Organophosphates are widely used as agricultural pesticides after
organochlorine pesticides were forbidden. Many toxic organophosphates
persist in the environment and tend to accumulate in the body fat of animals
occupying a higher trophic level (Wang et al., 2005). The potential
risks to humans resulting from the usage of a pesticide must be carefully
assessed before the product is registered. One of the components in the
risk assessment is the determination of the amount of pesticide to which
the applicator is exposed. Traditional methods estimated dermal exposure
by measuring the amount of pesticide deposited on absorbent patches worn
on the applicator`s body (Franklin, 1984). A detailed laboratory toxicity
study on laboratory mice was conducted as part of a comprehensive laboratory
and field study to field validate laboratory-based risk assessment of
pesticides (Meyers and Wolff, 1994).
Globally, the prevalence of chronic, non-communicable diseases is
increasing at an alarming rate. About 18 million people die every
year from cardiovascular disease, for which diabetes and hypertension
are major predisposing factors (Hossain et al., 2007). There are
several opposing data on the effect of organophosphate pesticides on blood
glucose levels. For instance, blood glucose increased in rats treated
with a single ip dose of 650 mg kg-1 of malathion (Rodrigues
et al., 1986).
Based on the observations on increased agricultural applications of these
chemicals in one hand and the increased metabolic disease in the globe
in another, a detailed set of experimental studies are suggested to find
a possible correlation between them.
This study was designed to investigate the effect of two selected organophosphate
insecticides, malathion (MLT) and azynphos methyl (AZP), on blood glucose
levels in fasting and postprandial conditions in the mouse as an experimental
MATERIALS AND METHODS
This study was performed in the year 2007 in Urmia University, Faculty
of Veterinary Medicine, Urmia, Iran.
Animals: Forty-two adult, male mice (20-25 g b.wt.) were used
in this study. They were fed with commercial chow and tap water ad
lib and kept at room temperature with 12 h artificial light in 24
Experimental protocol: Animals were divided into 7 groups of
6 each. Once daily for 7 successive days, they were exposed by their entire
tail for 10 sec to either of the following solutions: Water (control),
AZP 0.1%, AZP 1%, AZP 10%, MLT 0.1%, MLT 1%, or MLT 10%. Animals were
kept fasting on the nights on days 0, 3 and 7. Blood glucose was measured
on days 1, 4 and 8 once before feeding the animals and once again 60 min
after pesticide exposure and feeding the animals (no exposure to chemicals
on day 8 was done). For this, a light general anesthesia was induced by
inhalation of diethyl ether. Thereafter, the end point of the tail was
incised and a drop of blood was obtained. Blood was transferred onto the
strips of a hand glucometer (Bionime RightestTM GM 300, Bionime
GmbH, Switzerland). The level of glucose was determined with a sensitivity
of 1 mg dL-1.
Chemicals: Chemicals used were malathion (Ghazal Company, Tehran,
Iran), azynphos methyl (Bayer AG, Leverkeusen, Germany) and Diethyle ether
(Merck, Darmstadt, Germany).
Statistics: Data are presented as means±SEM. Differences
between groups were analyzed using one-way ANOVA and when p<0.05, data
were compared group by group with Bonferroni`s t-test (a post-ANOVA test).
A p-value smaller than 0.05 was considered to reflect a statistically
RESULTS AND DISCUSSION
There was no significant difference in the weight gain during the
study between control and treated animals, eliminating a considerable
effect on general health of the animals after exposure to the chemicals.
However, all animals treated with AZP 10% died within 24 h after the first
treatment whereas all other groups survived during the experimental work.
For this reason, the results of 10% concentration of the chemicals were
omitted in this study.
In control animals, the fasting blood glucose levels were 68.17±5.57,
115±6.54 and 95±4.87 mg dL-1 on days 1, 4 and
8, respectively. After feeding the animals, those values increased to
168.33±5.57, 170.67±9.12 and 156.33±14.55 mg dL-1.
The increase reached to the level of statistical significance in all cases
Neither AZP (Fig. 1A) nor MLT (Fig. 1C)
affected the fasting blood glucose in the animals at the concentrations
that were used. AZP-treated animals showed some decreased postprandial
glucose levels, which did not reach the level of significance (Fig.
1B). On day 1, MLT 1% prevented the increased postprandial glucose
levels (p<0.001). In the control animals it was 168.33±5.57
and in the treated animals it was declined to 113.17±11.94. This
effect persisted on day 4, however, it was not significant. The effect
was almost abolished on day 8 (Fig. 1D).
Present findings showed that AZP and MLT did not affect the fasting,
basal glucose levels in the mouse. However, there was a tendency to a
lower glucose levels after feeding the animals that were treated with
In the literature, there is a limited number of reports on the effect
of organophosphate compounds on glucose levels. For instance, blood glucose
was reported to increase in rats treated with a single ip dose of 650
mg kg-1 of MLT (Rodrigues et al., 1986). The effect
of a single oral dose of MLT (1 g kg-1 b.wt.) on the
||Fasting (A and C) and postprandial (B and D) blood glucose
levels in the mouse after exposure to AZP (A and B) or MLT (C and
D) at concentrations of 0% (),
or 1% ().
In all cases (except AZP 0.01% and MLT 1%), the postprandial glucose
levels were significantly higher than the fasting levels (p<0.05)
digestive and absorptive functions of the intestinal epithelium has been
investigated in rats. The absorption of glucose was considerably reduced
(35%) in pesticide fed animals (Chowdhury et al., 1980). In addition,
an early study suggested that intraventricular injection of MLT may cause
hyperglycemia, the mechanism of which was stipulated to be the accumulation
of Acetylcholine (Ramu and Korner, 1975). MLT was administered orally
for 4 weeks in the rat. Administration of malathion at doses of 100, 200
and 400 ppm increased plasma glucose concentrations by 25, 17 and 14%
of control, respectively (Abdollahi et al., 2004).
Although dermal LD 50 values for various organophosphate insecticides
have been determined in mice by application of solutions to hind feet
(Skinner and Kilgore, 1982) no study has been accomplished on the effect
of these substances on blood glucose levels using dermal application.
In fact, while people are exposed to organophosphate agents mostly through
dermal route, this kind of studies are neglected by most researchers all
over the world.
One of the reasons that could explain the difference between our findings
and those of the others is the chronic form of the exposure in this study.
Indeed, MLT had no effect on blood glucose levels when administered intragastrically
by stomach tube daily for 32 days (Rezg et al., 2006).
In conclusion, the current research work is the first one on the effect
of organophosphate pesticides on blood glucose after dermal application.
This route resembles what happens to people involved in the agricultural
and occupational exposure to pesticides in practice. The novel findings
is that these chemicals may prevent the postprandial blood glucose increase
which may be a positive impact in diabetics whereas it could be considered
a negative impact in healthy subjects.