Glucocorticoid metabolism and Na+transport in chicken intestine

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.

Therapeutic effects of inhaling aerosolized surfactant alone or with dexamethasone generated by a novel noninvasive apparatus on acute lung injury in rats

BACKGROUND

Pulmonary surfactant (PS) administration has been attempted for the treatment of adults with acute lung injury (ALI)/adult respiratory distress syndrome. Aerosolized surfactants inhaled by spontaneous breathing may be an effective method of surfactant-based therapies. Using a noninvasive apparatus, we evaluated the therapeutic effects of aerosolized PS alone or together with dexamethasone (Dex) on a rat model of ALI.

METHODS

Severe ALI was induced by intravenous injection of 20% oleic acid (0.2 mL/kg) into adult Sprague-Dawley rats. Animals were divided into eight groups: sham (n = 10); model (injury only, n = 10); normal saline (NS) aerosol driven by compressed air (air-NS, n = 13); PS aerosol driven by compressed air (air-PS, n = 13); NS aerosol driven by O2 (O2-NS, n = 13); PS aerosol driven by O2 (O2-PS, n = 13); Dex aerosol driven by O2 (O2-Dex, n = 13); and PS and Dex aerosol driven by O2 (O2-PS-Dex, n = 13). Blood gases, breathing rate, lung index, total protein, and proinflammatory cytokines (tumor necrosis factor-α, interleukin 1β, interleukin 6) in the bronchoalveolar lavage fluid (BALF), and lung histology were examined.

RESULTS

Animals treated with air-PS for 20 minutes had significantly improved lung function, reduced pulmonary edema, decreased concentration of total protein and proinflammatory cytokines in BALF, ameliorated lung injury, and improved animal survival. In the O2-PS group, the breathing rates and lung injury scores were significantly lower than that of the air-PS group. In the O2-PS-Dex group, lung edema, total protein, and inflammatory cytokines in BALF were significantly reduced in comparison with the O2-PS group.

CONCLUSION

Inhalation of aerosolized PS generated by the noninvasive apparatus could significantly reduce lung injury, while using oxygen line available in the clinical wards to generate PS aerosol is more convenient and adds further benefits. This method can also be used to deliver Dex and other therapeutic agents to ameliorate lung injury.

Fecal corticosterone metabolites and plasma corticosterone in Japanese quail selected for low or high plasma corticosterone responses to brief restraint

Fecal corticosterone metabolites and plasma corticosterone in Japanese quail selected for low- or high-plasma corticosterone responses to brief mechanical restraint (low- and high-stress lines), and in a line of unselected quail, were measured in this study. No line differences were observed in baseline plasma corticosterone concentrations, but fecal corticosterone metabolite concentrations and daily fecal corticosterone metabolite production were 20% higher in quail of the high-stress line than in unselected or low-stress quail for males and females living together in group cages (P < 0.05). No differences were observed between lines in corticosterone metabolite concentrations and production for male birds in individual cages. Baseline plasma corticosterone concentrations, fecal corticosterone metabolite concentrations, and production appeared to be higher for males and females in group cages compared with males in individual cages. This difference might have been because of greater corticosterone secretion by male quail living in mixed sex groups than living individually. Correlations between baseline plasma corticosterone concentrations and fecal corticosterone metabolite concentrations in low-stress and high-stress quail, and for all birds combined, were r = 0.521 (P = 0.038), r = 0.604 (P = 0.013), and r = 0.431 (P = 0.002), respectively. The low- and high-stress lines that have been selected for low- and high-corticosterone responses differ in other characteristics, including growth and reproductive performance, and the current results are consistent with the assumption that these other differences are a consequence of greater daily corticosterone secretion in quail of the high-stress line.

Transcriptional inhibition of intestinal NHE8 expression by glucocorticoids involves Pax5

Sodium/hydrogen exchangers (NHEs) are a family of proteins that transport sodium ions into the cells by moving protons out of the cells. They play a major role in sodium absorption, cell volume regulation, and intracellular pH regulation. Three out of nine identified NHEs (NHE2, NHE3, and NHE8) are expressed on the apical membrane of intestinal epithelial cells. Glucocorticoids have been found to regulate NHE3 function in the intestine, but it is unknown if they have a similar function on NHE8 expression. Interestingly, high glucocorticoid levels in the intestine coincide chronologically with the change from high expression of NHE8 to high expression of NHE3. Studies were performed to explore the role of glucocorticoids on NHE8 expression during intestinal maturation. Brush-border membrane vesicles were isolated from intestinal epithelia, and Western blotting was performed to determine NHE8 protein expression of suckling male rats treated with methylpredisolone. Real-time PCR was used to quantitate NHE8 mRNA expression in rats and Caco-2 cells. Human NHE8 promoter activity was characterized through transfection of Caco-2 cells. Gel mobility shift assays (GMSAs) were used to identify the promoter sequences and the transcription factors involved in glucocorticoid-mediated regulation. Our results showed that the expression of NHE8 mRNA and protein was decreased in glucocorticoid-treated rats and human intestinal epithelial cells (Caco-2). The activity of the human NHE8 gene promoter transfected in Caco-2 cells was also reduced by glucocorticoid treatment. GMSAs suggested that the reduction in promoter activity in the presence of glucocorticoids was due to enhanced transcription factor Pax5 binding on the NHE8 proximal promoter region. In conclusion, this study showed that glucocorticoids inhibit NHE8 gene expression by increasing Pax5 binding on NHE8 gene promoter, suggesting an important role for Pax5 during intestinal maturation.

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.

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 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.

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

Glucocorticoids influence the function of numerous tissues. Although there are a very large number of studies that have investigated the local metabolism of glucocorticoids in mammals, the knowledge of this metabolism in birds is limited. The local concentration of corticosterone is critical for both glucocorticoid- and mineralocorticoid-dependent activity, and we have therefore carried out studies of corticosterone metabolism in various chicken organs. It was found that corticosterone was metabolized to 20-dihydrocorticosterone, and in some tissues also to 11-dehydrocorticosterone and 11-dehydro-20-dihydrocorticosterone. The activity of 20-hydroxysteroid dehydrogenase (20HSD), responsible for the transformation of corticosterone to 20-hydroxy derivatives, was abundant in the kidney and intestine, with lower levels in the liver and testis. Low levels of 20HSD were detected in the brain and ovaries. In contrast, 11-hydroxysteroid dehydrogenase (11HSD) activity was only found in the kidney and intestine. No activity was observed in the brain, testis, or ovaries. The treatment of chickens with estrogens stimulated 20HSD activity in the kidney, intestine, and oviduct and 11HSD activity in the liver and oviduct. Kinetic studies for corticosterone yielded an apparent Km for 11HSD in the nanomolar (Km = 21 +/- 5 nmol.l(-1)) and for 20HSD in the micromolar range (Km = 3.7 +/- 0.3 micromol.l(-1)). When progesterone or 5alpha-dihydrotestosterone were used instead of corticosterone, the tissues reduced the former to 20beta-dihydroprogesterone and the latter to both 5alpha,3alpha- and 5alpha,3beta-dihydrotestosterone. The data presents the first evidence for corticosterone metabolism via 11beta-, 3alpha/3beta-, and 20beta-hydroxysteroid dehydrogenases in various chicken organs and provide support for the theory of prereceptor modulation of glucocorticoid signals in avian tissues.

Aquaporins in chicken: Localization of ck-AQP5 along the small and large intestine

Aquaporins (AQPS) are transmembrane water channels poorly investigated in birds. Using degenerated primers and RT-PCR, we identified in kidney and gastrointestinal tract of Hubbard chickens (Gallus gallus) three fragments, corresponding to ck-AQP2, ck-AQP4, and ck-AQP5 mRNAs. Comparison of nucleotide ck-AQPs sequences to their rat and human orthologues revealed an overall identity of 75-90%. Expression in the renal and gastrointestinal systems of the three ck-AQPs mRNA was analysed by Northern assays. Transcript of ck-AQP2 was only identified in kidney. ck-AQP4 mRNA was highly expressed in brain, and to a lesser extent in kidney and stomach. ck-AQP5 mRNA was found in jejunum and ileum, and to a lesser extent in colon and lung. In situ hybridisation showed ck-AQP5 mRNA in the crypt cells of jejunum, ileum and colon, whereas it was absent from the cells lining the villi. Levels of ck-AQP5 mRNA (analyzed by Northern and in situ hybridisation assays) and protein (analysed by immunohistochemistry) decreased from the jejunum to the colon. This work confirmed the presence of AQPs in chicken, and showed that chicken and mammalian AQPs share a high degree of similarity in nucleotide sequence and tissue distribution.