Cardiovascular effects of Buthus martensii (Karsch) scorpion venom

Venom Components of Iranian Scorpion Hemiscorpius lepturus Inhibit the Growth and Replication of Human Immunodeficiency Virus 1 (HIV-1)

Background:

During the recent years, significant progress has been achieved on development of novel anti-viral drugs. Natural products are assumed as the potential sources of novel anti-viral drugs; therefore, there are some previous studies reporting the anti-viral compounds from venomous animals. Based on the significant value for tracing of non-toxic anti-viral agents from natural resources, this study was aimed to investigate the anti-viral activity of some HPLC purified fractions derived from the venom of Iranian scorpion, Hemiscorpius lepturus, against human immunodeficiency virus 1 (HIV-1) and herpes simplex virus 1 (HSV-1).

Methods:

H. Lepturus crude venom was subjected to reverse phase HPLC analysis to determine its active components precisely where four dominant fractions obtained at retention time of 156-160 minutes. The phospholipase A2 and hemolytic activities of the purified fractions were first evaluated. Then the anti-viral activity was measured using single cycle HIV (NL4-3) replication and HSV (KOS) plaque reduction assays.

Results:

The H. lepturus crude venom inhibited HIV replication by 73% at the concentration of 200 µg/ml, while it did not show significant anti-HSV activity. It also inhibited the cell-free viral particles in a virucidal assay, while it showed no toxicity for the target cells in a proliferation assay. The four HPLC fractions purified from H. lepturus inhibited HIV with IC₅₀ of 20 µg/ml.

Conclusion:

H. lepturus venom contains components with considerable anti-HIV activity insofar as it has virucidal activity that offers a novel therapeutic approach against HIV infection. Our results suggest a promising pilot for anti-HIV drug discovery with H. lepturus scorpion venom.

Echocardiologic evaluation and follow-up of cardiovascular complications in children with scorpion sting in coastal South India

Introduction and Objective:

Scorpion stings are a common emergency in India and many other tropical countries. In India, the red scorpions are more prevalent, and their venom is more likely to cause myocardial dysfunctions. There are very few studies conducted on this problem. The following study was done in Andhra Pradesh and aimed to identify cardiovascular complications of scorpion stings in children with a follow-up of 6 months

Study Design:

Prospective observational study.

Setting:

Children admitted with scorpion sting in a tertiary care hospital between December 2009 and November 2010 and followed-up till May 2011.

Results:

Scorpion stings account for 1 in every 36 admissions. Maximum cases were in 0–3 years age group. Electrocardiogram changes were seen in 76% cases and myocarditis in 42% cases. Echocardiography revealed decreased ejection fraction (EF), transient mitral regurgitation and wall motion abnormalities were observed. Average EF improved from 16% on day 1 to 47.94% and 59% on day 5 and 14 respectively, which was highly statistically significant. By the end of 1 month, all the survivors had normal EF and no residual cardiac dysfunction was observed at 6 months.

Conclusion:

Scorpion stings, a common and fatal medical emergency in India, produce echocardiographic changes without any long term residual damage on myocardial activity.

Scorpion envenomation among children: clinical manifestations and outcome (analysis of 685 cases)

Our objective was to characterize both epidemiologically and clinically manifestations after severe scorpion envenomation and to define simple factors indicative of poor prognosis in children. We performed a retrospective study over 13 years (1990-2002) in the medical intensive care unit (ICU) of a university hospital (Sfax-Tunisia). The diagnosis of scorpion envenomation was based on a history of scorpion sting. The medical records of 685 children aged less than 16 years who were admitted for a scorpion sting were analyzed. There were 558 patients (81.5%) in the grade III group (with cardiogenic shock and/or pulmonary edema or severe neurological manifestation [coma and/or convulsion]) and 127 patients (18.5%) in the grade II group (with systemic manifestations). In this study, 434 patients (63.4%) had a pulmonary edema, and 80 patients had a cardiogenic shock; neurological manifestations were observed in 580 patients (84.7%), 555 patients (81%) developed systemic inflammatory response syndrome (SIRS), and 552 patients (80.6%) developed multi-organ failure. By the end of the stay in the ICU, evolution was marked by the death in 61 patients (8.9%). A multivariate analysis found the following factors to be correlated with a poor outcome: coma with Glasgow coma score ≤ 8/15 (odds ratio [OR] = 1.3), pulmonary edema (OR = 2.3), and cardiogenic shock (OR = 1.7). In addition, a significant association was found between the development of SIRS and heart failure. Moreover, a temperature > 39°C was associated with the presence of pulmonary edema, with a sensitivity at 20.6%, a specificity at 94.4%, and a positive predictive value at 91.7%. Finally, blood sugar levels above 15 mmol/L were significantly associated with a heart failure. In children admitted for severe scorpion envenomation, coma with Glasgow coma score ≤ 8/15, pulmonary edema, and cardiogenic shock were associated with a poor outcome. The presence of SIRS, a temperature > 39°C, and blood sugar levels above 15 mmol/L were associated with heart failure.

Epidemiological, clinical characteristics and outcome of severe scorpion envenomation in South Tunisia: multivariate analysis of 951 cases

The aim of this retrospective descriptive study was to describe both epidemiologically and clinically manifestations following severe scorpion envenomation and to define simple predictive factors which can be used in routine practice in general Intensive Care Units (ICU) as an indicator of poor prognosis. Cases were collected from hospital patients' files during 13-year (1990-2002) period in the medical Intensive Care Unit of a university hospital (Sfax - Tunisia). The diagnosis of scorpion envenomation was based on a history of scorpion sting. Nine hundred fifty-one patients, who were admitted for a scorpion sting, were analyzed. There were 769 patients (80.8%) in the grade III group (with cardiogenic shock and/or pulmonary edema or severe neurological manifestation (coma and/or convulsion)) and 182 patients (19.2%) in the grade II group (with systemic manifestations). Scorpion envenomation is more frequent in summer; indeed 82.3% of our patients were admitted between June and September. The mean age (+/-SD) was 14.7 +/- 17.4 years, ranging from 0.5 to 90 years. In this study 739 patients (77.8%) had neuromuscular signs, 700 patients (73.6%) had gastrointestinal signs and 585 patients (61.5%) had a pulmonary edema, while 195 patients (20.5%) had a cardiogenic shock. The mean blood sugar on admission was at 11.32 +/- 5.66 mmol/l, a high blood sugar level (>11 mmol/l) was observed in 39% of cases. The mean blood urea was at 7.1 +/- 3.2 mmol/l, it was above 10 mmol/l in 10.7% of cases. The mean of leucocytes was at 17 418 +/- 7833 cells/mm(3), it was above 11 000/mm(3) in 80% of cases. In the end of the stay in ICU, evolution was marked by the improvement of 879 patients (92.5%) while 72 patients (7.5%) died. A multivariate analysis found the following factors to be correlated with a poor outcome: age less than 5 years (OR = 2.27), fever >38.5 degrees C (OR = 2.79), coma with Glasgow coma score < or =8/15 (OR = 9.87), pulmonary edema (OR = 8.46), leucocytes >25 000 cells/mm3 (OR = 2.35) and blood urea >8 mmol/l (OR = 4.02). Moreover, in children group, a significant association was found between PRISM score and mortality rate, this model had a high discriminative power with an area under the ROC curve at 0.93. In the adult patients a significant association was found between SAPS II score and mortality rate, this model had a high discriminative power with an area under the ROC curve at 0.82. In summary, in severe scorpion envenomation, age less than 5 years, fever >38.5 degrees C, coma with Glasgow coma score < or =8/15, pulmonary edema, leucocytes >25 000 cells/mm3 and blood urea >8 mmol/l were associated with a poor outcome.

Effect and mechanisms underlying scorpion toxin action from Androctonus australis garzonii on atrial natriuretic peptide in rat atria: an in vitro study

Scorpion envenomation is considered public health problem in Northern African countries. The mechanisms of cardiac dysfunction following scorpion envenomation are not fully understood. This study examined the effect and mechanisms underlying scorpion toxin action from Androctonus australis garzonii on atrial natriuretic peptide (ANP) release from rat atrium using in vitro organ perifusion. Male Sprague Dawley rats were used in this study. Three experiments were conducted. In experiment 1, atrial tissues were exposed either to Krebs-bicarbonate buffer medium (control) or to scorpion toxin (10(-8) M to 10(-6) M). In experiment 2, animals were chemically sympathectomized with a single intraperitoneal injection of 6-hydroxydopamine (6-OHDOPA) at a dose of 40 microg/g 24 h before sacrifice. Vehicle-treated rats served as control. Atrial tissues were collected and perifused in the presence of 10(-6) M scorpion toxin. In experiment 3, atrial tissues were exposed to 10(-6) M scorpion toxin either in the absence or presence of 10(-6) M propranolol (a beta-adrenoceptor blocker), or 10(-6) M tetrodotoxin (a sodium channel blocker). ANP levels released in the perifusion medium were determined by radioimmunoassay. The scorpion toxin at 10(-6) M induced a significant (p<0.01) increase (106%) in ANP levels. This effect was decreased (20%) by 6-OHDOPA. Propranolol and tetrodotoxin significantly (p<0.01) inhibited 55% and 60%, respectively, the toxin-induced ANP release. The data show that the North African scorpion toxin from Androctonus australis garzonii increases the ANP release in rat atrium through stimulation of sympathetic cardiac nerves and sodium channels activation.

Indian black scorpion (Heterometrus bengalensis Koch) venom induced antiproliferative and apoptogenic activity against human leukemic cell lines U937 and K562

Venoms are rich source of several bioactive compounds that possess therapeutic potentials. The different constituents of scorpion venom can modulate cell proliferation, cell growth and cell cycle. In the present communication, the cytotoxic activity of Indian black scorpion (Heterometrus bengalensis) venom was explored on human leukemic U937 and K562 cells. Scorpion venom induced U937 and K562 cell growth inhibition and the IC(50) value calculated to be 41.5 microg/ml (U937) and 88.3 microg/ml (K562). The scorpion venom showed characteristic features of apoptosis such as membrane blebbing, chromatin condensation and DNA degradation in both the cells as evidenced by confocal, fluorescence, scanning electron microscopy. Scorpion venom (IC(50) dose, 48 h) induced DNA fragmentation as evidenced by comet formation. Flow-cytometric assay revealed a significant amount of apoptotic cells (early and late) due to scorpion venom treatment. The venom induced cell cycle arrest was observed with maximum cell accumulation at sub-G(1) phase. Thus, the Indian scorpion (H. bengalensis) venom possessed antiproliferative, cytotoxic and apoptogenic activity against human leukemic cells.

INVESTIGATION OF THE MICROCIRCULATION AND THE STATE OF OXIDATIVE STRESS IN THE RAT AFTER SCORPION ENVENOMATION

1. Severe cases of scorpion envenomation (SE) generally show both respiratory and cardiocirculatory dysfunction. However, the pathophysiology of SE remains controversial. In the present study, we tried to explain the pathophysiology of the haemodynamic perturbations and cardiac failure in rats poisoned by the venom of Buthus occitanus tunetanus through a histomorphometric study of myocardial and muscular skeletal microcirculation and analysis of the oxidative stress state in order to evaluate the implication of the inflammatory process in the pathogenesis of SE. 2. Experiments were performed on 96 rats divided into 16 groups (n = 6 in each group). Two groups were used to determine the optimum conditions of venom administration and times when to measure haemodynamic parameters. The B. occitanus tunetanus venom was administered at a dose of 800 microg/kg and tissues were removed 5 and 20 min after envenomation. Six groups were used for histomorphometric study: two control groups, two poisoned groups an two melatonin-pretreated and poisoned groups. The histomorphometric study was performed on isolated hearts and skeletal muscles. The final eight groups of rats (two control groups, two envenomated groups, two control groups pretreated with melatonin and two groups pretreated and envenomated) were used to investigate the state of tissue oxidative stress during SE and to evaluate the anti-oxidant effect of melatonin on rats poisoned with B. occitanus tunetanus venom. This study was based on the determination of tissue malondialdehyde in isolated organs as an indicator of thiobarbituric acid-reactive substances (TBARS). Melatonin was injected at a dose of 5 mg/kg, i.v., 15 min before the administration of serum or venom. Data were compared using analysis of variance and Tukey's test for multiple pair-wise comparisons. 3. Five minutes after venom injection, a significant reduction in the mean relative volume of venules and arterioles in the heart and skeletal muscles of poisoned rats was noted. Twenty minutes after venom injection, these volumes were significantly increased in the heart and skeletal muscles of poisoned rats. Pretreatment of envenomated rats with melatonin resulted in a significant decrease in the mean relative volume of the venules and arterioles in the heart and skeletal muscles 5 and 20 min after venom injection compared with untreated envenomated rats. Investigation of the oxidative stress state showed a highly significant increase in TBARS in poisoned rats compared with control groups 5 and 20 min after venom injection. Melatonin pretreatment of rats poisoned with B. occitanus tunetanus venom resulted in an important and highly significant reduction of TBARS compared with untreated envenomated rats. 4. It appears from the results of the present study that administration of B. occitanus tunetanus venom engendered an excessive myocardial and skeletal muscular vasoconstriction attributed to massive catecholamine release followed by arteriolar and venular vasodilatation. This venous stasis at the muscular microcirculation could be due to myocardiac failure. However, the concomitant presence of arteriolar vasodilatation suggests an inflammatory process in the pathophysiology of SE. This process was suggested by the genesis of a state of oxidative stress in relation to the important lipoperoxidation, which was inhibited by administration of the anti-oxidant melatonin. Thus, melatonin pretreatment seemed to accentuate the first phase of vascular reactivity in envenomed rats and inhibit the second vasodilator phase observed 20 min after administration of the venom.

Effects of voltage-gated Na+ channel toxins from Tityus serrulatus venom on rat arterial blood pressure and plasma catecholamines

Scorpion toxins interact with ionic channels of excitable cells, leading to a massive release of neurotransmitters. Voltage-gated Na+ channel toxins are mainly responsible for the toxic effects of scorpion envenoming and can be classified into two classes: alpha- and beta-neurotoxins. TsTX-V and TsTX-I from Tityus serrulatus venom (TsV) are, respectively, examples of these toxins. In this work, we compared the effects of these toxins on mean arterial pressure (MAP) and catecholamines release in rats. Toxins were isolated by ion exchange chromatography (TsTX-I) followed by RP-HPLC (TsTX-V). All experiments were performed on conscious unrestrained rats previously catheterised. The toxins (15 and 30 microg/kg) and TsV (50 and 100 microg/kg) were injected intravenously. MAP was continuously monitored through femoral catheter. Epinephrine (E) and norepinephrine (NE) levels were determined by RP-HPLC with electrochemical detection, at 10 min before and 2.5, 30 and 90 min after treatments. Maximal pressor effects were observed at 2.5-3.5 min. TsV induced intense long lasting increase in MAP, as did TsTX-I. TsTX-V showed the lowest pressor effects. TsV showed the highest effects on catecholamines release, followed by TsTX-I and TsTX-V with maximal effect at 2.5 min, followed by a gradual reduction, however remaining higher than controls. Although both toxins act on Na+ channels, TsTX-I displayed significant and more intense effects on catecholamines release and blood pressure than TsTX-V. It seems that the toxicity of TsTX-V is not related only with its ability to release catecholamines, indicating that other neurotransmitters, may be involved in its toxicity.

[Cardiovascular dysfunction following severe scorpion envenomation. Mechanisms and physiopathology]

The seriousness of scorpion envenomation results essentially from left cardiac function with pulmonary oedema and/or a state of shock. Adrenergic myocarditis, toxic myocarditis and myocardial ischemia are the 3 mechanisms that explain the cardiac dysfunction. Myocardial ischemia is not only due to the release of catecolamines but also the effect of the cytokines and/or neuropeptide Y on the coronary vessels. The cardiac damage can be due or enhanced by the depressive effect of the cytokines on the myocardial cells. The frequently observed hyperglycaemia only enhances the state of the already damaged myocardium.

Evidence of myocardial ischaemia in severe scorpion envenomation. Myocardial perfusion scintigraphy study

OBJECTIVE

To explore the myocardial perfusion by thallium-201 scintigraphy for patients with evidence of myocardial damage after scorpion envenomation.

DESIGN

Prospective study over 1-year period.

SETTING

Medical intensive care unit of a university hospital (Sfax, Tunisia).

PATIENTS

We have prospectively included six patients admitted for scorpion envenomation over a period of 1 year in the 22-bed intensive care unit (ICU) of our university hospital. The evidence of myocardial damage was confirmed by electrocardiography and echocardiography in all patients. Myocardial perfusion scintigraphy ((201)Tl scintigraphy) coupled with radionuclide ventriculography ((99m)Tc) was performed for all patients, occurring 32 h on average (range 12-72 h) after the sting.

RESULTS

Radionuclide ventriculography was abnormal in all cases; the abnormalities observed were similar to those observed by echocardiography. Moreover (201)Tl scintigraphy showed evidence of myocardial hypoperfusion in all cases. The myocardial hypoperfusion grade and localisation were more marked in the abnormal localisation shown by echocardiography and electrocardiography, compared to the normal wall. Repeated studies, obtained only in two patients within 6 and 15 days, respectively, showed considerable, but not complete, improvement of wall motion and myocardial perfusion. Segments with improved perfusion showed greatly improved regional wall motion.

CONCLUSION

This study confirms the evidence of myocardial hypoperfusion after severe scorpion envenomation.

Effect of Venom from the Scorpion Leiurus Quinquestriatus on Rat Vascular Aortic Rings

The present study was designed to examine the effects of venom from the scorpion Leiurus quinquestriatus hebraeus (Lqh) on the contractility of rat aortic rings. We first examined the effect of Lqh venom on the contractile tension of isolated rat vascular aortic rings and then whether long-term exposure to the venom reduces the contractility of vascular smooth muscle by increasing the production of nitric oxide. Following the administration of 33 microg/mL of crude Lqh venom, contractile tension increased by 18.9 +/- 11.4 percent. The administration of 2.4 x 10(-7) M noradrenaline (NA) led to a 31.6 +/- 8.2 percent increase in tension (p < 0.01). The effects induced by NA and Lqh venom were similar and additive (p < 0.01). Pretreatment with the alpha-adrenergic blocker phenoxybenzamine (0.2 microM) eliminated the effect of the venom, whereas the calcium-channel blocker verapil (8.3 microM) merely attenuated the effect. Incubation of the rings with Lqh venom for 16 to 18 h, followed by NA stimulation, led to a 15 to 20 percent decrease in tension (p < 0.001). Treatment with N-omega-nitro-L-arginine methyl ester (110 microM), a constitutional nitric oxide inhibitor, restored the tension to control values. Treatment with S-methyl-isothiourea (0.1 microM), an inducible nitric oxide synthesis inhibitor, had no effect on contractile tension. The results of the present study suggest that the effect of Lqh venom on isolated aortic rings is induced via sympathetic nerve terminals. Calcium had little effect on the smooth muscle contractility of aortic rings incubated with the venom. No evidence was found to support nitric oxide synthesis after the long-term exposure of the rings to Lqh venom.

Molecular cloning and functional expression of a gene encoding an antiarrhythmia peptide derived from the scorpion toxin

From a cDNA library of Chinese scorpion Buthus martensii Karsch, full-length cDNAs of 351 nucleotides encoding precursors (named BmKIM) that contain signal peptides of 21 amino acid residues, a mature toxin of 61 residues with four disulfide bridges, and an extra Gly-Lys-Lys tail, were isolated. The genomic sequence of BmKIM was cloned and sequenced; it consisted of two exons disrupted by an intron of 1622 bp, the largest known in scorpion toxin genomes, inserted in the region encoding the signal peptide. The cDNA was expressed in Escherichia coli. The recombinant BmKIM was toxic to both mammal and insects. This is the first report that a toxin with such high sequence homology with an insect-specific depressant toxin group exhibits toxicity to mammals. Using whole cell patch-clamp recording, it was discovered that the recombinant BmKIM inhibited the sodium current in rat dorsal root ganglion neurons and ventricular myocytes and protected against aconitine- induced cardiac arrhythmia.

Evidence for a direct action of Tityus serrulatus scorpion venom on the cardiac muscle

The ability of toxins to activate the cardiovascular system plays an important role in the morbidity and lethality of the Tityus serrulatus scorpion envenoming. Most of the actions of the scorpion toxins are indirect and due to the release of adrenergic and cholinergic neurotransmitters. Accordingly, treatment following envenoming is targeted towards inhibition of adrenergic and cholinergic receptors. Here, we have sought evidence for a direct action of T. serrulatus venom on the isolated rat heart (Langendorff's method). We show that the bradycardia induced by T. serrulatus venom was completely blocked by atropine, a muscarinic receptor antagonist. Similarly, the increase in heart rate that follows the venom-induced bradycardia was totally inhibited by a beta(1)-adrenoceptor antagonist or by chemical sympathetic denervation with 6-hydroxydopamine. In contrast to these findings, the venom-induced increase in contractile force was not modified by beta(1)-adrenoceptor blockade or by chemical sympathetic denervation. The results clearly demonstrate that the chronotropic effects of T. serrulatus are dependent on neurotransmitter release, but the inotropic effects are not. The neurotransmitter-independent increase in contractility seems to be a direct action of the venom on cardiomyocytes. We suggest that this direct effect on cardiac fibers may play a role in the development of cardiac arrhythmias and contractility defects following envenoming with T. serrulatus scorpion.

Hyperosmolality-induced abnormal patterns of calcium mobilization in smooth muscle cells from non-diabetic and diabetic rats

Hyperglycemia and/or hyperosmolality may disturb calcium homeostasis in vascular smooth muscle cells (SMCs), leading to altered vascular contractility in diabetes. To test this hypothesis, the KCl-induced increases in [Ca2+]i in primarily cultured vascular SMCs exposed to different concentrations of glucose were examined. With glucose concentration in solutions kept at 5.5 mM, KCl induced a fast increase in [Ca2+]i which then slowly declined (type 1 response) in 83% of SMCs from non-diabetic rats. In 9% of non-diabetic SMCs KCl induced a slow increase in [Ca2+]i (type 2 response). Interestingly, under the same culture conditions KCl induced type 1 and type 2 responses in 47 and 35% of SMCs from diabetic rats. When SMCs from non-diabetic or diabetic rats were cultured in 36 mM glucose, KCl induced a fast increase in [Ca2+]i which, however, maintained at a high level (type 3 response). The sustained level of [Ca2+]i in the presence of KCl was significantly higher in cells cultured with 36 mM glucose than that in non-diabetic cells cultured with 5.5 mM glucose. Furthermore, the hyperglycemia-induced alterations in calcium mobilization were similarly observed in cells cultured in high concentration of mannitol (30.5 mM) or L-glucose, indicating that hyperosmolality was mainly responsible for the abnormal calcium mobilization in diabetic SMCs.

Haemodynamic patterns in patients with scorpion envenomation

OBJECTIVE

To study cardiovascular haemodynamics following scorpion envenomation.

SETTING

Intensive care unit of a university hospital.

PATIENTS

Eight patients with Indian red scorpion (Mesobuthus tamulus) stings.

INTERVENTION

Captopril (6.25 to 12.5 mg orally) every 30 minutes until pulmonary oedema resolved.

MAIN OUTCOME MEASURES

Haemodynamic data obtained by pulmonary artery catheterisation.

RESULTS

Two haemodynamic patterns were seen. There was a predominant vascular effect in one patient, with severe hypertension, tachycardia, increased systemic vascular resistance index (SVRI = 5893 dyn.s.cm-5), and normal cardiac index (2.73 l/m2). A predominant myocardial effect with left ventricular dysfunction and normal right ventricular function was seen in the other seven patients, with tachycardia, pulmonary oedema, mild hypotension, reduced stroke volume (mean (SD), 25.9 (8.3) ml/m2), normal SVRI (1812 (831) dyn.s.cm-5), and increased pulmonary artery wedge pressure (PAWP = 25 (4.4) mm Hg). Following mild dehydration pulmonary oedema subsided (PAWP = 14 (8.5) mm Hg) in three of these patients, but hypovolaemic shock developed (right atrial pressure (RAP) = 1.3 (2.1) mm Hg); pulmonary oedema recurred with rehydration. One patient developed fatal cardiogenic shock with raised PAWP (27 mm Hg) and RAP (11 mm Hg), and vasodilatation (SVRI = 1129 dyn.s.cm-5). Stroke volume (30.5 (8.7) ml/m2) and cardiac output (4.3 (1.5) 1/m2) improved with resolution of pulmonary oedema (PAWP = 14.4 (4.2) mm Hg) following afterload reduction with captopril.

CONCLUSIONS

Mild envenomation causes severe vasoconstriction and hypertension. Severe envenomation produces predominant left ventricular dysfunction with normal systemic vascular resistance manifesting as pulmonary oedema or severe hypotension depending on the fluid balance. Shock due to biventricular dysfunction and vasodilatation occurs terminally.

Resurgence of carbon monoxide: an endogenous gaseous vasorelaxing factor

Carbon monoxide (CO) is an endogenously generated gas that may play an important physiological role in the regulation of vascular tone. The CO-induced vasorelaxation, as a result of a direct action on vascular smooth muscles, has been demonstrated in many cases. Three major cellular mechanisms are proposed to explain the vasorelaxing effect of CO. These include the activation of soluble guanylyl cyclase, stimulation of various types of K channels, and inhibition of the cytochrome P450 dependent monooxygenase system in vascular smooth muscle cells. An interaction between CO and nitric oxide may also significantly contribute to the fine tuning of vascular tone. Furthermore, alterations in either the endogenous production of CO or the vascular responsiveness to CO have been encountered in several pathophysiological situations. A better understanding of the vascular effects of CO and the underlying cellular and molecular mechanisms will pave the way for the establishment of the role played by CO in vascular physiology and pathophysiology.Key words: carbon monoxide, heme oxygenase, smooth muscles, vasorelaxation.

Clinical description of Parabuthus transvaalicus scorpionism in Zimbabwe

An epidemiological and clinical study of Parabuthus transvaalicus scorpionism was conducted in Zimbabwe. Ten per cent of stings resulted in severe scorpionism. The clinical features of 17 patients with severe envenomation were primarily neuromuscular, with significant parasympathetic nervous system and cardiac involvement. The clinical course was prolonged compared to other scorpion syndromes, and significant therapeutic benefit was demonstrated in terms of hospital stay in response to species specific antivenom. The case fatality rate was 0.3%, with deaths in children below 10 years and adults above 50 years. The mortality rate in the district was 2.8 per 100,000 per year. This syndrome from a buthid scorpion resembles in many respects buthid scorpionism described elsewhere in the world, but shows important differences, notably cardiac involvement in the absence of clinical evidence of circulating catecholamines. The relevance of these findings to buthid scorpionism generally are presented as a hypothesis, in which it is postulated that the cardiac effects of the toxins are direct and primary, and autonomic effects secondary but synergistic, determining the ultimate clinical picture.