Corticosterone metabolism in chicken tissues: evidence for tissue-specific distribution of steroid dehydrogenases

Comparative study on the gene expression of corticosterone metabolic enzymes in embryonic tissues between Tibetan and broiler chickens

Glucocorticoids (GCs) are an essential mediator hormone that can regulate animal growth, behavior, the phenotype of offspring, and so on, while GCs in poultry are predominantly corticosterones. The biological activity of GCs is mainly regulated by the intracellular metabolic enzymes, including 11β-hydroxysteroid dehydrogenases 1 (11β-HSD1), 11β-hydroxysteroid dehydrogenases 2 (11β-HSD2), and 20-hydroxysteroid dehydrogenase (20-HSD). To investigate the embryonic mechanisms of phenotypic differences between breeds, we compared the expression of corticosterone metabolic enzyme genes in the yolk-sac membrane and chorioallantoic membrane (CAM). We described the tissue distribution and ontogenic patterns of corticosterone metabolic enzymes during embryonic incubation between Tibetan and broiler chickens. Forty fertilized eggs from Tibetan and broiler chickens were incubated under hypoxic and normoxic conditions, respectively. Real-time fluorescence quantitative PCR was used to examine the expression of 11β-HSD1/2, and 20-HSD mRNA in embryonic tissues. The results showed that the expression levels of yolk-sac membrane mRNA of 11β-HSD2 and 20-HSD in Tibetan chickens on E14 (embryonic day of 14) were significantly lower than those of broiler chickens (P < 0.05), and these genes expression of CAM in Tibetan chickens were higher than those of broiler chickens (P < 0.05). In addition, the three genes in the yolk-sac membrane and CAM were followed by a down-regulation on E18 (embryonic day of 18). The 11β-HSD1 and 11β-HSD2 genes followed a similar tissue-specific pattern: the expression level was more abundantly in the liver, kidney, and intestine, with relatively lower abundance in the hypothalamus and muscle, and the expression level of 20-HSD genes in all tissues tested was higher. In the liver, 20-HSD of both Tibetan and broiler chickens showed different ontogeny development patterns, and hepatic mRNA expression of 20-HSD in broiler chickens was significantly higher than that of Tibetan chickens of the same age from E14 to E18 (P < 0.05). This study preliminarily revealed the expression levels of cortisol metabolic genes in different tissues during the development process of Tibetan and broiler chicken embryos. It provided essential information for in-depth research of the internal mechanism of maternal GCs programming on offspring.

Age-related change of hepatic uridine diphosphate glucuronosyltransferase and sulfotransferase activities in male chickens and pigs

The hepatic activities of uridine diphosphate glucuronosyltransferase (UGT) and sulfotransferase (SULT) of male Ross 708 broiler chickens at the age of 1, 7, 14, 28, and 56 days and male Camborough-29 pigs at the age of 1 day and 2, 5, 10, and 20 weeks were investigated. Glucuronidation and sulfation of 4-nitrophenol were used to evaluate the activities. Porcine hepatic UGT and SULT activities were low at birth, peaked at around 5-10 weeks, and then declined. Both hepatic UGT and SULT activities of chickens were high at hatch and declined. Chicken hepatic UGT activity had a peak at the age of 28 days. Affinity of hepatic SULT to 4-nitrophenol is similar in chickens and pigs, but the affinity of hepatic UGT in pigs was about 10 times higher than that in chickens. 4-nitrophenol was predominantly conjugated by SULT instead of UGT in chicken livers from hatch to day 56. Conversely, hepatic UGT contributed predominantly in 4-nitrophenol conjugation than the SULT in pigs from birth to 20 weeks. Therefore, age has significant impact on hepatic activities of UGT and SULT, and the importance of UGT and SULT on conjugation is different in chickens and pigs.

Does corticosterone regulate the onset of breeding in free-living birds?: The CORT-Flexibility Hypothesis and six potential mechanisms for priming corticosteroid function

For many avian species, the decision to initiate breeding is based on information from a variety of environmental cues, including photoperiod, temperature, food availability, and social interactions. There is evidence that the hormone corticosterone may be involved in delaying the onset of breeding in cases where supplemental cues, such as low food availability and inclement weather, indicate that the environment is not suitable. However, not all studies have found the expected relationships between breeding delays and corticosterone titers. In this review, we present the hypothesis that corticosterone physiology mediates flexibility in breeding initiation (the "CORT-Flexibility Hypothesis"), and propose six possible corticosterone-driven mechanisms in pre-breeding birds that may delay breeding initiation: altering hormone titers, negative feedback regulation, plasma binding globulin concentrations, intracellular receptor concentrations, enzyme activity and interacting hormone systems. Based on the length of the breeding season and species-specific natural history, we also predict variation in corticosterone-regulated pre-breeding flexibility. Although few studies thus far have examined mechanisms beyond plasma hormone titers, the CORT-Flexibility Hypothesis is grounded on a solid foundation of research showing seasonal variation in the physiological stress response and knowledge of physiological mechanisms modulating corticosteroid effects. We propose six possible mechanisms as testable and falsifiable predictions to help clarify the extent of HPA axis regulation of the initiation of breeding.

Determinants and significance of corticosterone regulation in the songbird brain

Songbirds exhibit significant adult neuroplasticity that, together with other neural specializations, makes them an important model system for neurobiological studies. A large body of work also points to the songbird brain as a significant target of steroid hormones, including corticosterone (CORT), the primary avian glucocorticoid. Whereas CORT positively signals the brain for many functions, excess CORT may interfere with natural neuroplasticity. Consequently, mechanisms may exist to locally regulate CORT levels in brain to ensure optimal concentrations. However, most studies in songbirds measure plasma CORT as a proxy for levels at target tissues. In this paper, we review literature concerning circulating CORT and its effects on behavior in songbirds, and discuss recent work suggesting that brain CORT levels are regulated independently of changes in adrenal secretion. We review possible mechanisms for CORT regulation in the avian brain, including corticosteroid-binding globulins, p-glycoprotein activity in the blood-brain barrier and CORT metabolism by the 11ß hydroxysteroid dehydrogenases. Data supporting a role for CORT regulation within the songbird brain have only recently begun to emerge, suggesting that this is an avenue for important future research.

Immunoreactive cortisone in droppings reflect stress levels, diet and growth rate of gull-billed tern chicks

Blood levels of corticosterone have been traditionally analyzed to assess stress levels in birds; however, measuring steroid hormone metabolites in feces and droppings has gained much interest as a noninvasive technique successfully used for such purposed in vertebrates. Diet may affect these fecal metabolite levels (e.g., due to nutritional stress), however, this variable has not been taken into account in studies with chicks despite the great dietary flexibility of many avian species. In this study, we addressed for the first time this key issue and validated the technique in wild gull-billed tern chicks (Gelochelidon nilotica). Several enzyme immunoassays were used to determine the most appropriate test to measure the stress response. Subsequently, we performed an experiment in captivity to assess adrenocortical activity in gull-billed tern chicks fed with two diets: piscivorous vs. insectivorous. Finally, the relation between the chicks' growth rate and excreted immunoreactive glucocorticoid metabolites (EGMs) was also evaluated. We found the immunoreactive cortisone metabolites to be a good index of stress (as being an index of adrenocortical reactivity) in chicks of this species. Fish-fed chicks had higher levels of cortisone metabolites when comparing both concentration and total daily excreted metabolites. Within each treatment diet, cortisone metabolite levels and growth rates were negatively correlated. These findings suggest that the diet should be considered when using this technique for comparative purposes and highlight the trade-off between stress levels and chicks growth rates.

Chronic stress alters concentrations of corticosterone receptors in a tissue-specific manner in wild house sparrows (Passer domesticus)

The physiological stress response results in release of glucocorticoid hormones such as corticosterone (CORT). Whereas short-term activation of this response helps animals cope with environmental stressors, chronic activation can result in negative effects including metabolic dysregulation and reproductive failure. However, there is no consensus hormonal profile of a chronically-stressed animal, suggesting researchers may need to look beyond hormone titers to interpret the impacts of chronic stress. In this study, we brought wild house sparrows (Passer domesticus) into captivity. We then compared glucocorticoid and mineralocorticoid receptor concentrations in sparrows exposed either to a standardized chronic stress protocol (n=26) or to standard husbandry conditions (controls; n=20). We used radioligand binding assays to quantify receptors in whole brain, liver, kidneys, spleen, gonads, gastrocnemius and pectoralis muscle, omental and subcutaneous fat, and bib and back skin. In most tissues, CORT receptors did not differ between controls and stressed animals, although we found marginal increases in receptor density in kidney and testis in stressed birds at some time points. Only in pectoralis muscle was there a robust effect of chronic stress, with both receptor types higher in stressed animals. Increased pectoralis sensitivity to CORT with chronic stress may be part of the underlying mechanism for muscle wasting in animals administered exogenous CORT. Furthermore, the change in pectoralis was not paralleled by gastrocnemius receptors. This difference may help explain previous reports of a greater effect of CORT on pectoralis than on other muscle types, and indicate that birds use this muscle as a protein reserve.

Corticosterone metabolism by chicken follicle cells does not affect ovarian reproductive hormone synthesis in vitro

Glucocorticoids affect reproductive hormone production in many species. In chickens, elevated plasma corticosterone down-regulates testosterone and progesterone concentrations in plasma, but also in egg yolk. This suppression could be mediated via the hypothalamic-pituitary system but also via local inhibition of gonadal activity by glucocorticoids. As the latter has not been tested in birds yet, we tested if corticosterone directly inhibits ovarian steroid synthesis under in vitro conditions. We hypothesized that degradation of corticosterone by follicular cells impairs their ability to synthesize reproductive hormones due to either inhibition of enzymes or competition for common co-factors. Therefore, we first established whether follicles degrade corticosterone. Follicular tissue was harvested from freshly euthanized laying hens and incubated with radiolabelled corticosterone. Radioactive metabolites were visualized and quantified by autoradiography. Follicles converted corticosterone in a time-dependent manner into metabolites with a higher polarity than corticosterone. The predominant metabolite co-eluted with 20β-dihydrocorticosterone. Other chicken tissues mostly formed the same metabolite when incubated with corticosterone. In a second experiment, follicles were incubated with either progesterone or dehydroepiandrosterone. Corticosterone was added in increasing dosages up to 1000 ng per ml medium. Corticosterone did not inhibit the conversion of progesterone and dehydroepiandrosterone into a number of different metabolites, including 17α-hydroxyprogesterone, androstenedione and testosterone. In conclusion, avian tissues degrade corticosterone mostly to 20β-dihydrocorticosterone and even high corticosterone dosages do not affect follicular hormone production under in vitro conditions.

Pharmacological characterization of intracellular glucocorticoid receptors in nine tissues from house sparrow (Passer domesticus)

Glucocorticoid hormones play a key role in the stress response, but plasma concentrations vary based on physiological, environmental, or social parameters. However, hormone titers alone do not determine organismal response. To enhance our understanding of glucocorticoid actions we can examine 'downstream' factors in the organismal stress response, measuring glucocorticoid receptors across target tissues. Here, we characterized intracellular binding sites for CORT (corticosterone, the avian glucocorticoid) in house sparrow (Passer domesticus) brain, liver, skeletal muscle, spleen, fat, testes, ovary, kidney and skin. We used radioligand binding assays to identify total capacity, relative density and affinity for CORT of intracellular receptors in each tissue. Most evidence supported two binding sites similar to mammalian low-affinity glucocorticoid receptor (GR) and a high-affinity mineralocorticoid receptor (MR) for brain, liver, kidney and testes, and only a GR-like receptor for muscle, spleen, fat, ovary and skin. However, kidney data were somewhat more complicated, possibly hinting at a mineralocorticoid function for CORT and/or GR in birds. In all tissues, GR and MR affinities were close to published house sparrow values (K(d)~6 nM for GR, and ~0.2 nM for MR). Taken together, these data show that CORT receptor distribution appears to be as widespread in birds as it is in mammals, and suggest that independent regulation of peripheral receptors in different target tissues may play a role in CORT's diverse physiological effects.

Effects of corticosterone treatment in laying Japanese quail

1. The effects of exogenous corticosterone on plasma corticosterone concentrations, body weight, food intake, the percentage of birds that laid an egg each day and egg weight were measured in laying Japanese quail. Data were collected from birds in the week before corticosterone treatment began, during a 21-d treatment period, and in the 22 d after treatment ended. 2. Groups of quail were treated with corticosterone at three different concentrations in their drinking water. Corticosterone intakes were calculated for each bird and birds were then assigned to 4 intake groups. The groups were 0 (control group), 0.31-0.60, 0.61-0.90, 0.91-1.50 or >1.51 mg corticosterone/bird/d. 3. Plasma corticosterone concentrations in the 4 intake groups increased from around 1 ng/ml on the day before corticosterone treatment began to maximum mean concentrations of 13-18 ng/ml on day 14 of treatment. Mean corticosterone concentrations did not change between day 14 of treatment and the day after treatment ended, and had decreased in only one of 4 intake groups one week later. 4. Mean body weight in the highest intake group remained significantly lower than in controls 22 d after corticosterone treatment ended. Whilst there was no clear effect of corticosterone on food intake during treatment, mean food intake in the three highest corticosterone intake groups was significantly lower than in controls in the week after treatment ended. The percentage of birds that laid an egg each day and egg weight were both decreased by corticosterone, and the percentage of birds that laid an egg each day remained significantly lower in the highest corticosterone intake group compared with controls in the third week after treatment ended. 5. It is suggested that elevated plasma corticosterone concentrations in quail after treatment ended were maintained by a hyperactive hypothalamo-pituitary-adrenal axis for at least one week. Although none of the negative effects of corticosterone were evident in the group of quail with the lowest corticosterone intakes, the findings of the present study show that corticosterone treatment can affect birds for up to several weeks after corticosterone intake ends.

11beta-hydroxysteroid dehydrogenase type 2 in zebra finch brain and peripheral tissues

The enzyme 11betaHSD2 inactivates glucocorticoids by synthesizing metabolites that bind poorly to mineralocorticoid and glucocorticoid receptors. Oscine songbirds (Passeriformes) are important models for investigating stress hormone effects on brain and behavior but nothing is known about 11betaHSD2 activity in the songbird brain. We measured 11betaHSD2 mRNA expression and enzymatic activity in brain of adult and developing male and female zebra finches. Since 11betaHSD2 plays an important role in GC metabolism in some peripheral organs we measured mRNA and catalytic activity also in the adult liver, kidney colon and gonads. 11betaHSD2 mRNA was detected in all brain regions examined with expression in the cerebellum and hypothalamus greater in females than in males; expression in ovaries was greater than in testes. No differences were detected in the other peripheral tissues. Catalytic activity of 11betaHSD2 could be measured in brain, but at low levels and no sex differences were measured in any region tested. Because 11betaHSD2 protects mineralocorticoid sensitive tissues from inappropriate CORT action, we also measured mineralocorticoid receptor (MR) expression in adult brain kidney and liver. MR mRNA was detected in all tissues with similar levels of expression in neural and peripheral tissues. The wide distribution of 11betaHSD2 and MR throughout the songbird brain suggests that concentrations of glucocorticoids may be locally regulated in brain to modulate their actions on MR and possibly also glucocorticoid receptors (GR). Notable differences between mRNA expression and activity point to post-transcriptional regulation of the 11betaHSD2 enzyme.

Pharmacological characterization of intracellular, membrane, and plasma binding sites for corticosterone in house sparrows

The diversity and specificity of glucocorticoid effects are dependent on cell-specific receptor mechanisms. Three known corticosteroid receptors mediate tissue effects of glucocorticoids in vertebrates: two intracellular receptors that act primarily as ligand-activated transcription factors, and a membrane-associated receptor. The intracellular receptor sub-types have been well characterized in mammals, however relatively little is known about them across non-mammalian vertebrates. The membrane-associated receptors are poorly characterized in most vertebrate taxa. To explore the basis for glucocorticoid action in birds, we pharmacologically characterized the three putative corticosteroid receptors in the brain, as well as a plasma corticosterone binding globulin, in the house sparrow (Passer domesticus). We found that house sparrow brain cytosol contained two distinguishable binding sites for corticosterone. A high affinity, mineralocorticoid-like receptor had subnanomolar affinity for corticosterone (K(d) approximately 0.2 nM). However, this 'MR-like' high-affinity receptor did not bind RU28318 or canrenoic acid, two compounds that bind mammalian MR with high affinity. A lower-affinity, glucocorticoid-like receptor in brain cytosol bound corticosterone with an average K(d)=5.61 nM. This GR-like receptor showed subnanomolar affinity for RU 486. MR- and GR-like receptors were found in equal numbers in whole brain assays (average B(max)=69 and 62 fmol/mg protein, respectively). House sparrow brain membranes contain a single binding site specific for glucocorticoids, with characteristics consistent with a steroid/receptor interaction. Corticosterone affinity for this putative membrane receptor was approximately 24 nM, with apparent B(max)=177 fmol/mg protein. House sparrow plasma contained a single binding site for [(3)H]corticosterone. Specific binding to plasma sites was inhibited by glucocorticoids, progesterone, and testosterone. Testosterone binding to this corticosteroid binding globulin is noteworthy as sex steroid-specific binding globulins have not been identified in birds. Taken together, these data extend our ability to evaluate the comparative actions of glucocorticoids, increase our understanding of mechanisms behind the tissue specificity of glucocorticoid action, and offer insight into the evolution of glucocorticoid action in vertebrates.

Maternal low-protein diet programmes offspring growth in association with alterations in yolk leptin deposition and gene expression in yolk-sac membrane, hypothalamus and muscle of developing Langshan chicken embryos

The present study was aimed to investigate the mechanism underlying the influence of maternal low-protein (LP) diet on offspring growth in the chicken. One hundred and twenty Chinese inbred Langshan breeder hens were allocated randomly into two groups fed diets containing low (10%, LP) or normal (15%) crude protein levels. Low dietary protein did not affect the body weight of hens, but significantly decreased the laying rate and egg weight. The yolk leptin content was significantly lower in eggs laid by LP hens, while no differences were detected for yolk contents of corticosterone, tri-iodothyronine (T3) or thyroxine. Despite significantly lower hatch weight, the LP offspring demonstrated obviously higher serum T3 concentration, which is in accordance with the faster post-hatch growth rate achieving significantly heavier body weight and pectoralis major muscle weight 4 weeks post-hatching. Expression of 20-hydroxysteroid dehydrogenase (20-HSD) mRNA in the yolk-sac membrane was significantly down-regulated at embryonic day 14, whereas that of transthyretin and leptin receptor (LepR) was not altered. Moreover, hypothalamic expression of 20-HSD, glucocorticoid receptors, thyrotropin-releasing hormone and LepR mRNA was significantly up-regulated in the LP group compared with their control counterparts. In the pectoralis major muscle, significantly higher expression of insulin-like growth factor (IGF)-I and IGF-I receptor mRNA was observed in LP embryos. The present study provides evidence that maternal LP diet programmes post-hatch growth of the offspring. The associated alterations in yolk leptin deposition as well as in yolk-sac membrane, fetal hypothalamus and muscle gene expression may be involved in mediating such programming effect in the chicken.

Cloning of chicken 11beta-hydroxysteroid dehydrogenase type 1 and its tissue distribution

11beta-Hydroxysteroid dehydrogenase type 1 (11HSD1) is an enzyme that interconverts active 11-hydroxy glucocorticoids (cortisol, corticosterone) and their inactive 11-oxo derivatives (cortisone, 11-dehydrocorticosterone). Although bidirectional, it is considered to operate in vivo as an 11-reductase that regenerates active glucocorticoids and thus amplifies their local activity in mammals. Here we report the cloning, characterization and tissue distribution of chicken 11HSD1 (ch11HSD1). Its cDNA predicts a protein of 300 amino acids that share 51-56% sequence identity with known mammalian 11HSD1 proteins, while in contrast to most mammals, ch11HSD1 contains only one N-linked glycosylation site. Analysis of the tissue distribution pattern by RT-PCR revealed that ch11HSD1 is expressed in a large variety of tissues, with high expression in the liver, kidney and intestine, and weak in the gonads, brain and heart. 11-Reductase activity has been found in the liver, kidney, intestine and gonads with low or almost zero activity in the brain and heart. These results provide evidence for a role of 11HSD1 as a tissue-specific regulator of glucocorticoid action in non-mammalian vertebrates and may serve as a suitable model for further analysis of 11HSD1 evolution in vertebrates.

Chicken 11beta-hydroxysteroid dehydrogenase type 2: partial cloning and tissue distribution

NAD(+)-dependent 11beta-hydroxysteroid dehydrogenase (11HSD2) converts glucocorticoids to 11-oxo derivatives and thus decreases their local concentration and prevents them from activating corticosteroid receptors. In this paper we report the partial cloning, characterization and tissue distribution of chicken 11HSD2. A cDNA of 991bp was cloned from kidney mRNA by reverse transcription and polymerase chain reaction. At the amino acid level, the sequence of PCR product had 56-59% homology with mammalian and 46-48% with fish 11HSD2. The consensus sequences of the short-chain dehydrogenase/reductase superfamily such as the catalytic activity motif Tyr-X-X-X-Lys and cosubstrate-binding motif Gly-X-X-X-Gly-X-Gly, were found in the cloned cDNA. Analysis of the tissue expression of chicken 11HSD2 mRNA and NAD(+)-dependent 11beta-oxidase activity showed a similar tissue distribution pattern in the majority of tissues. High levels of expression and activity were found in kidney, small intestine, colon and oviduct; low in ovary and almost zero in brain, liver and testis.

Corticosterone oxidative neutralization by 11-beta hydroxysteroid dehydrogenases in kidney and colon of the domestic fowl

In mammalian organs involved in sodium reabsorption, the 11-beta hydroxysteroid dehydrogenases (11betaHSDs) oxidize glucocorticoids (GC) from their 11-alcohol form to their 11-keto state and therefore prevent their binding to mineralocorticoid (MC) receptors (MR) and the development of a MC excess syndrome. In birds the information about 11betaHSDs and GC metabolism in such organs is scarce. Herein, we report the expression and enzymatic activity of 11betaHSDs in the kidney and colon of chickens. Both organs express 11betaHSD2-like mRNA. With NAD(+), microsomes from both tissues oxidized corticosterone (CS) into 11-dehydrocorticosterone (DHC) with K(m) of 200 and 20nM and V(max) of 13 and 2pmol/mg protein/min in the kidney and colon, respectively. Thiram, a specific 11betaHSD2 inhibitor, suppressed this oxidation in kidney. The expression and action of the putative 11betaHSD3 were also tested. The chicken colon, and to a greater extent the kidney, expressed 11betaHSD3-like mRNA. Microsomal fractions from both tissues oxidized CS into DHC in the presence of NADP(+) with K(m) of 150 and 4nM and V(max) of 5 and 0.3pmol/mg protein/min for the kidney and the colon, respectively. This oxidation was not affected when NADP(+) conversion into NAD(+) was inhibited by excess pyrophosphate or a phosphatase inhibitor cocktail. In microsomes of chicken's duodenum, where 11betaHSD1-like mRNA expression is high, NADP(+)-dependent oxidation of CS into DHC has a low-affinity K(m) of 1130nM. This study documented the expression and activity of two enzymes that convert CS into DHC, one is 11betaHSD2-like and the other is similar to the putative mammalian 11betaHSD3.

Corticosterone metabolites in blue tit and pied flycatcher droppings: effects of brood size, ectoparasites and temperature

The hypothalamic-pituitary-adrenal (HPA) axis of birds induces the secretion of corticosterone (CORT) as a response to different ecological variables. In this study we tested experimentally if manipulations of brood size or ectoparasitism led to subsequent differences in the concentration of excreted CORT metabolites of adult and nestling blue tits (Cyanistes caeruleus). No significant effect of the manipulation of brood size was detected in adults or nestlings. No significant effect of ectoparasitism was detected in males or nestlings, although females from uninfested nests showed lower concentrations of excreted CORT metabolites. In addition, we analysed if weather conditions had an influence on the concentration of excreted CORT metabolites of blue tits and pied flycatchers (Ficedula hypoleuca) breeding in the same forest. We detected no effect of weather conditions on adults, but nestlings of both species showed a negative correlation between their excreted CORT metabolites and the average mean temperatures they were subjected to during their growth. This effect was not found in blue tits in a colder year, suggesting that the sensitivity of the HPA axis to ambient temperature may be subjected to interannual variation. Moreover, we found a positive effect of the maximum temperature on the day of sampling on the concentration of CORT metabolites of blue tit nestlings in one of the years. These results suggest that weather conditions may act as environmental stressors to which the HPA axis of blue tit and pied flycatcher nestlings may be sensitive.

Distinct features of dehydrocorticosterone reduction into corticosterone in the liver and duodenum of the domestic fowl (Gallus gallus domesticus)

The mammalian 11-beta hydroxysteroid dehydrogenase type 1 (11 betaHSD1) reduces glucocorticoids (GC) at C11 from the 11-keto-GC nonactive form to the 11-hydroxy-GC active form, an action essential for survival. Whereas GC metabolism at C11 and the role of 11 betaHSD1 are studied extensively in mammals, information about these in birds is scattered. Herein, we report the GC bidirectional metabolism in chickens. In hens' liver and duodenal mucosa, 11 betaHSD1-like mRNA expression was detected; and 11 betaHSD1-like immunoreactivity was found linked to membranes of hepatocytes and duodenal enterocytes. With either NADH or NADPH, the membranal fraction of liver and duodenal mucosa converted dehydrocorticosterone (A) into corticosterone (B) with K(m) (1.1-8.7 microM) and V(max) (10-40 pmol/mg protein/min) values similar to those reported for mammalian 11 betaHSD1. In the presence of NADP(+) or NAD(+), these membranal fractions oxidized B into A. With either NADPH or NADH, the cytosol of chicken liver and duodenal mucosa reduced A into B (K(m) of 1.1 - 2.3 microM and V(max) of 260-960 pmol/mg protein/min). These cytosolic fractions did not convert any amount of B into A when incubated with either NADP(+) or NAD(+). This may suggest that chicken liver and duodenal mucosa express 11 betaHSD1 that is a membrane-bound oxoreductase which uses both NADPH/NADP(+) and NADH/NAD(+) as cosubstrates. The substantial reduction of A into B (but no conversion of B into A) found in the cytosol is most likely executed by a unidirectional soluble reductase, different than 11 betaHSD1.