Gender Differences in the Haematotoxicity and Weight Changes Associated with Exposure to Gasoline Vapours in Wistar Albino Rats
F Uboh, M Akpanabiatu, P Ebong, I Umoh
gasoline-vapours, gender-differences, growth-depression, haematotoxicity, weight-loss
F Uboh, M Akpanabiatu, P Ebong, I Umoh. Gender Differences in the Haematotoxicity and Weight Changes Associated with Exposure to Gasoline Vapours in Wistar Albino Rats. The Internet Journal of Toxicology. 2007 Volume 5 Number 2.
Gender differences in haematotoxicity and weight changes associated with exposure to gasoline vapours (6hrs/day for 20 weeks) in rats was assessed in this study. The results showed that the levels of Hb, PCV and RBC counts in both male and female rats reduced significantly, while the WBC count increased significantly (P<0.05) in female and insignificantly (P>0.05) in male rats, exposed to gasoline vapours. The comparative percentage decrease in Hb, PCV, RBC were significantly higher (P<0.05) in female rats than males. Also, the comparative percentage increase in WBC in females was significantly higher (P<0.05) than males. Moreover percentage weight increase was significantly higher in males and lower in females, while percentage growth rate decreased significantly (P<0.05) in both male and female rats exposed to gasoline. The results of this study showed that haematotoxicity and weight changes associated with exposure to gasoline vapours are sex-dependent; with females being more vulnerable.
Liquid gasoline is composed of approximately 150 different hydrocarbons including 60 -70% alkanes, 25 – 35% aromatics, and 5 – 10% alkenes 1 . The liquid gasoline may evaporates or be burnt to release vapours into the environment. These are ubiquitous in the environment and constitute some pollutants in the atmosphere. However, the overall constituents of gasoline fumes depend on the composition of the liquid gasoline, which varies with brand, and storage time 1 . Also, the relative proportion of individual chemical constituents in the liquid and vapour forms of gasoline differs substantially, with the more volatile components disproportionately represented in the vapour 2,3
According to Wixtrom and Brown 3 , the public is annually exposed to vapours from billions of gallons of unleaded gasoline (UG), and that the major route of exposure of workers to the gasoline fumes is by inhalation during the production and transportation of the UG, and of general public during refueling at service stations. Moreover, it has been reported that after inhalation of equal concentrations of petroleum vapour, lower concentrations of saturated hydrocarbons than unsaturated and aromatics are found in humans and animals blood 4 . Frequent exposures to gasoline vapours or any of the hazardous constituents (particularly benzene, hexane, tetraethyl lead and xylene) are reported to be haematotoxic 5,6 .
Also, according to Rothman
Anaemia is known to be one of the most dreadful diseases that is widely spread in the world. Causes range from malnutrition, infection, exposure to reactive chemical agents that can interact and destroy the blood cells or depress blood cells formation. Anaemic condition may be reliably assessed by measuring the levels of haematocrit, haemoglobin and red blood cells in circulation 11,12 . From these reports, it is understood that haemoglobin levels are age –, and sex – dependent. DeMaeyer
Materials And Methods
All animal experiments were carried out in strict compliance with the guidelines of the Institutional Animals Ethics Committee on the care and use of laboratory animals. Thirty two male and female adults
Exposure to Gasoline Vapours
A nose-inhalation exposure method earlier described 10,13,14 was modified and used in this study. In this modification, the cages housing the animals in the test groups were placed in 2.835m 3 exposure chambers (2 cages to one chamber), each with two open 1000 cm 3 calibrated beakers containing 500cm 3 of liquid gasoline. The gasoline was allowed to evaporate freely within the exposure chambers at ambient humidity and temperature, and the whole animals in the cages were exposed to the vapours (17.8 2.6 cm 3 hr -1 kg -1 m -3 day -1 ) generated from direct evaporation of the liquid gasoline. The exposure period of 6 hours (9.00 am to 3.00 pm) daily was adopted for 20 weeks. At the end of each day of exposure, the animals were transferred to gasoline vapour –free section of the experimental animal house.
During the exposure period, the initial and final volumes of the liquid gasoline were respectively noted before and after daily exposure. The daily differences in volume were used to estimate the relative concentrations of the vapour used in this exposure method.
The liquid gasoline (PMS blend) was obtained from Mobil Refueling Station, Marian Road, Calabar, Nigeria.
Collection and Analysis of Blood
At the end of the exposure period, blood samples were collected by cardiac puncture into heparinised sample bottles. The whole blood samples were used for the determination of the levels of haemoglobin, haematocrit, red blood cells and white blood cells counts. Haemoglobin and haematocrit levels were determined by the methods described by Alexander and Griffiths 15,16 . All absorbance readings for haemoglobin determinations were made using DREL 3000 HACH model spectrophotometer. The total red and white blood cells were counted by microscopic visual identification methods described by Dacie and Lewis 17 .
Determination of Weight increase and Growth rate
Total body weight of each rat was measured using a chemical balance, before and after the experimental period and recorded as initial and final body weight, (i.e., IBW and FBW, respectively). The mean body weight for each group was determined from the measured total body weights. Weight changes were expressed as percentage weight increase and percentage growth rate, where:
Percentage weight increase was calculated from the formula:
Percentage growth rate was calculated from the formula
Student's t-test was used to evaluate the significance of the differences between the mean values of the respective test groups and the control groups. A significant change was accepted at P<0.05.
Results And Discussion
The results of this study on the effect of exposure to gasoline vapour on some haematological indices (Hb, PCV, RBC and WBC) and total body weight in female and male
From Table 1, the Hb, PCV levels and RBC counts in the male rats exposed to gasoline vapour, i.e., male test rats (9.6 ± 0.6g/dl, 45.0 ± 0.6% and 6.55 x 10 6 ± 363.1 cells mm -3 , respectively) were significantly lower (P<0.05), while the WBC counts (5.059 x 10 3 ± 741.0 cells mm -3 ) was significantly higher (P<0.05), compared respectively with the Hb, PCV levels and RBC counts (12.3 ± 0.3g/dl , 48.0 ± 1.3% and 7.69 x 10 6 ± 261.2 cells mm 3 , respectively) and WBC counts (4.392 x 10 3 ± 551.0 cells mm -3 ) obtained for the male control rats. Also, the Hb, PCV levels and RBC counts in the female rats exposed to gasoline vapour, i.e., female test rats (9.5 ± 0.7g/dl, 41.8 ± 0.9% and 5.35 x 10 6 ± 456.2 cells mm -3 , respectively) decreased significantly (P<0.05), while the level of WBC (4.858 x 10 3 ± 611.4 cells mm -3 ) was increased significantly (P<0.05), compared with the Hb, PCV, RBC levels and WBC counts in the female control rats (12.5 ± 0.8g/dl, 45.7 ± 1.1%, 6.90 x 10 6 ± 193.5 cells mm -3 and 3.483 x 10 3 ± 879.3 cells mm -3 , respectively).
These results showed that the Hb, PCV levels and RBC counts decreased by 22.0±1.3, 6.3± 0.9 and 14.8± 1.5 percents, respectively in male rats, and by 24.2 ±2.1, 8.5± 1.2 and 22.5 ±1.8 percents, respectively in female rats; whereas WBC counts increased by 13.2±1.6 percents in male rats, and 28.3±2.3 percents in female rats, following exposure to gasoline vapour (figure 1). The decrease in the Hb, PCV levels and RBC counts, as well as the increase in WBC counts following exposure to gasoline vapour is observed to be sex-dependent, with the females being more vulnerable.
Table 2 shows the results of the effect of exposure to gasoline vapour on the total body weights of male and female
In this study, changes in the HB, PCV Level, RBC, WBC counts and total body weights, following exposure of male and female rats to gasoline vapour, were used to assess whether the haematotoxic and weight loss effects earlier reported for PMS in rats 10 , are sex-dependent. It is clear that UG composition is highly variable between manufacturers and over time 2 . Hence, the health risk associated with exposure to gasoline vapour may also vary with blend and storage period. Various health hazards associated with exposure to the vapours from different blends of gasoline used in the United States has been extensively studied 18,19,20 . For instance, API 91 – 01 blend of UG vapour has been reported to increase the incidence of liver tumours in a chronic bioassay in female mouse 20 . Also, inhalation of PS – 6 UG and MTBE blends has been reported to be hepatocarcinogenic in female mice, only at high dosage 18,20,21 . Moreso, the haematotoxic effect earlier reported in our study 10 , indicates that inhalation exposure to PMS blend of gasoline vapour may be a predisposing factor to anaemia.
Anaemia, one of the most widely spread diseases in the world, is known to has multifactorial causes 5,8,21,22,23,24 . It is generally known that iron, folate and vitamin B12 deficiencies, malnutrition and infections are the leading causes of anaemia 22,23 . However, our previous study indicated that the roles of chemical agents (such as composite constituents of kerosene and gasoline fumes) may be equally important in the causation of anaemia 10 . Also, d'Azevedo
The results of this study therefore showed that gasoline fumes contain such chemical agents which when inhaled in appreciable concentration can interact with specific tissues in the body and cause reduction in the Hb and PCV levels, RBC counts and total body weight; and increase in the WBC counts. These observation agree with the results reported for workers heavily exposed to benzene and rats exposed to benzene and xylene by inhalation 5,6,7,8 . According to these reports, benzene toxicity causes both bone marrow depression and leukaemogenesis, damaging multiple classes of haematopoietic cells and a variety of haematopoietic cells functions. Similar effect on weight increase has been reported for female mice 23 . Although the specific mechanism(s) through which gasoline vapours exhibits haematotoxic effect is (are) not clearly understood, it is believed that it may be as a result of bone marrow depression, with reduction in the rate of formation and development of erythrocytes committed stem cells as reported for benzene toxicity 8 , or increased destruction of the red blood cells, as reported for carbon disulphide toxicity 9 . The various constituents of the gasoline vapours might have been metabolized to various reactive species which can selectively interact with the red blood cells membrane proteins and damage the cells. Moreover, the increase in the WBC counts following exposure to gasoline vapours, observed in this study, may be one of the mechanisms devised to defend the body against the toxicity effects of the vapours constituents.
From the results of this study, it is interesting to observe that the haematotoxic effect, weight loss and growth depression associated with gasoline vapours are sex-dependent in rat, and that females are more vulnerable to the effects. The specific molecular mechanism(s) of this sex-dependent toxicity effects is (are) not clear. However, with reference to the result of our recent findings 14 , the interplay of the differences in the actions and functions of sex hormonal secretions may be assumed to be implicated. In conclusion, the female gender of rats is observed to be more susceptible to the haematotoxic effect, weight loss, and growth depression associated with exposure to gasoline vapours.