Cardiovascular and respiratory effects of Gaboon viper venom

Changes in the arterial blood pressure, heart rate and normal ECG parameters of rat after envenomation with Egyptian cobra (Naja haje) venom

1. The effect of Egyptian cobra (Naja haje) venom on the normal electrical activity of the cardiac muscles (ECG) and arterial blood pressure of envenomated rats were investigated in this study. 2. Rats were divided into three groups. The first group was injected im with saline and considered as control group. Rats of the second and third groups were injected IM with 0.02 micrograms and 0.04 micrograms cobra venom/gim b.wt, respectively. 3. Mean blood pressure (MBP), heart rate (HR) and four different ECG parameters (PR and QT intervals, R and T wave amplitudes) were measured over 1 h following envenomation. 4. The low dose (0.02 micrograms/g) of N. haje venom caused hypotension accompanied by an increase in the HR, whereas hypertension and bradycardia developed after injection of the high dose (0.04 micrograms/g) of venom. 5. There was a decrease in the P-R interval after administration of the low dose and prolongation of it after the high dose. The Q-T interval and R-wave amplitude were significantly increased after injection of both doses. T-wave amplitude was significantly elevated only after injection of the high dose. 6. The present results indicate that the Egyptian cobra (N. haje) venom significantly alters the arterial blood pressure and ECG parameters of envenomated rats. The suggests that impairment of the electrical activity of cardiac muscle may be one of the reasons why victims of cobra bite die.

The Gaboon viper, Bitis gabonica: hemorrhagic, metabolic, cardiovascular and clinical effects of the venom

The effects of Bitis gabonica venom have been studied in several animal species, including the monkey, dog, rabbit, rat and guinea pig. Further information has been provided by observations on the effects of snake bite in man. Bitis gabonica venom exerts a number of cytotoxic and cardiovascular effects: cytotoxic effects include widespread hemorrhage, caused by the presence of two hemorrhagic proteins. These hemorrhagins bring about separation of vascular endothelial cells and extravasation of blood into the tissue spaces. Metabolic alterations include decreased oxygen utilization by tissues and increased plasma glucose and lactate concentrations. Metabolic non-compensated acidosis has also been seen in the rat as a consequence of the cytotoxicity of the venom. Cardiovascular effects include disturbances in atrio-ventricular conduction and reduction in amplitude and duration of the action potential brought about by a decreased calcium membrane conductance. A progressive decrease in myocardial contractility can also be attributed to the decreased calcium conductance, which together with the severe acidosis may cause death in experimental animals. A severe, though reversible, vasodilatation was observed after envenomation due to unidentified compounds in the venom. In man, envenomation causes a variable clinical picture depending on the time course and severity of envenomation. Frequently seen effects include hypotension, hemorrhage at the site of the bite and elsewhere and disseminated intravascular coagulation. Envenomation can be satisfactorily treated with antivenom.

Isolation and characterisation of two haemorrhagic proteins (HTa and HTb) from the venom of Bitis gabonica (Gaboon viper)

Two distinct haemorrhagic proteinases, HTa and HTb, were isolated from the venom of Bitis gabonica by gel filtration and ion-exchange chromatography with native mol. wts of 180,000 and 111,000, respectively. After reduction with dithiothreitol, smaller mol. wts of 77,600 and 69,200 were recorded for HTa and HTb, suggesting that under native conditions the haemorrhagins exist as dimeric molecules. Both toxins possessed caseinolytic and collagenase activity although HTa was 15-36 times more potent than HTb with respect to collagenase activity. No zinc could be detected in the toxins; however, dialysis against ethylenediamine tetracetic acid (EDTA) reduced caseinolytic activity, suggesting the dependence of the latter on other metal ions. HTa and HTb had a marked effect on the intrinsic cascade coagulation mechanism (factors IX, XI and XII) but no effect on the final common coagulation pathway (factor X and prothrombin). Light and electron microscopical studies demonstrated that both HTa and HTb caused organ-specific lesions, with the lungs, diaphragm and body wall muscle being most affected. HTa caused widespread haemorrhage whilst HTb caused discrete focal lesions near the site of injection and elsewhere. However, both toxins appeared to cause capillary rupture by the separation of cells from one another and both caused cell detachment and cell death of bovine endothelial cells cultured in vitro, consonant with the massive disruption of capillaries seen in vivo.

Effects of sand viper (Cerastes cerastes) venom on isolated smooth muscle and heart and on haematological and cardiovascular parameters in the guinea-pig

The effects of the venom of the sand viper (Cerastes cerastes) on haematological and cardiovascular parameters and on isolated ileum, trachea, pulmonary artery and atrium from the guinea-pig were studied. In concentrations from 0.2 micrograms/ml to 0.6 mg/ml, snake venom caused concentration-dependent relaxation of the longitudinal ileal segments and the epinephrine-precontracted pulmonary artery rings, increased the tone of the tracheal rings and increased the rate of the spontaneously beating atrium but depressed the amplitude of its contraction. Low doses (0.04-0.4 mg) of the venom caused transient small depression of both heart rate and contractility of the isolated perfused heart. A higher dose (1.0 mg) significantly inhibited both parameters and delayed their recovery. An i.v. injection of 0.12 mg/kg of the snake venom to anaesthetized guinea-pigs had no effect on red blood cell count, haemoglobin concentration or the haematocrit value but significantly reduced the circulating white blood cells, the plasma clotting time and erythrocyte deformability. Also, i.v. injections of 0.02-0.2 mg/kg of the venom caused initial depression of the systolic and the diastolic blood pressure followed by complete or partial recovery and subsequent hypotension. These observations indicate that C. cerastes venom has multiple sites of action which may help in better understanding the pathology of bites by this snake.

Acidotic effect of gaboon viper (Bitis gabonica) venom in the urethane-anaesthetized rat

1. Intravenous venom (4 mg/kg) caused a non-compensated metabolic acidosis. 2. Bicarbonate concentration, base excess, standard base excess and pH all fell dramatically. 3. A respiratory impairment occurred characterized by pulmonary oedema and a fall in arterial pO2. 4. Acidosis occurred soon after venom when pO2 was still normal, indicating that changes in tissue metabolism contributed to the acidosis independently of reduced oxygen availability.

Comparison of the physiological effects in rabbits of gaboon viper (Bitis gabonica) venoms from different sources

The cardiovascular, respiratory and metabolic effects of B. gabonica venoms obtained from specimens originating from Ghana, Togo, Nigeria, Uganda and Tanzania were examined in anaesthetized rabbits. Intravenous injection of all venoms (0.125-2.0 mg/kg) induced hypotension. Nigeria venom was the least potent in this respect. Following doses of all venoms there was a brief bradycardia and a transient increase in respiratory rate and depth. At high doses (greater than or equal to 1.0 mg/kg), all venoms induced severe ST depression and T wave inversion. In addition, Togo venom, and to a lesser extent Tanzania and Ghana venoms, were potent in inducing extrasystoles. None of the venoms produced any significant changes in haematocrit, plasma proteins or arterial blood gas and pH levels. All venoms increased blood glucose and lactate levels by 1.3-2.1 fold and 2.2-4.0 fold respectively while the respiratory quotient remained unchanged. Togo venom was significantly (P less than 0.05) more lethal than the other venoms. The pattern of haemorrhage observed at post-mortem was the same for all venoms with the heart, ureters, adrenals, kidneys, lungs, stomach and intestines being the most affected. When combined on a subspecies basis, the results suggest that there are no significant differences in the physiological effects of venoms representing B. g. rhinoceros (West African gaboon viper) and B. g. gabonica (East African gaboon viper).

Acid-base, plasma lactate and glucose changes in the rabbit following administration of Gaboon viper (Bitis gabonica) venom

The acid-base and metabolic effects of Bitis gabonica venom administered intravenously to the anaesthetised rabbit were studied. Doubling doses of venom from 0.125 mg/kg to 1.0 mg/kg were used. Venom caused progressive and significant increases in plasma glucose and plasma lactate levels although oxygen consumption only became significantly lower after the fourth dose. Standard base excess (SBE) became significantly more negative after the third dose of venom and the fall in pH became significant at the same point. The results indicate that venom induces a metabolic acidosis in the rabbit and because the acidosis occurs in the absence of any fall in arterial PO2, it cannot be considered a consequence of impaired pulmonary ventilation. The reduction in oxygen uptake is likely to occur at a cellular level with a shift from aerobic to anaerobic metabolism hence the increase in plasma lactate levels. However, the magnitude of the acidosis is unlikely to be the principal cause of death under experimental conditions.

Evidence for the presence of histamine in Gaboon viper (Bitis gabonica) venom

Venom from B. gabonica produced a dose-dependent contraction of both isolated guinea-pig ileum and rabbit aortic strip preparations. The venom-induced contraction was not antagonised by pretreatment with atropine, phentolamine, methysergide or indomethacin, however, it was blocked by the prior addition of chlorpheniramine or cyproheptadine. Upon exhaustive dialysis of the venom, the dialysate contracted both preparations, while the dialysed venom had no effect. Paper and thin-layer chromatography of the venom showed a spot with an Rf value corresponding to authentic histamine. Biological assay of the crude venom on the guinea-pig ileum showed that it contained the equivalent of 2-10 micrograms of histamine per mg dry weight of crude venom. pA2 values for chlorpheniramine using either the venom or histamine as agonists were not significantly different.

The effects of Gaboon viper (Bitis gabonica) venom on the electrical and mechanical activity of the guinea-pig myocardium

The effects of Bitis gabonica venom were tested on guinea-pig heart, using both Langendorff preparations and isolated atrial strips or papillary muscles. In the self-paced whole heart, a single passage of 50 micrograms of venom per ml produced in sequence: irregularities of the A-V conduction and decrease of the contractile strength, progressive failure to relax and systolic arrest of the heart. Pretreatment with atropine reduced but did not abolish these effects. Venom recycled through the heart was effective at a much lower dose. The relationship between resting membrane potential and [K+]o was unaffected by envenomation, suggesting that the action of the venom cannot be ascribed to a loss of ionic selectivity of the cell membrane. The peak amplitude of action potentials declined in papillary muscle exposed to venom at physiological [K+]o, while in atrial cells it was affected only at higher [K+]o. Maximum upstroke rate of the action potential vs. resting potential at different [K+]o gave a sigmoid relationship, characterized by a higher upper asymptote as compared to controls, and by a shift of the curve towards more negative voltage values. A marked shortening of the action potential duration, paralleled by a decrease in time to peak tension, was recorded as well. 'Slow' action potentials, elicited in 20 mM K+ solution, were completely abolished within 10 min of perfusion with venom. These results are consistent with the hypothesis that the venom interacts with both transmembrane Ca2+ inflow and Ca2+ binding at the external side of the cell membrane. A transient positive inotropic effect induced by the venom was observed in papillary muscle and in atropinized atrium. This effect was abolished by previous administration of reserpine to the animal or by addition of propranolol to the perfusing solution, suggesting a venom-induced release of both adrenergic and cholinergic transmitters from nerve endings within the cardiac tissue.

The effect of gaboon viper (Bitis gabonica) venom on cardiac stroke work in the anaesthetized rabbit

The effect of Bitis gabonica venom administered intravenously in the rabbit at the dose of 0.125 mg/kg (approximately 10% of LD50) has been studied. Venom caused marked changes in cardiovascular parameters principally a precipitous but transient fall in total peripheral resistance and arterial blood pressure. Furthermore in the period occurring between 5 and 30 min after the injection of venom, a transient increase in stroke work was observed as a result of the ejection of an increased stroke volume against a blood pressure which had already returned to normal. Such a transient inotropic effect has also been observed in other small mammals and could be attributed to an adrenergic mechanism.

The Gaboon viper (Bitis gabonica): its biology, venom components and toxinology

The Gaboon viper has acquired an impressive reputation which is at least partly unfounded. This handsome animal with such striking features is undoubtedly docile which accounts for the very low incidence of bite amongst humans. There are only six detailed clinical reports on the effect of bite and these are summarized in the review. The viper does indeed produce prodigious amounts of venom, but the toxicity, weight for weight, is rather low compared to other poisonous snakes. Venom extractions have been carried out on four snakes over a 13-year-period and the effects of this venom have been studied in a variety of experimental animals. Systemic envenomation is characterized by immediate abrupt hypotension, subsequent cardiac damage and dyspnoea. The individual venom components responsible for these effects have not been isolated but it seems likely that the two enzymes which have been studied extensively (phospholipase A2 and the thrombin-like enzyme, gabonase) do not contribute significantly to lethality. We propose three principal activities which give rise to the major signs of systemic envenomation. Haemorrhagin; causing widespread damage to microvasculature which leads to the pulmonary oedema and hence dyspnoea, and locally causes blistering. Cardiotoxin; a long-acting material causing cardiac muscle damage, arrhythmia and ultimately cardiac failure. Peripheral vasodilator; a short acting effect, operating either locally via bradykinin formation and/or unknown peptides or centrally on the vasomotor centre.

The effect of Bitis gabonica (Gaboon viper) snake venom on external iliac and mesenteric arterial circulation in the dog

The effects of Gaboon viper (Bitis gabonica) venom on external iliac and mesenteric arterial blood flow and resistance were investigated in eight anaesthetized, close-chest dogs. Venom doses in the range 0.125-0.5 mg/kg produced a profound fall in external iliac and mesenteric arterial resistance, which recovered to control values after 30 min. After a third dose of venom, the mean arterial blood pressure failed to recover and the animals died after a period of severe hypotension. External iliac arterial blood flow rose concomitantly with the fall in external iliac resistance and decreased to a value significantly below control after 30 min. Paradoxically, mesenteric blood flow fell during the period of vasodilation. The results suggest that widespread vasodilation of muscle vascular beds (of which the external iliac circulation is representative) leads to shunting of blood away from the less-dilated mesenteric circulation. Venom-induced peritoneal haemorrhage caused a fall in blood volume and increase in viscosity. These undoubtedly contributed to the severe haemodynamic deterioration of the preparations after the third injection of the venom.