Dexamethasone-treated Animals Research Articles

Regulation of expression of the [3H]-dofetilide binding site associated with the delayed rectifier K+ channel by dexamethasone in neonatal mouse ventricle.

Developmental shortening of cardiac action potential duration in mouse appears to result, at least in part, from replacement of the rapid component of the delayed rectifying potassium current (IKr) with the transient outward current (ItO1). This developmental decrease in the IKr current density was paralleled by a loss of the high affinity [3H]-dofetilide binding site and loss of prolongation of action potential duration by dofetilide. Since glucocorticoid treatment prevented the developmental shortening of action potential duration in rats in the perinatal period, we hypothesized that chronic dexamethasone treatment would alter the developmental loss of IKr channel expression in mice. Accordingly, 10-day-old mice were randomly allocated to chronic in vivo dexamethasone treatment (1 mg/kg) or placebo treatment for 3-5 days. At 15 days of life, transmembrane action potentials were recorded in right ventricular endocardium and [3H]-dofetilide equilibrium binding studies were performed. The baseline action potential duration in the dexamethasone-treated animals was significantly greater than that in the control group (66+/-3 v 54+/-10 ms, respectively; P<0.01). Moreover, dofetilide significantly prolonged action potential duration in the dexamethasone-treated animals, but had no effect on the placebo-treated group (P<0.01). In addition, a high affinity [3H]-dofetilide binding site (Kd 96+/-21 nM and Bmax 69+/-13 fmoles/mg protein) was observed in the dexamethasone-treated group (n=5), whereas no specific [3H]-dofetilide binding was observed in the placebo-treated group. In conclusion, dexamethasone modulates developmental regulation of IKr channel expression in mouse ventricle.

The protective effect of dexamethasone against radiation damage induced by interstitial irradiation in normal monkey brain.

The protective effect of dexamethasone against radiation damage is unclear. We examined the effect of early treatment of high-dose dexamethasone on iridium-192-induced damage to normal brain tissue. Brain damage induced by interstitial irradiation with iridium-192 was evaluated with sequential magnetic resonance imaging and proton magnetic resonance spectroscopy in 11 adult monkeys, with or without short-term high-dose dexamethasone treatment. Dexamethasone (1 mg/kg of body weight/d) was administered intramuscularly to five irradiated animals every 24 hours, beginning 2 days before and ending 7 days after irradiation. Magnetic resonance imaging and proton magnetic resonance spectroscopy were performed 1 week, 1 month, and 3 months after irradiation. Magnetic resonance imaging performed 1 week after irradiation revealed marked edema in five nontreated animals. In dexamethasone-treated animals, the volume of edema was reduced significantly, compared to that of nontreated animals, 1 week and 1 month after irradiation. The volume of ring enhancement in dexamethasone-treated animals was also reduced significantly, compared to that of nontreated animals, 3 months after the irradiation. Proton magnetic resonance spectroscopy spectra revealed that N-acetylaspartate and choline peaks were reduced 1 week after irradiation in both groups. However, there were no statistically significant differences between the two groups at any time points. These results suggest that dexamethasone treatment may have an antiedema effect at an early stage and may modify subsequent development of vascular and inflammatory changes but may have no effect of preventing radiation-induced necrosis and the reduction of N-acetylaspartate after brachytherapy.

The neutrophil migration induced by tumour necrosis factor alpha in mice is unaffected by glucocorticoids

Macrophages harvested from the peritoneal cavities of rats release a neutrophil chemotactic factor (MNCF) in response to stimulation with Gram-negative bacterial lipopolysaccharide (LPS). MNCF has been shown to be active in rats treated with dexamethasone, a glucocorticoid that usually inhibits the neutrophil migration induced in this species by interleukin (IL)-1, tumour necrosis factor alpha (TNFα), IL-8, C5a and leukotriene B4 (LTB4). Here we report that macrophages harvested from peritoneal cavities of mice, and stimulated in vitro with LPS, also release a factor that induces neutrophil migration in dexamethasone-treated animals. This chemotactic activity was neutralized by the incubation of the LPS-stimulated macrophage supernatants with a purified polyclonal IgG anti-mouse TNFα. In addition, significant amounts of TNF were detected in the supernatants. The neutrophil migration induced by intraperitoneal administration of recombinant murine TNFα was also unaffected by pretreatment of the mice with dexamethasone. Moreover, neutrophil migration induced by intraperitoneal injection of LPS was completely blocked by pretreatment of the mice with a monoclonal antibody against murine TNFα. In conclusion, our results support the hypothesis that, in contrast to the role of TNF in rats (where it indirectly induces neutrophil migration), in mice, it may be an important mediator in the recruitment of neutrophils to inflammatory sites.

Expression of IGF-II and H19 mRNA in the neonatal rat during normal maturation and after dexamethasone administration.

In this study, the expression of IGF-II and H19 was examined in the liver, skeletal muscle and choroid plexus of the neonatal rat during normal maturation and after the administration of dexamethasone. If the two genes share common regulatory elements as postulated by an enhancer competition system, their patterns of expression should remain similar throughout maturation and after treatment with dexamethasone. In the liver, down-regulation of IGF-II and H19 during maturation and after dexamethasone administration was shown. This is consistent with the hypothesis that IGF-II and H19 are regulated by common enhancers. In the secretory cells of the choroid plexus, where expression of IGF-II is known to be biallelic, IGF-II was expressed in both untreated and dexamethasone-treated animals, regardless of age, whereas H19 expression was not detectable. This is consistent with the postulate that only one gene from each allele can be engaged by the enhancers. In skeletal muscle, H19 continues to be expressed in the adult after IGF-II is switched off suggesting that IGF-II can also be regulated independently of H19.

Differential effects of betamethasone and dexamethasone fetal administration of parturition in sheep

We tested the hypothesis that betamethasone is more potent than dexamethasone in inducing the essential mechanisms of parturition in sheep. Twenty-one sheep were instrumented under general anesthesia with maternal and fetal arterial and venous catheters and myometrial electromyogram electrodes at 117 days' gestation (dGA). At 125 dGA at 12:00 PM, after 2 days of baseline recording, either saline (n = 7, control group), betamethasone (n = 7), or dexamethasone (n = 7) was administered into the fetal jugular vein at a rate of 10 micrograms/hour. A total dose of 0.48 mg was given over the next 48 hours. The animals underwent autopsy 3 days after the end of the infusion period (130 dGA), or earlier if labor resulted from the glucocorticoid administration. Daily maternal and fetal arterial blood samples (4 mL) for hormone measurement were taken at 10:00 AM throughout the study period. Additional arterial blood samples were taken if the animal developed labor. Maternal plasma progesterone and fetal ACTH and cortisol concentrations were measured by radioimmunoassay, and corticosteroid-binding globulin (CBG) binding capacity was determined by saturation analysis. Myometrial activity was monitored continuously throughout the experimental protocol. All seven betamethasone-treated animals developed labor after the glucocorticoid infusion regimen. In contrast, only two of seven dexamethasone-treated animals developed labor. Fetal treatment with betamethasone produced a greater and earlier fall in maternal plasma progesterone than fetal treatment with dexamethasone. Both betamethasone and dexamethasone treatments elevated fetal plasma CBG to similar binding capacities. Elevated fetal plasma ACTH and cortisol concentrations at the end of the infusion period in both betamethasone-and dexamethasone-treated animals were not related to the development of labor-type contractions. These data support the hypothesis that betamethasone is more potent than dexamethasone in inducing the essential mechanisms of parturition in sheep.

The expulsion of Echinostoma trivolvis: suppressive effects of dexamethasone on goblet cell hyperplasia and worm rejection in C3H/HeN mice.

C3H/HeN mice were infected with Echinostoma trivolvis metacercariae on day 0, given intramuscular injections of dexamethasone daily for 5 or 7 days, and necropsied on days 5, 8, 12, 15, 20 and 30 p. i. Controls consisted of mice that were infected with echinostomes, but were not treated with dexamethasone. Dexamethasone treatment caused a delay in worm expulsion from the small intestine of the hosts, and the increase in goblet cell numbers that occurred in untreated mice was markedly delayed in the treated mice. Mast cell number in the small intestine increased rapidly from just after day 5 p. i. and reached a peak on day 15 p. i. in both dexamethasone-treated and control mice, although the increase in cell numbers was delayed slightly in the dexamethasone-treated mice. The eosinophil number in the small intestine of dexamethasone-treated mice was suppressed until 8 days p. i. and then increased reaching a peak on day 12 p. i., although the number was about one half that of the control. As determined on day 12 p. i., the mean body area of worms from dexamethasone-treated animals was significantly greater than that of the controls. Histological examination of the small intestine showed that the goblet and Paneth cell hyperplasia seen in mice infected with E. trivolvis was suppressed by dexamethasone treatment. Transmission electron microscopy revealed no marked ultrastructural differences in the small intestine of the dexamethasone-treated and control mice except that the former had an increased number of intracristal granules in mitochondria, an increase in vesicles in the apical epithelial cells and an increase in amorphous bodies and autophagic vacuoles in the Paneth cells. These results indicate that dexamethasone treatment delayed the expulsion of E. trivolvis from the small intestine of the host mouse in association with the suppression of goblet cell hyperplasia and increase in the number of mast cells and eosinophils.

Cellular localization and regulation of CHIF in kidney and colon.

Channel inducing factor (CHIF) is a novel cDNA recently cloned from a rat distal colon cDNA library of dexamethasone-treated animals. While its expression in Xenopus oocytes evokes a potassium channel activity similar to that induced by Isk (minK), its cellular role is not clear. CHIF exhibits significant homologies with proteins that are putatively regulatory (phospholemman, gamma-subunit of Na(+)-K(+)-ATPase, Mat-8) while it differs from the small-conductance potassium channel Isk. We have studied the tissue specificity of CHIF expression in rat by in situ hybridization. CHIF is selectively present in the distal parts of the nephron (medullary and papillary collecting ducts and end portions of cortical collecting tubule) and in the epithelial cells of the distal colon. No expression of CHIF was found in renal proximal tubule, loop of Henle and distal tubule, proximal colon, small intestine, lung, choroid plexus, salivary glands, or brain. To gain some insight into CHIF function, we have investigated, using in situ hybridization and ribonuclease protection assay, whether CHIF mRNA expression could be altered in some situations. In the distal colon, corticosteroid hormones, sodium restriction, low-potassium diet, and metabolic acidosis significantly increased CHIF mRNA expression. In the kidney, metabolic acidosis was the only condition that showed an increase in CHIF mRNA expression. Some of these treatments also altered the expression of the colonic H(+)-K(+)-ATPase mRNA. In summary, CHIF mRNA is selectively expressed in the medullary collecting duct of the kidney and in the epithelium of the distal colon; its expression varies differently in these two target tissues after alterations in corticosteroid status, potassium depletion, and metabolic acidosis. The precise cell-specific functions of CHIF remain to be established.

Immediate inflammatory responses to adenovirus-mediated gene transfer in rat salivary glands.

Although replication-deficient adenoviruses can efficiently transfer genes to the salivary glands, the current vectors precipitate an immediate, transient decrease in salivary function. To study the cause of this salivary hypofunction, 10(6)-10(10) plaque-forming units (pfu) of the vector AdCMV beta gal were delivered by retrograde ductal infusion to the submandibular glands (SMGs) of rats. Microscopic analysis of infected glands showed a dose-related, rapidly developing inflammatory response, which at the highest amount of virus was characterized by a predominantly neutrophil-containing infiltrate, focal necrosis, and edema. Moreover, the glands of nude rats developed similar morphologic changes to those of immunocompetent rats. After 3 days, the volume of stimulated saliva secreted from SMGs receiving AdCMV beta gal (6.75 x 10(9) pfu) was approximately 20% that of controls. UV-inactivated virus caused a similar decrease in saliva output. We evaluated to what extent the anti-inflammatory glucocorticoid, dexamethasone, could suppress inflammation and preserve salivary function. Three days after infusion with a high dose of AdCMV beta gal (6.75 x 10(9) pfu), the glands from dexamethasone-treated animals showed markedly less inflammation and no necrosis. Furthermore, there was no significant difference in the average amount of saliva secreted from the infected glands (105 +/- 17 microliters) compared to the control glands (123 +/- 18 microliters). In addition, dexamethasone extended the expression of beta-galactosidase in the SMGs. These results suggest that the adenovirus-mediated acute inflammation in rat SMG is responsible for diminished gland function and transgene expression. Furthermore, we demonstrate a useful role for glucocorticoids in controlling acute inflammation during experimental gene transfer with current adenovirus vectors.

DEXAMETHASONE NEUROPROTECTION IS ASSOCIATED WITH PRESERVED EXPRESSION OF BCL-2 AND SUPPRESSION OF GLIAL FIBRILLARY ACID PROTEIN (GFAP). ▴ 1226

We have presented data showing apoptosis is suppressed by dexamethasone in a neonatal rat model of hypoxic-ischemic encephalopathy (HIE) without affecting the generation of free radicals or lipid peroxidation. We examined the effects of dexamethasone on an apoptosis related gene (bcl-2) and on glial cells as marked by glial fibrillary acid protein (GFAP) immunostaining.Model: 7 day old rat pups underwent unilateral carotid artery ligation and exposure to 8% oxygen for 2.5 hours. Animals were pretreated with dexamethasone (0.1 mg/kg) or vehicle. Measurements: Northern blot, Western blot, immunohistochemistry. Results: Bcl-2 expression is elevated in dexamethasone-treated animals compared to vehicle-treated animals at 1 hour after HIE (p = 0.02). Differences were not discernable at 6 and 24 hours post-HIE. Bcl-2 protein was not significantly greater in dexamethasone-treated animals over vehicle-treated animals by Western blot but immunohistochemistry showed preserved bcl-2 staining in dexamethasone-treated animals. Despite no difference in peroxynitrite exposure GFAP immunoreactivity is markedly diminished in dexamethasone-treated animals. Conclusion: Preserved bcl-2 transcription and translation is associated with neuronal survival following HIE further supporting the role of apoptosis as a mechanism of cell death in HIE. GFAP immunoreactivity, a marker of glial cell activation following HIE, is also associated with the dexamethasone neuroprotective effect despite apparent equal exposure to peroxynitrite, a marker of nitric oxide production -an inducer of GFAP. Glial cells may play an important role in apoptosis following HIE. (Supported by the Heart and Stroke Foundation of Canada, the Medical Research Council of Canada, the Ackman Travelling Scholarship, University of Melbourne, Australia).

EFFECT OF DEVELOPMENT AND DEXAMETHASONE ON α1B-ADRENOCEPTOR MRNA IN RAT CAROTID ARTERY USING QUANTITATIVE COMPETITIVE RTPCR. † 1494

We have observed maturation of α1-adrenoceptor (AR) response over the first two weeks of life in isolated carotid arteries from rats. Carotid arteries from rats treated postnatally with dexamethasone have accelerated maturation of α1-AR response which is accompanied by an increase inα1A-AR mRNA. We tested the hypothesis that an increase in mRNA in a different α1-AR subtype, α1B, was responsible for the differences seen in isolated vessel responses. Pups were treated daily with dexamethsone(DEX) 0.4 μg/gm body weight or the same volume of saline from day of life(DOL) 2-4, carotid artery removed on DOL 4 and total RNA isolated. RNA was also obtained from carotid artery of rats on DOL 10. To determine quantitative differences between animal groups, a competitive template was constructed consisting of α1B-AR cDNA with 168bp DNA insertion. Oligonucleotide primers specific for α1B-AR gene were synthesized. PCR product was distinguished by expected appropriate size and unique restriction endonuclease cleavage. These data indicate that the increased response to phenylephrine with maturation or in dexamethasone-treated animals is not explained by a change in α1B-AR mRNA. The results suggest that the increased vessel contraction may be due to post-transcriptional effects on α1-AR subtypes or other changes in the signal transduction pathway.Table

Reduced NPY induced feeding in diabetic but not steroid-treated rats: lack of evidence for changes in receptor number or affinity.

Concentrations of the potent hypothalamic appetite stimulating peptide neuropeptide Y (NPY), and its mRNA, are increased in rats with experimental diabetes, suggesting a role in the hyperphagia of this disorder. The 2-h feeding responses to intracerebroventricular (i.c.v.) injection of neuropeptide Y (NPY) (5, 10, and 15 mu g doses) were measured in male Wistar rats treated with streptozotocin (55 mg/kg) to induce diabetes. Streptozotocin-diabetic rats given i.c.v. NPY exhibited reduced feeding responses compared to controls (P < 0.05). Dexamethasone treated rats exhibit similar changes in NPY content and mRNA in the hypothalamus to those seen in diabetes, but are not hyperphagic. Feeding responses were also measured in this model, to assess whether high levels of endogenous NPY might account for the reduced response in diabetes. In contrast, the feeding response to NPY in comparison to controls was unaltered in dexamethasone treated rats. To investigate whether altered NPY receptor number or affinity, was the underlying mechanism for these divergent responses, receptor binding experiments were performed using (125)I-PYY and membranes prepared from rat hypothalamus. No significant difference was found in receptor number or affinity between the 2 groups (B(max): 114.7 +/- 18.9 vs 127.4 +/- 27.1 fmol/mg protein, K(d): 99.6 +/- 28.2 vs 135.1 +/- 32.4 pM). Similarly no difference was found between hypothalamic membranes prepared from dexamethasone-treated and control animals. NPY receptor subtypes in the hypothalamus were compared with that of cortex (predominantly Y1) and hippocampus (predominantly Y2) using the Y1-specific ligand [Leu(31)Pro(34)] NPY. These studies showed that the binding profile in the hypothalamus most closely matched that in the hippocampus, suggesting that the majority of hypothalamic receptors were of the Y2 subtype. Receptor autoradiography revealed low binding in the hypothalamus, and particularly in the paraventricular nucleus of the hypothalamus. Competition with [Leu(31)Pro(34)] NPY confirmed that only a low density of binding to Y1 like receptors was present in the hypothalamus. No difference was observed between control and streptozotocin treated animals. The feeding response to exogenous NPY is reduced in experimental diabetes, but not in dexamethasone treated rats. These differing responses do not appear to be due to altered NPY receptor number or affinity in the hypothalamus.

A Novel cis-Acting Element in a Liver Cytochrome P450 3A Gene Confers Synergistic Induction by Glucocorticoids plus Antiglucocorticoids

The induction by dexamethasone of rat liver CYP3A1 differs from classical glucocorticoid gene regulation in part because both glucocorticoids and antiglucocorticoids such as pregnenolone 16 alpha-carbonitrile (PCN) induce CYP3A1 through transcriptional gene activation. In the present study, we transiently expressed in primary cultures of rat hepatocytes plasmids consisting of CYP3A1 5'-flanking sequences fused to a chloramphenicol acetyltransferase reporter plasmid. Deletional analysis identified a 78-base pair (bp) element located approximately 135 bp upstream of the transcriptional start site that was inducible by treatment of the cultures with dexamethasone or PCN and was induced synergistically by dexamethasone plus PCN. Nuclear extract from control rat liver protected two regions within the 78-bp sequence against digestion with DNase I. The same two regions were protected when nuclear extracts from dexamethasone-treated animals were used. Analysis of both of the "footprints" (FP1 and FP2) failed to reveal a classical sequence for the glucocorticoid-responsive element. A 33-bp element that includes FP1 sequences inserted into the chloramphenicol acetyltransferase reporter plasmid and transiently expressed in rat hepatocytes conferred a profile of dexamethasone and PCN induction similar to that of the 78-bp element. However, an Escherichia coli expressed glucocorticoid receptor protein failed to protect sequences within FP1 in DNase I footprinting experiments and failed to change its mobility in gel shift assays. Moreover, as judged by the gel shift assay, the specific protein binding to this fragment was the same whether nuclear extracts from the liver of untreated or dexamethasone-treated rats were used. We conclude that the activation of CYP3A1 gene transcription by glucocorticoids may involve proteins already bound to the controlling element in the CYP3A1 gene through a mechanism in which GR in the presence of hormone does not bind directly to CYP3A1 DNA.

Glucocorticoid and progesterone inhibit involution and programmed cell death in the mouse mammary gland.

Milk production during lactation is a consequence of the suckling stimulus and the presence of glucocorticoids, prolactin, and insulin. After weaning the glucocorticoid hormone level drops, secretory mammary epithelial cells die by programmed cell death and the gland is prepared for a new pregnancy. We studied the role of steroid hormones and prolactin on the mammary gland structure, milk protein synthesis, and on programmed cell death. Slow-release plastic pellets containing individual hormones were implanted into a single mammary gland at lactation. At the same time the pups were removed and the consequences of the release of hormones were investigated histologically and biochemically. We found a local inhibition of involution in the vicinity of deoxycorticosterone- and progesterone-release pellets while prolactin-release pellets were ineffective. Dexamethasone, a very stable and potent glucocorticoid hormone analogue, inhibited involution and programmed cell death in all the mammary glands. It led to an accumulation of milk in the glands and was accompanied by an induction of protein kinase A, AP-1 DNA binding activity and elevated c-fos, junB, and junD mRNA levels. Several potential target genes of AP-1 such as stromelysin-1, c-jun, and SGP-2 that are induced during normal involution were strongly inhibited in dexamethasone-treated animals. Our results suggest that the cross-talk between steroid hormone receptors and AP-1 previously described in cells in culture leads to an impairment of AP-1 activity and to an inhibition of involution in the mammary gland implying that programmed cell death in the postlactational mammary gland depends on functional AP-1.

Leukocyte transmigration, but not rolling or adhesion, is selectively inhibited by dexamethasone in the hamster post-capillary venule. Involvement of endogenous lipocortin 1.

This study investigates the effect of dexamethasone on leukocyte extravasation in the post-capillary venules of the hamster cheek pouch, using an intravital microscopy technique, and seeks to clarify the potential involvement of the steroid-inducible protein lipocortin 1. Topical application of FMLP (10 nmol), or substance P (10 nmol), to the superfused cheek pouch induced at the level of the post-capillary venules the three characteristic phenomena of leukocyte rolling, adhesion, and transmigration. Pretreatment of hamsters with an anti-inflammatory dose of dexamethasone (1 mg/kg) increased lipocortin 1 levels in circulating leukocytes as assessed by flow cytometry, but did not modify either leukocyte rolling or the number of adherent cells; however approximately 65% of the adherent leukocytes subsequently detached and returned to the blood stream, whereas those that entered into the diapedesis process exhibited a long latency (approximately three- to fourfold longer than in control animals) before transmigration. In hamsters passively immunized with a polyclonal anti-lipocortin 1 serum, leukocyte diapedesis started at similar times in both control and dexamethasone-treated animals, whereas a significant prolongation was observed in those animals treated with a non-immune sheep serum. These observations indicate that 1) lipocortin 1 is elevated in circulating leukocytes following dexamethasone treatment; 2) the step of leukocyte extravasation affected by dexamethasone in the actual transmigration process, and 3) this specific effect upon leukocyte diapedesis is mediated by endogenous lipocortin 1.

Evaluation of CP-99,219, a new fluoroquinolone, for treatment of experimental penicillin- and cephalosporin-resistant pneumococcal meningitis

CP-99,219 is a new fluoroquinolone that has excellent activity against gram-positive organisms including penicillin- and cephalosporin-resistant Streptococcus pneumoniae strains. In our well-established rabbit model of meningitis, we conducted experiments to determine the concentrations of CP-99,219 in cerebrospinal fluid (CSF) after intravenous administration and its ability to eradicate two penicillin-resistant pneumococcal isolates. The peak and trough concentrations of CP-99,219 in the CSF were from 19 to 25% of the concentrations simultaneously obtained in serum and were unaffected by concomitant dexamethasone administration. Compared with untreated (control) animals, three doses of CP-99,219 given 5 h apart significantly reduced the bacterial count in CSF by 5 to 6 log10 CFU at 10 h. Although 47% of the dexamethasone-treated animals and 18% of those not given the steroid had positive cultures at 24 h (14 h after administration of the last antibiotic dose), the mean bacterial counts did not change from those observed at 10 h. Additionally, only results for animals infected with one of the two pneumococcal strains appeared to be affected by concomitant dexamethasone therapy.

Prenatal hormonal therapy improves pulmonary compliance in the nitrofen-induced CDH rat model

Neonates with congenital diaphragmatic hernia (CDH) experience a high mortality despite intensive medical and surgical management. The associated pulmonary hypoplasia is accompanied by an underlying biochemical deficiency that bears similarity to respiratory distress syndrome (RDS) in the premature newborn. Using therapies extrapolated from those used to treat RDS, the authors have previously shown correction of the immature pulmonary biochemical indices in the nitrofen rat CDH model. This study investigates the functional and histological outcome of prenatal hormone therapy on CDH rats. Compared with saline-treated CDH controls, dexamethasone-treated CDH animals achieved significant increases in lung distensibility ( P = .0006) and functional residual capacity ( P = .004); CDH rats treated with combined dexamethasone and thyrotropin-releasing hormone (TRH) showed improved functional residual capacity ( P = .043) and alveolar stability ( P = .025); CDH animals treated with TRH alone (TRH-CDH) showed no improvement in any parameter tested. Histologically, the lungs from dexamethasone- and dexamethasone-TRH-treated CDH animals showed changes that included narrow septal walls, increased air saccule size, and thinning of the pulmonary interstitium compared with the lungs of saline or TRH-CDH rats, which were developmentally arrested at the canalicular stage. Lung weights and lung weight-body weights ratios were similar in all CDH rats, confirming that treatment did not impair pulmonary growth. These results support the potential clinical use of prenatal pharmacological therapies to treat human fetuses with prenatally diagnosed CDH.

The effect of dexamethasone on the course of Echinostoma caproni and E. trivolvis infections in the golden hamster (Mesocricetus auratus).

Golden hamsters (Mesocricetus auratus) were given intramuscular injections of dexamethasone and infected with Echinostoma caproni or E. trivolvis. All animals were necropsied on day 14 postinfection. Dexamethasone treatment at high doses resulted in increased parasite recovery. Decreased total white blood cell counts and decreased relative splenic weights were observed in corticosteroid-treated hamsters. Dexamethasone-treated animals also demonstrated significantly lower mean parasite dry weights for E. caproni. Specific serum IgG against the parasites was not detected in corticosteroid-treated hamsters on day 14 postinfection.

In vitro fertilization and culture of ova from heifers infected with bovine herpesvirus-1 (BHV-1)

Oocytes collected from heifers infected experimentally with bovine herpesvirus-1 (BHV-1, 10(8) TCID(50)/ml) and from dexamethasone-treated (stressed) BHV-1 seropositive animals were matured, fertilized and co-cultured in vitro for 7 d prior to being tested for the presence of the virus. Nineteen of the 21 infected donors yielded embryos and follicular fluids that were BHV-1 positive. Oviductal cells (17 21 ) and uterine fluids (14 21 ) were also positive. Titers for the positive samples ranged 10(1.6)-10(9.6) TCID(50)/ml. The cleavage rate and the proportion of blastocysts that developed from oocytes of BHV-1 infected animals were 26% (n=361) and 6% compared with 56% (n=112) and 26% for uninfected control donors (P<0.05). In contrast, embryos produced from dexamethasone-treated animals tested negative for BHV-1 and yielded 11% blastocysts as compared with 25% for the control group. The results indicate that transferable-stage embryos can be produced by IVF from infected BHV-1 animals and that such embryos are associated with the virus, and might have potential for disease transmission.

Influence of Dexamethasone on Intimal Thickening in Experimental Vein Graft

The influence of dexamethasone on vein graft intimal hyperplasia was studied in a rat model. The iliolumbar vein was grafted to the common iliac artery in 42 rats. Twenty animals were treated with dexamethasone 0.1 mg/kg per day by injection for 3 weeks; 22 control animals received saline injections. Grafts were harvested at 3 weeks and longitudinal sections prepared. Five deaths and considerable morbidity was seen in the dexamethasone-treated animals. All grafts in the surviving animals in both groups were patent at 3 weeks. Intimal thickening, measured in the proximal, mid and distal graft, was found to be maximal in the proximal graft and least in the mid-portion of the graft. Dexamethasone reduced intimal thickening throughout the graft; the median thickness of the proximal graft was 30 microns (control 50 microns), in the mid-graft 10 microns (control 30 microns) and in the distal graft 20 microns (control 30 microns). This reduction was statistically significant in the mid-graft only (P < 0.05; Mann-Whitney U test). The small effect on anastomotic intimal thickening suggests that dexamethasone is of limited use in the prevention of vein graft intimal hyperplasia in clinical practice.

Effects of thiazolidinediones on glucocorticoid-induced insulin resistance and GLUT4 glucose transporter expression in rat skeletal muscle

Thiazolidine-2,4-diones, a new class of oral antihyperglycemic agents, have been shown to be effective in improving insulin sensitivity in a number of animal models of insulin resistance, and recent investigation has suggested that the mechanism of action of these agents may include upregulation of the GLUT4 (insulin-regulatable) glucose transporter. We studied the efficacy of two of these agents, pioglitazone and englitazone, in preventing glucocorticoid-induced insulin resistance in rats, and examined the potential role of changes in GLUT4 expression in their action in skeletal muscle. Rats were treated with 0.1 mg/d dexamethasone for 6 to 7 days with or without either pioglitazone (10 mg/kg/d) or englitazone (50 mg/kg/d). Both thiazolidinediones decreased the elevated fasting serum glucose and insulin levels in dexamethasone-treated animals. Dexamethasone treatment alone decreased insulin-stimulated 2-deoxyglucose uptake into isolated soleus muscles to 35% of control values. The addition of pioglitazone or englitazone increased insulin-stimulated 2-deoxyglucose uptake by 74% and 57%, respectively. Whereas dexamethasone treatment alone increased GLUT4 protein content in rat soleus muscle by 25%, additional treatment with pioglitazone or englitazone did not further significantly alter GLUT4 levels. We conclude that thiazolidinediones enhance insulin responsiveness in skeletal muscle during glucocorticoid treatment, but their mode of action in this setting is not via upregulation of GLUT4 expression.