theanine ( n - ethyl--glutamine ) is a unique non - protein amino acid found in tea . theoretically , it has 2 chiral isomers , d- and l - theanine , and the biological activity of l - theanine is very high in vivo . l - theanine is an important bioactive component of tea , and has many physiological functions , such as regulating immune response , preventing diseases , anti - tumor , relaxing neural tension , and anti - oxidation stress . previous studies have shown that l - theanine can enhance innate immune function by regulating the secretion of immune cytokines . bukowski et al .   demonstrated that ingestion of l - theanine by drinking tea induces innate immune response and immunologic memory in humans . the explanation is that l - theanine can be degraded by glutaminase to glutamate and ethylamine in vivo , and the latter , as a non - peptide alkylamine antigen , can be subsequently recognized by the gamma delta t cells (  t cells ) in peripheral blood , and the primed  t cells further participate in a memory response . such priming also results in a non - memory response to whole bacteria and lipopolysaccharide , which is characterized by interleukin-12 ( il-12)-dependent secretion of interferon- ( ifn- ) by  t cells and their proliferation . further clinical studies   have found that oral administration of l - theanine enhances the activity of  t cells , promotes the secretion of ifn- , and further inhibits tumor activity . the possible mechanism could be that l - theanine metabolite - ethylamine induces the prenyl pyrophosphate accumulation by inhibiting the mevalonate pathway , and then promotes the proliferation of  t cells . wen et al .   demonstrated that adding 400 mg l - theanine / kg daily in the diet increases the level of secretory iga in the jejunum and the levels of il-2 and ifn- in the serum of baby chickens . hwang et al .   proposed that treatment of -glucan ( 400 mg / kg feed ) plus l - theanine ( 80 mg / kg feed ) in weaning piglets lessens the inflammatory responses against gram - negative bacterial infection via the inhibition of pro - inflammatory cytokines ( e.g. , ifn- and tnf-f ) hyperproduction and enhancement of anti - inflammatory cytokine ( il-10 ) production in vivo after lipopolysaccharide exposure , in a time - dependent manner . reported that oral administration of l - theanine and l - cysteine can increase igg level in the blood of mice . takagi et al .   showed out that combined administration of l - theanine and l - cystine before primary immunization enhances the serum antigen - specific igm and igg levels in 24-month - old mice , reduces the lung viral titers at day 6 , and increases the anti - influenza - virus igg antibody at day 10 after influenza virus infection in 13-month - old mice , and that the serum il-10/ifn- ratio is elevated in the spleens of mice . after being absorbed into the body , l - theanine can penetrate the blood - brain barrier and regulate the secretion of neurotransmitters of central nervous system cells   and levels of hormones such as corticosterone ( cort ) and adrenaline ( epi ) in the serum . .   demonstrated that l - theanine can increase levels of 5-hydroxytryptamine ( 5-ht ) and noradrenaline , and decrease levels of adrenocorticotropic hormone and cort in the hippocampus and prefrontal cortex of rats . .   found that l - theanine injection into the rat brain striatum increases the concentration of glycine and dopamine ( da ) in the perfusate by activating -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors . another study   has shown that when mother rats are fed l - theanine ad libitum , the concentrations of da , 5-ht , glycine and -amino butyric acid are increased in the 3-week - old infant rat brain , and the mrna level of nerve growth factor is increased in the cerebral cortex and hippocampus . reported that when young rats are provided water containing 0.3% l - theanine for 3 weeks after weaning and are subjected to water - immersion stress for 30 min , the serum cort level is less in l - theanine - treated rats than that in the control group , even after exposure to stress . takeda et al .   reported that when young rats are provided water containing 0.3% l - theanine after birth , the serum cort level is also markedly decreased . it has been reported that   oral administration of l - theanine decreases the levels of da , noradrenaline ( na ) , and cort , but increases 5-ht content in the brain cortex , hippocampus , and striatum of mice . hence , l - theanine has a regulatory function in the secretion of immune cytokines , neurotransmitters , and hormones . according to the amino acid sequence and molecular size , phospholipase c ( plc ) isozymes in the mammalian cells are divided into 4 main types : plc- , plc- , plc- , and plc -  . plc- is in charge of transmitting neuroendocrine signaling , and causes nerve impulses and the secretion of glands . the plc- is involved in the regulation of cell growth , proliferation , and differentiation by mediating the mitotic signals . recent studies   have suggested that the expression of plc can broadly reflect antioxidant capacity in vivo , and the activation of plc and protein kinase c ( pkc ) causes  t cells to react quickly against pathogen invasion , further regulating the immune function . activation of plc by l - theanine , hormones , and neurotransmitters combining with cell surface receptors induces cell proliferation , differentiation , secretion , and contraction . however , the role plc plays in the process of regulating cytokine secretion by l - theanine is unclear . in this study , based on the premise that l - theanine has the ability to regulate the secretion of immune cytokines , neurotransmitters , and hormones , we further hypothesized that l - theanine could improve the immunity and resistance to stress via the activation of plc subunits in rats . this experiment was therefore designed to determine the contents of immune cytokines , immunoglobulins , neurotransmitters , hormones , and mrna expression of related regulatory protein plc after the intragastric administration of 3 doses ( low , middle , and high ) of l - theanine solution for 2 weeks , to determine which dose of l - theanine has the best immunomodulatory effect and to explore the possible l - theanine - induced regulation mechanism in immune function in rats . this experiment was conducted according to the animal care guidelines of the animal care committee , institute of subtropical agriculture , the chinese academy of sciences , changsha city , hunan province , china ( no . l - theanine ( assay : 99.2% , chemical synthesis ) was purchased from hongya yaxing biotechnology co. , ltd ( meishan , sichuan , china ) . elisa kits for il-2 , il-4 , il-6 , il-10 , ifn- , adrenaline ( epi ) , cort , da , and 5-ht determination were purchased from huamei biotechnology co. , ltd ( wuhan , hubei , china ) . thirty - two male and 32 female sprague dawley rats ( sd rats , 3 weeks old ) weighing 7492.2 g were purchased from hunan slack jingda laboratory animal co. , ltd ( changsha , hunan , china ) . the animals were individually housed in plastic cages on the floor under laboratory conditions ( 253c , 705% relative humidity , good ventilation , and a 12-h light / dark cycle ) , and had free access to food and pure water . the sd rats were acclimated for 3 days , then l - theanine was administered during fasting ( 15:0017:00 h ) via gastric intubation . during the whole experiment , the rats were examined for any abnormalities suggestive of health problems , and their body weights ( bw ) were recorded every day to determine the average daily gain ( adg ) for each group . the rats were randomly assigned into 4 groups with 16 rats ( 8 males and 8 females ) each . the control rats ( con ) received gastric perfusion of 1 ml of 0.9% nacl solution once per day . the rats in the other groups  low - dose l - theanine administration ( lt ) , middle - dose l - theanine administration ( mt ) , and high - dose l - theanine administration ( ht )  received gastric perfusion of 3 different doses of l - theanine ( 50 , 200 , and 400 mg / kg bw / day , respectively ) pre - dissolved in 0.9% nacl solution , and each rat was administered 1 ml of the solution once per day for 14 days . on completion of the treatment , rats were fasted overnight , then were placed in a sealed specimen jar with ether anesthesia for 4 min , and then the samples were collected . blood was collected from the jugular vein by the standard procedure into blood collection tubes with potassium edta anticoagulant . then the blood samples were centrifuged at 3500 rpm for 15 min at 4c , and the serum samples were stored at 80c until assay . after flushing out the blood with 0.9% saline , the brains were removed and fractionated into the hypothalamus , pituitary , and hippocampus under ice - cold conditions . at the same time , the heart , liver , spleen , kidney , and thymus were quickly collected and their weights were recorded to calculate the organ index ( oi : the ratio of organ weight to body weight , g / kg ) . the tissue samples were homogenized , the homogenates were centrifuged at 3500 rpm / min for 10 min at 4c , and the supernatants were subjected to further measurement . il-2 , il-4 , il-6 , il-10 , ifn- , epi , and cort were assayed in the serum ; il-2 , il-4 , il-6 , and ifn- were assayed in the spleen ; and da and 5-ht were assayed in the hypothalamus , pituitary , and hippocampus . the profiles in the serum and tissue samples were determined according to the protocols of the respective elisa kits . the serum igm and igg were determined by automatic biochemistry analyzer ( synchron clinical system cx4 pro , beckman coulter , usa ) according to the instructions . total rna was isolated with the ezna rna - solv reagent ( omega bio - tek , norcross , ga , usa ) and cdna synthesis was performed using the revert aid first strand cdna synthesis kit ( applied biosystems , thermo fisher scientific , usa ) . for relative quantification of gene expression , the abi prism 7900 ht fast real - time pcr system ( applied biosystems , foster , ca ) was used . primers were designed using the primer 3 plus program , and sequences are listed in table 1 . the reaction system contained 5 l sybr 
 premix ex taq ( 2 ) , 0.2 l pcr forward primer ( 10 m ) , 0.2 l pcr reverse primer ( 10 m ) , 0.2 l rox reference dye ( 50 ) , 1.0 l cdna , and 3.4 l sterilized ddh2o . the thermal profile for all reactions was 30 s at 95c , then 40 cycles of denaturation at 95c for 5 s and annealing at 60c for 30 s. at the end of each cycle , fluorescence monitoring was performed for 15 s. each reaction was completed with a melting curve analysis to ensure the specificity of the reaction . all the samples were analyzed in duplicate , and the relative amount of each specific transcript was obtained after normalization against the endogenous control -actin . statistical analyses were conducted by one - way analysis of variance ( anova ) using the mixed proc of sas ( version 8.2 , sas institute , cary , nc , usa ) . the main effect tested was the dose of l - theanine . when indicated by anova , means were separated using least significant differences . l - theanine ( assay : 99.2% , chemical synthesis ) was purchased from hongya yaxing biotechnology co. , ltd ( meishan , sichuan , china ) . elisa kits for il-2 , il-4 , il-6 , il-10 , ifn- , adrenaline ( epi ) , cort , da , and 5-ht determination were purchased from huamei biotechnology co. , ltd ( wuhan , hubei , china ) . thirty - two male and 32 female sprague dawley rats ( sd rats , 3 weeks old ) weighing 7492.2 g were purchased from hunan slack jingda laboratory animal co. , ltd ( changsha , hunan , china ) . the animals were individually housed in plastic cages on the floor under laboratory conditions ( 253c , 705% relative humidity , good ventilation , and a 12-h light / dark cycle ) , and had free access to food and pure water . the sd rats were acclimated for 3 days , then l - theanine was administered during fasting ( 15:0017:00 h ) via gastric intubation . during the whole experiment , the rats were examined for any abnormalities suggestive of health problems , and their body weights ( bw ) were recorded every day to determine the average daily gain ( adg ) for each group . the rats were randomly assigned into 4 groups with 16 rats ( 8 males and 8 females ) each . the control rats ( con ) received gastric perfusion of 1 ml of 0.9% nacl solution once per day . the rats in the other groups  low - dose l - theanine administration ( lt ) , middle - dose l - theanine administration ( mt ) , and high - dose l - theanine administration ( ht )  received gastric perfusion of 3 different doses of l - theanine ( 50 , 200 , and 400 mg / kg bw / day , respectively ) pre - dissolved in 0.9% nacl solution , and each rat was administered 1 ml of the solution once per day for 14 days . on completion of the treatment , rats were fasted overnight , then were placed in a sealed specimen jar with ether anesthesia for 4 min , and then the samples were collected . blood was collected from the jugular vein by the standard procedure into blood collection tubes with potassium edta anticoagulant . then the blood samples were centrifuged at 3500 rpm for 15 min at 4c , and the serum samples were stored at 80c until assay . after flushing out the blood with 0.9% saline , the brains were removed and fractionated into the hypothalamus , pituitary , and hippocampus under ice - cold conditions . at the same time , the heart , liver , spleen , kidney , and thymus were quickly collected and their weights were recorded to calculate the organ index ( oi : the ratio of organ weight to body weight , g / kg ) . the tissue samples were homogenized , the homogenates were centrifuged at 3500 rpm / min for 10 min at 4c , and the supernatants were subjected to further measurement . il-2 , il-4 , il-6 , il-10 , ifn- , epi , and cort were assayed in the serum ; il-2 , il-4 , il-6 , and ifn- were assayed in the spleen ; and da and 5-ht were assayed in the hypothalamus , pituitary , and hippocampus . the profiles in the serum and tissue samples were determined according to the protocols of the respective elisa kits . the serum igm and igg were determined by automatic biochemistry analyzer ( synchron clinical system cx4 pro , beckman coulter , usa ) according to the instructions . total rna was isolated with the ezna rna - solv reagent ( omega bio - tek , norcross , ga , usa ) and cdna synthesis was performed using the revert aid first strand cdna synthesis kit ( applied biosystems , thermo fisher scientific , usa ) . for relative quantification of gene expression , the abi prism 7900 ht fast real - time pcr system ( applied biosystems , foster , ca ) was used . primers were designed using the primer 3 plus program , and sequences are listed in table 1 . the reaction system contained 5 l sybr 
 premix ex taq ( 2 ) , 0.2 l pcr forward primer ( 10 m ) , 0.2 l pcr reverse primer ( 10 m ) , 0.2 l rox reference dye ( 50 ) , 1.0 l cdna , and 3.4 l sterilized ddh2o . the thermal profile for all reactions was 30 s at 95c , then 40 cycles of denaturation at 95c for 5 s and annealing at 60c for 30 s. at the end of each cycle , fluorescence monitoring was performed for 15 s. each reaction was completed with a melting curve analysis to ensure the specificity of the reaction . all the samples were analyzed in duplicate , and the relative amount of each specific transcript was obtained after normalization against the endogenous control -actin . statistical analyses were conducted by one - way analysis of variance ( anova ) using the mixed proc of sas ( version 8.2 , sas institute , cary , nc , usa ) . the main effect tested was the dose of l - theanine . when indicated by anova , means were separated using least significant differences . as illustrated in table 2 , splenic oi of the treatment groups increased ( linear , p<0.001 ; quadratic , p<0.001 ) with the doses of l - theanine . there were no differences ( p>0.05 ) in the oi of liver , heart , kidney , thymus , and adg among the 4 groups . as shown in table 3 , the content of il-4 in the serum linearly decreased ( p<0.001 ) with the increasing doses of l - theanine . the administration of l - theanine linearly decreased the contents of il-6 ( p<0.001 ) and il-10 ( p=0.01 ) in the serum with the incremental doses of l - theanine . the ratio of il-4 to ifn- in the serum was also linearly decreased ( p<0.001 ) with the increasing doses of l - theanine . igm level in the mt group was higher ( p=0.034 ) than that in the lt group . there were no differences ( p>0.05 ) in the serum il-2 , ifn- , igg , and splenic ifn- , il-2 , il-4 , and ratio of il-4 to ifn- among the 4 groups . as depicted in table 4 , the da content was increased in the pituitary ( linear and quadratic , p<0.001 ) and hippocampus ( linear , p<0.001 ) with the increasing doses of l - theanine , with the highest values found in the mt and ht groups , respectively . the 5-ht content was elevated in the pituitary ( quadratic , p=0.005 ) and hippocampus ( linear , p=0.003 ) with the increasing levels of l - theanine , with the highest values in the mt and ht groups , respectively . however , in the hypothalamus , the 5-ht content decreased ( linear , p=0.002 ) with the inclusive levels of l - theanine , and the lowest value was found in the ht group . there were no differences ( p>0.05 ) in the hypothalamus among the 4 groups . serum epi content increased ( linear , p=0.007 ) but serum cort content decreased ( linear , p=0.013 ; quadratic , p<0.001 ) with the increasing doses of l - theanine ; the highest and lowest values were in the ht and mt groups , respectively . the mrna expression of plc subtypes ( plc-1 , plc-1 , and plc-1 ) in the liver , spleen , and heart are given in table 5 . l - theanine administration decreased the mrna expression of plc-1 ( quadratic , p=0.002 ) and plc-1 ( linear , p=0.007 ; quadratic , p=0.010 ) in the rat livers . however , there were no differences ( p>0.05 ) in the plc-1 in rat livers among the 4 groups . the administration of l - theanine also depressed mrna expression of plc-1 ( linear and quadratic , p<0.001 ) and plc-1 ( linear , p<0.0001 ) in the rat spleens . however , the mrna expression of splenic plc-1 was up - regulated ( p=0.038 ) in the lt group compared with the con group . in the heart , the administration of l - theanine stimulated the mrna expression of plc-1 ( linear , p<0.0001 ) , plc-1 ( linear , p<0.0001 ; quadratic , p=0.015 ) , and plc-1 ( linear , p<0.0001 ; quadratic , p=0.002 ) , and were the highest in the ht group . as illustrated in table 2 , splenic oi of the treatment groups increased ( linear , p<0.001 ; quadratic , p<0.001 ) with the doses of l - theanine . there were no differences ( p>0.05 ) in the oi of liver , heart , kidney , thymus , and adg among the 4 groups . as shown in table 3 , the content of il-4 in the serum linearly decreased ( p<0.001 ) with the increasing doses of l - theanine . the administration of l - theanine linearly decreased the contents of il-6 ( p<0.001 ) and il-10 ( p=0.01 ) in the serum with the incremental doses of l - theanine . the ratio of il-4 to ifn- in the serum was also linearly decreased ( p<0.001 ) with the increasing doses of l - theanine . igm level in the mt group was higher ( p=0.034 ) than that in the lt group . there were no differences ( p>0.05 ) in the serum il-2 , ifn- , igg , and splenic ifn- , il-2 , il-4 , and ratio of il-4 to ifn- among the 4 groups . as depicted in table 4 , the da content was increased in the pituitary ( linear and quadratic , p<0.001 ) and hippocampus ( linear , p<0.001 ) with the increasing doses of l - theanine , with the highest values found in the mt and ht groups , respectively . the 5-ht content was elevated in the pituitary ( quadratic , p=0.005 ) and hippocampus ( linear , p=0.003 ) with the increasing levels of l - theanine , with the highest values in the mt and ht groups , respectively . however , in the hypothalamus , the 5-ht content decreased ( linear , p=0.002 ) with the inclusive levels of l - theanine , and the lowest value was found in the ht group . serum epi content increased ( linear , p=0.007 ) but serum cort content decreased ( linear , p=0.013 ; quadratic , p<0.001 ) with the increasing doses of l - theanine ; the highest and lowest values were in the ht and mt groups , respectively . the mrna expression of plc subtypes ( plc-1 , plc-1 , and plc-1 ) in the liver , spleen , and heart are given in table 5 . l - theanine administration decreased the mrna expression of plc-1 ( quadratic , p=0.002 ) and plc-1 ( linear , p=0.007 ; quadratic , p=0.010 ) in the rat livers . however , there were no differences ( p>0.05 ) in the plc-1 in rat livers among the 4 groups . the administration of l - theanine also depressed mrna expression of plc-1 ( linear and quadratic , p<0.001 ) and plc-1 ( linear , p<0.0001 ) in the rat spleens . however , the mrna expression of splenic plc-1 was up - regulated ( p=0.038 ) in the lt group compared with the con group . in the heart , the administration of l - theanine stimulated the mrna expression of plc-1 ( linear , p<0.0001 ) , plc-1 ( linear , p<0.0001 ; quadratic , p=0.015 ) , and plc-1 ( linear , p<0.0001 ; quadratic , p=0.002 ) , and were the highest in the ht group . in the current study , we found that the intragastric administration of l - theanine only caused a linear increase of splenic oi in the rats , while other organ indices were not affected , indicating that l - theanine administration increased the splenic weight . because the spleen is an important immune system organ , we thus inferred that l - theanine probably had the potential to further improve the immune function of rats . in the immune system , cytokines are important regulatory molecules . specifically , il-4 stimulates and activates b lymphocytes , promotes the proliferation and differentiation of t lymphocytes , and thereby regulates humoral immunity . il-10 can inhibit the activation of t lymphocytes and nk cells activity and subsequently decrease cytokines secretion ( e.g. , il-2 and ifn- ) , finally suppressing cellular immune response . ifn- promotes b lymphocytes to secrete igg , while it inhibits the secretion of il-4-induced igg and ige . in our study , the ifn- level in the serum of the ht group was increased compared to the mt group . l - theanine administration resulted in linear decrease in il-4 , il-6 , and il-10 in the serum . these results indicate that l - theanine can alleviate the inflammatory response to gram - negative bacteria infection and regulate il-4- , il-6- , and il-10-mediated humoral immune response . hwang et al .   reported that weaning piglets administered l - theanine ( 80 mg / kg feed ) did not show differences in the levels of ifn- and il-10 in vivo regardless of lps treatment . reported that delivering 190 mg of l - theanine per day in humans increased the capacity of  t cells to secrete ifn- by up to 15-fold in response to challenge with ethylamine or dead bacteria . the differences between our study and previous studies appear to be due to the animal species and the dosage of l - theanine administered . in healthy mammals the ratio of t - helper lymphocytes th2/th1 is kept in balance , which is characterized by il-4/ifn- . under the impacts of various antigens , cytokines , antigen - presenting cells , and other factors , the th2/th1 balance might be upset , shifting towards the conversion of th1 or th2 status , termed th1 or th2 drift . as a result , the immune homeostasis of cytokines networks is damaged , causing further changes in immune status , as well as the emergence and development of many diseases . in our study , we found that the intragastric administration of l - theanine dramatically reduced the ratio of th2/th1 in the serum of the rats and led to a shift in the th2/th1 balance towards th1 , enhancing resistance to pathogens . in which the serum th2/th1 ratio was decreased by l - theanine administration at 6 h and 24 h , respectively , after antigenic stimulation in mice . neuroendocrine - immune network - related studies   have confirmed that the neuro - endocrine system and the immune system can share cytokines , hormones , and neurotransmitters and generate extensive and close contact . hormones secreted by the neuroendocrine system can regulate immune function , and immune response can also change the of neuroendocrine system . the results of this study showed that after intragastric administration of l - theanine to the rats for 2 weeks continuously , the secretion levels of da and 5-ht were elevated to some extent in the pituitary and hippocampus . these results further validated findings of a previous report in which peng et al . demonstrated that the gastric perfusion of 20 and 100 mg / kg l - theanine both increased the content of 5-ht in the hippocampus and prefrontal cortex of rats . reported that da and 5-ht were significantly increased in the brain tissues of one - week - old rats whose mothers had been fed 2% l - theanine in water ad libitum while pregnant . in addition , we noted that the serum cort content decreased with low - dose and middle - dose administration of l - theanine . this result was in agreement with previous reports in which weanling rats   or their dams   fed 0.3% l - theanine in water for 3 weeks had lower cort level in the serum of the weanling rats . however , our results are not consistent with the findings of yamada et al . , who reported that oral l - theanine administered at 4 g / kg bw / day increased the cort concentration in the blood of rats ( bw , 60280 g ; 78 weeks old ) . in our opinion , this discrepancy can be ascribed to the different l - theanine doses , route of administration , and growth stage of experimental rats . therefore , our results suggest that l - theanine can promote the secretion of monoamine neurotransmitters ( da and 5-ht ) in the pituitary and hippocampus , and change cort secretion in serum of rats . further research is needed to explore the effect of l - theanine on interactions between neuroendocrine and immune systems . in this study , l - theanine decreased the mrna expression of plc-1 , plc-1 , and plc-1 in the liver and plc-1 and plc-1 in the spleen in a dose - dependent manner . the results indicate that l - theanine inhibited the plc - signal pathway in liver and spleen . in the spleen , 50 mg / kg l - theanine administration stimulated the plc-1 gene expression . because the spleen is where b and t lymphocytes aggregated , we inferred that l - theanine might promote the proliferation and differentiation of lymphocytes by upregulating plc-1 gene expression . our current results showed that l - theanine administration increased the mrna expressions of plc-1 and plc-1 in a dose - dependent manner in the heart . because plc-1 is involved in the regulation of the cell cycle , plc-1 protein coded by the plc-1 gene played important roles in the regulation of ca homeostasis and preventing injury to cardiomyocytes , we inferred that l - theanine could promote the growth of cardiomyocytes and protect the heart . plc-1 expression was also increased in the rat hearts , indicating that the plc-1 gene might be involved in protection of cardiomyocytes . in our study , the expressions of plc isomers were different in liver , spleen , and heart , indicating that l - theanine has tissue - specific biological effects in rats and that l - theanine administration regulates the plc - related pathway . the relationship between plc isomers and cytokine secretion regulated by l - theanine has not been investigated ; therefore , there is a topic needing further investigation . intragastric administration of 400 mg / kg l - theanine for 2 weeks improved immune function and resistance to stress in rats by increasing the splenic weight , elevating the secretion of ifn- in the serum and da and 5-ht in the pituitary and hippocampus , altering the balance of th2/th1 , inhibiting the cort level in the serum , and up - regulating the mrna expression of plc in the heart .
backgroundthis study aimed to investigate the regulatory effects of l - theanine on secretion of immune cytokines , hormones , and neurotransmitters , and mrna expression of phospholipase c ( plc ) in rats , and to explore its regulatory mechanism in immune function.material/methodssixty-four sprague - dawley rats received daily intragastric infusion of different doses of l - theanine solution [ 0 , 50 ( lt ) , 200 ( mt ) , and 400 ( ht ) mg / kg bw ] . 
 cytokines , immunoglobulins , and hormones in the serum , neurotransmitters , and mrna expression of plc in the relevant tissues were assayed.resultsl-theanine administration increased the splenic organ index and decreased the contents of ils-4/6/10 and the ratio of il-4/ifn- in the serum . 
 high - dose l - theanine administration increased the levels of dopamine and 5-hydroxytryptamine in the pituitary and hippocampus , resulting in decrease in corticosterone level in the serum . 
 l - theanine administration decreased the mrna expressions of plc isomers in the liver and plc-1 and plc-1 in the spleen . 
 interestingly , mrna expressions of plc-f1 in the spleen and plc isomers mrna in the heart were up - regulated by l - theanine administration.conclusionsadministration of 400 mg / kg bwl - theanine improved immune function of the rats by increasing the splenic weight , altering the th2/th1 cytokine balance , decreasing the corticosterone level in the serum , elevating dopamine and 5-hydroxytryptamine in the brain , and regulating the mrna expression of plc isomers in the heart .