Effects Of Melittin Research Articles

Melittin inhibits TGF-β-induced pro-fibrotic gene expression through the suppression of the TGFβRII-Smad, ERK1/2 and JNK-mediated signaling pathway.

Renal fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) proteins such as type I collagen, fibronectin, and by the increased expression of PAI-1. This study evaluated the anti-fibrotic effect of bee venom and its major compounds (melittin and apamin) on TGF-β-induced pro-fibrotic gene expression. Bee venom and melittin significantly suppressed type I collagen, fibronectin, and PAI-1 protein expression in the TGF-β-treated kidney fibroblast. However, apamin only inhibited the expression of fibronectin and type I collagen. These results indicated that the inhibitory effects of bee venom on TGF-β-induced pro-fibrotic gene expression are caused by melittin. Moreover, we attempted to elucidate mechanisms underlying the anti-fibrotic effect of melittin. Melittin dramatically inhibited the phosphorylation of TGFβRII and Smad2/3. Also, melittin inhibited the phosphorylation of ERK1/2 and JNK, but not the phosphorylation of PI3K, Akt, and p38. These results suggested that melittin inhibits TGF-β-induced pro-fibrotic genes expression through the suppression of TGFβR-Smad2/3, ERK1/2, and JNK phosphorylation, and melittin can be used as a clinical drug for the treatment of fibrosis associated with renal diseases.

Effect of melittin on mice stomach

Melittin, the main bee venom component, has many positive biological effects and a relatively low toxicity in various cell types. However, there is no evidence of the effect of melittin on gastrointestinal cells. In the present study, we investigated the histological and immuonohistochemical effects of melittin on mice stomach. Adult male mice (Albino Swiss) were randomly divided into two groups (7 mice for each group): control group and melittin only treated group (10 and 40μg/kg). These mice were sacrificed, then samples from the stomach were collected and prepared for histopathological studies by using alcian blue stain and immuonohistochemical studies by using smooth muscle actin (SMA) antibody. Treatment with melittin alone do not cause any harmful effect on the stomach tissue where the microscopic examination of Alcian blue stained section showed the normal distribution of the mucous secreting cells of the stomach tissues. On other hand, no changes were observed on smooth muscle cells. This study demonstrated the safety of using melittin on gastrointestinal tissues if used in definite dose and for suitable duration, which offers an opportunity for its use as a treatment for many diseases of the gastrointestinal tract.

Physiological and Histological Studies on the Effect of Melittin on Mice Jejunum

Melittin is a major polypeptide in honey bee venom that has been usedtraditionally against chronic inflammation and cancer. The aim of this work is study theeffect of melittin on the mice jejunum from the physiological and histological points,then determine the safe dosage and duration on cells and tissues. Adult male mice(Albino Swiss) were divided into two groups (7 mice for each group): control group andmelittin only treated group (10 and 40 µg/kg). The samples from the jejunum were collectedand prepared for histological and physiological studies. Melittin has no cytotoxic effects,where the alcian blue stained sectioned showed the normal distribution of the mucoussecreting cells and the levels of IL-1b in the jejunum mice treated with melittin (10 or 40µg/kg) for 3 or 5 days were closed to control, whereas these levels were significantlydecreased compared to control after treated for 10 days for each doses. These studiessuggest that the using of melittin in small doses and short duration were safe and don’tcause any toxic effects on the jejunum tissue. Therefore, melittin might be effective intreatment of gastrointestinal diseases.

Multiple Membrane Interactions and Versatile Vesicle Deformations Elicited by Melittin

Melittin induces various reactions in membranes and has been widely studied as a model for membrane-interacting peptide; however, the mechanism whereby melittin elicits its effects remains unclear. Here, we observed melittin-induced changes in individual giant liposomes using direct real-time imaging by dark-field optical microscopy, and the mechanisms involved were correlated with results obtained using circular dichroism, cosedimentation, fluorescence quenching of tryptophan residues, and electron microscopy. Depending on the concentration of negatively charged phospholipids in the membrane and the molecular ratio between lipid and melittin, melittin induced the “increasing membrane area”, “phased shrinkage”, or “solubilization” of liposomes. In phased shrinkage, liposomes formed small particles on their surface and rapidly decreased in size. Under conditions in which the increasing membrane area, phased shrinkage, or solubilization were mainly observed, the secondary structure of melittin was primarily estimated as an α-helix, β-like, or disordered structure, respectively. When the increasing membrane area or phased shrinkage occurred, almost all melittin was bound to the membranes and reached more hydrophobic regions of the membranes than when solubilization occurred. These results indicate that the various effects of melittin result from its ability to adopt various structures and membrane-binding states depending on the conditions.

Phospholipase-Catalyzed Hydrolysis in an Artificial Cell Membrane in the Presence of Melittin

Biomimicry involves the use of the structure and function of biological systems as models for the design and engineering of materials and machines. An artificial cell membrane was developed using biomembrane components, and the membrane, formed by a lipid bilayer, was analyzed using surface plasmon resonance (SPR) to monitor hydrolysis by phospholipase (PL). The simultaneous atomic force microscope (AFM) images show that PL catalyzed the nanometer-scale hydrolysis of the artificial lipid biomembranes through enzymatic hydrolysis. In addition, it was confirmed that the combination of PL and melittin allowed the control of enzyme hydrolysis for the degradation of the lipid bilayer. Regarding the expected activating effect of melittin on hydrolysis, no difference with respect to the non-treated lipid membrane was observed in the AFM images. It is assumed that the partitioning of melittin into the membrane might prevent the binding or hydrolysis of Phospholipase A2 (PLA2). This study provides basic knowledge on a new approach for patterning biomimicking lipid membranes on a nano-scale.

CALORIMETRIC DETERMINATION OF PHOSPHOLIPID-MELITTIN INTERACTIONS

The effect of melittin incorporated into the phospholipid bilayer DPPC at mole fractions up to 3.75 mol% have been investigated. The study reveals a considerable influence of melittin on the phase transition profile and volumetric properties of the DPPC bilayer. The temperature dependence of the coefficient of expansion, a , and the volume fluctuations of DPPC – melittin bilayer membranes in their different transition phases were determined by using pressure perturbation calorimetry (PPC), a relatively new and efficient technique, and differential scanning calorimetry (DSC). The experiments were carried out in the temperature range from 10 to 85 °C. Incorporating melittin up to 1.25 mol% into the lipid bilayer abolishes the pretransition. Remarkably, there is no shift in the transition temperature up to 2.5 mol% melittin, while more than one shoulder is observed at the low-temperature side of the DSC peak for 3.75 mol%, and a slight shift in melting temperature, T m to 32 o C. This could be linked to the lytic property of melittin at these high peptide concentrations.

The mediation of the central histaminergic system in the pressor effect of intracerebroventricularly injected melittin, a phospholipase A2 activator, in normotensive rats

Melittin is a polypeptide component of bee venom that leads to an increase in arachidonic acid release and subsequently in prostaglandin synthesis by activating phospholipase A2. Recently we demonstrated that centrally or peripherally administrated melittin caused pressor effect and central thromboxane A2 (TXA2) and cholinergic system mediated these effects of melittin. Also centrally injected histamine leads to pressor and bradycardic response by activating central histamine receptors in normotensive rats and central cholinergic system involved the effects of histamine. The present study demonstrates an involvement of the central histaminergic system in melittin-induced cardiovascular effect in normotensive rats. Experiments were carried out in male Sprague Dawley rats. Intracerebroventricularly (i.c.v.) injected melittin (0.5, 1 and 2nmol) caused dose- and time-dependent increases in mean arterial pressure (MAP) and decrease in heart rate (HR) as we reported previously. Moreover, H2 receptor antagonist ranitidine (50nmol; i.c.v.) almost completely and H3/H4 receptor antagonist thioperamide (50nmol; i.c.v.) partly blocked melittin-evoked cardiovascular effects, whereas H1 receptor blocker chlorpheniramine (50nmol; i.c.v.) had no effect. Also centrally injected melittin was accompanied by 28% increase in extracellular histamine concentration in the posterior hypothalamus, as shown in microdialysis studies.In conclusion, results show that centrally administered melittin causes pressor and bradycardic response in conscious rats. Moreover, according to our findings, there is an involvement of the central histaminergic system in melittin-induced cardiovascular effects.

Melittin has an inhibitory effect on TNF-α-induced migration of human aortic smooth muscle cells by blocking the MMP-9 expression

Matrix metalloproteinases-9 (MMP-9) plays an important role in the pathogenesis of atherosclerosis and migration of vascular smooth muscle cells (VSMCs) after an arterial injury. In this study, we investigated the potential molecular mechanisms underlying the anti-atheroscleroic effects of melittin, a major component of bee venom, in human aortic smooth muscle cells (HASMCs). Melttin significantly suppressed MMP-9 and MMP-2 secretion, as well as TNF-α-induced MMP-9 expression in the HASMCs. In addition, we found that the inhibitory effects of melittin on TNF-α-induced MMP-9 protein expression are associated with the inhibition of MMP-9 transcription levels. Mechanistically, Melittin suppressed TNF-α-induced MMP-9 activity by inhibiting the phosphorylation of p38 and ERK1/2, but did not affect the phosphorylation of JNK and Akt. Reporter gene and western blotting assays showed that melittin inhibits MMP-9 transcriptional activity by blocking the activation of NF-κB via IκBα signaling pathway. Moreover, the matrigel migration assay showed that melittin reduced TNF-α-induced HASMC migration. These results suggest that melittin suppresses TNF-α-induced HASMC migration through the selective inhibition of MMP-9 expression and provide a novel role of melittin in the anti-atherosclerotic action.

Effect of Melittin and Gain-of-Function Melittin Analogs, Discovered by High-Throughput Screening, on Bilayer Properties: An Electrical Impedance Spectroscopy Study

Melittin, the main peptide component of European Honey Bee venom, is a 26-amino acid peptide that permeabilizes bacterial and mammalian cells, as well as synthetic lipid vesicles. Melittin is one of the most studied pore forming peptides, and researchers hold it as a framework for designing engineered peptides pores. We have sought to optimize the potency of melittin, by applying orthogonal high throughput screen strategies to select for gain-of-function analogs of melittin. Here we use electrochemical impedance spectroscopy (EIS) to compare the activity of melittin and one gain-of-function melittin analogue. While EIS studies of melittin show a decrease in admittance with a transient recovery we find a strikingly different bilayer response to the melittin analogue- an exponential decay with a half-life of 15-30 seconds. These experiments demonstrate the remarkable ability of the gain-of-function melittin analogue to form stable pores on lipid bilayers. Thus the engineered analogues have many applications in biotechnology and as anti-cancer therapeutics.

Melittin inhibits cerulein-induced acute pancreatitis via inhibition of the JNK pathway

The major compound of bee venom, melittin, has been used as an anti-inflammatory reagent for decades. However, the potential of melittin to ameliorate acute pancreatitis (AP) is unknown. Our aim was to investigate the effect of melittin on cerulein-induced AP. Pre- and post-treatment with melittin inhibited histological changes in the pancreas and lungs during cerulein-induced AP. Pancreatic weight/body weight ratios; digestive enzymes, including amylase and lipase; serum and pancreatic cytokine expression; and myeloperoxidase activity were decreased. In addition, treatment with melittin inhibited the activation of c-Jun NH2-terminal protein kinase (JNK) in the pancreas during cerulein-induced pancreatitis. In accordance with the results of in vivo experiments, melittin reduced cerulein-induced cell death, and production of inflammatory cytokines. In conclusion, our results suggest that melittin attenuated AP and AP-associated lung injury through the inhibition of JNK activation.

Protective effect of melittin on inflammation and apoptosis in acute liver failure

Acute hepatic failure remains an extremely poor prognosis and still results in high mortality. Therefore, better treatment is urgently needed. Melittin, a major component of bee venom, is known to inhibit inflammatory reactions induced by lipopolysaccharide (LPS) or tumor necrosis factor (TNF)-α in various cell types. However, there is no evidence of the anti-inflammatory and anti-apoptotic effect of melittin on liver cells. In the present study, we investigated the effects of melittin on D: -galactosamine (GalN)/lipopolysaccharide (LPS)-induced acute hepatic failure. Acute liver injury was induced with GalN/LPS to determine in vivo efficacy of melittin. Mice were randomly divided into four groups: sterile saline treated group (NC), melittin only treated group (NM), GalN/LPS-treated group (GalN/LPS), and GalN/LPS treated with melittin group (M+GalN/LPS). Mice were given intraperitoneal GalN/LPS with or without melittin treatment. Liver injury was assessed biochemically and histologically. Inflammatory cytokines in the serum, apoptosis of hepatocytes, and cleavage of caspase-3 in the liver were determined. The expression of TNF-α and interleukin (IL)-1β were increased in the GalN/LPS group. However, treatment of melittin attenuated the increase of inflammatory cytokines. The M+GalN/LPS group showed significantly fewer apoptotic cells compared to the GalN/LPS group. Melittin significantly inhibited the expression of caspase and bax protein levels as well as cytochrome c release in vivo. In addition, melittin prevented the activation of the transcription factor nuclear factor-kappa B (NF-κB) induced by GalN/LPS. These results clearly indicate that melittin provided protection against GalN/LPS-induced acute hepatic failure through the inhibition of inflammatory cytokines and apoptosis.

PEG-stabilized lipid disks as carriers for amphiphilic antimicrobial peptides

Antimicrobial peptides hold potential as a possible alternative, or complement, to conventional antibiotics but new, safe and efficient means are needed for formulation and administration of the peptides. In this study we have investigated the utility of a novel type of lipid particles, the polyethylene glycol-stabilized lipid disks, as carriers for the model peptide melittin. The structural integrity of the carrier particle when loaded with the peptide was investigated using cryo-transmission electron microscopy. Liposome leakage upon addition of the peptide–lipid disks was monitored as a means to verify the membrane lytic effect of the formulation. The susceptibility of melittin to tryptic digestion was studied and compared in the absence and presence of lipid disks. Finally, the antibacterial effect of the peptide–lipid disk formulation was compared to that of free melittin after both single and repeated exposure to Escherichia coli. The results show that melittin can redistribute from the disk into a new host membrane and that formulation in the disks does not compromise melittin's membrane permeabilizing ability. Further, the peptide was found to be fully protected against degradation when bound to the disks. Time-kill experiments revealed that all the antibacterial effect of melittin administered in free form was gone after a single exposure to E. coli. In contrast, the disk formulation showed significant cell-killing effect also upon a second exposure to bacteria, indicating an extended release of peptide from the lipid disks. These results suggest that the lipid disks constitute a new class of promising carriers for peptide antibiotics.

Protective effects of melittin on transforming growth factor-β1 injury to hepatocytes via anti-apoptotic mechanism

Melittin is a cationic, hemolytic peptide that is the main toxic component in the venom of the honey bee ( Apis mellifera). Melittin has multiple effects, including anti-bacterial, anti-viral and anti-inflammatory, in various cell types. However, the anti-apoptotic mechanisms of melittin have not been fully elucidated in hepatocytes. Apoptosis contributes to liver inflammation and fibrosis. Knowledge of the apoptotic mechanisms is important to develop new and effective therapies for treatment of cirrhosis, portal hypertension, liver cancer, and other liver diseases. In the present study, we investigated the anti-apoptotic effect of melittin on transforming growth factor (TGF)-β1-induced apoptosis in hepatocytes. TGF-β1-treated hepatocytes were exposed to low doses (0.5 and 1 μg/mL) and high dose (2 μg/mL) of melittin. The low doses significantly protected these cells from DNA damage in TGF-β1-induced apoptosis compared to the high dose. Also, melittin suppressed TGF-β1-induced apoptotic activation of the Bcl-2 family and caspase family of proteins, which resulted in the inhibition of poly-ADP-ribose polymerase (PARP) cleavage. These results demonstrate that TGF-β1 induces hepatocyte apoptosis and that an optimal dose of melittin exerts anti-apoptotic effects against TGF-β1-induced injury to hepatocytes via the mitochondrial pathway. These results suggest that an optimal dose of melittin can serve to protect cells against TGF-β1-mediated injury.

Melittin activates TRPV1 receptors in primary nociceptive sensory neurons via the phospholipase A2 cascade pathways

Previous studies demonstrated that melittin, the main peptide in bee venom, could cause persistent spontaneous pain, primary heat and mechanical hyperalgesia, and enhance the excitability of spinal nociceptive neurons. However, the underlying mechanism of melittin-induced cutaneous hypersensitivity is unknown. Effects of melittin applied topically to acutely dissociated rat dorsal root ganglion neurons were studied using whole-cell patch clamp and calcium imaging techniques. Melittin induced intracellular calcium increases in 60% of small (<25 μm) and medium (<40 μm) diameter sensory neurons. In current clamp, topical application of melittin evoked long-lasting firing in 55% of small and medium-sized neurons tested. In voltage clamp, melittin evoked inward currents in sensory neurons in a concentration-dependent manner. Repeated application of melittin caused increased amplitude of the inward currents. Most melittin-sensitive neurons were capsaicin-sensitive, and 65% were isolectin B4 positive. Capsazepine, the TRPV1 receptor inhibitor, completely abolished the melittin-induced inward currents and intracellular calcium transients. Inhibitions of signaling pathways showed that phospholipase A(2), but not phospholipase C, was involved in producing the melittin-induced inward currents. Inhibitors of cyclooxygenases (COX) and lipoxygenases (LOX), two key components of the arachidonic acid metabolism pathway, each partially suppressed the inward current evoked by melittin. Inhibitors of protein kinase A (PKA), but not of PKC, also abolished the melittin-induced inward currents. These results indicate that melittin can directly excite small and medium-sized sensory neurons at least in part by activating TRPV1 receptors via PLA2-COXs/LOXs cascade pathways.

Melittin enhances apoptosis through suppression of IL-6/sIL-6R complex-induced NF-κB and STAT3 activation and Bcl-2 expression for human fibroblast-like synoviocytes in rheumatoid arthritis

Objective Resistance to apoptosis of fibroblast-like synoviocytes (FLS) is considered as a major characteristic in RA. This study was designed to identify whether melittin has a pro-apoptotic effect in IL-6/sIL6R-stimulated human FLS by investigating the expression of mitochondrial apoptosis-related genes, nuclear factor-κB (NF-κB), and signal transducer and activators of transcription (STAT) activation. Methods Cell viability was determined using a MTT assay after melittin treatment. Expressions of STAT3 and mitochondrial apoptosis-related genes induced by the IL-6/sIL-6R complex were determined by real time-polymerase chain reaction and western blotting. The expression of NF-κB p65 following IL-6 stimulation was determined by western blot analysis. The effects of melittin on the expression of apoptosis-related genes and the transcription factors NF-κB p65 and STAT3 were assessed in FLS. Apoptosis of FLS was determined by TUNEL-labeling to detect DNA strand breaks and DNA fragmentation assays. Caspase-3 activity was determined by a colorimetric assay. Results IL-6/sIL-6R induced the activation of the transcription factors, STAT3, NF-κB p65 (nucleus), and Bcl-2. Melittin increased the expression of pro-apoptosis-related molecules, namely caspase-3, caspase-9, Apaf-1, and cytosolic cytochrome c, in a dose-dependent manner after treatment with IL-6/sIL-6R. Melittin inhibited STAT3 activation, translocation of NF-κB p65 into the nucleus, and expression of anti-apoptotic genes such as Bcl-2 and mitochondrial cytochrome c. Conclusions The pro-apoptotic effects of melittin likely result from inhibition of the activation of the transcription factors, STAT3 and NF-κB p65, and regulation of mitochondrial apoptosis-related genes. Melittin is thus a promising therapeutic option for RA as it induces apoptosis in apoptosis-resistant synoviocytes.

Ultrastructural observation on sterilization of melittin

ABSTACT: The effects of melittin on growth and bacteriostasis of four pathogens were extensively investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated that the melittin had a marked bacteriostatic effect on the four pathogenic bacteria. Among these, E. cacotowora was influenced most powerfully and quickly, the yeast and F. fulva were the second, and the S. aureus was inhibited by a low concentration but was killed by a high concentration. It was observed in the experiments that melittin killed pathogenic bacteria in three ways. One was by pore formation. After integrating melittin into the plasma membrane, a vacuole was formed then penetrated, resulting in bacterial content leakage. The vacuole also experienced plasmolysis and the growing cavity destroyed the membrane. A third effect was the formation of vacuoles in the cells which induced the pycnosis of the cytoplasm resulting in a cell death. The mechanism of melittin bacteriostasis was the result of integrating melittin with phospholipid double layers of the plasmalemma and the endomembranes.

Melittin Inhibits Atherosclerosis in LPS/High-Fat Treated Mice Through Atheroprotective Actions

Atherosclerosis is influenced by multiple environmental factors that involve a complex interaction between blood components and the arterial wall and is characterized by inflammatory reactions. Melittin has been used in treatment of various chronic inflammatory diseases. We investigated the effects of melittin regulated atherosclerotic changes in an animal model of atherosclerosis. Atherosclerotic mice were induced by intraperitoneal (i.p) injection of lipopolysaccharide (LPS, 2 mg/kg) three times a week and an atherogenic diet for 12 weeks. Melittin (0.1 mg/kg) treatment was administered with i.p injection. Melittin treatment showed that total cholesterol and triglyceride levels decreased in atherosclerotic mice however, high-density lipoprotein cholesterol (HDL-C) levels were higher in atherosclerotic mice treated with melittin than in atherosclerotic mice. H&E staining showed that heart and descending aorta were significantly recovered by melittin, compared to atherosclerotic mice. In addition, melittin decreased the expression levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule (ICAM)-1, fibronectin and transforming growth factor (TGF)-β1 in atherosclerotic mice. In vitro, melittin decreased LPS-induced THP-1 cells-derived macrophages TNF-α and IL-1β expression levels and nuclear factor (NF)-κB signal pathway. These results demonstrate that melittin has an anti-atherogenic effect by suppression of pro-inflammatory cytokines and adhesion molecules.

Effect of α-helical peptides on liposome structure: A comparative study of melittin and alamethicin

Cryo-transmission electron microscopy was used in combination with turbidity and leakage measurements to explore and compare the membrane perturbing effects of melittin and alamethicin on POPC-based liposomes of varying composition. The results show that the two peptides, despite their differences in physico-chemical properties and proposed mode of action, induce similar structural effects on the liposomes. Importantly, whereas low peptide concentrations leave pure POPC liposomes intact and seemingly unperturbed, POPC liposomes supplemented with 40 mol.% cholesterol change their shape, rupture and fuse in response to the addition of both melittin and alamethicin. In the case of alamethicin, but not melittin, fusion is effectively prevented by inclusion of 10 mol.% POPG in the liposome membranes. By means of a competitive binding assay we furthermore show that alamethicin, in line with earlier findings for melittin, possess high affinity for positively curved lipid surfaces. Moreover, results from the present study show that magainin 2 has a similar preference for curved surfaces.

The Anti-Arthritic Effects of Synthetic Melittin on the Complete Freund's Adjuvant-Induced Rheumatoid Arthritis Model in Rats

Bee venom (BV) has been used for millennia in Chinese traditional medicine to treat rheumatoid arthritis (RA). However, its components and mechanism remain unclear, which has hampered its development and application for the treatment of RA. In this study, we examined the anti-arthritis effects of melittin, which composes nearly 50% of the dry weight of whole BV, on the complete Freund's adjuvant-induced (CFA-induced) RA model in rats. The RA animal models were treated with solutions of BV, melittin, and saline by injection into a specific acupoint (Zusanli). The BV and melittin treatments statistically diminished the thickness of the arthroses in the injected side of the paw, compared to the saline treatment. Melittin therapy also significantly reduced arthritis-induced nociceptive behaviors, as assessed by the thermal hyperalgesia test. In addition, CFA-induced Fos expression in the superficial layer of the lumbar spinal cord was significantly suppressed by the BV and melittin treatments, compared to the saline treatment. These results indicate that melittin is an effective anti-arthritis component of whole bee venom, making it a promising candidate as an anti-arthritis drug.

Cardiovascular effect of peripheral injected melittin in normotensive conscious rats: Mediation of the central cholinergic system

Recently we demonstrated that centrally administrated melittin, a phospholipase A 2 (PLA 2) activator, caused the pressor effect in normotensive, conscious rats. In the present study, we aimed to determine the cardiovascular effect of peripherally injected melittin and the involvement of the central cholinergic system on these effects in the normotensive conscious rats. For this reason, 250, 500 or 1000 μg/kg doses of melittin were injected intraperitoneally to normotensive male Sprague Dawley rats. Melittin produced dose- and time-dependent increases in mean arterial pressure (MAP) and heart rate (HR). Both peripheral (5 mg/kg; i.p.) and central (500 μg; i.c.v.) pretreatment with indomethacin, nonselective inhibitor of cyclooxygenase (COX) 1 and 2, totally abolished cardiovascular effect of melittin. Intraperitoneal (i.p.) pretreatment with propranolol, a nonselective β-adrenergic receptor blocker, completely abolished the tachycardic response to melittin. Also, the pressor effect of melittin was partially attenuated in these rats. In order to test the mediation of the central cholinergic system on the pressor and tachycardic effects of melittin, the rats were pretreated with atropine sulfate (10 μg; i.c.v.), a cholinergic nonselective muscarinic receptor antagonist, mecamylamine (50 μg; i.c.v.), a cholinergic nonselective nicotinic receptor antagonist, methyllycaconitine (10 μg; i.c.v.) or α-bungarotoxin (10 μg; i.c.v.), selective antagonists of α7 subtype nicotinic acetylcholine receptors (α7nAChRs) 15 min prior to melittin (500 μg/kg; i.p.) injection. Pretreatment with mecamylamine, methyllycaconitine or α-bungarotoxin partially diminished the pressor and tachycardic response to melittin in the normotensive conscious rats whereas pretreatment with atropine sulfate had no effect. In conclusion, our data demonstrate that peripherally administered melittin exerts a clear pressor and tachycardic effect by activating COX pathway. The activation of central cholinergic nicotinic receptors, predominantly α7nAChRs, appears to be involved in the pressor and tachycardic effects of the drug.