat adrenal medulla

We applied microdialysis technique to the left adrenal medulla of anesthetized rats and examined the effects of intravenous Mg(2+) infusion on presynaptic acetylcholine (ACh) release and postsynaptic catecholamine release induced by electrical stimulation of splanchnic nerves. The dialysis probes were perfused with Ringer's solution containing neostigmine. Low-dose MgSO4 (25 μmol/kg/min for 30 min i.v.) increased mean plasma Mg(2+) concentration to 2.5mM; the administration suppressed norepinephrine (NE) release by approximately 30% and epinephrine (Epi) release by approximately 20%, but did not affect ACh release. High-dose MgSO4 (50 μmol/kg/min for 30 min i.v.) increased mean plasma Mg(2+) concentration to 3.8mM; the administration suppressed ACh release by approximately 25%, NE release by approximately 60% and Epi release by approximately 45%. Administration of Na2SO4 (50 μmol/kg/min for 30 min i.v.) did not change the release of ACh, NE or Epi. Local administration of nifedipine (200 μM) suppressed NE release by approximately 40% and Epi release by approximately 30%, but did not affect ACh release. In the presence of nifedipine, low-dose MgSO4 did not suppress the release of ACh, or further suppress NE or Epi compared to nifedipine alone, but high-dose MgSO4 suppressed ACh release by approximately 25% and further suppressed NE release by approximately 60% and Epi release by approximately 50% compared to nifedipine alone. In conclusion, intravenous administration of Mg(2+) inhibits both presynaptic ACh release and postsynaptic catecholamine release in the adrenal medulla, but L-type Ca(2+) channel-controlled catecholamine release may be more sensitive to Mg(2+) than non-L-type Ca(2+) channel-controlled ACh release.

Polysialic acid as a drug carrier: evaluation of a new polysialic acid–epirubicin conjugate and its comparison against established drug carriers

This paper explores the potential of polysialic acid (PSA) as a carrier for low molecular weight anticancer drugs. A PSA–epirubicin (Epi) conjugate was synthesized and compared against Epi conjugates containing established carriers, namely: N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers, poly(ethylene glycol) (PEG) and polyglutamic acid (PGA). Biological assessments in the breast cancer cell line MCF-7 and in the anthracycline resistant MCF-7/DX showed that the PSA–Epi conjugate had the highest activity (40% and 30% cell death in the two cell lines at 1 μM Epi equiv., respectively). FACS studies confirmed internalization of all conjugates by cholesterol-dependent endocytosis. PSA–Epi showed release of Epi (40% at 5 h) when incubated with lysosome extracts. In vivo evaluation showed that all conjugates had a significantly longer half-life compared to free Epi. This study also allowed an investigation on the effect of the polymeric carrier on the biological activity of a conjugate, with the biodegradability of the carrier emerging as an important feature.

Tityus zulianus venom induces massive catecholamine release from PC12 cells and in a mouse envenomation model

Scorpion envenomation is a public health problem in Venezuela, mainly produced by Tityus discrepans (TD) and Tityus zulianus (TZ). Accidents by these two species differ clinically. Thus, TZ envenomation is associated with high mortality in children due to cardiopulmonary disorders, as a result of, excessive amounts of plasma catecholamines (Epinephrine) release from adrenal medulla, probably via the voltage-gated sodium-channel activated by specific scorpion toxins. This Epi release is, in part responsible, for some of the envenomation clinical consequences, resembling those described for patients presenting catecholamine-releasing tumors (pheochromocytoma). In this work, BALB/c mice and rat pheochromocytoma-derived PC12 cells were used to provide in vivo and in vitro models, respectively, on which the basis for the TZ-mediated catecholamine release mechanism could be elucidated. In mice, TZ venom increased, at 1h post-injection, the Epi plasma levels in 4000%, which remained elevated for 24h. A significant rise in plasma levels of the catecholamine catabolite 3-Methoxy-4-Hydroxy-Phenyl-Glycol (MHPG) was also observed. In [3H]dopamine-loaded PC12 cells, TZ venom potentiated the carbamylcholine (CC)-mediated release of [3H]dopamine, as shown by the leftward shift in the CC-dose-response curves. Moreover, TZ venom also displayed the maximal [3H]dopamine releasing activity compared to TD venom, with significant reduction of the EC50 for CC. The nicotinic-acetylcholine receptor (nAChR) blocker hexamethonium induced a significant inhibition of the [3H]dopamine release produced by CC in PC12 cells but the TZ-elicited release of [3H]dopamine was 70% hexamethonium-insensitive, suggesting unidentified TZ toxins affecting other regulatory mechanisms of catecholamine secretion.

Impaired adrenergic- and corticotropic-axis outflow during exercise in chronic obstructive pulmonary disease

Exercise stimulates coordinated release of the sympathoadrenal hormones adrenocorticotropic hormone (ACTH), cortisol, norepinephrine (NE), and epinephrine (Epi). The study hypothesis was that chronic obstructive pulmonary disease (COPD) is marked by heightened sympathoadrenal outflow at comparable relative workloads. The location of the study was at a clinical research unit. Eight healthy men and 9 men with stable COPD (forced expiratory volume at 1 second <75% predicted) were studied. Volunteers rested (baseline) or exercised at individual submaximal (35% ± 5%) or maximal oxygen consumption. Blood was sampled every 2 minutes for 40 minutes concurrently. Two-way analysis of covariance was applied to examine group (healthy/COPD) and exercise (3 levels) effects on ACTH, cortisol, NE, and Epi release and regularity (estimable by approximate entropy). The timing of peak hormone concentrations was Epi, 14 minutes; NE, 16 minutes; ACTH, 22 minutes; and cortisol, 34 minutes in both cohorts. Type of exercise regimen influenced all 4 hormones (each P < .001), and subject group (control vs COPD) affected cortisol (P < .001) and Epi (P = .048) responses. Exercise regimen and group together controlled ACTH, cortisol, and Epi (each P < .001), but not NE, responses. In particular, endocrine responses were attenuated in COPD compared with control subjects. Approximate entropy analysis also identified loss of maximal exercise-induced ACTH-secretory regularity in COPD patients (P = .042). These outcomes demonstrate impaired rather than augmented exercise-associated sympathocorticotropic-axis outflow in patients with COPD even when outcomes are normalized to maximal oxygen consumption, suggesting that factors other than fitness are at work.

Role of Ca 2+-activated K + channels in catecholamine release from in vivo rat adrenal medulla

To elucidate the role of Ca 2+-activated K + (K Ca) channels in the presynaptic acetylcholine (ACh) release from splanchnic nerve endings and the postsynaptic catecholamine release from chromaffin cells, we applied microdialysis technique to the left adrenal medulla of anesthetized rats and investigated the effects of local administration of K Ca channel antagonists through dialysis probes on the release of ACh and/or catecholamine, induced by electrical stimulation of splanchnic nerves or local administration of ACh through the dialysis probes. Nerve stimulation-induced release: in the presence of a cholinesterase inhibitor, neostigmine, large-conductance K Ca (BK) channel antagonists, iberiotoxin and paxilline enhanced the presynaptic ACh release and postsynaptic norepinephrine (NE) and epinephrine (Epi) release. Small-conductance K Ca (SK) channel antagonists, apamin and scyllatoxin enhanced the Epi release without any changes in ACh or NE release. In the absence of neostigmine, ACh release was not detected. Iberiotoxin and paxilline enhanced NE and Epi release. Apamin and scyllatoxin had no effect on NE or Epi release. Exogenous ACh-induced release: iberiotoxin and paxilline enhanced the Epi release, but had no effect on the NE release. Apamin and scyllatoxin enhanced both NE and Epi release. In conclusion, BK channels on splanchnic nerve endings play an inhibitory role in the physiological catecholamine release from adrenal medulla by limiting presynaptic ACh release while SK channels do not. BK channels on Epi-storing cells may play an inhibitory role in nerve stimulation-induced Epi release. SK channels on NE- and Epi-storing cells play a minor role in nerve stimulation-induced catecholamine release.

Chronic intermittent hypoxia induces hypoxic sensitivity in adult rat adrenal medulla via oxidative stress

Catecholamine (CA) secretion from adult adrenal medulla is insensitive to direct effects of acute hypoxia. Given that adrenal medulla contributes to elevated plasma CA in rats exposed to chronic intermittent hypoxia (CIH), in the present study, we examined whether CIH promotes CA efflux by acute hypoxia from adrenals in adult rats and if so by what mechanisms. Experiments were performed on adult male rats exposed to 10d of CIH. In control animals, acute hypoxia had no effect, whereas nicotine (100 μM) evoked epinephrine (Epi) or norepinephrine (NE) efflux from ex vivo adrenal medulla. In sharp contrast, in CIH animals, acute hypoxia evoked robust efflux of both Epi and NE, whereas the effects of nicotine were attenuated or absent. Cytosolic and mitochondrial aconitase enzyme activities, indices of O2. −generation, were down-regulated in CIH adrenal medulla. Systemic administration of superoxide dismutase (SOD) mimetic, a scavenger of O2. − prevented acute hypoxia-evoked release of Epi and NE from CIH conditioned adrenal medulla. Furthermore, SOD mimetic prevented increases in arterial blood pressure and elevated plasma CA in CIH conditioned rats. These observations demonstrate that CIH up-regulates hypoxic sensing in adult adrenal medulla via mechanisms involving increased generation of O2. − and hypoxia-evoked CA secretion from adrenal medulla contributes, in part, to elevated blood pressure during CIH (Supported by NIH HL-25830).

Beta1-adrenergic receptor blockade attenuates angiotensin II-mediated catecholamine release into the cardiac interstitium in mitral regurgitation.

This study tested the hypothesis that beta1-adrenoreceptor blockade modulates the angiotensin II (Ang II)-evoked neural release of norepinephrine (NE) and epinephrine (Epi) into the cardiac interstitial fluid (ISF) space in experimentally induced mitral regurgitation (MR) in the dog. Normal dogs (n=8) were compared with dogs with MR of 2 (n=8) and 4 (n=6) weeks' duration and with dogs with MR treated with beta1-receptor blockade (RB; extended-release metoprolol succinate, 100 mg QD; MR+beta1-RB) that was started 24 hours after MR induction for 2 (n=6) and 4 weeks (n=8). Left ventricular end-diastolic dimension increased 20% as plasma Ang II levels increased >5-fold in both MR and MR+beta1-RB dogs at 2 and 4 weeks. Ang II infusion into the left atrium produced increases in ISF NE and Epi in normal dogs, which were further increased in 2- and 4-week MR dogs but were restored to normal in 4-week MR+beta1-RB dogs. Ang II infusion produced 4-fold increases in circulating NE and Epi in 2- and 4-week MR dogs that returned to normal in 4-week+beta1-RB dogs. Left ventricular angiotensin-converting enzyme activity and ISF Ang II were increased in 4-week MR dogs but were decreased in 4-week MR+beta1-RB dogs. beta1-RB decreases renin-angiotensin system sympathostimulation and activation by attenuating the Ang II-mediated NE and Epi release into the cardiac ISF and circulation and by decreasing left ventricular angiotensin-converting enzyme expression in the early phases of volume overload.

Eprosartan decreases the pulse pressure response to sympathoadrenal activation in humans

Angiotensin II facilitates catecholamine release from the adrenal medulla and neuronal norepinephrine release. Animal experiments suggest that the non-biphenyl AT1-blocker eprosartan (EPRO) might possess specific sympathoinhibitory properties. We aimed to clarify if EPRO inhibits sympathetic reactivity in humans. 16 healthy male volunteers participated in a randomized double-blind cross-over study to receive a single dose EPRO of 600 mg vs. placebo followed by insulin-induced hypoglycemia [i.v. bolus; 0,15IU/kg] on two study days one week apart. The hypoglycemia-induced sympathoadrenal reactivity was mapped by invasive continuous blood pressure monitoring and frequent measurement of forearm blood flow (FBF), arterial and venous concentrations of glucose, catecholamines epinephrine and norepinephrine (EPI; NE), renin (PRC) and angiotensin II (AngII). Acute AT1-receptor blockade was effective since EPRO induced a 8–10 fold increase of circulating PRC and AngII. Plasma glucose decreased equally during placebo and EPRO from baseline 5,9 mM to 1,9 mM during which circulating EPI increased about 12 fold. Musculocutaneous NE release was unaltered during EPRO compared to placebo while the cumulative measure of adrenal EPI release (AUCEPI) was reduced by 20 % though not statistically significant (P=0,14). However, the EPI-induced pulse pressure response (PPR) was significantly blunted by EPRO: AUCPPR,Placebo = 39920 ± 2000 mmHg5 • min. vs. AUCPPR,EPRO= 37120±1680 mmHg • min. (P=0,0037). Moreover, EPRO tended to inhibit the EPI induced increase of FBF by 13% (P=0.077). The EPRO-induced inhibition of EPI release was not statistically significant. However EPRO highly significantly inhibits the classical EPI-induced pulse pressure response to sympathoadrenal activation. Thus EPRO appears to possess unique though ill-understood sympathoinhibitory properties.

Brain angiotensin receptors and sympathoadrenal regulation during insulin-induced hypoglycemia.

Simultaneous blockade of systemic AT1 and AT2 receptors or converting enzyme inhibition (CEI) attenuates the hypoglycemia-induced reflex increase of epinephrine (Epi). To examine the role of brain AT1 and AT2 receptors in the reflex regulation of Epi release, we measured catecholamines, hemodynamics, and renin during insulin-induced hypoglycemia in conscious rats pretreated intracerebroventricularly with losartan, PD-123319, losartan and PD-123319, or vehicle. Epi and norepinephrine (NE) increased 60-and 3-fold, respectively. However, the gain of the reflex increase in plasma Epi (Deltaplasma Epi/Deltaplasma glucose) and the overall Epi and NE responses were similar in all groups. The ensuing blood pressure response was similar between groups, but the corresponding bradycardia was augmented after PD-123319 (P < 0.05 vs. vehicle) or combined losartan and PD-123319 (P < 0.01 vs. vehicle). The findings indicate 1) brain angiotensin receptors are not essential for the reflex regulation of Epi release during hypoglycemia and 2) the gain of baroreceptor-mediated bradycardia is increased by blockade of brain AT2 receptors in this model.

Cyanide intoxication induced exocytotic epinephrine release in rabbit myocardium

Cyanide intoxication, which has been used as a model of energy depletion at cardiac sympathetic nerve terminals, causes non-exocytotic release of norepinephrine (NE). However, the effect of cyanide intoxication on cardiac epinephrine (Epi) release remains unknown. Using cardiac microdialysis in the rabbit, we measured dialysate Epi and NE concentrations as indices of myocardial interstitial Epi and NE levels, respectively. Local administration of sodium cyanide (30 mM) through the dialysis probe increased both Epi and NE levels (from 11.3±2.3 to 32.3±4.4 pg/ml and from 33.6±6.1 to 389.0±71.8 pg/ml, respectively, mean±S.E., P<0.01). Local desipramine (100 μM) administration suppressed the cyanide induced NE response without affecting the Epi response. In contrast, local ω-conotoxin GVIA (10 μM) administration partially suppressed the cyanide induced NE response and totally abolished the Epi response. In conclusion, cyanide intoxication causes N-type Ca 2+ channel dependent exocytotic Epi release as well as inducing N-type Ca 2+ channel independent non-exocytotic NE release.

Local epinephrine release in the rabbit myocardial interstitium in vivo

Although several investigations have suggested cardiac epinephrine (Epi) release, local Epi release in the myocardial interstitium in vivo has not been measured. Using cardiac microdialysis in the rabbit, we measured dialysate Epi and norepinephrine (NE) concentrations as indices of myocardial interstitial Epi and NE levels, respectively. Exocytotic release induced by local administration of KCl (100 mM) through the dialysis probe increased Epi to 24.2±13.2 pg/ml from a control value of 3.2±3.6 pg/ml ( P<0.01, n=6). Non-exocytotic release induced by the local administration of tyramine (10 μg/ml) also increased Epi to 34.6±15.3 pg/ml ( p<0.05 from control, n=6). We conclude that Epi can be released via both exocytotic and non-exocytotic release mechanisms from the heart.

Cardiorenal epinephrine kinetics: evidence for neuronal release in the human heart.

There are experimental data suggesting that epinephrine (Epi) may act as a cotransmitter in sympathetic nerves, stimulating presynaptic beta 2-receptors and enhancing norepinephrine (NE) release. To examine neuronal Epi release, patients with congestive heart failure and hypertension and healthy subjects were examined with the isotope-dilution method. At baseline, small cardiac and renal Epi spillovers were found in patients. During intense supine exercise, cardiac NE and Epi spillovers increased concomitantly with similar magnitude, whereas no renal Epi spillover could be detected. Blockade of neuronal uptake 1 caused a consistent decrease in both cardiac and renal fractional extractions of NE and Epi. The present study demonstrates baseline cardiorenal Epi release in patients with congestive heart failure and renal Epi release in hypertensive patients. Furthermore, Epi is removed by neuronal uptake in both the heart and kidney, and cardiac Epi spillover increases during exercise. This study, in contrast to other results, provides evidence for cardiac neuronal Epi release.