Impact of endocrine disruptors on ovarian steroidogenesis.

Production of steroid hormones by the ovary plays a key role in the female phenotype maintenance, as well as is critical for regular ovarian processes, including follicle growth, oocyte maturation and ovulation. Thus, optimal ovarian steroid synthesis is an indispensable requisite for the female reproductive health. In the past decades, along with an increased incidence of female reproductive disorders, an increasing concern for the potential reproductive impact of exogenous factors, particularly of environmental pollutants with endocrine disrupting properties, has risen. The scientific studies report that ovarian steroid hormone production is being recognized as an important target for the action of endocrine disrupting chemicals (EDCs). The fact that these chemicals have been detected in the biological samples of general population, and even directly in the follicular fluid of women, emphasizes the demands for testing the influence of EDCs on ovarian steroidogenesis. For these purposes, different methodological approaches have been employed, from in vivo studies on female rodents to in vitro experimental procedures using steroidogenically active follicular cells. In the present review, the effects of selected EDCs (pesticides, phthalate and phenol derivatives, and halogenated arylhydrocarbons) on the processes of ovarian steroidogenesis are summarized, and possible mechanisms of action of these agents are outlined.

Bisphenol A alone or in combination with estradiol modulates cell cycle- and apoptosis-related proteins and genes in MCF7 cells.

OBJECTIVE: Bisphenol A (BPA) with its estrogenic properties is intensively studied since its presence in the environment and human body. Besides other adverse effects, the compound is suspected of contributing to hormone-related cancers. The present study was aimed to investigate short time (24 h) effects of BPA on the important genes/proteins involved in apoptosis and the cell cycle progression in the breast cancer cells MCF7. The experimental design covered cell treatment with a broad BPA concentration scale: 10-12M corresponding to ubiquitous exposure, 10-9M relevant to human levels, and 10-6M as experimentally usual. We further investigated the combined effects of low BPA dose (10-12M) with physiological concentration of estradiol (E2) (10-9M). METHODS: The expression of particular proteins and genes was studied by Western blotting and real time RT-PCR, respectively. RESULTS: Estrogenic effect of BPA was confirmed in the following checkpoints: mRNA expression of estrogen receptor α, expression of cyclin D1 and A2 proteins and CCNA2 gene, Bax and Bcl2 protein levels. For both cyclins protein levels, the maximum stimulation was present at 10-9M BPA and the effects resembled the "inverted U"-shape, a nonmonotonic dose-response curve reported for the action of xenoestrogens. The combined effect of low BPA dose with physiological E2 concentration differ from those of individual compounds, the character of stimulatory response is neither additive nor synergistic. CONCLUSIONS: The results obtained strongly support the evidence of BPA and BPA+E2 proliferation-promoting effects in human breast carcinoma cells, even after short time exposure, partially via reduced rate of apoptosis by the action of BPA+E2.

Effects of 4-nonylphenol and/or diisononylphthalate on THP-1 cells: impact of endocrine disruptors on human immune system parameters.

The aim of the present work is to investigate the link between two endocrine disruptor compounds (EDCs), which are chemicals that interfere with the hormone system in human and wildlife, and the human immune response through a study of their effects on the THP-1 human cell line which was used as a model for macrophages. We used two EDCs, diisononylphthalate (DiP) and 4-n-nonylphenol (NP) alone or in combination in order to evaluate the effects of these compounds on several parameters of the immune response - cytokine secretion, phagocytosis and the putative implication of the estrogen receptors - by studying the level of MAPK activation. NP and DiP strongly reduced phagocytosis and modify cytokine secretions. Indeed, differentiated THP-1 cell exposures (i) to 5 and 10 microM of combination of NP and DiP induced an IL-8 level in the medium respectively of 28.9 and 45 percent higher than the level obtained for the control (untreated cells), (ii) to combination of NP and DiP at 10 microM induced an increase of IL-1ß level in comparison to the control level, (iii) to combination of NP and DiP induced an increase of TNF-α level whatever the concentration of EDCs tested (between 0 and 10 microM). Lastly, differentiated THP-1 cell exposure to NP, DiP alone or in combination (2 microM for each condition) induced a decrease of ERK1/2 phosphorylation in comparison to ERK1/2 phosphorylation level of the control. Moreover, differentiated THP-1 cell treatments by ICI-182780 (an estrogen receptor antagonist) supressed the EDC effects on ERK1/2 phosphorylation level which indicates an estrogen receptor-dependent pathway. These results suggest that EDCs have the ability to alter the human immune function, maybe by interfering with endocrine balance.

Alcohol intake modifies leptin, adiponectin and resistin serum levels and their mRNA expressions in adipose tissue of rats.

OBJECTIVE: Alcohol intake is known to interfere with endocrine system functions thus inducing hormonal and metabolic imbalance. The aim was to investigate the impact of chronic intake of mild alcohol concentration on serum leptin, adiponectin and resistin and their gene expression in epididymal adipose tissue (EAT) of rats. METHODS: The 28 days study was based on 3 experimental groups of adult male Wistar rats: 1/ ad libitum intake of 6 % ethanol solution and pelleted diet (A), 2/ pair fed animals (PF) fed pelleted diet in the same caloric amount as A rats on previous day (alcohol+diet), 3/ control rats (C) with unrestricted intake of water and pelleted diet. RT-PCR method was used for determination of adipokines gene expression in epididymal adipose tissue, serum levels were measured by ELISA kits. RESULTS: The animals of A group were characterized by reduced food and energy intake (-10 % vs C), lower body mass gain, reduced epididymal fat mass with smaller adipocytes. Alcohol consumption significantly increased glycemia, serum insulin was not affected. The raise of NEFA in A and PF rats gives the evidence of intensified lipolysis due to the deficiency of energy intake. Alcohol consumption significantly increased serum leptin and resistin, elevated adiponectin was present in A and PF rats. In parallel with increased serum levels the expression of adiponectin gene in epididymal adipose tissue was elevated in the same A and PF rats. Leptin and resistin mRNA levels were similar as in C regardless of alcohol intake or pair-fed feeding. Increased leptin and resistin levels positively correlated with glycemia and negatively with the size of adipocytes. Elevated serum leptin and resistin together with high adiponectin after chronic moderate alcohol intake could contribute to alteration of energy metabolism either individually or in reciprocal coordination. CONCLUSIONS: 28 days consumption of 6 % ethanol solution changed the nutritional status of rats and induced significant elevation of serum leptin and resistin, while elevated gene expression in epididymal adipose tissue was proved for adiponectin only. Elevated serum adipokines could contribute to increased glycemia and altered glucose homeostasis.

Hormone response to stress in rat strains of different susceptibility to immunologic challenge.

OBJECTIVE: The aim of this study was to compare the changes in plasma levels of hormones involved in modulation of the immune system function after exposure to stress in two rat strains with different susceptibility to immunoantigens. METHODS: Adult rat males of Lewis (LEW) and Fischer 344 (FIS) strains were exposed to restrain stress for 2 hours and blood samples were collected during stress exposure. Other groups of animals were exposed to restrain stress for 2 hours and sacrificed 3 hours later for blood and organ collection. Corticosterone, testosterone, dehydroepiandrosterone, 17beta-estradiol and progesterone were estimated by radioimmunoassay, epinephrine and norepinephrine levels were determined by radioenzymatic method. RESULTS: The levels of plasma corticosterone and catecholamines were significantly higher during stress exposure in FIS as compared to LEW rats. Greater decrease of testosterone levels and higher levels of estradiol were noted after exposure to stress in LEW rats. Higher values of progesterone plasma levels were noted in FIS rats after stress. CONCLUSIONS: These results demonstrated the differences in the response of catecholamines, adrenal and gonadal steroids after exposure to stress in LEW and FIS rats with lower levels of hormones with anti-inflammatory action in LEW rats.

Long-time alcohol intake modifies resistin secretion and expression of resistin gene in adipose tissue.

Elevated serum resistin is implicated in insulin resistance associated with obesity and type 2 diabetes mellitus. Alcohol consumption interferes with the nutritional status, metabolic and hormonal activity of the drinker. Impact of ethanol intake on resistin level and resistin metabolic effects is unknown. Effect of long-time (28 days) ad libitum moderate alcohol (6% ethanol solution) intake on serum resistin and resistin mRNA level in adipose tissue of rats (A) was compared to control (C) and pair-fed (PF) animals. PF rats were fed the same caloric amount as A rats on previous day. Alcohol consumption resulted in reduction of food and energy intake, decreased body mass gain, epididymal fat pads mass and smaller adipocytes (vs. C rats). Alcohol intake significantly increased serum resistin and glucose, insulinemia remained unchanged. Systemic insulin resistance was not proved by HOMA, QUICKI and McAuley indexes, but impaired insulin effect on glucose transport in isolated adipocytes was present. Elevated serum resistin was positively correlated with glycemia (r = 0.88, p < 0.01) and negatively with fat cell size (r = -0.73, p < 0.05). High resistin level as the consequence of long-time alcohol intake could contribute to smaller adipocytes, higher glycemia, attenuation of insulin-stimulated glucose transport in adipocytes. Diminished resistin gene expression in adipose tissue of A and PF rats was present.

Kojic acid and its derivatives: history and present state of art.

Kojic acid (5-hydroxy-2-hydroxymethyl-4-pyranone) represents an attractive polyfunctional skeleton for development of biologically active compounds. The authors prepared a great variety of kojic acid derivatives and selected biological properties have been studied. Thus, kojic acid derivatives are promising compounds that might advantageously be used in human and/or veterinary medicine and also in preparation of new, even more biologically active preparations.

Inhibitory effect of cadmium and tobacco alkaloids on expansion of porcine oocyte-cumulus complexes.

Studies aimed at the influence of smoking on reproductive functions have found out fertility disorders in smokers occurring at any stage of reproductive processes. In our experiments the role of cadmium, nicotine and anabasine was investigated in the expansion of oocyte-cumulus complexes (OCC) isolated from large antral porcine follicles. Suppression of FSH-induced cumulus expansion and significant inhibition of synthesis and accumulation of hyaluronic acid in the cell/matrix compartment of the OCC was observed in the presence of different concentrations of tested compounds. The suppressive effect of cadmium and tobacco alkaloids on the cumulus expansion was accompanied by decreased progesterone production by cumulus cells during 42 h incubation of the OCC with FSH.

Components of cigarette smoke inhibit expansion of oocyte-cumulus complexes from porcine follicles.

The role of alkaloids in cigarette smoke was investigated in the cumulus expansion of oocyte-cumulus complexes (OCC) isolated from large antral porcine follicles. Suppression of the cumulus expansion stimulated by FSH was observed in the presence of different concentration of cadmium, anabasine and nicotine but not its metabolite cotinine. There were comparable inhibitory effects of cadmium and nicotine on the synthesis and accumulation of hyaluronic acid in the cell/matrix compartment of OCC. The inhibitory effect of tested compounds on the cumulus expansion was accompanied by decreased progesterone synthesis by cumulus cells during 42 h incubation of OCC with FSH. The results suggest that cigarette smoking may affect intrafollicular processes, which are responsible for normal ovulation and fertilization.

Long lasting cadmium intake is associated with reduction of insulin receptors in rat adipocytes.

The effects of chronic cadmium exposure on adipose tissue have not been extensively reported. In adult Wistar male rats we investigated in vivo effect of 6 weeks lasting cadmium intake in drinking tap water (CdCl2 9,7 mg/l). Insulin receptors in isolated adipocytes from epididymal fat and glucose transporter protein GLUT4 content in fat tissue plasma membranes were determined. Control and Cd treated rats had similar water intake with subsequent heavy augmentation of Cd content in liver of experimental animals. In comparison with controls, Cd intake did not influence body mass increment and fat cell size, but significantly increased serum glycemia and moderately elevated insulinemia. Cadmium intake significantly reduced (approximately 50%) both, total insulin receptors number and density of the receptors in fat cells. No differences in the content of GLUT4 in crude plasma membranes of adipose tissue were observed. Diminished insulin receptors in adipocytes could account for diabetogenic effect of long lasting cadmium intake.

Terguride treatment attenuated prolactin release and enhanced insulin receptor affinity and GLUT 4 content in obese spontaneously hypertensive female, but not male rats.

Glucose tolerance, serum insulin, insulin receptors in epididymal fat tissue, and GLUT 4 content in muscle, as well as serum prolactin, were studied in obese and lean spontaneously hypertensive rats (SHRs) of both sexes. Obese animals displayed insulin resistance and decreased capacity of high-affinity binding sites of insulin receptors in fat tissue plasma membranes. GLUT 4 content in musculus quadriceps was diminished only in obese females. Terguride treatment lowered prolactin serum levels, which was concomitant with ameliorated insulin sensitivity in obese animals of both sexes. Similarly, only in obese females, terguride significantly increased the affinity of high-affinity insulin-binding sites and normalized GLUT 4 content. Our results document downregulation of insulin receptors and GLUT 4 in obesity and suggest a role for prolactin in obesity-induced insulin resistance, particularly in female rats.

Effect of cadmium and mercury on the nuclear retinoic acid receptors.

The actions of retinoic acids (RA) are mediated by their cognate nuclear receptors--ligand inducible transcription factors (retinoic acid receptors (RAR)). Possible interactions of toxic heavy metals on the RAR system are of interest due to involvement of the RAR system in multiple systemic processes. We assayed cadmium chloride and mercury chloride for their influence on the RAR system in rat and in cell culture. Mercury chloride was observed to decrease the maximal binding capacity in vitro of RARs for all-trans RA in liver nuclear fraction containing sets of nuclear receptors by seventy percent at a concentration of 0.1 mmol/l, though not cadmium chloride. Neither mercury chloride nor cadmium chloride induced any changes with respect to mRNA levels of RAR and binding properties of nuclear receptor fraction for RA or retinoic acid responsive elements (RARE) in male Wistar rats receiving tap water with cadmium chloride (9.7 mg/l) or mercury chloride (11.5 mg/l) for six weeks. In rat pituitary GH4C1 cells, neither mRNA levels nor binding properties for RARE in cell culture were affected by non-toxic concentrations of these heavy metals. From the data obtained it is suggested that, in vivo, cadmium or mercury have no significant impact on RA nuclear receptor system.

Elevated AT1 receptor protein but lower angiotensin II-binding in adipose tissue of rats with monosodium glutamate-induced obesity.

Age-related hypertrophy of adipose tissue has been associated with a significant decrease in the number of angiotensin II receptors. The aim of this study was to investigate the characteristics of angiotensin II receptors in hypertrophic adipose tissue in animal obesity model using rats postnatally treated with monosodium glutamate. Angiotensin II is known to induce hypertrophy in several tissues of the cardiovascular system and might do the same in fat tissue. The expression and binding properties of angiotensin II AT(1) receptors in epididymal fat tissue of adult rats were studied using membrane-binding, RT-PCR, and immunoblotting. The amount of AT(1) receptor mRNA did not differ significantly between obese and control rats. Despite that glutamate-treated rats displayed approximately 4-times more AT(1) receptor immunoreactive protein content in fat tissue cell membranes than the controls did. In contrast, binding experiments showed a significant (40.3 +/- 6.2 %) decrease of (125)I-Sar(1)-Ile(8)-angiotensin II-binding to fat tissue cell membranes in obese rats compared to controls. In conclusion, the present study provides evidence for the low binding properties associated with an accumulation of AT(1) receptor protein in cell membranes of the fat tissue of rats with glutamate-induced obesity. Discrepancies among angiotensin II-binding, AT(1) receptor protein, and AT(1) receptor mRNA levels indicate a possible defect in the receptor protein, which remains to be identified. The results obtained support a role of angiotensin II and AT(1) receptors in the pathogenesis of obesity.

Effects of exposure to space flight on endocrine regulations in experimental animals.

This minireview summarizes the results of the observations on changes in endocrine functions of rats exposed to space flights for various periods. The results found after space flights are compared with those obtained from rats in acute or repeated restrain stress. A slight increase of plasma catecholamine levels was observed in rats after space flight of longer duration (>14 days), but no changes in catecholamine content in the activity of catecholamine synthesizing enzymes were noted in adrenal medulla and in hypothalamus. The norepinephrine content was, however, decreased in several nuclei selected from hypothalamus of flight rats. Plasma corticosterone levels were increased after space flight and morphological examination of pituitary showed elevated activity of corticotrophs. However, the plasma levels of ACTH were not increased in rats 6 hours after space flight. These changes in plasma hormone levels affected the activity of enzymes involved in metabolism of amino acids in liver and lipolysis in adipose tissue. The plasma levels of testosterone and triiodothyronine were diminished after space flight suggesting the suppression of the thyroid and gonadal activity. Increase of plasma insulin and glucose levels were found in rats after space flight, but the glucagon values were not changed. Comparing these results from flight rats with the animals exposed to acute or repeated stress indicate that long stay in microgravity do not represent very intensive stressogenic stimulus for adrenocortical and sympatho-adrenomedullar systems, and hormone alterations observed after space flight may be due to acute gravitational stress resulting from a return to Earth gravity. Therefore further studies including the inflight animal experiments on a board of International Space Station are necessary for elucidation of the effects of microgravity on endocrine functions.

Terguride attenuates prolactin levels and ameliorates insulin sensitivity and insulin binding in obese spontaneously hypertensive rats.

Glucose tolerance, serum insulin, insulin receptors in epididymal fat tissue, circulating total cholesterol and triglyceride concentrations as well as serum prolactin were studied in obese and lean spontaneously hypertensive rats (SHR) of both sexes. Obese animals displayed insulin resistance and elevated insulin and triglyceride concentrations. Moreover, in obese rats the increased mass of epididymal fat tissue was accompanied with decreased capacity of high affinity binding sites of insulin receptors in the tissue plasma membranes. Terguride treatment lowered prolactin serum levels which was accompanied by ameliorated insulin sensitivity in obese animals of both sexes. In addition, terguride treatment decreased serum insulin and triglyceride concentrations in obese females and at the same time enhanced the affinity of high affinity insulin binding sites. Our results show that obesity in SHR is associated with a decreased capacity of insulin receptors and that prolactin may play a role in obesity-induced insulin resistance, particularly in female rats.

Endocrine responses to space flights.

Simultaneously with human space flights several series of observations were performed by using experimental animals--mainly rats--exposed to space flights on board of special satellites BION-COSMOS or in Shuttle Transportation Systems (STS). The aims of these experiments were to study in more details: the mechanisms of the changes in bones and skeletal muscle, the alterations of the function of immune system, the radiation effects on organism, the mechanism of the changes of endocrine functions, the evaluation of the role of hormones in alteration of metabolic processes in organism. The advantages of these animal experiments were the possibilities to analyze not only the plasma samples, but it was possible to obtain samples of organs or tissues: for morphological and biochemical analysis for studies of the changes in enzyme activities and in gene expressions, for measurement of metabolic processes and for investigation of the hormone production in endocrine glands and estimation of the response of tissues to hormones. It was also possible to compare the endocrine response to spaceflight and to other stress stimuli. These animal studies are interesting for verification of some hypothesis in the mechanism of adaptation of human organism to the changes of gravity. The disadvantage was, however, that the animals in almost all experiments could be examined only after space flight. The actual inflight changes were investigated only in two SLS flights. In this short review it is not possible to evaluate all hormonal data available on the response of endocrine system to the conditions of space flights. Therefore we will concentrate on the response of pituitary adrenocortical system, pituitary thyroid and pituitary gonadal functions.

Effects of new hypoglycemic agent A-4166 on lipolysis and lipogenesis in rat adipocytes.

OBJECTIVE: To test the effects of novel oral hypoglycemic agent A-4166 on lipolysis and lipogenesis in adipocytes from normal rats and non-obese, hypertriglyceridemic, insulin resistant and hypertensive rats (HTG) fed basal or high fat diet. METHODS: Adult male Wistar rats and hereditary HTG rats (from our own colony) were used. They were fed either basal or high fat diet for three weeks. On the day of observation the active substance A-4166 was administered intragastrically by gavage 30 minutes before decapitation. Blood was collected for the determination of insulin, glycemia, non esterified fatty acids (NEFA) by using commercial kits. The isolated adipocytes were prepared from epididymal fat pads and lipolysis (by measurement of glycerol release) and lipogenesis (by estimation of labeled glucose incorporation into lipids) were determined. RESULTS: The administration of A-4166 results in increased serum insulin and decreased serum glucose level in all rats irrespective of the diet. A significant diminution of serum NEFA levels was observed in A-4166 administered Wistar and HTG rats fed high fat diet. In both groups of rats fed basal diet the lipolysis was not affected by A-4166. However, a decrease of lipolysis was found after A-4166 in Wistar rats fed high fat diet. The stimulation of lipolysis by norepinephrine was not influenced by A-4166. A lowered basal lipolysis was found in HTG rats fed high fat diet. The stimulation of lipolysis by norepinephrine was diminished in HTG rats as compared to Wistar animals. Administration of A-4166 did not affect the stimulation of lipolysis by norepinephrine in HTG rats. A decrease of stimulatory action of insulin on lipogenesis was found in Wistar rats fed high fat diet and in all groups of HTG rats. The administration of A-4166 did not change the basal lipogenesis and also the effect of insulin on lipogenesis. CONCLUSIONS: Besides the hyperinsulinemic and hypoglycemic effect of A-4166 also an influence on nonesterified fatty acid serum levels was observed in rats fed high fat diet. This can be partially explained by an antilipolytic action of hyperinsulinemia after A-4166. The studies of lipogenesis showed that Wistar rats fed high fat diet and HTG animals are resistant to the stimulatory action of insulin on lipogenesis and that administration of A-4166 did not affect this response to insulin.

Modulation of cAMP level by tedisamil in guinea pig heart.

Tedisamil is antiarrhythmic class III drug with antifibrillating/defibrillating potency linked to enhancement of intermyocyte gap junctional electrical coupling most likely via its sympathomimetic cAMP-related mechanisms. This study was designed to examine the effect of tedisamil on cAMP level in guinea pig hearts in vivo and in vitro in Langendorff preparation. The drug was administered either as a bolus into vena jugularis in dosage 1.0 and 1.5 mg/kg or into the perfusion solution at a concentration of 1.5 x 10(-6) mol/l. In additional experiments, this period was followed by brief 10 min global ischemia, induced by clamping of the aorta or perfusion. After 10 min from the onset of tedisamil administration as well as after 10 min of ischemia the ventricular tissue was immediately frozen for cAMP immunoassay. Tedisamil caused in normal heart small but significant dose-dependent increase of myocardial cAMP (pmol/mg) level in vivo 1.8 and 2.5 vs. 1.4 as well as in vitro 1.1 vs. 0.8 (p < 0.05) conditions. Ischemia itself induced accumulation of cAMP in both, in vivo and in vitro experiments, 2.6 vs. 1.4 and 1.3 vs. 0.8, respectively. The preischemic elevation of cAMP by tedisamil was not potentiated by following ischemia, on the contrary, decline of the cyclic nucleotide was detected comparing to ischemia itself. In conclusion, tedisamil increased cAMP level in normal heart and prevented additional ischemia-related elevation of this nucleotide. The results indicate modulation of myocardial cAMP level by tedisamil, which may account for its protective effect on gap junctional electrical coupling.

Late effects of postnatal administration of monosodium glutamate on insulin action in adult rats.

Early postnatal administration of monosodium glutamate (MSG) to rats induces obesity, hyperinsulinemia and hyperglycemia in adulthood, thus suggesting the presence of insulin resistance. We therefore investigated the effects of insulin on glucose transport and lipogenesis in adipocytes as well as insulin binding to specific receptors in the liver, skeletal muscle and fat tissues. An increase of plasma insulin, glucose and leptin levels was found in 3-month-old rats treated with MSG during the postnatal period. The attenuation of insulin stimulatory effect on glucose transport was observed in MSG-treated rats. Despite the lower basal and insulin-stimulated glucose uptake, the incorporation of glucose into lipids was significantly higher in MSG-treated rats, suggesting a shift in glucose metabolism towards lipid synthesis in fat tissue. Insulin binding to plasma membranes from the liver, skeletal muscle and adipocytes was decreased in MSG-treated rats. This is in agreement with the lower insulin effect on glucose transport in these animals. Furthermore, a decreased amount of GLUT4 protein was found in adipocytes from MSG-treated obese rats. The results demonstrated an attenuation of insulin effect on glucose transport due to a lower insulin binding and lower content of GLUT4 protein in MSG-treated rats. However, the effect of insulin on lipogenesis was not changed. Our results indicated that early postnatal administration of MSG exerts an important effect on glucose metabolism and insulin action in adipocytes of adult animals.

Quantitation of GABA transporter 3 (GAT3) mRNA in rat brain by competitive RT-PCR.

Gamma-amino butyric acid is the major inhibitory neurotransmitter in the brain. GABA transporters (GATs) remove GABA from the synaptic cleft. Till now, five distinct GABA transporters have been cloned and termed consecutively GAT1 to GAT4 and vGAT. To study the mechanisms by which tolerance and dependence associated with drugs enhancing GABAergic transmission is brought upon we analysed the mRNA expression levels of GATs in various brain regions under different conditions. In this paper, we describe our protocol for measurement of GAT3 mRNA expression, and its validation through control experiments for the various steps. We performed competitive reverse transcription and polymerase chain reaction (RT-PCR) with a competitor cRNA as internal standard. Different amounts of competitor cRNA were added to total RNA prepared from different tissue samples, reverse-transcribed and PCR amplified. The PCR amplification gave two products: the GAT wild type fragment and the competitor fragment. PCR products were separated by gel electrophoresis and band intensities were determined from which the relative and absolute abundance of GAT3 mRNA was calculated by regression analysis. Validation experiments in our laboratory showed a 6% intra-assay and a 15% inter-assay variability of this method.