Activation by Phoneutria nigriventer spider venom of autonomic nerve fibers in the isolated rat heart

Lethality and histopathological alterations caused by Phoneutria nigriventer spider venom from Argentina: Neutralization of lethality by experimental and therapeutic antivenoms

Although the spiders of the genus Phoneutria cause envenomation and their presence has been described in several provinces of the north of Argentina, they are not as common as other spiders of sanitary importance. In the present work, we studied the toxicity of samples of venom of Phoneutria spiders from the provinces of Misiones (where severe envenomation and deaths by Phoneutria have been recorded) and Jujuy (where no deaths have been recorded and severe envenomations are not frequent). To this end, we assessed the lethal potency in mice and guinea pigs and the histopathological alterations caused by both venoms, as well as the neutralization by the commonly used therapeutic antivenom produced by the Butantan Institute in Brazil and by an experimental antivenom developed with venom of P. nigriventer from Misiones. There were no differences in the lethality of the venoms of spiders from both regions. Post mortem examination showed that the heart and lungs were the most affected organs, while important pulmonary edema was seen macroscopically. Histological analysis showed edema, atelectasis, emphysema and cardiac lesion in both experimental models. The antivenoms assayed showed good neutralization of the venoms in the two experimental models. Despite the different geographic origins, the venoms showed similar toxicity and both the experimental antivenom and therapeutic antivenmos were able to neutralize the venoms of Argentinean P. nigriventer.

Activation of β-adrenoceptors by dobutamine may induce a higher expression of peroxisome proliferator-activated receptors δ (PPARδ) in neonatal rat cardiomyocytes

Recent evidence showed the role of peroxisome proliferator-activated receptors (PPARs) in cardiac function. Cardiac contraction induced by various agents is critical in restoring the activity of peroxisome proliferator-activated receptors δ (PPARδ) in cardiac myopathy. Because dobutamine is an agent widely used to treat heart failure in emergency setting, this study is aimed to investigate the change of PPARδ in response to dobutamine. Neonatal rat cardiomyocytes were used to examine the effects of dobutamine on PPARδ expression levels and cardiac troponin I (cTnI) phosphorylation via Western blotting analysis. We show that treatment with dobutamine increased PPARδ expression and cTnI phosphorylation in a time- and dose-dependent manner in neonatal rat cardiomyocytes. These increases were blocked by the antagonist of β1-adrenoceptors. Also, the action of dobutamine was related to the increase of calcium ions and diminished by chelating intracellular calcium. Additionally, dobutamine-induced action was reduced by the inhibition of downstream messengers involved in this calcium-related pathway. Moreover, deletion of PPARδ using siRNA generated the reduction of cTnI phosphorylation in cardiomyocytes treated with dobutamine. Thus, we concluded that PPARδ is increased by dobutamine in cardiac cells.

Venom effects on monoaminergic systems

The monoamines, dopamine, epinephrine, histamine, norepinephrine, octopamine, serotonin and tyramine serve many functions in animals. Many different venoms have evolved to manipulate monoaminergic systems via a variety of cellular mechanisms, for both offensive and defensive purposes. One common function of monoamines present in venoms is to produce pain. Some monoamines in venoms cause immobilizing hyperexcitation which precedes venom-induced paralysis or hypokinesia. A common function of venom components that affect monoaminergic systems is to facilitate distribution of other venom components by causing vasodilation at the site of injection or by increasing heart rate. Venoms of some scorpions, spiders, fish and jellyfish contain adrenergic agonists or cause massive release of catecholamines with serious effects on the cardiovascular system, including increased heart rate. Other venom components act as agonists, antagonists or modulators at monoaminergic receptors, or affect release, reuptake or synthesis of monoamines. Most arthropod venoms have insect targets, yet, little attention has been paid to possible effects of these venoms on monoaminergic systems in insects. Further research into this area may reveal novel effects of venom components on monoaminergic systems at the cellular, systems and behavioral levels.

Role of Ca2+ in vascular smooth muscle contractions induced by Phoneutria nigriventer spider venom

Phoneutria nigriventer venom (PNV) contracts vascular tissues and increases arterial blood pressure. This study aimed to investigate the mechanisms involved on PNV-induced contractions of rabbit mesenteric and celiac arteries. Strips of mesenteric and celiac arteries were suspended in a cascade system and superfused with warmed and oxygenated Krebs solution. PNV was dialyzed in order to exclude the participation of biogenic amines in the contractions elicited by the venom. Noradrenaline (NA, 30-300 pmol), PNV (1-10 microg), Bay K-8644 (0.3-3 nmol) and KCl (10-100 micromol) dose-dependently contracted the preparations. Ca(2+)-free solution reduced by 38 and 83% the PNV-induced contractions of mesenteric and celiac arteries, respectively. Subsequent infusion of EGTA (0.2 mM) suppressed the residual contractions. Nifedipine (1 microM) and verapamil (10 microM) abolished PNV- and Bay K-8644-evoked contractions, whereas those induced by NA were reduced to a lesser extent. Lanthanum chloride (0.2 mM) inhibited by 75-90% the mesenteric and celiac contractions mediated by PNV. Caffeine (2 mM) fully blocked contractions induced by NA (95% mean inhibition), but only partly reduced those induced by PNV (35% mean inhibition). Ryanodine (10 microM) inhibited by 50% the contractions evoked by NA, but had no effect on the PNV-induced contractions in both tissues. Our findings indicate that PNV contracts vascular smooth muscle mainly due to increased influx of Ca(2+) from extracellular sources.

Triazines facilitate neurotransmitter release of synaptic terminals located in hearts of frog (Rana ridibunda) and honeybee (Apis mellifera) and in the ventral nerve cord of a beetle (Tenebrio molitor)

Three triazine herbicides, atrazine, simazine and metribuzine, and some of their major metabolites (cyanuric acid and 6-azauracil) were investigated for their action on synaptic terminals using three different isolated tissue preparations from the atria of the frog, Rana ridibunda, the heart of the honeybee, Apis mellifera macedonica, and the ventral nerve cord of the beetle, Tenebrio molitor. The results indicate that triazines facilitate the release of neurotransmitters from nerve terminals, as already reported for the mammalian central nervous system. The no observed effect concentration, the maximum concentration of the herbicide diluted in the saline that has no effect on the physiological properties of the isolated tissue, was estimated for each individual preparation. According to their relative potency, the three triazines tested can be ranked as follows: atrazine (cyanuric acid), simazine>metribuzine (6-azauracil). The action of these compounds on the cholinergic (amphibians, insects), adrenergic (amphibian) and octopaminergic (insects) synaptic terminals is discussed.

Effects of the venom of a Mygalomorph spider (Lasiodora sp.) on the isolated rat heart

We studied the effect of the venom of the Brazilian spider, Lasiodora sp. (Mygalomorphae, Theraphosidae), on force generation and electrical activity in the isolated rat heart. Previous work showed that this venom is excitotoxic to excitable cells due to Na(+) channel gating modifier activity [Toxicon 39 (2001) 991]. In the isolated heart, the venom (10-100 microg bolus administration) caused a dose-dependent bradycardia, with transient cardiac arrest and rhythm disturbances. The electrocardiogram showed that the reduction of heart rate was due to sinus bradycardia, sinus arrest and partial or complete A-V block. All of the effects were reversible upon washout of the venom. The effect of the venom was potentiated by the anticholinesterase neostigmine (3.3 microM), suppressed by the muscarinic acetylcholine receptor antagonist atropine (1.4 microM), and inhibited by the vesicular acetylcholine transporter inhibitor (-)-vesamicol (10 microM). Tetrodotoxin (200 nM) did not inhibit the effect of the venom. Together, these data suggest that this Lasiodora venom evokes vesicular release of acetylcholine from parasympathetic nerve terminals by activating tetrodotoxin-resistant Na(+) channels.

Endothelium-dependent relaxation of rat mesenteric arterial rings by a Phoneutria nigriventer venom fraction

Phoneutria nigriventer spider venom has been described as acting on several cardiovascular sites. In the present paper, a semi-purified fraction of this spider venom was studied to observe any contractile or relaxing effect in rat mesenteric arterial rings (MAR). Spider venom was first fractionated by gel filtration and subsequently by gradual isocratic steps in 0.1% trifluoroacetic acid. The first fraction of this last fractionation step is studied in the present paper and due to its main effect, it was named NORF (nitric oxide releasing fraction). No direct contractile effect was induced by NORF in relaxed MAR, suggesting no NORF-induced neurotransmitter release in this preparation. No significant influence of NORF was observed on concentration-response curves to phenylephrine on endothelium-denuded MAR, but a significant inhibitory shift of concentration-respense curves was observed on endothelium-preserved MAR (EC50 = 0.39 +/- 0.07 microM for control and EC50 = 0.68 +/- 0.14 microM with NORF). NORF induced concentration-dependent relaxation in endothelium-preserved phenylephrine pre-contracted MAR but not in endothelium-denuded MAR. NORF-induced relaxation was inhibited by the nitric oxide synthase inhibitor L-NAME (N(omega)-nitro-arginine methyl ester). Indomethacin or HOE-140 (D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin) had no significant effect on NORF-induced relaxation. Acetylcholine- and NORF-induced relaxation of pre-contracted MAR were differently inhibited by atropine. The pA2 value for atropine-acetylcholine was 9.78 +/- 0.06 and that for atropine-NORF was 8.53 +/- 0.30 (P<0.01). These observations suggest that NORF induces concentration-dependent liberation of nitric oxide from MAR endothelium and that a non-muscarinic mechanism might be involved in this effect. Our data suggest no involvement of prostanoids or bradykinin in the relaxing mechanism.