Electrocardiographic studies with scorpion (Buthus minax, L. Koch) venom.

The intravenous injection of Buthus minax venom into rabbits caused an initial brief bradycardia followed by tachycardia and then a prolonged bradycardia. The initial bradycardia is probably due to central vagal stimulation, while the tachycardia is possibly due to sympathetic stimulation and release of tissue catecholamines. The venom caused depression of the ST segment and symmetrical inversion of the T wave possibly due to coronary vasoconstriction leading to anterior wall infarction. Some of the electrocardiographic effects of the venom appeared to be mediated through hyperkalemia and hypocalcemia as evidenced from the tall, slender and peaked T wave, the wide QRS complex and the prolonged ST segment. The effect of the venom in causing sympathetic stimulation and release of tissue catecholamines seemed to mask the effects of electrolytes, since more pronounced effects were shown after blocking the B-adrenergic receptors with propranolol or depleting the catecholamine stores with reserpine. Treatment with atropine, aminophylline or the specific antivenin failed to protect the rabbits against the electrocardiographic effects of the venom.     

Effects of the venom of the yellow scorpion (Leiurus quinquestriatus) on the isolated work-performing guinea pig heart

In the isolated work-performing guinea pig heart, infusion of venom solutions (0·1 mg/1) of the yellow scorpion (Leiurus quinquestriatus) causes a 30–150 sec initial slowing of the heart followed by an irregular tachycardia with strong positive inotropic effects and an increase in heart rate and contractility of long duration. Alpha-adrenergic, 5-hydroxytryptamine and histamine H₁ and H₂ receptor stimulation are not involved in these cardiac effects. By the use of atropine and hexamethonium, the first phase of bradycardia can be shown to be caused predominantly by parasympathetic stimulation originating from ganglionic and postganglionic stimulation. The second phase of irregular tachycardia is caused by a mixed sympathetic-parasympathetic stimulation with sympathetic dominance, originating from postganglionic stimulation. The third phase of increased contractility and heart rate, which is little influenced by autonomic blockade, can be considered as a direct effect of the venom on the heart.     

Pharmacological studies of scorpion (Androctonus amoreuxi Aud. & Sav.) venom.

Venom from the scorpion Androctonus amoreuxi was fractionated into eight components by cellulose acetate electrophoresis, using barbitone buffer pH 8·6. Only one of the electrophoretic fractions was lethal in mice. The ld₅₀ of the venom following i.m. injection into mice was estimated to be 0·88 ± 0·06 mg per kg. The cardiovascular effects of the venom appeared to be mediated through stimulation of both parts of the autonomic nervous system with predominance of sympathetic stimulation, and release of tissue catecholamines. The venom markedly decreased the tone of the spontaneously contracting rat uterus in all states of uterine function except in pregnancy where it produced a stimulant effect. The uterine inhibitory effect of the venom is probably due to stimulation of the β-adrenergic receptors as it was blocked by propranolol. The venom first increased the amplitude and then blocked the twitches of the rat phrenic nerve-hemidiaphragm and caused contracture and decrease of twitch height of the tibialis anterior muscle preparation. Of the various fractions separated by cellulose acetate electrophoresis, only three fractions showed activity on the various preparations studied.     

Some pharmacological studies with scorpion (Pandinus exitialis) venom

Venom from the scorpion Pandinus exitialis was fractionated on Cellogel membranes into at least 14 bands in acetate buffer pH 4·2, and into 16 bands, 4 of which exhibited cathodic mobility, in barbitone buffer, pH 8·6. The venom was fractionated into 6 fractions using Biogel P 100. The ld₅₀ of the venom following i.p. injection into mice was estimated to be 40 mg/kg. The cardiovascular effects of the venom appeared to be mediated through stimulation of the autonomic nervous system with a predominance of sympathetic stimulation, and release of tissue catecholamines. On the rat uterus the venom produced a powerful contraction which was greatly attenuated by methysergide and completely blocked by meclofenamic acid indicating that the contraction is mediated partly by the serotonin content of the venom and partly through the release of kinins, prostaglandins and/or slow reacting substance.     

Cardiac effects of Stomolophus meleagris (cabbage head jellyfish) toxin.

Electrocardiograms recorded from rabbits and rats injected intravenously with toxin from Stomolophus meleagris showed bradycardia followed by inversion of the P and T waves, alterations of the QRS complex, ventricular extrasystoles, atrioventricular block, bizarre ventricular patterns, and fibrillation. Analysis of plasma samples taken after the onset of electrocardiographic abnormalities were characterized by hemolysis, hyponatremia and hyperkalemia when compared to plasma taken before injection of toxin. Sublethal doses of toxin produced an increase in lactate dehydrogenase (LDH) levels in serum, but did not increase creatine phosphokinase levels. Electrophoretic analysis of the serum LDH isoenzymes following injection of toxin did not indicate severe cardiac tissue damage. This toxin appears to disrupt cardiac rhythmicity and myocardial conduction pathways in a manner consistent with other coelenterate toxins. The observed hyperkalemia appears to result from hemolysis and generalized tissue destruction, although the serum enzyme and isoenzyme assays did not suggest severe myocardial infarction.     

Renal and cardiovascular effects of Bothrops marajoensis venom and phospholipase A2

Bothrops marajoensis is found in the savannah of Marajó Island in the State of Pará and regions of Amapá State, Brazil. The aim of the work was to study the renal and cardiovascular effects of the B. marajoensis venom and phospholipase A₂ (PLA₂). The venom was fractionated by Protein Pack 5PW. N-terminal amino acid sequencing of sPLA₂ showed amino acid identity with other lysine K49 sPLA₂s of snake venom. B. marajoensis venom (30 μg/mL) decreased the perfusion pressure, renal vascular resistance, urinary flow, glomerular filtration rate and sodium tubular transport. PLA₂ did not change the renal parameters. The perfusion pressure of the mesenteric bed did not change after infusion of venom. In isolated heart, the venom decreased the force of contraction and increased PP but did not change coronary flow. In the arterial pressure, the venom and PLA₂ decreased mean arterial pressure and cardiac frequency. The presence of atrial flutter and late hyperpolarisation reversed, indicating QRS complex arrhythmia and dysfunction in atrial conduction. In conclusion, B. marajoensis venom and PLA₂ induce hypotension and bradycardia while simultaneously blocking electrical conduction in the heart. Moreover, the decrease in glomerular filtration rate, urinary flow and electrolyte transport demonstrates physiological changes to the renal system.     

Pharmacological studies of the venom from the scorpion Buthus minax (L. Koch)

The venom from the scorpion Buthus minax produced a positive inotropic effect on isolated rabbit and guinea pig hearts but no alteration in rate. The cardiac stimulant action was blocked by propranolol and was absent in reserpinized hearts, indicating the possibility of an indirect action of the venom, probably through the release of catecholamines. In the reserpinized hearts, and in normal hearts after propranolol treatment, the venom produced bradycardia which was blocked by atropine. The venom produced a marked hypertensive effect in cats, dogs, rats and guinea pigs, which was blocked by tolazoline and phenoxy-benzamine. In cats and rats the hypertensive effect was preceded by brief hypotension which was partially blocked by atropine. The venom markedly decreased the rate of flow in the perfused hindquarter of the rat and moderately increased capillary permeability. It stimulated the rabbit intestine and guinea pig ileum, an action which was largely blocked by atropine. It increased the size of twitches in the isolated, indirectly stimulated, phrenic hemidiaphragm of the rat and contracted the rectus abdominis muscle of the frog. The latter effect was blocked by tubocurarine. The venom decreased the respiration rate in cats and dogs but caused a slight increase in depth. The decrease in respiration rate was blocked by carotid sinus denervation. It is postulated that the venom stimulates both the sympathetic and parasympathetic systems.     

The Dragon’s Paralysing Spell: Evidence of Sodium and Calcium Ion Channel Binding Neurotoxins in Helodermatid and Varanid Lizard Venoms

Bites from helodermatid lizards can cause pain, paresthesia, paralysis, and tachycardia, as well as other symptoms consistent with neurotoxicity. Furthermore, in vitro studies have shown that Heloderma horridum venom inhibits ion flux and blocks the electrical stimulation of skeletal muscles. Helodermatids have long been considered the only venomous lizards, but a large body of robust evidence has demonstrated venom to be a basal trait of Anguimorpha. This clade includes varanid lizards, whose bites have been reported to cause anticoagulation, pain, and occasionally paralysis and tachycardia. Despite the evolutionary novelty of these lizard venoms, their neuromuscular targets have yet to be identified, even for the iconic helodermatid lizards. Therefore, to fill this knowledge gap, the venoms of three Heloderma species (H. exasperatum, H. horridum and H. suspectum) and two Varanus species (V. salvadorii and V. varius) were investigated using Gallus gallus chick biventer cervicis nerve–muscle preparations and biolayer interferometry assays for binding to mammalian ion channels. Incubation with Heloderma venoms caused the reduction in nerve-mediated muscle twitches post initial response of avian skeletal muscle tissue preparation assays suggesting voltage-gated sodium (Na_V) channel binding. Congruent with the flaccid paralysis inducing blockage of electrical stimulation in the skeletal muscle preparations, the biolayer interferometry tests with Heloderma suspectum venom revealed binding to the S3–S4 loop within voltage-sensing domain IV of the skeletal muscle channel subtype, Na_V1.4. Consistent with tachycardia reported in clinical cases, the venom also bound to voltage-sensing domain IV of the cardiac smooth muscle calcium channel, Ca_V1.2. While Varanus varius venom did not have discernable effects in the avian tissue preparation assay at the concentration tested, in the biointerferometry assay both V. varius and V. salvadorii bound to voltage-sensing domain IV of both Na_V1.4 and Ca_V1.2, similar to H. suspectum venom. The ability of varanid venoms to bind to mammalian ion channels but not to the avian tissue preparation suggests prey-selective actions, as did the differential potency within the Heloderma venoms for avian versus mammalian pathophysiological targets. This study thus presents the detailed characterization of Heloderma venom ion channel neurotoxicity and offers the first evidence of varanid lizard venom neurotoxicity. In addition, the data not only provide information useful to understanding the clinical effects produced by envenomations, but also reveal their utility as physiological probes, and underscore the potential utility of neglected venomous lineages in the drug design and development pipeline.     

Studies on the central vasomotor reflexes in cats after intraventricular administration of whole venom of Dendroaspis jamesoni.

Administration into the lateral ventricles of whole venom (100μg) of Dendroaspis jamesoni consistently produced hypotension and bradycardia in cats in a dose one-tenth of that required to produce the same effect by the intravenous route. No hypotension or bradycardia occurred after the perfusate was tapped through the caudal end of the aqueduct of Sylvius. The cardiovascular response was again observed after injection of venom into the third ventricle and the perfusate tapped through the cisterna magna. Injection of venom directly into the cisterna magna did not produce any cardiovascular response. The site of action of the venom appeared to be on the floor of the fourth ventricle, possibly the vasomotor centre. This was confirmed when intraventricular administration of the venom depressed centrally mediated cardiovascular reflexes, viz. pressor response following carotid occlusion and following electrical stimulation of the central end of the left vagus nerve after bilateral cervical vagotomy and carotid denervation. The venom also decreased the depressor response to electrical stimulation of the central cut end of the right vagus nerve. These cardiovascular responses were central effects and from the results obtained after bilateral vagotomy removal of both stellate ganglion and transection of the spinal cord (C-2) it was evident that the efferent nervous pathway for the central cardiovascular effects of the venom was the sympathetic nervous system.     

Action cardiovasculaire de trois venins de scorpions nord africains (Androctonus australis,Leiurus quinquestriatus,Buthus occitanus) et de deux toxines extraites de l'un d'entre eux

The complex cardiovascular actions of the venoms of three North African scorpions and of the toxins I and II isolated from one of them (Aa) are characterized by: (1) an action on the sympathetic ganglia. There is a release of catecholamines from nerve endings which is responsible for the hypertension, peripheral vasoconstriction, lachrymation, salivation, breathing spasms and an indirect positive inotropic effect. Later, ganglionic blockade (except for toxin I) produces a block of the vascular tone leading to hypotension. (2) An action on the heart. There was noted a direct inotropic effect, bradycardia and a toxic effect (negative inotropism and arrhythmia) leading to fibrillation. There is an involvement of the muscarinic intracardiac receptors and particularly of the beta-adrenergic receptors. The venom of the scorpion Androctonus australis is different from the other two venoms in that it produces the strongest discharge of catecholamines and it contains toxin I which differs from toxin II in that it has no ganglionic-blocking effect: the bradycardia by toxin I is also greater than with toxin II and its cardiotoxic action is hardly antagonized by propranolol.     

Possible mechanisms of anti-cholinergic drug-induced bradycardia

Summary Atropine-induced bradycardia is traditionally ascribed to central vagal stimulation, although bradycardia has also been observed after administration of quarternary amines. Pirezepine, a selective M₁-antagonist, causes bradycardia in therapeutic doses for which a peripheral mechanism is postulated. This hypothesis has been investigated in healthy volunteers.Atropine 0.5 mg caused significant bradycardia from 210 min and pirenzepine 10 mg after 60 min. After prior beta-blockade, the bradycardic action of the anti-cholinergic drugs was more marked. Pirenzepine-induced bradycardia was reversed by higher doses of atropine.It is suggested that atropine- and pirenzepine-induced bradycardia results from M₁-blockade of sympathetic ganglia. In addition, low concentrations of atropine and therapeutic doses of pirenzepine may cause an increase in acetylcholine, perhaps due to a presynaptic effect on nerve endings.     

PREMATURE VENTRICULAR CONTRACTIONS ORIGINATING FROM THE RIGHT VENTRICULAR OUTFLOW TRACT: THREE-DIMENSIONAL DISTRIBUTION OF THE TARGET SITES AND THEIR ELECTROCARDIOGRAPHIC CHARACTERISTICS

• 1 The purpose of the present study was to explore the relationship between electrocardiogram (ECG) patterns of right ventricular outflow tract (RVOT) premature ventricular contractions and the three‐dimensional distribution of the target sites.
• 2 Thirty‐three consecutive patients were included in the study. The target sites were identified by non‐contact mapping and confirmed by successful ablation. The distribution of the target sites in the three‐dimensional reconstructed geometry of the RVOT was classified in three directions: (i) anterior (A)/posterior (P); (ii) free wall (F)/septal (Se); and (iii) superior (Su)/inferior (I). The ECG characteristics were then analysed according to the three‐dimensional distribution of the target sites.
• 3 The following indices were helpful to identify the position of the target site: (i) QRS duration (≥ 150 msec = F; < 150 msec = Se; P < 0.05); (ii) the R wave pattern in the inferior leads (RR′ or Rr′ = F; R = Se; P < 0.05); (iii) the R wave amplitude in the inferior leads (high = Se; low = F; P < 0.05); (iv) the initial r wave width in lead V₁ (wide = F; narrow = Se; P < 0.05); (v) the QS wave amplitude in aVR and aVL (if aVR < aVL, A; if aVR ≥ aVL, P; P < 0.05); and (vi) the initial r wave amplitude in lead V₁ and V₂ (if V₁ ≥ 0.15 mV and V₂ ≥ 0.3 mV, Su; if V₁ < 0.15 mV or V₂ < 0.3 mV, I; P < 0.05).
• 4 In conclusoin, the ECG characteristics were associated with target site locations in all three directions.

     

An update on risk factors for drug-induced arrhythmias

A variety of drugs, either anti-arrhythmics or non-antiarrhythmics, have been associated with drug-induced arrhythmias. Drug-induced arrhythmias are usually observed in the presence of long QT interval or Brugada electrocardiographic pattern. Clinical risk factors, such as female gender, structural heart disease, metabolic and electrolyte abnormalities, bradycardia and conduction disease, increased drug bioavailability, and silent channelopathies act as ‘‘effect amplifiers’’ which can make an otherwise relatively safe drug dangerous with regard to risk for polymorphic ventricular tachycardia in the setting of QT interval prolongation. A drug-induced type 1 electrocardiographic pattern of Brugada syndrome is considered highly proarrhythmic. Specific electrocardiographic markers including the corrected QT interval, QRS duration, T_peak–T_end/QT ratio, and others may predict the risk of arrhythmias in both situations. The present review highlights on the current clinical and electrocardiographic risk factors for prediction of drug-induced arrhythmias.     

Evaluation of the Lethal Potency of Scorpion and Snake Venoms and Comparison between Intraperitoneal and Intravenous Injection Routes

Scorpion stings and snake bites are major health hazards that lead to suffering of victims and high mortality. Thousands of injuries associated with such stings and bites of venomous animals occur every year worldwide. In North Africa, more than 100,000 scorpion stings and snake bites are reported annually. An appropriate determination of the 50% lethal doses (LD₅₀) of scorpion and snake venoms appears to be an important step to assess (and compare) venom toxic activity. Such LD₅₀ values are also commonly used to evaluate the neutralizing capacity of specific anti-venom batches. In the present work, we determined experimentally the LD₅₀ values of reference scorpion and snake venoms in Swiss mice, and evaluated the influence of two main venom injection routes (i.e., intraperitoneal (IP) versus intravenous (IV)). The analysis of experimental LD₅₀ values obtained with three collected scorpion venoms indicates that Androctonus mauretanicus (Am) is intrinsically more toxic than Androctonus australis hector (Aah) species, whereas the latter is more toxic than Buthus occitanus (Bo). Similar analysis of three representative snake venoms of the Viperidae family shows that Cerastes cerastes (Cc) is more toxic than either Bitis arietans (Ba) or Macrovipera lebetina (Ml) species. Interestingly, the venom of Elapidae cobra snake Naja haje (Nh) is far more toxic than viper venoms Cc, Ml and Ba, in agreement with the known severity of cobra-related envenomation. Also, our data showed that viper venoms are about three-times less toxic when injected IP as compared to IV, distinct from cobra venom Nh which exhibited a similar toxicity when injected IP or IV. Overall, this study clearly highlights the usefulness of procedure standardization, especially regarding the administration route, for evaluating the relative toxicity of individual animal venoms. It also evidenced a marked difference in lethal activity between venoms of cobra and vipers, which, apart from the nature of toxins, might be attributed to the rich composition of high molecular weight enzymes in the case of viper venoms.     

Altered hormone sensitivity of adenylate cyclase in myocardial sarcolemma of renal hypertensive rats

Adenylate cyclase activity was studied in the myocardial sarcolemmal membranes from sham-operated control and renal hypertensive rats (RHR). Basal adenylate cyclase activity was not significantly different in RHR as compared to control rats. The stimulation of adenylate cyclase by adenosine, epinephrine and norepinephrine was diminished in RHR, whereas dopamine-sensitive adenylate cyclase was almost completely abolished. The decreased responsiveness of adenylate cyclase to catecholamines was associated with a decrease in the V_max. Furthermore, the stimulation of enzyme activity by F^? and forskolin was also decreased. The data indicate that, in renal hypertension, the responsiveness of adenylate cyclase to various hormones and to agents (forskolin and F^?) which do not act through receptors is impaired.     

A study on the cause of death produced by Angusticeps-type toxin F7 isolated from eastern green mamba venom

The cause of death due to toxin F₇, an angusticeps-type toxin, isolated from the venom of Dendroaspis angusticeps was studied in anesthetized mice. The carotid arterial blood pessure, the ECG and the respiratory movements were recorded. Within a few minutes after i.v. injection of F₇ (1 mg/kg), both the rate and amplitude of the respiratory movements decreased and respiratory arrest took place within 15 min in most cases. Before respiratory arrest, marked bradycardia with various types of arrhythmia and oscillation of blood pressure were observed. Artificial ventilation could abolish these cardiovascular changes and maintain the blood pressure for a long period. Toxin F₇ caused a transient and slight increase of arterial blood pressure which could be prevented by hexamethonium. Intracisternal application of F₇ (1 mg/kg) caused a long-lasting hypertension and bradycardia and the respiratory arrest time was significantly longer than after i.v. injection. A large dose (50 mg/kg i.p.) of atropine, but not smaller doses (5–10 mg/kg), protected mice against respiratory failure induced by F₇. In rats, the phrenic nerve discharge was prolonged during respiratory depression. Since F₇ has a potent anticholinesterase activity, it is concluded that the respiratory failure induced by F₇ is peripheral in origin, chiefly, if not entirely, due to its anticholinesterase activity.     

Involvement of presynaptic dopamine receptors in the antihypertensive response to 2-NN-dimetnylamino-5,6-dihydroxy-1,2,3,4-tetrahydronaphthalene(M-7)

M-7, 1 and 3 mg kg^?1 s.c., elicits an antihypertensive response and bradycardia in conscious spontaneously hypertensive rats (SHR) and causes inhibition of stimulation-evoked pressor responses and tachycardia in pithed SHR. Metoclopramide (30 mg kg^?1 i.p.), but not piperoxan (5 mg kg^?1 i.p.), abolishes the antihypertensive effect and inhibition of stimulation-evoked pressor responses produced by M-7 (1 mg kg^?1 s.c.) in SHR. Conversely, piperoxan, but not metoclopramide, reduces the bradycardia and inhibition of stimulation-evoked tachycardia produced by M-7. Metoclopramide (30 mg kg^?1 i.p.) did not affect the cardiovascular responses elicited by intracerebroventricular administration of either clonidine (1 μg) or M-7 (3 μg). These results suggest that the antihypertensive effect of M-7 may be mediated by stimulation of presynaptic dopamine receptors on sympathetic nerves to the vasculature and is independent of the bradycardia, which is probably due to stimulation of presynaptic α₂-adrenoceptors on cardiac sympathetic nerve endings.     

Three Peptide Modulators of the Human Voltage-Gated Sodium Channel 1.7, an Important Analgesic Target,from the Venom of an Australian Tarantula

Voltage-gated sodium (Na_V) channels are responsible for propagating action potentials in excitable cells. Na_V1.7 plays a crucial role in the human pain signalling pathway and it is an important therapeutic target for treatment of chronic pain. Numerous spider venom peptides have been shown to modulate the activity of Na_V channels and these peptides represent a rich source of research tools and therapeutic lead molecules. The aim of this study was to determine the diversity of Na_V1.7-active peptides in the venom of an Australian Phlogius sp. tarantula and to characterise their potency and subtype selectivity. We isolated three novel peptides, μ-TRTX-Phlo1a, -Phlo1b and -Phlo2a, that inhibit human Na_V1.7 (hNa_V1.7). Phlo1a and Phlo1b are 35-residue peptides that differ by one amino acid and belong in NaSpTx family 2. The partial sequence of Phlo2a revealed extensive similarity with ProTx-II from NaSpTx family 3. Phlo1a and Phlo1b inhibit hNa_V1.7 with IC₅₀ values of 459 and 360 nM, respectively, with only minor inhibitory activity on rat Na_V1.2 and hNa_V1.5. Although similarly potent at hNa_V1.7 (IC₅₀ 333 nM), Phlo2a was less selective, as it also potently inhibited rNa_V1.2 and hNa_V1.5. All three peptides cause a depolarising shift in the voltage-dependence of hNa_V1.7 activation.     

Histopathological effects of Naja haje snake venom and a venom gland extract of the scorpion Buthus quinquestriatus on the liver,suprarenal gland and pancreas of mice

Lethal doses of Naja haje snake venom produced central and midzonal hydropic degeneration in hepatic lobules. Buthus quinquestriatus scorpion venom gland extract caused peripheral zonal hydropic degeneration, sinusoidal dilatation and disruption. Fatty degenerative changes started earlier after use of the scorpion preparation. Both preparations depleted glycogen, inhibited succinic dehydrogenase and increased alkaline phosphatase activity in degenerated hepatocytes. Signs of regeneration followed sublethal doses of Naja haje venom. Lethal doses of both venom preparations caused rupture of the capsule of the suprarenal gland and detachment of its cortex. Blood extravasated in the medulla. Zona fasciculata cells were hypertrophied and vacuolated and cortical lipids increased. Depletion of ascorbic acid and medullary catecholamines occurred. After a single sublethal dose the zona reticularis region increased in thickness due to proliferation of its cells. These cells invaded the medullary clumps. Repeated sublethal doses increased the thickness of both the zona fasciculata and reticularis. In the pancreas, lethal doses of both venom preparations produced vacuolization of alpha and beta cells. Partial and complete degranulation were observed in hydropically degenerated beta cells. Alpha cells showed decreased alkaline phosphatase activity.