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Thomas JR, Woodley SK. Testing the immunocompetence handicap hypothesis: Testosterone manipulation does not affect wound healing in male salamanders. Gen Comp Endocrinol 2017; 247:8-15. [PMID: 28343933 DOI: 10.1016/j.ygcen.2017.03.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2016] [Revised: 01/30/2017] [Accepted: 03/22/2017] [Indexed: 01/14/2023]
Abstract
In vertebrates, a bidirectional relationship exists between the immune system and the hypothalamic-pituitary-gonadal axis. In addition, sexual dimorphism in immunity has been documented in many vertebrates as well as some invertebrates, and males are generally less immunocompetent than their female counterparts. A possible explanation for this is described by the immunocompetence handicap hypothesis (ICHH), which proposes that elevated testosterone (T) levels direct resources towards the promotion of secondary sexual characteristics at a cost to immune function. To further test the ICHH, we examined the effects of T on cutaneous wound healing, an integrative measure of immunity, using male Allegheny Mountain dusky salamanders; a species that has sexually dimorphic courtship glands and testosterone-dependent mating behavior. We did this via two methods: surgical manipulation and transdermal delivery of T. In both experiments, elevated plasma T did not delay wound healing. Interestingly, intact animals healed more slowly than animals that had undergone prior invasive surgery, suggesting that the prior surgery had an immune-priming effect that enhanced healing of a second wound.
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Affiliation(s)
- Jessica R Thomas
- Department of Biological Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, USA.
| | - Sarah K Woodley
- Department of Biological Sciences, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, USA
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Bourke CH, Capello CF, Rogers SM, Yu ML, Boss-Williams KA, Weiss JM, Stowe ZN, Owens MJ. Prenatal exposure to escitalopram and/or stress in rats: a prenatal stress model of maternal depression and its treatment. Psychopharmacology (Berl) 2013; 228:231-41. [PMID: 23436130 PMCID: PMC3963147 DOI: 10.1007/s00213-013-3030-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Accepted: 02/06/2013] [Indexed: 02/05/2023]
Abstract
RATIONALE A rigorously investigated model of stress and antidepressant administration during pregnancy is needed to evaluate possible effects on the mother. OBJECTIVE The objective of this study was to develop a model of clinically relevant prenatal exposure to an antidepressant and stress during pregnancy to evaluate the effects on maternal care behavior. RESULTS Female rats implanted with 28-day osmotic minipumps delivering the SSRI escitalopram throughout pregnancy had serum escitalopram concentrations in a clinically observed range (17-65 ng/ml). A separate cohort of pregnant females exposed to a chronic unpredictable mild stress paradigm on gestational days 10-20 showed elevated baseline (305 ng/ml), and acute stress-induced (463 ng/ml), plasma corticosterone concentrations compared to unstressed controls (109 ng/ml). A final cohort of pregnant dams were exposed to saline (control), escitalopram, stress, or stress and escitalopram to determine the effects on maternal care. Maternal behavior was continuously monitored over the first 10 days after parturition. A reduction of 35 % in maternal contact and 11 % in nursing behavior was observed due to stress during the light cycle. Licking and grooming behavior was unaffected by stress or drug exposure in either the light or dark cycle. CONCLUSIONS These data indicate that: (1) clinically relevant antidepressant treatment during human pregnancy can be modeled in rats using escitalopram; (2) chronic mild stress can be delivered in a manner that does not compromise fetal viability; and (3) neither of these prenatal treatments substantially altered maternal care post parturition.
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Affiliation(s)
- Chase H. Bourke
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - Catherine F. Capello
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - Swati M. Rogers
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - Megan L. Yu
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - Katherine A. Boss-Williams
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - Jay M. Weiss
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
| | - Zachary N. Stowe
- Department of Psychiatry, Pediatrics and Obstetrics & Gynecology, University of Arkansas for Medical Sciences, Little Rock, AR, USA
| | - Michael J. Owens
- Laboratory of Neuropsychopharmacology, Department of Psychiatry and Behavioral Sciences, Emory University, Atlanta, GA, USA
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3
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Amasheh S, Milatz S, Krug SM, Bergs M, Amasheh M, Schulzke JD, Fromm M. Na+ absorption defends from paracellular back-leakage by claudin-8 upregulation. Biochem Biophys Res Commun 2008; 378:45-50. [PMID: 19000657 DOI: 10.1016/j.bbrc.2008.10.164] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2008] [Accepted: 10/30/2008] [Indexed: 11/19/2022]
Abstract
In distal colon, the limiting factor for Na(+) absorption is represented by the epithelial sodium channel (ENaC). During absorption, high transepithelial Na(+) gradients are observed. In human colon and in HT-29/B6-GR cells, we investigated whether Na(+) back-leakage is prevented by paracellular sealing. Tissues and cells were incubated with corticosteroids. Barrier properties were analyzed in electrophysiological experiments. Subsequently, analysis of ENaC and tight junction protein expression, localization, and regulation was performed. In colon, nanomolar aldosterone induced sodium absorption via ENaC. Concomitantly, paracellular (22)Na(+) permeability was reduced by half and claudin-8 within the tight junction complex was nearly doubled. Real-time PCR validated an increase of claudin-8 transcripts. Two-path impedance spectroscopy following ENaC induction in HT-29/B6-GR revealed a specific increase of paracellular resistance. These results represent an important physiological implication: Na(+) absorption is paralleled by claudin-8-mediated sealing of the paracellular barrier to prevent Na(+) back-leakage, supporting steep Na(+) gradients in distal colon.
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Affiliation(s)
- Salah Amasheh
- Institute of Clinical Physiology, Charité, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany
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Huang BS, Cheung WJ, Wang H, Tan J, White RA, Leenen FHH. Activation of brain renin-angiotensin-aldosterone system by central sodium in Wistar rats. Am J Physiol Heart Circ Physiol 2006; 291:H1109-17. [PMID: 16603700 DOI: 10.1152/ajpheart.00024.2006] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Functional studies indicate that the sympathoexcitatory and pressor responses to an increase in cerebrospinal fluid (CSF) [Na+] by central infusion of Na+-rich artificial cerebrospinal fluid (aCSF) in Wistar rats are mediated in the brain by mineralocorticoid receptor (MR) activation, ouabain-like compounds (OLC), and AT1-receptor stimulation. In the present study, we examined whether increasing CSF [Na+] by intracerebroventricular infusion of Na+-rich aCSF activates MR and thereby increases OLC and components of the renin-angiotensin system in the brain. Male Wistar rats received via osmotic minipump an intracerebroventricular infusion of aCSF or Na+-rich aCSF, in some groups combined with intracerebroventricular infusion of spironolactone (100 ng/h), antibody Fab fragments (to bind OLC), or as control gamma-globulins. After 2 wk of infusion, resting blood pressure and heart rate were recorded, OLC and aldosterone content in the hypothalamus were assessed by a specific ELISA or radioimmunoassay, and angiotensin-converting enzyme (ACE) and AT1-receptor binding densities in various brain nuclei were measured by autoradiography using 125I-labeled 351 A and 125I-labeled ANG II. When compared with intracerebroventricular aCSF, intracerebroventricular Na+-rich aCSF increased CSF [Na+] by approximately 5 mmol/l, mean arterial pressure by approximately 20 mmHg, heart rate by approximately 65 beats/min, and hypothalamic content of OLC by 50% and of aldosterone by 33%. Intracerebroventricular spironolactone did not affect CSF [Na+] but blocked the Na+-rich aCSF-induced increases in blood pressure and heart rate and OLC content. Intracerebroventricular Na+-rich aCSF increased ACE and AT1-receptor-binding densities in several brain nuclei, and Fab fragments blocked these increases. These data indicate that in Wistar rats, a chronic increase in CSF [Na+] may increase hypothalamic aldosterone and activate CNS pathways involving MR, and OLC, leading to increases in AT1-receptor and ACE densities in brain areas involved in cardiovascular regulation and hypertension.
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Affiliation(s)
- Bing S Huang
- Hypertension Unit, University of Ottawa Heart Institute, H360, 40 Ruskin St., Ottawa, Ontario, Canada K1Y 4W7
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Barmeyer C, Amasheh S, Tavalali S, Mankertz J, Zeitz M, Fromm M, Schulzke JD. IL-1beta and TNFalpha regulate sodium absorption in rat distal colon. Biochem Biophys Res Commun 2004; 317:500-7. [PMID: 15063785 DOI: 10.1016/j.bbrc.2004.03.072] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2004] [Indexed: 11/30/2022]
Abstract
The epithelial Na+ channel (ENaC) provides the main absorptive pathway of the distal large intestine. This study aimed to characterize regulatory influences of cytokines in rat late distal colon. After 6 h incubation with either IL1beta, TNFalpha, IFNgamma, or combinations of TNFalpha and IFNgamma, ENaC was measured as electrogenic Na+ transport after 8 h induction by 3 nM aldosterone (JNa) in totally stripped specimens in the Ussing chamber. Subsequently, alpha-, beta-, and gamma-ENaC subunit mRNAs were analyzed by Northern blotting. The gamma-ENaC promoter was cloned and characterized by reporter gene assays. IL-1beta and TNFalpha, but not interferon-gamma, decreased JNa. In parallel, beta- and gamma-ENaC transcription was inhibited, whereas alpha-ENaC was unaffected. gamma-ENaC promoter activity was inhibited by IL-1beta and TNFalpha but not by IFNgamma. We conclude that the pro-inflammatory cytokines IL-1beta and TNFalpha inhibit electrogenic sodium absorption in rat distal colon by mRNA expression regulation of the beta- and gamma-ENaC subunits.
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Affiliation(s)
- Christian Barmeyer
- Department of Gastroenterology, Infectious Diseases and Rheumatology, Campus Benjamin Franklin, Charité University Medicine Berlin, 12200 Berlin, Germany
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Epple HJ, Amasheh S, Mankertz J, Goltz M, Schulzke JD, Fromm M. Early aldosterone effect in distal colon by transcriptional regulation of ENaC subunits. Am J Physiol Gastrointest Liver Physiol 2000; 278:G718-24. [PMID: 10801264 DOI: 10.1152/ajpgi.2000.278.5.g718] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Aldosterone-induced sodium absorption is mediated by the epithelial Na(+) channel (ENaC). It is thought that the "early effect" is not based on genomic regulation of ENaC expression, because ENaC subunit transcription was reported to start later than Na(+) transport. We investigated electrogenic Na(+) absorption (J(Na)) and, in identical tissues, mRNA expression of ENaC subunits in early (EDC) and late (LDC) distal colon of the rat. In both segments, 8-h in vitro incubation with 3 nM aldosterone enhanced expression of beta- and gamma-ENaC mRNA and induced J(Na). J(Na) was 10 times higher in LDC than in EDC. alpha-ENaC mRNA was unchanged in EDC, whereas it decreased in LDC. In LDC, beta- and gamma-ENaC mRNA was induced 1 h after aldosterone addition, whereas J(Na) became apparent >1 h later. Downregulation of alpha-ENaC mRNA did not take part in acute regulation because it started after a lag time of 3 h. Time correlation of beta- and gamma-ENaC induction and J(Na) stimulation suggests that the early aldosterone effect on Na(+) absorption in distal colon is caused by transcriptional upregulation of beta- and gamma-ENaC expression.
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Affiliation(s)
- H J Epple
- Department of Clinical Physiology, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, 12200 Berlin, Germany
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7
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Grotjohann I, Schulzke JD, Fromm M. Electrogenic Na+ transport in rat late distal colon by natural and synthetic glucocorticosteroids. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:G491-8. [PMID: 9950824 DOI: 10.1152/ajpgi.1999.276.2.g491] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
The potency of in vitro-added corticosteroids to stimulate electrogenic Na+ absorption (JNa, the Na+ absorptive short-circuit current blockable by 10(-4) M amiloride) was determined in rat late distal colon. JNa was determined 8 h after steroid addition from the drop in short-circuit current caused by 10(-4) M amiloride. The concentration dependency of JNa was obtained for seven corticosteroids and compared with that established for aldosterone. Apparent mineralocorticoid potencies as determined from apparent Michaelis-Menten constant (Km) values were as follows: aldosterone 1. 2 nM >> RU-28362 20 nM = deoxycorticosterone 20 nM > deoxycortisol 36 nM >/= dexamethasone 37 nM >> corticosterone 170 nM > cortisol 210 nM. These steroids exhibited Vmax values of 9-13 micromol. h-1. cm-2 and similar concentration dependencies. Hill coefficients were between 1.6 and 2.1, suggesting cooperative effects between activated receptors. We conclude that corticosteroids exhibit graded mineralocorticoid potency instead of a sharp partition into exclusive groups of mineralocorticoid and nonmineralocorticoid hormones. The low apparent Km value of RU-28362 for mineralocorticoid action and the need for high concentrations of the mineralocorticoid antagonist mespirenone to block this response indicated that JNa in a native mammalian epithelium can be mediated by the glucocorticoid receptor. Glucocorticoid receptor-specific amounts of RU-28362 in combination with mineralocorticoid receptor-specific amounts of aldosterone or of the mineralocorticoid antagonist spironolactone showed cooperative action, suggesting a heterodimeric activation of JNa by the glucocorticoid receptor and mineralocorticoid receptor.
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Affiliation(s)
- I Grotjohann
- Institut für Klinische Physiologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, D-12200 Berlin, Germany
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8
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Grotjohann I, Gitter AH, Köckerling A, Bertog M, Schulzke JD, Fromm M. Localization of cAMP- and aldosterone-induced K+ secretion in rat distal colon by conductance scanning. J Physiol 1998; 507 ( Pt 2):561-70. [PMID: 9518713 PMCID: PMC2230785 DOI: 10.1111/j.1469-7793.1998.561bt.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
1. Aldosterone- and adrenaline-induced K+ secretion were investigated in rat late distal colon using conductance scanning and Ussing chamber techniques. K+ secretion was unmasked by the K+ channel blocker tetraethylammonium (TEA). Electrogenic Na+ absorption was inhibited by amiloride. Rb+ net fluxes consistently measured about 80% of K+ secretion estimated using change in short-circuit current (delta ISC) measurements. 2. Partial block of K+ absorption by mucosal ouabain did not change TEA-sensitive K+ secretion. Thus, K+ absorption and K+ secretion are not coupled. 3. Additivity of Rb+ fluxes as well as delta ISC caused by 3 nM aldosterone (6 h in vitro incubation) and, subsequently, adrenaline suggested additivity of aldosterone-induced and cAMP-mediated K+ secretion in the presence of amiloride. 4. Conductance scanning under control conditions revealed a small TEA-sensitive K+ conductivity in surface epithelium (0.3 +/- 0.2 mS cm-2) but not in crypts, as well as a small basal K+ secretion in surface epithelium (delta ISC = 0.3 mumol h-1 cm-2), which increased during sham incubation. 5. Aldosterone (3 nM, 6 h in vitro incubation) resulted, after correction for the basal K+ secretion, in a K+ secretion of delta ISC = 0.9 mumol h-1 cm-2. Aldosterone induced a TEA-sensitive conductivity of 1.1 +/- 0.3 mS cm-2 in surface epithelium, but not in crypts. 6. Adrenaline (5 microM) caused, in fresh tissue, a K+ secretion of delta ISC = 1.2 mumol h-1 cm-2 and equal conductivity changes in crypts (0.7 +/- 0.2 mS cm-2) and surface epithelium (0.7 +/- 0.1 mS cm-2). 7. We conclude that K+ secretion induced by aldosterone in physiological concentration is restricted to surface epithelium, whereas cAMP-mediated K+ secretion is located equally in crypts and surface epithelium.
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Affiliation(s)
- I Grotjohann
- Institut für Klinische Physiologie, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Germany
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9
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el Fazaa S, Gharbi N, Gauquelin G, Gharib C, Kamoun A. [Effects of simulated weightlessness on the hypophyseal-cortical-adrenal axis in the pregnant rat]. Arch Physiol Biochem 1997; 105:53-7. [PMID: 9324416 DOI: 10.1076/apab.105.1.53.13150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The eventual part of stress in the hormonal responses to simulated weightlessness was studied during gestation in the rat. We have compared these responses with the effects of two other situations well-known to provoke stress: ultrasounds and denutrition. An increase of blood and adrenal corticosterone levels was found in mothers after denutrition, neither after ultrasounds nor after simulated weightlessness. In foetuses, a decrease of weight was noted after denutrition and simulated weightlessness. Foetal suprarenal corticosterone remained normal when mothers were submitted to simulated weightlessness. In this group, a decrease in foetal weight was found that could be explained by non suprarenal hormonal factors or by circulation disturbances.
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Affiliation(s)
- S el Fazaa
- Département de Biologie, Faculté des Sciences de Tunis, Tunisie
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10
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Metz CJ, Ise T, Häberle DA. Chloralose/ketamine anaesthesia preserves a form of postprandial sodium chloride balance in Wistar rats. Pflugers Arch 1996; 432:944-7. [PMID: 8772148 DOI: 10.1007/s004240050220] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Studies on the mechanisms underlying Na balance in anaesthetized rats are complicated by the fact that the most frequently used barbiturate anaesthetics attenuate or abolish this phenomenon. In the present study we show that a combination of nonbarbiturate anaesthetics: chloralose (140 mg/kg i.v.) and ketamine (30 mg/kg i.m. ), preserve the ability of rats to excrete intragastrically applied NaCl loads dose dependently. Thus rats anaesthetized with this regime excreted 86-102% of in- tragastrically applied NaCl whereas rats anaesthetized with thiobutabarbitone sodium (Inactin) excreted only 20-28%. We conclude that chloralose/ketamine anaesthesia is suitable for studies on Na balance mechanisms.
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Affiliation(s)
- C J Metz
- Dept. of Physiology, Pettenkoferstr 12, D-80336 Munich, Germany
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11
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Li M, Shen Y, Halloran BP, Baumann BD, Miller K, Wronski TJ. Skeletal response to corticosteroid deficiency and excess in growing male rats. Bone 1996; 19:81-8. [PMID: 8853849 DOI: 10.1016/8756-3282(96)00170-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The study was designed to investigate bone histomorphometric changes induced by corticosteroid deficiency and supplementation at different dose levels in the rat skeleton. Male rats were adrenalectomized (ADX) or sham-operated and divided into six groups. At 2 days after surgery, sham-operated control rats (CON + PLA) and one group of ADX rats (ADX + PLA) were implanted subcutaneously (s.c.) with placebo pellets. ADX rats in the remaining four groups (ADX + C25, ADX + C50, ADX + C100, and ADX + C300) were implanted sc with corticosterone pellets designed to release 25, 50, 100, or 300 mg of the hormone over a 60 day period. Each ADX rat was also implanted sc with an aldosterone pellet (2.5 mg) similarly designed to release its contents over the same time period. All rats were killed at 3 weeks after implantation of pellets. Terminal blood samples were collected for serum biochemistry and the proximal tibial metaphyses (PTM), tibial diaphyses, and first lumbar vertebrae (LV) were processed undecalcified for quantitative bone histomorphometry. A dose-dependent increase in serum corticosterone concentration was observed in ADX rats implanted with hormone pellets. In comparison to CON + PLA rats, ADX + PLA rats had lower cancellous bone volume associated with a stimulation in longitudinal bone growth, an increase in mineral apposition rate, and a trend for increased osteoclast and osteoblast surfaces in PTM. In contrast, cancellous bone of ADX + C25 rats was preserved at nearly the CON + PLA level. However, the higher doses of corticosterone increased cancellous bone mass, but decreased longitudinal bone growth and all indices of bone resorption and formation in a dose-dependent manner in PTM. Similar cancellous bone changes were observed in the LV of corticosterone-treated rats, with the exception of a lack of an hormonal effect on cancellous bone mass. In the tibial diaphysis, corticosterone inhibited periosteal bone formation in a dose-dependent manner, but did not affect cortical bone mass. The results indicate that corticosteroid deficiency induces cancellous osteopenia, whereas supplementation with a near physiologic dose of the hormone prevents this bone loss in ADX rats. Furthermore, corticosteroid excess inhibits bone growth and bone turnover in a dose-dependent manner, but does not induce cancellous osteopenia in growing male rats.
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Affiliation(s)
- M Li
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville 32610, USA
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12
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Asher C, Wald H, Rossier BC, Garty H. Aldosterone-induced increase in the abundance of Na+ channel subunits. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:C605-11. [PMID: 8770001 DOI: 10.1152/ajpcell.1996.271.2.c605] [Citation(s) in RCA: 191] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The highly selective, amilorideblockable Na+ channel is a major target to the natriferic action of the mineralocorticoid aldosterone. This rat epithelial Na+ channel (rENaC) has been recently cloned from colon and is composed of three homologous subunits denoted alpha-, beta-, and gamma-rENaC (C. M. Canessa, L. Schild, G. Buell, B. Thorens, L. Gautschi, J.-D. Horisberger, and B. C. Rossier. Nature Lond. 367: 463-467, 1994). We have tested the effects of corticosteroids on the abundance of mRNA coding for each subunit in kidney cortex and distal colon. Chronic treatment of rats with aldosterone or dexamethasone evoked in kidney cortex a small induction of alpha-rENaC and no change in beta- and gamma-rENaC. In distal colon, however, beta- and gamma-rENaC were strongly induced by either aldosterone or dexamethasone, whereas alpha-rENaC was constitutively expressed. Most of the aldosterone-induced increase in beta- and gamma-rENaC mRNA took place during 3-24 h after plasma aldosterone was elevated. A similar differential induction of rENaC subunits in kidney and colon was also evoked by a Na(+)-free diet. The effects of salt deprivation were reversed by resalinating rats with a half time of < 2 h, suggesting a high turnover rate of at least beta- and gamma-rENaC. The data are consistent with the possibility that induction of channel subunits contributes to the chronic but not the acute response to aldosterone in the colon. Such a mechanism is not likely to play a major role in cortical collecting ducts.
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Affiliation(s)
- C Asher
- Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel
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13
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Köckerling A, Sorgenfrei D, Fromm M. Electrogenic Na+ absorption of rat distal colon is confined to surface epithelium: a voltage-scanning study. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:C1285-93. [PMID: 8498487 DOI: 10.1152/ajpcell.1993.264.5.c1285] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
There is no quantitative assignment of large intestinal electrogenic Na+ absorption to surface epithelium and crypts so far. We determined the spatial distribution of electrogenic Na+ absorption to crypts and surface epithelium of rat late distal colon using a modified voltage-scanning technique. Voltage deflections resulting from external 30-Hz current were sensed by an extracellular microelectrode stepping at 0.7 Hz above crypt openings or surface epithelium. Local conductances were calculated applying a planar model of electrical field distribution to surface epithelium and a electrostatic disk source model to the crypts. These models were confirmed by methodological experiments where the electrode position was varied in vertical and horizontal direction. Electrogenic Na+ absorption was detected by blocking apical Na+ channels by mucosal 0.1 mM amiloride. Under control conditions surface epithelium contributed 44% (2.0 +/- 0.2 mS/cm2) and crypts 56% (2.6 +/- 0.2 mS/cm2) to the total conductance of 4.6 +/- 0.4 mS/cm2. Electrogenic Na+ absorption was induced by 6 h in vitro incubation in a medium containing 3 nM aldosterone. This caused a short-circuit current (ISC) of 12.1 +/- 0.8 mumol.h-1.cm-2, which was paralleled by a 2.5-fold increase in surface epithelial conductance to 5.1 +/- 0.4 mS/cm2, whereas crypt conductance was not significantly altered (3.0 +/- 0.2 mS/cm2). Amiloride reversed ISC to -0.8 +/- 0.1 mumol.-1.cm-2 and decreased surface epithelium conductance to 2.3 +/- 0.3 mS/cm2 but again had no significant effect on crypt conductance (2.5 +/- 0.3 mS/cm2). Sham incubation (no hormones added) for 6 h neither induced electrogenic transport nor altered local epithelial conductances.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- A Köckerling
- Institut für Klinische Physiologie, Klinikum Steglitz, Freie Universität Berlin, Germany
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14
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Bogićević M, Ilić S, Djordjević V, Ivić M, Koraćević D, Stefanović V. Thyroid hormone profiles in experimental acute renal failure. Ren Fail 1993; 15:173-9. [PMID: 8469784 DOI: 10.3109/08860229309046149] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Thyroid hormone profiles were determined in two groups of dogs made uremic, either by i.v. uranyl nitrate 10 mg/kg BW injection or by bilateral ureteral ligation, and in one group of sham-operated animals. Each group consisted of 6 dogs and served as its own control. From blood samples taken in 12-h intervals up to 144 h for uranyl nitrate-injected dogs and 96 h for operated dogs, serum levels of T4, T3, fT4, fT3, rT3, and cortisol were measured by radioimmunoassays. The results obtained in both groups of uremic dogs showed an initial sharp fall of T4, T3, fT4, and fT3 followed by a plateau or retarded decrease. In sham-operated dogs the fall of these hormones was slight and of short duration. Reverse T3 had a tendency to increase in all groups examined, but a significant elevation was recorded only after bilateral ureteral ligation. In this group cortisol serum levels were found the highest, being also significantly increased in the other two groups. The temporal coincidence of the most marked alterations in T3, rT3, and cortisol serum concentrations indicates a significant role of stress in thyroid dysfunction. Although serum creatinine rise and weight loss were not parallel with thyroid hormone alterations, the involvement of uremic compounds and malnutrition in this process is also quite clear. Thus, the data presented suggest simultaneous influences of uremic toxins, stress, and malnutrition on the induction of thyroid dysfunction in dogs made uremic by uranyl nitrate injection or bilateral ureteral ligation.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Bogićević
- Institute of Nephrology and Hemodialysis, University Clinical Center, Nis, Yugoslavia
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Fromm M, Schulzke JD, Hegel U. Control of electrogenic Na+ absorption in rat late distal colon by nanomolar aldosterone added in vitro. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:E68-73. [PMID: 8430790 DOI: 10.1152/ajpendo.1993.264.1.e68] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
It has been possible to obtain in a mammalian epithelium of dietetically and surgically untreated animals a dose response of in vitro-added aldosterone (Aldo, 10(-10) to 10(-5) M) on electrogenic Na+ absorption (JeNa). JeNa was measured in the Ussing chamber on stripped rat late distal colon 8 h after in vitro addition of Aldo. Submaximal effects were obtained at 3 nM Aldo; after a lag time of 2 h, short-circuit current (Isc) increased to a maximum of 234 +/- 15 microA/cm2 and dropped after 0.1 mM amiloride to -18 +/- 3 microA/cm2, resulting in JeNa of 9.4 +/- 0.6 mumol.h-1 x cm-1. Net Na+ tracer fluxes and Isc exhibited parallel time courses, so that electroneutral Na+ transport was not induced in late distal colon by acute Aldo. A plot of JeNa vs. Na conductance revealed an electromotive force (ENa) of 126 +/- 1 mV for all Aldo concentrations tested. Kinetic data were as follows: Michaelis constant 1.2 nM, maximal velocity (Vmax) 10.5 mumol.h-1 x cm-2, and Hill coefficient 2.1. In contrast to the large effect in late distal colon, 3 nM Aldo caused JeNa of < 1 mumol.h-1 x cm-2 in early distal colon, proximal colon, and cecum. Antimineralocorticoid sensitivity and ENa did not vary with Aldo concentration or time of the experiment, consistent with a unique mechanism during the early and late response up to 8 h, as well as at mineralocorticoid and glucocorticoid Aldo concentrations. Acute Aldo in a range of 0.1-10 nM fully controls JeNa between zero and Vmax in late distal colon.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Fromm
- Institut für Klinische Physiologie, Freie Universität Berlin, Germany
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16
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Abstract
The present study investigated the renal function in male Sprague-Dawley rats receiving continuous NaHCO3 (0.077 M) infusion. The renal effects of aldosterone administration in this preparation were also examined. Continuous NaHCO3 infusion significantly (p less than 0.01) depressed plasma aldosterone concentration to 2.36 +/- 1.22 nmol (n = 8) when compared to saline infused rats (4.36 +/- 0.72 nmol, n = 7). The low plasma aldosterone levels in HCO3- infused rats was associated with renal loss of large amounts of K+ and hypokalaemia. Aldosterone administration (42 pmol/min) for 2 h significantly (p less than 0.01) reduced the Na+ excretion rate in bicarbonate infused rats from a mean peak of 9.82 +/- 1.16 to 5.16 +/- 1.20 mumol/min (n = 8). Aldosterone administration did not alter renal excretion in saline-infused rats. It is concluded that NaHCO3 loading depressed endogenous aldosterone secretion, and that this lowered endogenous plasma aldosterone level allows the mineralocortoid effect of exogenous aldosterone to be observed.
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17
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Fromm M, Schulzke JD, Hegel U. Aldosterone low-dose, short-term action in adrenalectomized glucocorticoid-substituted rats: Na, K, Cl, HCO3, osmolyte, and water transport in proximal and rectal colon. Pflugers Arch 1990; 416:573-9. [PMID: 2235298 DOI: 10.1007/bf00382692] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The short-term action of aldosterone in physiological concentration on net fluxes of Na, K, Cl, HCO3, osmolytes, and water was examined in the proximal colon and rectal colon of adrenalectomized (ADX) rats in vivo. The measuring time was 12 h, divided in eight periods of 90 min. (a) Aldosterone alone (6 nmol h-1 kg-1) did not stimulate transport in ADX rats. In these experiments plasma [K] increased to fatal values. A basal glucocorticoid substitution of 24 nmol h-1 kg-1 corticosterone caused plasma K to stay constant throughout the experiment, so that epithelial transport was not handicapped by non-specific effects of ADX, but this also did not restore the decreased transport of ADX rats to control values. Under these conditions (absence of aldosterone) in the rectal colon Na and H2O transport was zero, whereas in the proximal colon flux rates were depressed by between 30% and 50%. In contrast, basal glucocorticoid substitution of 18 nmol h-1 kg-1 corticosterone plus infusion of 6 nmol h-1 kg-1 aldosterone caused transport stimulation to values not significantly different from those of non-ADX controls. We conclude that after ADX, aldosterone at physiological concentrations increases transport if, as a prerequisite, a basal glucocorticoid substitution is provided. Transport of Na, K, and H2O is under the total control of aldosterone in the rectal colon but is only moderately altered in the proximal colon.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M Fromm
- Institut für Klinische Physiologie, Freie Universität Berlin
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Hegel U, Fromm M. Electrical measurements in large intestine (including caecum, colon, rectum). Methods Enzymol 1990; 192:459-84. [PMID: 2074804 DOI: 10.1016/0076-6879(90)92087-t] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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Turnamian SG, Binder HJ. Regulation of active sodium and potassium transport in the distal colon of the rat. Role of the aldosterone and glucocorticoid receptors. J Clin Invest 1989; 84:1924-9. [PMID: 2592566 PMCID: PMC304073 DOI: 10.1172/jci114380] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
To determine whether mineralocorticosteroids and glucocorticosteroids have specific effects on colonic electrolyte transport, we compared the effect of aldosterone and RU 28362, a glucocorticoid receptor-specific agonist that does not bind to the aldosterone receptor, on unidirectional Na, Cl, and K fluxes across isolated mucosa of the rat distal colon. Continuous infusion of aldosterone for 7 d produced changes in four specific transport processes: induction of both active electrogenic, amiloride-sensitive sodium absorption and active electrogenic potassium secretion, enhancement of active electroneutral potassium absorption, and inhibition of electroneutral Na-Cl absorption, the predominant transport process in this epithelium. In contrast, continuous infusion of RU 28362 for 1-11 d produced a sustained increase in electroneutral Na-Cl absorption. This glucocorticoid receptor-specific agonist did not induce electrogenic sodium absorption nor affect either potassium absorption or secretion. These studies demonstrate that aldosterone (i.e., mineralocorticoid) and glucocorticoid receptors modulate separate and specific changes in active sodium and potassium transport. These results suggest that other glucocorticoids (e.g., dexamethasone, methylprednisolone) are not glucocorticoid receptor-specific and that their effects on electrogenic sodium absorption and potassium transport most likely represent the binding of these agonists to the aldosterone receptor.
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Affiliation(s)
- S G Turnamian
- Department of Internal Medicine, Yale University, New Haven, Connecticut 06510
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Schulzke JD, Fromm M, Hegel U, Riecken EO. Ion transport and enteric nervous system (ENS) in rat rectal colon: mechanical stretch causes electrogenic Cl-secretion via plexus Meissner and amiloride-sensitive electrogenic Na-absorption is not affected by intramural neurons. Pflugers Arch 1989; 414:216-21. [PMID: 2755775 DOI: 10.1007/bf00580966] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The initial phase of in vitro experiments in Ussing-type chambers on large intestine is characterized by short-circuit currents (ISC) declining from high starting values to a lower plateau within 0.5 h. The origin of this "initial ISC-transient" was investigated by ISC measurements on partially stripped segments of rat rectal colon. Transport was pre-stimulated in vivo by keeping animals in barbiturate-anesthesia for 5 h prior to tissue preparation. This procedure caused by endogenous aldosterone-liberation amiloride-sensitive Na-absorption to become the predominant electrogenic transport. The initial ISC-transient was abolished by tetrodotoxin (TTX, 1 microM), indicating a neuronal mediation of this phenomenon. In order to identify the transport which was subject to neuronal control, the amiloride-sensitive Na-absorption was measured during electrical field stimulation (bipolar rectangular pulses: 5 Hz, 1 ms, +/- 6 mA). There was no difference to unstimulated controls. In contrast, the initial ISC-transient was dependent on Cl in the bath following Michaelis-Menten-kinetics (KM = 20 mM) and could be prevented by 10 microM serosal bumetanide. Then, initial filling of the Ussing-chamber was imitated during the course of the experiment by removal and immediate re-addition of the bathing fluid. This procedure caused ISC-changes of similar appearance as the initial ISC-transient. To verify that indeed mechanical stretch is the sensory stimulus triggering the initial ISC-transient, the effect of small pressure oscillations was studied. This also produced an ISC-transient which was TTX-sensitive and was abolished after removal of the submucosal plexus Meissner by total stripping.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J D Schulzke
- Medizinische Klinik, Abteilung für Gastroenterologie, Freie Universität Berlin
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Thomas DH, Skadhauge E. Function and regulation of the avian caecal bulb: influence of dietary NaCl and aldosterone on water and electrolyte fluxes in the hen (Gallus domesticus) perfused in vivo. J Comp Physiol B 1989; 159:51-60. [PMID: 2738202 DOI: 10.1007/bf00692683] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The function of the caecal bulb, and its adaptation to chronic high- or low-Na+ intake, was investigated by in vivo perfusion of anaesthetised birds. Effects of acute aldosterone injection (125 micrograms.kg-1 body mass) were also measured. Evidence was found for primary active net absorption of Na+, inducing parallel Na-linked absorption of water and Cl- and secretion of K+. Around 20-35% of total Cl- absorption and K+ secretion were independent of Na+ fluxes, and these components appear to be driven by passive processes with apparent conductances of 6.3 X 10(-3) (GCl) and 1.1 X 10(-3) (GK) S.cm-2. Acetate (40 mM) stimulated Na+ fluxes (8.5-9.9 microEq.cm-2.h-1) and Na-linked water fluxes (27-44 microliters.cm-2.h-1). Increased coupling ratios (2.9-4.6 microliters.microEq-1) and other data indicate that these effects may be due to increased osmotic permeabilities of barriers involved in the Na-linked water transfer pathway. Low-Na+ maintenance enhanced EPD (49-69 mV, serosa positive) and all net fluxes: JNa (6.8-11.6); JK (-3.2--4.3); JCl (4.3-5.6 microEq.cm serosal area-2.h-1); Jv (28-43 microliters.cm-2.h-1) (mucosal-serosal fluxes positive). Acute aldosterone enhanced JNa (10.8-14.0 microEq.cm-2.h-1) and EPD (54-66 mV) by 3 h after injection, but had no effect on the Na-linked components of JK or JCl.
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Affiliation(s)
- D H Thomas
- School of Pure and Applied Biology, University of Wales, Cardiff, United Kingdom
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Bastl CP. Regulation of cation transport by low doses of glucocorticoids in in vivo adrenalectomized rat colon. J Clin Invest 1987; 80:348-56. [PMID: 2956277 PMCID: PMC442244 DOI: 10.1172/jci113079] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
A dose response curve for glucocorticoid-induced proximal and distal colonic cation transport in vivo was established in adrenalectomized rats. All doses (0.5-50 nmol/100 g body wt) stimulated sodium absorption. Distal sodium absorption did not saturate at dexamethasone levels that saturate the glucocorticoid receptor but also bind to greater than 35% of aldosterone receptors. Saturation of the pure glucocorticoid response occurred in both segments with RU26988, a synthetic glucocorticoid that does not occupy aldosterone receptors. Maximum velocities for pure glucocorticoid-induced sodium absorption were 15 and 16 mu eq/min per g dry tissue, and Michaelis constants (Km) were 4.2 and 4.6 X 10(-9) mol/liter for proximal and distal colon. Kms are similar to the dissociation constant for the colonic glucocorticoid receptor and too low for significant aldosterone receptor occupancy. Dexamethasone increased sodium absorption significantly within 30 min of injection, suggesting the response is not dependent on new protein synthesis. Similar time and dose responses in proximal and distal colon suggest glucocorticoids stimulate the same pathway in both segments.
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Fromm M, Hegel U. Net ion fluxes and zero flux limiting concentrations in rat upper colon and rectum during anaesthesia-induced aldosterone liberation. Pflugers Arch 1987; 408:185-93. [PMID: 2436140 DOI: 10.1007/bf00581350] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Thiobutabarbital anaesthetized and abdominally operated control rats develop high endogenous plasma levels of both aldosterone and corticosterone during the course of a 12 h experiment. This effect was used as a model for examining 'acute' steroid action (i) on net ion and water fluxes and (ii) on zero flux luminal limiting concentrations in rat upper colon (proximal 50% of large intestine) and rectum (distal 40%). Experiments of both kinds consisted of 8 independent 90 min measuring periods. (i) In rectum net fluxes of Na, K, osmolytes (sum of all solutes) and water started at low levels around zero, began to rise about 2 h after plasma levels of aldosterone had increased, and reached plateau values around the 6th hour of anaesthesia. In upper colon, fluxes of Na, K, Cl, and osmolytes were high from the beginning and did not vary significantly with time. (ii) At zero flux conditions limiting concentrations of Na in the hormonally unstimulated phase of the experiment were 20 +/- 3 mM in upper colon and 22 +/- 3 mM in rectum. After maximal endogenous aldosterone liberation zero flux concentrations were 5.2 mM in upper colon and 2.2 mM in rectum, corresponding to luminal fluid to plasma ratios (LF/P) of 0.040 and 0.016, respectively. Amiloride reduced the maximal Na gradient in rectum to a LF/P of 0.3 but was not effective in upper colon and did not prevent the stimulating effect of aldosterone in this segment. Under all experimental conditions zero flow concentrations of K were higher than consistent with a solely passive distribution, indicating simultaneous passive and active secretion in both segments. In contrast to the findings of others, the luminal fluid remained isoosmolar with plasma in all zero flux experiments.(ABSTRACT TRUNCATED AT 250 WORDS)
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Schulzke JD, Fromm M, Hegel U. Epithelial and subepithelial resistance of rat large intestine: segmental differences, effect of stripping, time course, and action of aldosterone. Pflugers Arch 1986; 407:632-7. [PMID: 3797217 DOI: 10.1007/bf00582644] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Epithelial and subepithelial electrical resistances of rat large intestine were measured by means of a 4-electrode AC impedance technique in three segments, colon ascendens, colon descendens and rectum. Epithelial resistance of colon ascendens and colon descendens was about 35 omega X cm2 and not different between these two segments. It was, however, about 3 times higher in rectum (99 omega X cm2). This finding is in accord with our previous observation of about 3-fold higher net fluxes of ions and water in colon ascendens and colon descendens than in rectum. It confirms the concept of a main functional difference between the terminal part of the large intestine (rectum) and the more proximal segments (colon). The acutely (within hours) varied level of aldosterone by keeping the rats for 7 h in anaesthesia caused in the rectum a more than 10-fold increase in short circuit current (Isc) and transepithelial voltage but no significant decrease in resistance. Similarly, the decline in Isc, as regularly observed in the early phase of in vitro measurements on partially stripped large intestine, was paralleled by voltage changes but not by changes in resistance. We conclude that the wide range of resistance values published so far was caused to a great extent by including various portions of colon or rectum. By comparing intact (not stripped) and partially stripped preparations (muscularis propria removed) of the rectum it was shown that partial stripping did not alter the epithelial resistance but reduced the subepithelial resistance in this segment from 26 to 8 omega X cm2, or by 68%.(ABSTRACT TRUNCATED AT 250 WORDS)
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Mujais SK, Chekal MA, Jones WJ, Hayslett JP, Katz AI. Modulation of renal sodium-potassium-adenosine triphosphatase by aldosterone. Effect of high physiologic levels on enzyme activity in isolated rat and rabbit tubules. J Clin Invest 1985; 76:170-6. [PMID: 2991336 PMCID: PMC423735 DOI: 10.1172/jci111942] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The purpose of this study was to determine the nephron site, time course, and mechanism of mineralocorticoid action on renal tubular Na-K-ATPase in rats and rabbits, without dietary manipulation and by using the natural mineralocorticoid aldosterone. Sustained, high physiologic levels of circulating aldosterone mimicking those produced endogenously during potassium loading or sodium deprivation were provided by constant delivery of the hormone in doses of 5 or 50 micrograms/100 g body wt per 24 h, respectively, from osmotic minipumps implanted subcutaneously. In adrenal-intact rats receiving the 5-microgram dose, aldosterone levels were similar to those seen in animals fed a high K diet and produced a time-dependent increase in Na-K-ATPase activity in the cortical-collecting tubule (CCT) to a level 103% higher than in controls after 7 d (2,007 +/- 178 vs. 989 +/- 72 pmol/mm per h, P less than 0.001); the enzyme activity in the proximal convoluted tubule, medullary thick ascending limb, and the inner stripe of the medullary-collecting tubule did not change significantly. The increment in CCT Na-K-ATPase was larger (142%) in animals receiving for the same period of time the 50-micrograms dose, which produced circulating aldosterone levels similar to those of sodium-deprived rats. A significant stimulation of Na-K-ATPase activity was seen in the CCT of adrenalectomized rats after 24 h of treatment with either dose of the hormone, and at 12 h only in animals receiving the 50 micrograms/100 g per 24 h regimen. To determine whether the enhanced Na-K-ATPase activity produced by aldosterone is due to synthesis of new enzyme units or to alteration in its kinetics, we examined the ouabain-binding capacity and the affinity for Na and K of the enzyme from CCT of rabbits treated with 5 micrograms/100 g body wt per 24 h aldosterone for 3 d. These experiments revealed a parallel increment on Na-K-ATPase activity and specific [3H]ouabain binding in aldosterone-treated rabbits, while the affinity of the enzyme for either sodium or potassium was unaltered. The results of this study indicate that high physiologic levels of aldosterone simulating those measured during K loading or Na deprivation lead to a segment-specific increase in Na-K-ATPase activity in the CCT. This effect was time-and dose-dependent and was due to an increase in the number of active enzyme units. The segmental specificity and time course of the increase in enzyme activity suggest that modulation of Na-K-ATPase by aldosterone plays a role in the chronic adaptation of the CCT to altered availability of sodium and potassium, and therefore in the homeostasis of these cations by the kidney.
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