stress is described as any combination of environmental conditions ( such as temperature , relative humidity , immobility , and solar radiation ) that will cause the temperature of the environment to be higher than the temperature range of the animal s temperature zone / thermal neutral zone .
temperatures above the thermal neutral zone initiate physiological , anatomical , and behavioral responses the aim of which are to increase heat loss and decrease heat production in trying to maintain the body s temperature within its normal range .
episodes of restraint stress for two hours caused great loss of willingness in rats to eat ( 3 ) .
there is evidence that shows decreased weight gain in broiler chicks that were raised under heat stress conditions ( 4 ) .
immobility stress has been shown to have negative effects on some blood parameters in mice ( 5 ) .
peppermint ( mentha piperita ) is a medicinal plant of the labiatae family , and it possibly originated in eastern asia .
peppermint has been used extensively in herbal medicines , and it s believed that peppermint is efficient in the immune system and in fighting secondary infections ( 6 ) .
peppermint has biological activities , such as anti - bacterial , anti - fungal , and anti - oxidant properties ( 6 ) .
it has been reported that mint genera have adverse effects on induction of oxidative stress ( 7 ) .
the dietary inclusion of peppermint oil had benefical effects on some blood biochemical parameters of mice under immobility stress ( 5 , 8) .
thus , the current study was conducted to determine the effect of different levels of peppermint extract on body weight and the blood s biochemical parameters in adult male wistar rats .
to prepare the peppermint extract , we collected fresh leaves of peppermint in jiroft city , kerman , iran .
the plants were kept by the department of pharmacy at shiraz university of medical sciences .
the peppermint was dried at 45 c for five days , and , then , it was ground into tiny particles of powder and homogenized in 96% ethanol at a ratio of 1 part peppermint plant to 10 parts of ethanol .
the mixture was left to saturate for four days at 25 c by occasional shaking and stirring .
then , the mixture was filtered through filter paper , and the filtrate was intensified at low pressure and 45 c to prepare a dark , gummy , green extract .
then , we dissolved the extract in tween 20 ( 10% , w / v ) .
this study was performed at islamic azad university , arsanjan branch , located in shiraz province , following the preparation of the peppermint extract , 50 adult , healthy , male wistar rats ( aged in 2.53 months , weighing 190210 g ) were obtained from the animal house unit for this experiment .
the wistar rats were raised in wire - bottom cages at 22  2 c and 5565% relative humidity .
we initiated a 12-hr light - dark cycle at least a week before the study began , and the rats were maintained under standard housing conditions with free access to a standard diet and water ad libitum .
we recorded their body weights at the beginning and end of the study to determine the changes in body weight that occurred during the tests .
the animals were allocated randomly into five groups : t1 ( control group , received 0.3 ml distilled water ) , t2 , t3 , t4 and t5 received peppermint extract 75 , 150 , 300 and 600 mg / kg respectively .
blood samples were collected and centrifuged ( at 2000 g for 10 min ) ; serum was obtained for the measurement of glucose , cholesterol , triglycerides , hdl , ldl , albumin , globulin , and total protein by spectrophotometer ( shimadzu uv-1700 ) using a pars azmoon commercial kit package ( pars azmoon , co. , tehran , iran ) .
we used standard commercial kits for analysis as recommended by the manufacturer of these kits .
statistical analyses of the data were done with sas software ( version sas 9.1.3 . ) .
the data were statistically analyzed with one - way analysis of variance ( anova ) done through dennett s multiple comparison post - test .
the results were presented as mean  standard error mean . a value of p < 0.05 was considered to be statistically significant .
to prepare the peppermint extract , we collected fresh leaves of peppermint in jiroft city , kerman , iran .
the plants were kept by the department of pharmacy at shiraz university of medical sciences .
the peppermint was dried at 45 c for five days , and , then , it was ground into tiny particles of powder and homogenized in 96% ethanol at a ratio of 1 part peppermint plant to 10 parts of ethanol .
the mixture was left to saturate for four days at 25 c by occasional shaking and stirring .
then , the mixture was filtered through filter paper , and the filtrate was intensified at low pressure and 45 c to prepare a dark , gummy , green extract .
then , we dissolved the extract in tween 20 ( 10% , w / v ) .
this study was performed at islamic azad university , arsanjan branch , located in shiraz province , following the preparation of the peppermint extract , 50 adult , healthy , male wistar rats ( aged in 2.53 months , weighing 190210 g ) were obtained from the animal house unit for this experiment .
the wistar rats were raised in wire - bottom cages at 22  2 c and 5565% relative humidity .
we initiated a 12-hr light - dark cycle at least a week before the study began , and the rats were maintained under standard housing conditions with free access to a standard diet and water ad libitum .
we recorded their body weights at the beginning and end of the study to determine the changes in body weight that occurred during the tests .
the animals were allocated randomly into five groups : t1 ( control group , received 0.3 ml distilled water ) , t2 , t3 , t4 and t5 received peppermint extract 75 , 150 , 300 and 600 mg / kg respectively .
blood samples were collected and centrifuged ( at 2000 g for 10 min ) ; serum was obtained for the measurement of glucose , cholesterol , triglycerides , hdl , ldl , albumin , globulin , and total protein by spectrophotometer ( shimadzu uv-1700 ) using a pars azmoon commercial kit package ( pars azmoon , co. , tehran , iran ) .
we used standard commercial kits for analysis as recommended by the manufacturer of these kits .
statistical analyses of the data were done with sas software ( version sas 9.1.3 . ) .
the data were statistically analyzed with one - way analysis of variance ( anova ) done through dennett s multiple comparison post - test .
the results were presented as mean  standard error mean . a value of p < 0.05 was considered to be statistically significant .
the results indicated that rats treated with peppermint produced higher body weights ( p < 0.05 ) than the control group .
there were significant differences among the experimental groups ; rats that received 300 and 600 mg / kg of peppermint extract produced greater gains in body weight than the other groups ( 235.23 g and 230.17 g vs. 226.05 g or 224.35 g and 319.81 g ) . however , the rats that were treated with peppermint in groups t2 and t3 had the greatest gains in body weight compared to the control group .
tables 2 and 3 show the effects of the peppermint extract on the blood parameters of wistar rats during high temperature .
the results showed that the different levels of peppermint extract did not have any significant effects on serum hdl , total protein , globulin , or albumin ( p > 0.05 ) .
the serum contents of cholesterol , triglycerides , ldl , and glucose were significantly lower in the rats in groups t3 ,
the peppermint extract at high levels had increased effects on the blood parameters ( t4 and t5 vs. t3 ) .
as the results indicated , the peppermint extract increased the body weight gain in wistar rats during exposure to high temperature .
as mentioned before , stress had negative impacts on appetite and reduced appetite may decrease gains in body weight ( 3 ) .
unfortunately , we could find no study in the literature that showed the effect of peppermint extract on body weight in rats reared under heat stress condition . in similar study , akbari and torki showed that adding peppermint oil had no significant effects on body weight gain in broiler chicks reared under heat stress condition ( 8) .
parallel to our findings , they reported that supplementing their diets with peppermint powder at levels of 4 gm / kg increased body weight gain in broiler chicks ( 9 ) .
there is evidence that shows that adding herbal plants stimulates appetite , the secretion of gastrointestinal fluids , and improves digestion and absorption , thereby producing gains in body weight ( 10 ) .
there is evidence that shows that high temperature can break the homeostasis of cecal microflora and cause damage to the intestinal mucosa and immune function in animals ; however , extracts also reduce potentially pathogenic bacteria and cause a shift in the composition of the gut s microflora towards more beneficial bacteria , making it possible to increase body weight ( 11 ) .
this increase may be due partly to the menthol activity of peppermint , because menthol is an appetite - enhancing substance . in this study
, peppermint extract did not have a significant impact on the serum content of hdl , total protein , globulin , or albumin .
the peppermint supplements had no significant effect on the serum content of hdl in broiler chicks ( 9 ) .
peppermint essential oil and chromium picolinate improved the serum content of albumin in heat - stressed broiler chicks ( 8) .
the absence of concurrence among these studies may be a result of the levels at which the extract was administered .
in addition , other variables , such as differences in background of the selected animals , the types of animals or genera and age , and the severity of the stress may have affected the efficacy of extract usage , and therefore it was difficult to directly assess different studies that used extracts . in this study , administering the peppermint extract at high levels decreased the serum content of ldl , triglycerides , and cholesterol in wistar rats that were kept at high temperature .
it seemed that peppermint had anti - lipidemic benefits , but it can not show this benefit at low levels .
. showed that peppermint extract decreased the serum contents of ldl , cholesterol , and triglycerides in wistar rats compared with the control group ( 12 ) .
in one human study , peppermint decreased the contents of serum ldl , cholesterol , and triglycerides in university students ( 13 ) .
the decrease of total cholesterol , ldl cholesterol , and total triglycerides of the treatment group might have been related to the involvement of the proposed components in the antioxidant and excess cholesterol protection mechanisms .
heat stress can induce the synthesis of free radicals , which can damage cell membranes by lipid peroxidation of polyunsaturated fatty acids in the cell membrane , thereby destroying the integrity of the membrane ( 14 ) .
the idea was confirmed by young et al . who showed that herbs and spices , along with vitamins c and e ( anti - oxidant vitamins ) were even more effective at preventing lipid peroxidation in the tissues of birds ( 15 ) .
there was a positive correlation between the total phenol concentration of herbal plants and human low - density lipoprotein oxidation in vitro ( 16 ) .
also , marjani et al . reported a decrease in the serum content of malondialdehyde ( end product of lipid oxidation ) in mice reared under immobility stress when fed a diet supplemented by peppermint oil ( from 0.90 to 60 mg / kg ) ( 5 ) .
we believe that the decrease in the serum content of cholesterol may be a result of inhibition of hmg - coa reductive activity , which is a key regulatory enzyme in cholesterol synthesis . in this study , rats supplemented with peppermint at high levels produced lower serum concentrations of glucose .
peppermint reduced the serum concentration of glucose in wistar albino rats compared with control group ( 17 ) .
peppermint and chromium picolinate decreased serum glucose in heat - stressed broiler chicks ( 8) .
the antioxidant roles found in peppermint tea may be responsible for hypoglycemic effects ( 18 ) .
there is a significant correlation between the serum content of glucose and the levels of lipids .
we believe peppermint extract may influence the insulin - sensitive cell receptors or binding activity .
it is well - known that insulin reduces lipolysis in adipocytes and prevents gluconeogenesis , thereby decreasing the serum contents of triglycerides and glucose .
this idea was confirmed by xie et al . who showed that cinnamaldehyde ( the active component of cinnamon essential oil ) increased the release of insulin ( 19 ) .
supplementation with peppermint extract was effective in improving body weight gain compared with the control group .
treatment by peppermint extract did not improve the serum content of hdl , total protein , globulin , or albumin .
the results also suggested that supplementation with peppermint extract can reduce the serum concentrations of cholesterol , triglycerides , ldl and glucose triglycerides , and glucose .
this study showed , for the first time , that peppermint extract is able to reduce the serum lipids or glucose and increase the body weight of wistar rats kept at high temperatures , thereby helping to protect the rats against the deleterious consequences of lipoperoxidation and potentially ensuring antioxidant potential .
 introductionpeppermint is an efficient medicinal plant for the treatment of diseases , and it also can be used to produce raw materials in the pharmaceutical industry . 
 the purpose of the current study was to evaluate the effects of various levels of peppermint alcoholic extract on body - weight gain and blood biochemical parameters in adult male wistar rats.methodsthis experiment was conducted using a completely randomized design ( crd ) . 
 fifty adult , healthy , male wistar rats ( ages of 2.53 months ; weights of 190210 g ) were allocated randomly into five groups . 
 t1 was the control group in which the rats received 0.3 ml of distilled water ) . 
 groups t2 , t3 , t4 , and t5 received 75 , 150 , 300 , and 600 mg / kg of peppermint extract , respectively . 
 the rats received daily pretreatment by oral gavages for 21 days . 
 we recorded body weights at the beginning and at the end of the study to determine the changes in the body weights . 
 blood samples were collected for the measurement of glucose , cholesterol , triglycerides , hdl , ldl , albumin , globulin , and total protein . 
 statistical analysis of the data was done by sas software . 
 the data statistically analyzed using one - way analysis of variance ( anova ) , which was conducted through dennett s multiple comparison post-test.resultsthe results indicated that the rats treated with peppermint gained more weight ( p < 0.05 ) and also decreased the serum concentrations of triglycerides , total cholesterol , ldl , and glucose in t3 , t4 and t5 than the other groups ( p < 0.05).conclusionpeppermint extract had a positive effect on body - weight gain and some blood parameters in adult male wistar rats . 
 the findings showed that peppermint is a crucial substance at high temperature , and future research should be focused on determining the details of the mechanisms involved in producing the observed effects of peppermint extract . 
1. Introduction
2. Material and Methods
2.1. Collection and Preparation of Hydroalcoholic Extract
2.2. Location and Animals
2.3. Biochemical analysis
2.4. Statistical analysis
3. Results
4. Discussion
5. Conclusions