On-line version ISSN 1678-4936
J. Venom. Anim. Toxins vol. 5 n. 1 Botucatu 1999
1 Department of Physiology, Seth G.S. Medical College and K.E.M. Hospital, Parel, Mumbai 400 012, India.
ABSTRACT: Severe envenoming was induced in two groups of experimental dogs after subcutaneous (SQ) injection of venom of the scorpion (Mesobuthus tamulus concanesis, Pocock) (3.0 and 3.5 mg/kg body weight). The circulating levels of blood sugar, insulin, glucagon, and cortisol were assayed at 0, and 30, 60, 90 and 120 min after venom injection. There was an increase in the circulating levels of blood sugar, insulin, glucagon, and cortisol following envenoming.
Scorpion envenoming causes an autonomic storm resulting in a massive release of catecholamines, angiotensin II, glucagon, and cortisol accompanied by changes in insulin secretion. The rise in the counter-regulatory hormones (glucagon, cortisol, and catecholamines) oppose the anabolic actions of insulin resulting in a variety of clinical manifestations. These changes may lead to a syndrome of fuel-energy deficits and to an inability of the vital organs to utilise the existing metabolic substrates, ultimately resulting in multisystem organ failure (MSOF) and death.
KEY WORDS: scorpion envenoming, insulin, glucagon, cortisol, Mesobuthus tamulus concanesis.
Scorpion envenoming is a major health hazard in rural areas worldwide (29). The different mechanisms by which scorpion envenoming causes the death of the scorpion sting victims is not clearly known. Severe scorpion envenoming results in an autonomic storm which leads to a massive release of catecholamines (1,2,9-11), suppressed insulin secretions (16,23,24), and an increase in angiotensin II (28) levels. Angiotensin II stimulates the release of catecholamines, thereby synergising and amplifying each other's actions, and these may act, at least in part, at similar sites (7). We have already suggested that there could also be a rise in glucagon and cortisol secretions in severe scorpion envenoming. The elevated levels of the counter-regulatory hormones (glucagon, glucocorticoids, and catecholamines) oppose the anabolic actions of insulin resulting in fuel-energy deficits and an inability of the vital organs to utilise the existing metabolic substrates, which causes multisystem organ failure (MSOF), resulting in death. We demonstrate here the effects of scorpion venom on the circulating levels of blood sugar, insulin, glucagon, and glucocorticoids in experimental animals.
MATERIALS AND METHODS
A total of 21 healthy mongrel dogs of either sex (weight 8 ± 2 kg) were used in this study. After an overnight fast, the animals were anaesthetised with thiopentone sodium (35 mg/kg). The lyophilised red scorpion (Mesobuthus tamulus concanesis, Pocock) (earlier called Buthus tamulus) venom was purchased from Haffkine's Institute, Mumbai, India. Venom in saline (3.0 mg/kg) was given to a group of 9 dogs by subcutaneous injection (SQ). Blood was collected at 0, and 30, 60, 90, and 120 min following venom injection and processed for glucose (6) and insulin levels. Venom in saline (3.5 mg/kg) was given to the other 12 dogs. The blood from these animals was collected before venom administration and after 60 and 120 min. The blood samples were processed for blood glucose (6) and radioimmunoassay of insulin, glucagon, and cortisol. The radioimmunoassay kits were obtained from Diagnostic Products Corporation, Los Angeles, USA The results were statistically analysed using paired Student 't' test (3).
After envenoming (either 3.0 mg/kg or 3.5 mg/kg), the dogs showed several behavioural changes. These changes were: profuse thick ropy mucus salivary secretion, increased lacrimation, watery secretions from the nostrils, distended abdomen, increased frequency of urination, ejaculation, passing of stools (sometimes stained with either bile or blood), skeletal muscle fasciculations, clonus and tetany-like muscle contractions, irregular respiration, protrusion of eyeballs, and widely dilated pupils not reacting to light.
Table 1 shows the changes observed in blood glucose and insulin levels in the group of 9 experimental dogs before venom injection and after 30, 60, 90, and 120 min. There was an increase in blood sugar following venom injection. However, insulin levels fell 60 min and increased 90 min following envenoming.
Table 2 shows the changes in blood glucose, insulin, glucagon, and glucocorticoid levels in the group of 12 experimental dogs before venom injection, and after 60 and 120 min. These increased levels were significant when compared to the values obtained before venom injection in the same animals.
India harbours 99 species of scorpions, but not all scorpion stings result in victim death. Only 45 of these species, members of the Buthidae family, can cause fatalities. Elsewhere the most venomous species also belong to the Buthidae family: Androctonus from Algeria, Leiurus quinquestriatus from Israel and Jordan, Centruroides from Mexico, Buthus occitanus from Jordan, Tityus serrulatus from Brazil, Parabuthus from South Africa, Buthus occitanus from Sahara, Tityus trinitatis from Trinidad, and Centruroides sculpturatus from North America and many other countries (28). In spite of zoological differences resulting in venoms of differing chemical structure, the symptomatology following human envenomation is quite similar (28). The effect of the venom depends on the age of the offending scorpion, the season of the year, and the size (age and weight) of the victim (30).
The behavioural changes observed in the experimental animals following envenoming confirmed our earlier reports (19,22) and indicated an autonomic (sympathetic and parasympathetic) and neuro-muscular over-activity. The rise in the blood glucose levels observed in this study (Tables 1, 2) could be due to increased glycogenolysis stimulated by increased catecholamines (1,2,9-11,28), glucagon, cortisol, and changes in insulin secretion. The results of hyperglycaemia due to scorpion envenoming were in accordance with earlier work (16,18,19,24,27).
TABLE 1. Changes in blood glucose and insulin levels in anaesthetised dogs injected with 3 mg/kg of scorpion venom (Mean ± S. E. D.)
TABLE 2. Changes in blood glucose and hormonal levels in anaesthetised dogs injected with 3.5 mg/kg of scorpion venom. (Mean ± S.E.D)
In previous studies, intravenous injection of venom by the scorpion (Mesobuthus tamulus concanesis, Pocock) (4 mg/kg) in experimental dogs resulted in a suppressed insulin secretion (16,20,21,22), and subcutaneous injection of scorpion venom (3 mg/kg) in dogs resulted in suppression of insulin secretion 30 min after venom injection, and elevated insulin levels 60 min after venom injection (27). In this study, both insulin and blood glucose were found to be higher after 60 and after 120 min of venom injection (Table 2). These results confirmed the previous findings (12,27).
Inhibition of insulin release (15) and stimulation of glucagon secretion (14) by toxin from Leiurus quinquestriatus scorpion venom in rat pancreatic islets had already been demonstrated. These investigations (14,15) have suggested that norepinephrine release from sympathetic nerve endings is probably much greater when stimulated by scorpion venom toxin than by physiologic stimulation. Further, Johnson et al.(14,15) reported that the large release of glucagon caused by scorpion venom toxin suggests that norepinephrine released from the adrenergic nerve terminals of the pancreas may be a more effective stimulus to glucagon secretion than norepinephrine reaching the pancreas through the general circulation.
Glucocorticoids can also be released following stress or injury (8), as observed in this study. The sympatho-adrenal axis primarily serves to maintain the pressure flow relationship necessary for organ perfusion. Thus, during the "ebb phase", the insulin levels are reduced and with the onset of hypermetabolism, characteristic of the "flow phase", the hormonal environment is changed (8).
The presence of increased circulating levels of any one of these catabolic hormones that is glucagon, glucocorticoids, or catecholamines in a normal individual result in only minimal alterations in the metabolism and circulation (8). However, in the presence of increased circulating levels of all three catabolic counter-regulatory hormones, the effects of these hormonal actions are synergistic and sustained hepatic glucose production is observed (8). Thus, it appears that the simultaneous elaboration of the counter-regulatory hormones is partly responsible for the pathogenesis of a variety of clinical and biochemical manifestations following scorpion envenoming. This could be the reason for glycogenolysis in the atria, ventricle, liver, and skeletal muscles (4,5,21,22,24), hyperglycaemia (21,22,24 ), lipolysis and its products (18,22,23,24,27), increased protein breakdown products under the catabolic influence of the counter-regulatory hormones, and a simultaneous suppressed insulin secretion or insulin resistance.
Hyperinsulinism observed in this study could be equated with insulin resistance. Insulin resistance could be caused by a change in the receptor membrane, a change in hormone-receptor binding characteristics, or a change in post-receptor events (13,17).
Increased secretions of glucagon, cortisol, and catecholamines along with simultaneous reduction in insulin levels or insulin resistance stimulate glycogenolysis in skeletal muscle and promotes lactate production. Thus, under the conditions existing in scorpion envenoming, lactate is produced but not utilised contributing to lactic acidosis (22).
With the disturbed carbohydrate metabolism, dissimilation of fat is incomplete, since 'fats burn in the flame of carbohydrates' leading to ketosis (22) and this is aggravated by low glycogen content in the liver (4,5,22-24).
Insulin administration reversed the haemodynamic changes and pulmonary oedema in children and adults stung by venomous scorpions (25,31,32). Insulin administration in adult respiratory distress syndrome (ARDS) patients with multisystem organ failure (MSOF) following septic shock resulted in normal biochemical profile, radiological clearance of lungs, and clinical improvement (26). This could be due to insulin favouring glycogen deposition, inhibiting glycogenolysis and promoting glycogenesis, suppressing the mobilisation of fatty acids from adipose tissue, and promoting lipogenesis. Insulin administration following scorpion envenoming reversed the ECG and metabolic changes in experimental animals (19,21,24) as well as in scorpion sting victims (25,31,32) reducing angiotensin II levels (20), glycogenesis, and lipogenesis (22,25).
Severe scorpion envenoming is thus a syndrome of fuel-energy deficits and an inability of the vital organs to utilise the existing metabolic substrates. This ultimately may result in multisystem organ failure (MSOF) and death. These changes are brought about by a massive release of catecholamines, angiotensin II, glucagon, glucocorticoids, and either insulin deficiency, suppressed insulin secretion, or insulin resistance.
The authors thank the financial assistance from Indian Council of Medical Research, New Delhi (Task - Force Research Project No. 46/6/90 - B M S - 1). This research was conducted at Department of Physiology, L.T.M. Medical College, Sion, Mumbai, India.
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