|Year : 2015 | Volume
| Issue : 1 | Page : 60-64
Effects of methanol in blood pressure and heart rate in the rat
Kausar Jahan, D Mahmood, M Fahim
Department of Pharmacology, Faculty of Pharmacy, 1Department of Physiology, Hamdard Institute of Medical Sciences and Research, Jamia Hamdard, New Delhi, India
|Date of Submission||26-Feb-2014|
|Date of Decision||22-Apr-2014|
|Date of Acceptance||27-Jul-2014|
|Date of Web Publication||21-Jan-2015|
Department of Pharmacology, Faculty of Pharmacy, 1Department of Physiology, Hamdard Institute of Medical Sciences and Research, Jamia Hamdard, New Delhi
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: Methanol ingestion is an uncommon form of poisoning that can cause severe metabolic disturbances, blindness, permanent neurologic dysfunction and death. While methanol itself may be harmless, it converts, in vivo, to highly toxic formic acid. Methanol intoxication clinically manifests as ocular toxicity. The present study investigated the cardiovascular effects of methanol. Materials and Methods: On the day of the experiment, Wistar rats were anesthetized with urethane. The femoral artery on one side was exposed, and a polyethylene catheter was inserted into the artery for recording arterial blood pressure (ABP). The catheter was attached to a pressure transducer (Statham - P23D). Systolic blood pressure (BP), mean ABP, and heart rate were recorded on a power-lab data acquisition system with a computerized analysis program. Rats were administered with different dilutions (9.5%, 19.0%, 28.5%, 38.0%, 47.5%, 57.0%, 66.5%, 76%) of methanol (95% v/v, i.v.). Results: Of all dilutions of methanol, 66.5% dilution showed maximum decrease of diastolic BP from 124.64 ± 5.39 to 62.30 ± 11.90 mmHg; 76.0% dilution showed maximum decrease of systolic BP from 165.70 ± 5.57 to 112.11 ± 12.0 mmHg, and mean ABP from 160.61 ± 12.45 to 86.14 ± 4.11 mmHg. The heart rate increased (from 250 beats/s to near about 275 beats/s) following administration of methanol dilution from 19.0% till 76.0%. Conclusion: The present study is consistent with previous studies suggesting that methanol ingestion leads to severe hypotension as observed from decrease in diastolic BP, systolic BP, and mean ABP. However, severe increase of heart rate suggests activation of a compensatory mechanism to offset hypotension that eventually leads to death in methanol poisoning. Hence, this study emphasizes the need to monitor all the hemodynamic parameters in accidental methanol poisoning.
Keywords: Cardiovascular effects, heart rate, methanol, methanol poisoning
|How to cite this article:|
Jahan K, Mahmood D, Fahim M. Effects of methanol in blood pressure and heart rate in the rat. J Pharm Bioall Sci 2015;7:60-4
Methanol or methyl alcohol has been reported as toxic to humans, readily absorbed by ingestion and inhalation, and more slowly by skin exposure. ,,, Human body ingests small quantities of methanol which comes from eating fruits and vegetables. Nearly, half a gram daily ingestion of methanol was reported as safe for adults. Toxicity of methanol, in humans and primates, is reported to be mediated via its metabolites and not methanol per se. In the body, methanol is first oxidized to methanal (HCHO, formaldehyde), formic acid (HCOOH) and finally detoxified to carbon dioxide (CO 2 ). The main enzyme groups involved in each step are alcohol dehydrogenase, aldehyde dehydrogenase, and folate dependent mechanisms, respectively. , Though, formate has been reported as the building block for many biological molecules, and regarded as essential for survival, but high formate buildup in the human body after excessive methanol intake could cause severe toxicity and may even lead to death. , Therefore, it is regarded as the primary source of methanol poisoning; and in primates and humans including animals with a poor ability to metabolize this product fatal toxicity may occur from metabolic acidosis and neuronal toxicity. , Undissociated formic acid readily crosses the blood brain barrier leading to central nervous system toxicity, aggressive alkaline therapy is required to maintain formic acid in the dissociated form. , As a moderate inhibitor of cytochrome-c oxidase, formate may cause tissue oxygen utilization to be impaired leading to anaerobic respiration with subsequent increased lactate production, which may further contribute to the acidosis. ,, The relative affinity of alcohol dehydrogenase for ethanol is much greater than for methanol (20:1) and exploited therapeutically in methanol poisoning, where alcohol is given under medical supervision to reduce the production of formic acid. Fomepizole is a selective inhibitor of the metabolism of methanol.
It is readily absorbed by all routes and distributed in the body water (volume of distribution 0.6 L/kg), and extensively metabolized primarily through liver), but a fraction of it is excreted unchanged in the lungs and kidneys. The excretion of methanol is relatively slow (t½ is about 24 h) and is primarily excreted as formic acid in the urine, and peak serum concentrations are obtained within 30-90 min. , Methanol does not bind to plasma protein and is poorly distributed to fatty tissues. 
Elimination of methanol as formic acid occurs primarily via urinary excretion. At high concentrations, methanol elimination is saturated and is zero order with a rate of approximately
85 mg/L, about half the elimination rate of ethanol. Maximum excretion of formic acid may be as late as the 2 nd or 3 rd day following ingestion. Small quantities of methanol are excreted unchanged in the lung and the kidneys (2% of a dose of 50 mg/kg). Concentration of methanol in the urine may be 20-30% higher than in the blood.
Upon ingestion or inhalation, methanol initially has a narcotic effect followed by an asymptomatic period of approximately 10-15 h.  After this period, methanol may produce nausea, vomiting, dizziness, headaches, vertigo, respiratory difficulty, lethargy, and abdominal pain, and also pain in the extremities, visual disturbances, and metabolic acidosis. , The visual disturbances vary from spots or cloudiness of vision to complete blindness.  Methanol toxicity can result in coma and death by respiratory or cardiac arrest. In one study, symptoms of blurred vision, headaches, dizziness, nausea, and skin problems were reported in teachers' aides who were exposed to duplicating fluid containing 99% methanol while working with "spirit duplicators". 
Methanol is readily available and sell at a low price than alcohol, hence, constitute a potent adulterant of illicit liquor. In India, several outbreaks of methanol poisoning were reported in the past, in particular, in the rural areas and small cities. The adulteration of alcoholic beverages with methanol has caused severe disabilities and loss of human lives. The initial symptoms of methanol poisoning (drinking 1-4 ounces) may be delayed for as long as 12-18 h as the body metabolizes methanol to formate, and can consist of weakness, dizziness, headache, nausea vomiting, and blurred vision. In severe cases of accidental or reckless ingestion, methanol poisoning may lead to permanent blindness or death, although complete recovery is the rule in patients admitted early to the hospital.
There are several treatments available to combat methanol poisoning, including early treatment with sodium bicarbonate to help prevent visual impairment. In a hospital setting, hemodialysis is effective in removing both methanol and formate from the blood, and co-exposure to ethanol has been shown to reduce formate levels. In the case of skin exposure to methanol, washing immediately with soap and plenty of water can prevent further skin absorption.  Methanol produce toxic effect on almost all organ system, but central nervous system, cardiovascular system and respiratory systems are highly affected from methanol toxicity.
Literatures reporting methanol toxicity are replete, however, there is a paucity of data on hemodynamic effects of methanol, and the toxic effects of methanol and its metabolites on the cardiovascular system. , The data from this study present an insight into changes in hemodynamic in relation to sign and symptoms that result from methanol poisoning and hence their understanding is critical to the correct diagnosis.
Given the paucity of data, the present study sought to ascertain the hemodynamic effects of methanol, which included the effects on blood pressure (BP), mean arterial BP (ABP), pulse pressure and heart rate, in rats.
| Materials and Methods|| |
The study was carried on 12-week old male, Wistar albino rats weighing 150-200 g. The animals were housed in a group of six animals per cage and maintained at 20-30°C and 50-55% humidity in a natural light and dark cycle, with free access to food and water and kept under standard conditions in an animal house facility approved by the Committee for the Purpose of Control and Supervision of Experiments on Animals. The experimental protocol was approved by the Institutional Animal Ethics Committee, Jamia Hamdard. Utmost care was taken to ensure that animals were treated in the most humane and ethically acceptable manner.
On the day, of the experiment, rats were anaesthetized with the chloroform solution. Adequate anesthesia was indicated by the disappearance of pedal reflex. Rat was placed on a heated surgical table to maintain rectal temperature at 37°C. Trachea was cannulated to allow free breathing without any obstruction. The femoral artery on one side was exposed, and a polyethylene catheter was inserted into the artery for recording ABP. The catheter was attached to a pressure transducer (Statham - P23D). Potency of the catheter was maintained with a heparinized saline solution (5000 IU m/L, v/v). The pressure recording system was calibrated with the help of a mercury manometer before each experiment. Cannulation of the femoral vein of the other limb was performed to facilitate drug injection. Rats were administered with different dilutions (9.5%, 19.0%, 28.5%, 38.0%, 47.5%, 57.0%, 66.5%, 76%) of methanol (95% v/v, i.v.). Systolic BP mean ABP, and heart rate were recorded on a power-lab data acquisition system with a computerized analysis program.
Statistical analysis of the data were performed using one-way analysis of variance, where P < 0.05 were considered as significant, and was expressed as mean ± standard error of the mean.
| Results|| |
Of all the dilutions of methanol used, there was a statistical significant decrease (P < 0.05), that is, maximum decrease, of diastolic BP from 124.64 ± 5.39 to 62.30 ± 11.9 mmHg observed at the methanol dilution of 66.50%. Similarly, of all the dilutions of methanol used in our study, there was a statistical significant decrease (P < 0.05), that is, the maximum decrease, of systolic BP from 165.70 ± 5.57 to 112.11 ± 12.0 mmHg, and mean ABP from 160.61 ± 12.45 to 86.14 ± 4.11 mmHg observed at the methanol dilution of 76.0%. The heart rate increased (from 250 beat/s to nearly 275 beats/s) following administration of all the methanol dilution from 19.0% till 76.0% of methanol dilution, however, a statistical significant increase (P < 0.05) of heart rate was observed from 239.70 ± 28.80 to 313.55 ± 16.65 beat/s at the methanol dilution of 9.5% [Figure 1], [Figure 2], [Figure 3] and [Figure 4].
|Figure 1: Effect of different doses of methanol (95% v/v) on diastolic blood pressure (mmHg)|
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|Figure 2: Effect of different doses of methanol (95% v/v) on systolic blood pressure (mmHg)|
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|Figure 3: Effect of different doses of methanol (95% v/v) on mean arterial blood pressure (mmHg)|
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|Figure 4: Effect of different doses of methanol (95% v/v) on heart rate (beats/min)|
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| Discussion|| |
Methanol poisoning has been known to mankind since long times. However, literatures reporting adverse cardiovascular effects of methanol poisoning are lacking.
The present study investigated the effect of methanol poisoning in rats administered at a different methanol concentration. In this study in rats, we observed a decrease in diastolic BP, systolic BP and mean ABP albeit at different concentration of methanol. In methanol poisoning, low BP (hypotension) and respiratory arrest have been reported.
Previously, hemodynamic effects of successive intravenous infusions of 20% methanol in anesthetized, mechanically ventilated dogs have been assessed against any spontaneous changes occurring during saline infusions.  About 130-200 mg/100 ml or higher blood methanol concentrations progressively decreased stroke volume and cardiac output, systemic BP and blood flow through femoral and common carotid arteries, while total peripheral resistance increased. Death by cardiac arrest was reported to occur at blood concentrations exceeding 400 mg/100 ml. 
In our study, we observed an overall decreasing tendency of systolic BP, diastolic BP and mean ABP with increasing concentrations of methanol though there were little fluctuations in BP. While, the heart rate remained consistently raised at all methanol dilution administered except the lowest concentration (9.5% v/v) where, surprisingly, a greater increase in heart rate was noted. Hence, this can be regarded as an outlier and ignored for making interpretation in this study. The increase in heart rate could be attributed to the compensatory mechanism for methanol induced hypotension, a major symptom of methanol poisoning. By increasing heart rate, the compensatory mechanism tries to compensate the lowering of BP. The higher increase in heart rate itself is an independent predictor of cardiovascular, noncardiovascular, and total mortality in some population, leading to death.  It was suggested that methanol poisoning potentially alters hemodynamic parameters, as previously, methanol overdose was reported to show changes in the electrocardiogram (ECG) wherein patient developed right bundle branch block in addition to left anterior fascicular block, paroxysmal atrial fibrillation and increased left ventricular end-diastolic and end-systolic dimensions. ,,, In another report by Hazra et al. reported that the regression of ECG changes coincided with clinical improvement and suggested that they were caused by methanol poisoning.  Cardiac contractility and cardiac output were also reported to be reduced and arterial vasodilation develops, which might contribute to hypotension ventricular arrhythmia is often observed. 
Acidosis has been a well-documented diagnosis during methanol intoxication, but it is unclear whether it is derived directly from formic acid or due to its secondary effects of inducing lactic acidosis.  Independent of the etiology of the acidosis, it has been widely reported that metabolic acidosis can lead to various adverse effects to the cardiovascular system. In one animal study with dogs, increased susceptibility of the heart to ventricular fibrillation was found during metabolic acidosis.  In another animal study with rats, the authors concluded that acidosis produced a marked decrease in heart rate and an increase in P-R interval with no apparent effect on the duration of the QRS complex. 
Methanol being a potent toxicant in humans has been reported to occur naturally at a low level in most alcoholic beverages without causing harm. However, illicit drinks made from "industrial methylated spirits" [5% (v/v) methanol: 95% (v/v) ethanol] was reported to cause severe and even fatal illness. No-adverse-effect level for methanol has been poorly documented and, therefore, from the public health perspective, what should be the maximum concentration of methanol in an alcoholic drink that an adult human could consume without risking toxicity due to its methanol content is not widely known. 
In 2001, Paine and Davan reported that if an adult takes 4 × 25-ml standard measures of a drink containing 40% alcohol by volume over a period of 2 h, the maximum tolerable concentration of methanol in such a drink should be 2% (v/v) by volume. However, they suggested that this value only allowed a safety factor of 4 to cover variation in the volume consumed and for the effects of malnutrition (i.e. folate deficiency), ill health and other personal factors (i.e. ethnicity). In contrast, according to the current European Union general limit, 0.4% (v/v) methanol at 40% alcohol was reported to provide a greater margin of safety. In our study, we observed a consistent rise in heart rate starting after administration of 19% methanol dilution in rats indicating that the concentration lower than 19% could correspond to the safety margin of 0.4-2% (v/v) in clinical settings. 
| Conclusion|| |
The present study is consistent with previous studies suggesting that methanol ingestion leads to severe hypotension as observed from decrease in diastolic BP, systolic BP, and mean ABP. However, severe increase of heart rate suggests activation of a compensatory mechanism to offset hypotension that eventually leads to death in methanol poisoning. Hence, this study emphasizes the need to monitor all the hemodynamic parameters in accidental methanol poisoning. As, the present study is just a preliminary research work, and therefore it warrants further study to better manage methanol poisoning in actual clinical scenarios.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]