Helicobacter pylori downregulates expression of human ß-defensin 1 in the gastric mucosa in a type IV secretion-dependent fashion.

Helicobacter pylori establishes a chronic lifelong infection in the human gastric mucosa, which may lead to peptic ulcer disease or gastric adenocarcinoma. The human beta-defensins (hßDs) are antimicrobial peptides, hßD1 being constitutively expressed in the human stomach. We hypothesized that H. pylori may persist, in part, by downregulating gastric hßD1 expression. We measured hßD1 and hßD2 expression in vivo in relation to the presence, density and severity of H. pylori infection, investigated differential effects of H. pylori virulence factors, and studied underlying signalling mechanisms in vitro. Significantly lower hßD1 and higher hßD2 mRNA and protein concentrations were present in gastric biopsies from infected patients. Those patients with higher-level bacterial colonization and inflammation had significantly lower hßD1 expression, but there were no differences in hßD2. H. pylori infection of human gastric epithelial cell lines also downregulated hßD1. Using wild-type strains and isogenic mutants, we showed that a functional cag pathogenicity island-encoded type IV secretion system induced this downregulation. Treatment with chemical inhibitors or siRNA revealed that H. pylori usurped NF-κB signalling to modulate hßD1 expression. These data indicate that H. pylori downregulates hßD1 expression via NF-κB signalling, and suggest that this may promote bacterial survival and persistence in the gastric niche.

Helicobacter pylori-induced peptic ulcer disease is associated with inadequate regulatory T cell responses.

BACKGROUND AND AIMS: Helicobacter pylori infection is the major cause of peptic ulceration and gastric adenocarcinoma. To address the hypothesis that the human acquired immune response to H. pylori influences pathogenesis, we characterised the gastric T helper (Th) and regulatory T cell (Treg) response of infected patients. METHODS: The human gastric CD4(+) T cell response of 28 donors who were infected with H. pylori and 44 who were not infected was analysed using flow cytometry. The T cell associated mucosal cytokine response was analysed by real-time polymerase chain reaction assay of samples from 38 infected and 22 uninfected donors. Recombinant interleukin 10 (IL10) was added to co-cultures of H. pylori and AGS cells and its suppressive effects upon inflammatory responses were measured. RESULTS: We found that the H. pylori-specific response consists of both T helper 1 and 2 subsets with high levels of IL10-secreting Tregs. People with peptic ulcer disease had a 2.4-fold reduced CD4(+)CD25(hi)IL10(+) Treg response (p = 0.05) but increased Th1 and Th2 responses (Th1: 3.2-fold, p = 0.038; Th2: 6.1-fold, p = 0.029) compared to those without ulcers. In vitro studies showed that IL10 inhibited IL8 expression and activation of nuclear factor kappa B induced by H. pylori in gastric epithelial cells, and enhanced H. pylori growth in a bacterial-cell co-culture model. CONCLUSIONS: Together our data suggest that H. pylori induces a regulatory T cell response, possibly contributing to its peaceful coexistence with the human host, and that ulcers occur when this regulatory response is inadequate.

Effects of Helicobacter pylori on the cadherin-catenin complex.

BACKGROUND: The cadherin-catenin complex is the key component of the adherens junction in epithelial cells, and changes in this complex are implicated in gastric adenocarcinoma. Germline mutations in E-cadherin have been described in diffuse-type gastric adenocarcinoma. Helicobacter pylori infection is the first stage in gastric carcinogenesis. AIMS: To determine whether H pylori was associated with changes in the complex, and whether this was affected by virulence of the strain. METHODS: Epithelial cell lines were cultured with H pylori using the wild-type pathogenic and non-pathogenic strains and CagE null and VacA null isogenic mutants. Gastric biopsy specimens at endoscopy were obtained from patients with (n = 17) and without (n = 15) H pylori infection, and E-cadherin and beta-catenin expression was assessed by immunohistochemistry. H pylori was typed by polymerase chain reaction from these patients for CagE and VacA. RESULTS: In vitro studies showed that coculture with a pathogenic strain of H pylori led to disruption of epithelial junctional beta-catenin expression, but without evidence of nuclear translocation or signalling. This effect was independent of a functional Cag pathogenicity island and vacuolating activity, but dependent on live bacteria. No marked differences in beta-catenin or E-cadherin expression were seen in gastric biopsy specimens in patients with and without H pylori infection. CONCLUSION: Acute H pylori infection disrupts junctional beta-catenin in vitro, but chronic infection by H pylori has no effect on E-cadherin and beta-catenin expression, as seen in gastric biopsy specimens at the initial gastritis stage of the proposed Correa pathway of gastric carcinogenesis. A later effect at the later stages of atrophy or intestinal metaplasia cannot be ruled out.

Helicobacter pylori cagA+ strains and dissociation of gastric epithelial cell proliferation from apoptosis.

BACKGROUND: Infection with Helicobacter pylori induces chronic gastritis in virtually all infected persons, and such gastritis has been associated with an increased risk of developing gastric cancer. This risk is further enhanced with cagA+ (positive for cytotoxin-associated gene A) H. pylori strains and may be a consequence of induced gastric cell proliferation and/or alteration in apoptosis (programmed cell death) in the gastric epithelium. PURPOSE: To determine whether the H. pylori cagA genotype and another virulence-related characteristic, the vacA (vacuolating cytotoxin A) s1a genotype, differentially affect epithelial cell proliferation, apoptosis, and the histologic parameters of inflammation and injury, we quantitated these characteristics in infected and uninfected persons. METHODS: Fifty patients underwent upper gastrointestinal endoscopy, and biopsy specimens were taken. Apoptotic cells in the specimens were quantitated after terminal deoxynucleotidyl transferase labeling of DNA fragments with digoxigenin-deoxyuridine triphosphate; epithelial cell proliferation was scored by immunohistochemical analysis of the proliferation-associated antigen Ki-67. Antibodies directed against H. pylori and CagA protein were measured in the serum of patients by means of enzyme-linked immunosorbent assays. Analysis of H. pylori genomic DNA, by use of the polymerase chain reaction, was performed to determine the cagA and vacA genotypes. Acute and chronic inflammation, epithelial cell degeneration, mucin depletion, intestinal metaplasia, glandular atrophy, and vacuolation were each scored in a blinded manner. Reported P values are two-sided. RESULTS: Persons harboring cagA+ strains (n = 20) had significantly higher gastric epithelial proliferation scores than persons infected with cagA-strains (n = 9) or uninfected persons (n = 21) (P = .025 and P<.001, respectively), but the difference in cell proliferation between the latter two groups was not statistically significant. The number of apoptotic cells per 100 epithelial cells (apoptotic index) in persons infected with cagA+ strains was lower than in persons infected with cagA-strains (P = .05). Apoptotic indices in the cagA+ group were similar to those in the uninfected group (P = .2). Epithelial cell proliferation was significantly correlated with acute gastric inflammation, but only in the cagA+ group (r = .44; P = .006). The cagA+ and vacA s1a genotypes were found to be concordant, confirming the close relationship between these virulence-related genotypes. CONCLUSIONS: Gastric mucosal proliferation was significantly correlated with the severity of acute gastritis in persons infected with cagA+ vacA s1a strains of H. pylori. This increased proliferation was not accompanied by a parallel increase in apoptosis. IMPLICATIONS: Increased cell proliferation in the absence of a corresponding increase in apoptosis may explain the heightened risk for gastric carcinoma that is associated with infection by cagA+ vacA s1a strains of H. pylori.

Stimulation of adhesion molecule expression by Helicobacter pylori and increased neutrophil adhesion to human umbilical vein endothelial cells.

Helicobacter pylori upregulates endothelial adhesion molecules but the pattern is unclear. Human umbilical vein endothelial cells (HUVEC) were exposed to control medium or H. pylori 60190. Binding of monoclonal antibodies against P-selectin, E-selectin, vascular adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was determined using enzyme-linked immunosorbent assay. Binding of polymorphonuclear leukocytes to HUVEC was determined on cells exposed as above. After 6 h exposure to H. pylori, there were 30%, 124%, 167% and 100% increases in P-selectin, E-selectin, VCAM-1 and ICAM-1 levels and a 400% increase in polymorphonuclear leukocyte adhesion in HUVEC exposed to H. pylori. Effects of incubation for other intervals between 0 and 18 h are also described. H. pylori exerts some of its effects on gastric mucosa via gastric vasculature. This study gives insight into the pattern of H. pylori-associated endothelial adhesion molecule upregulation.

Hormone profiles for progesterone, oestradiol, prolactin, plasma renin activity, aldosterone and corticosterone during pregnancy and pseudopregnancy in two strains of rat: correlation with renal studies.

Plasma samples were obtained throughout pregnancy and pseudopregnancy from Sprague-Dawley (SD) rats and during pregnancy from rats of the Munich Wistar (MW) strain. The concentrations of progesterone, oestradiol, prolactin, plasma renin activity (PRA), aldosterone and corticosterone were measured by radioimmunoassay to establish hormonal profiles in the two strains of rat. Circulating progesterone concentrations in both strains of rat were significantly higher during pregnancy than in virgin controls, except at term in the SD group. The hormonal pattern for pseudopregnancy was similar to that of the first half of pregnancy. Oestradiol concentrations were similar to, or lower than, those in virgin controls throughout pseudopregnancy and for the first 2 weeks of pregnancy in both strains of rat. Increased concentrations of steroid were seen only in the pregnant groups towards term. In SD rats, highest prolactin concentrations were apparent during the first half of pregnancy and pseudopregnancy, and at term in the pregnant group. Pregnant MW rats showed a different profile for this hormone, with low levels throughout pregnancy except at term. In all groups PRA rose to a peak at day 9 and decreased to day 16. Pregnant SD rats also showed a significant increase at term. Aldosterone concentrations were significantly increased at several stages of pregnancy in both strains of rat, particularly during the second half of gestation. Pseudopregnant animals showed a different hormone profile, with no significant changes until day 16 when lower concentrations were recorded. There was little variation in the circulating corticosterone concentration except in pregnant rats at term when levels fell. These findings are discussed in relation to the known renal changes of pregnancy and pseudopregnancy.

Non-endoscopic tests in the diagnosis of Helicobacter pylori infection.

The urea breath test (UBT) and serological antibody detection are simpler and less expensive than endoscopic tests for the diagnosis of Helicobacter pylori. For the UBT, either non-radioactive 13C or radioactive 14C is used as an isotopic marker. 14C-UBTs are cheaper and are safe, but licensing regulations may make them inconvenient. Some UBTs have been simplified by omitting the normal test meal and encapsulating the urea to avoid metabolism by oral bacteria. These modified test need further validation, especially when used for assessing H. pylori status after treatment. Serological tests detect circulating IgG or IgA. They are of variable accuracy, the best performing as well as UBTs. Paired serum samples pre-treatment and 6 months post-treatment accurately assess treatment success. Rapid in-office tests appear less accurate and cannot be used for post-treatment assessment. In practice, for primary diagnosis of H. pylori infection, endoscopic tests are best because endoscopy allows assessment of treatment indications. Where indications already exist or taking biopsies is dangerous. UBTs or serology are suitable, but serology is cheaper and more convenient. After treatment, endoscopy is usually unnecessary and UBTs accurately assess H. pylori status at 4 weeks. Serology is an alternative only if results are not required before 6 months.

Interactions between Helicobacter pylori and other risk factors for peptic ulcer bleeding.

AIM: To investigate the role of Helicobacter pylori, expressing the virulence marker CAGA (cytotoxin associated gene product A) in ulcer complications and its interaction with nonsteroidal anti-inflammatory drugs (NSAIDs) and other risk factors. DESIGN: Case control study using conditional logistic regression analysis. SETTING: University and City Hospitals, Nottingham. SUBJECTS: 203 consecutive patients with ulcer bleeding and 203 age- and sex-matched controls. RESULTS: Ulcer bleeding was more likely with positive H. pylori serology (odds ratio = 3.3, 95% CI: 1.7--6.6 for CagA positive, but only OR = 1.6, 95% CI: 0.7-3.7 for CagA negative serology), current smoking (OR 2.2, 95% CI: 1.04-4.7), aspirin < or = 300 mg daily (OR 7.7, 95% CI: 2.8-20.6), all other nonsteroidal anti-inflammatory drugs (NSAIDs: OR 10.6, 95% CI: 3.1-35.7 for < or = 1 defined daily dose lower and OR 22.6, 95% CI: 6.2-82.0 for higher doses) and past ulcer history (OR 5.6, 95% CI: 2.3-14.1). Aspirin < or = 300 mg daily was used by 25.1% of patients vs. 7.4% of controls. Smoking only enhanced risk in the presence of H. pylori, with a synergistic interaction (interaction odds ratio = 4.9, 2.4-9.9, P=0.002). Conversely, risks with non-aspirin NSAIDs were reduced in the presence of H. pylori, particularly if CagA-positive (interaction odds ratio=0.21, 0.05-0.9, P=0.03). CONCLUSIONS: CagA positive H. pylori infection is associated with an increased risk of ulcer bleeding. The risk from non-aspirin NSAIDs is even higher, but is less in H. pylori infected people. Low-dose aspirin is now commonly associated with ulcer bleeding.

Safety and efficacy of 7-day rabeprazole- and omeprazole-based triple therapy regimens for the eradication of Helicobacter pylori in patients with documented peptic ulcer disease.

AIM: A double-blind, randomized study was designed to determine whether rabeprazole- and omeprazole-based triple therapy regimens are therapeutically equivalent in the eradication of Helicobacter pylori. METHODS: Three hundred and forty-five patients with current or previously active peptic ulcer and a positive H. pylori urease test were randomly assigned to receive RCA, OCA, RCM or OCM twice daily for 7 days (R, rabeprazole 20 mg; O, omeprazole 20 mg; C, clarithromycin 500 mg; A, amoxicillin 1000 mg; M, metronidazole 400 mg). H. pylori eradication was documented by negative 13C-urea breath tests at 4 and 12 weeks, and was evaluated using a 2 x 2 factorial design with proton pump inhibitor and antibiotic as factors. RESULTS: Overall eradication rates (per protocol/intention-to-treat) were 87%/77% and 85%/75% with rabeprazole and omeprazole, respectively (not significant). However, a statistical interaction between proton pump inhibitor and antibiotic was identified. RCA produced a somewhat higher eradication rate than OCA (94% vs. 84%; difference, 9.8%; 95% confidence interval, - 0.7% to + 20.4%), whereas RCM produced a lower eradication rate than OCM (79% vs. 86%; difference, 8.1%; 95% confidence interval, - 21.4% to + 5.1%). Ulcer healing rates were > 90% with H. pylori eradication. Each regimen was well tolerated. CONCLUSIONS: Rabeprazole- and omeprazole-based triple therapy regimens are therapeutically equivalent in the eradication of H. pylori and well tolerated. The statistical interaction observed between the proton pump inhibitor and supplementary antibiotic may be due to chance.

Enhanced eradication of Helicobacter pylori by pre- versus post-prandial amoxycillin suspension with omeprazole: implications for antibiotic delivery.

BACKGROUND: Strategies to improve antibiotic treatment of Helicobacter pylori infection are hampered by lack of knowledge about the route of antibiotic delivery. Post-prandial dosing with antibiotics prolongs their gastric residence time and improves their intragastric distribution, leading to improved local delivery compared with pre-prandial dosing. We aimed to assess whether pre- or post-prandial dosing. with amoxycillin suspension was more effective for H. pylori eradication in an amoxycillin/omeprazole regimen. METHODS: Seventy-nine patients with H. pylori infection were treated with omeprazole 40 mg o.m. for 28 days and amoxycillin suspension 500 mg q.d.s. for days 15-28, the amoxycillin being randomized to either 1 h before or immediately after food. RESULTS: The H. pylori eradication rate, for those completing the trial, was 67% (22/33) when amoxycillin suspension was given pre-prandially, compared with 39% (15/38) when it was given post-prandially (P < 0.05). Good compliance was achieved, with H. pylori eradication in 59% (28/46) of good compliers compared with 36% (9/25) of others completing the protocol (P < 0.05). CONCLUSION: When given with omeprazole, pre-prandial dosing with amoxycillin suspension is more effective for H. pylori eradication than post-prandial dosing. This is consistent with the hypothesis that systemic rather than local delivery of amoxycillin is important for H. pylori eradication.

Amoxycillin capsules with omeprazole for the eradication of Helicobacter pylori. Assessment of the importance of antibiotic dose timing in relation to meals.

BACKGROUND: Giving antibiotics after meals prolongs their gastric residence time and improves their intragastric distribution. We aimed to see whether this would result in improved eradication of Helicobacter pylori. METHODS: Eighty patients with H. pylori infection were treated with 40 mg omeprazole in the morning for 28 days and amoxycillin 500 mg q.d.s. for days 15-28. Amoxycillin dosing was randomised to either 1 h before or 10 min after food. Good compliance was pre-defined as missing less than four doses of amoxycillin or two of omeprazole. RESULTS: Amoxycillin dosing after meals was shown not to affect H. pylori eradication rate either when results were analysed on an intention-to-treat basis [amoxycillin before meals successful in 63% (25/40), after in 65% 26/40)] or for good compliers only [before meals 81% (17/21), after 71% (20/28)]. This excludes, with 95% confidence, a benefit of greater than 18% from dosing before, or 23% from dosing after meals. Good compliance, however, was shown to be important, with H. pylori eradication in 76% (37/49) of good compliers compared with 48% (11/23) of others completing the protocol (P < 0.05). CONCLUSIONS: The timing of antibiotic administration in relation to meals is not important in the treatment of H. pylori infection with this regimen of amoxycillin capsules and omeprazole. Good compliance, is however, an important determinant of treatment success.

Scintigraphic assessment of the intragastric distribution and gastric emptying of an encapsulated drug: the effect of feeding and of a proton pump inhibitor.

BACKGROUND: Local delivery of therapeutic agents to the stomach may be a useful strategy in the treatment of Helicobacter pylori infection. We aimed to see whether the intragastric distribution and gastric retention of a therapeutic agent could be improved, either by giving omeprazole or by dosing after a meal. METHODS: Twelve healthy volunteers took part in this double-blind placebo-controlled crossover study comparing the effects of omeprazole 20 mg twice daily for 5 days with placebo, and the fasted with the fed state, on the gastric emptying and intragastric distribution of a soluble scintigrapic marker contained in a drug capsule. RESULTS: Dosing after food profoundly prolonged gastric residence of the drug label, prolonging mean time to 50% emptying (T50) from 0.5 +/- 0.1 h in the fasted state to 2.0 +/- 0.2 h when given after food. Food also improved intragastric distribution by increasing delivery to the body and fundus. Omeprazole enhanced the effect of food, prolonging T50 to 2.9 +/- 0.3 h, but had no effect in fasted subjects. CONCLUSIONS: Dosing after food markedly improves the aspects of local drug delivery to the stomach investigated in this study, and omeprazole enhances this effect. Post-prandial dosing may, therefore, be useful for improving delivery of some anti-Helicobacter agents.

Helicobacter pylori genotypes, host factors, and gastric mucosal histopathology in peptic ulcer disease.

From 183 patients undergoing upper gastrointestinal endoscopy, we used antral and corpus gastric biopsies for bacterial culture and histopathologic examination, blood samples to detect immunoglobulin G antibodies against Helicobacter pylori, and H pylori genomic DNA to analyze cytotoxin-associated gene A (cagA) and vacuolating cytotoxin (vacA) genotypes. As expected, among H pylori biopsy-positive patients, those with duodenal ulcer (DU) (n = 34) had significantly more severe chronic and acute inflammation (P <.001) and epithelial degeneration (P =.004) in the gastric antrum than in the gastric corpus. Each of those 3 parameters and H pylori density were significantly higher in the antrum of patients with DU than in patients with gastric ulcer (GU) or no ulcer. Colonization with vacA s1/cagA-positive strains of H pylori was associated with inflammation and epithelial degeneration in gastric mucosa and increased risk for peptic ulcer disease (PUD), whereas colonization with vacA s2m2/cagA-negative strains was associated with mild gastric histopathology and was not associated with any significant risk for PUD. The predominant H pylori strains in African Americans were vacA s1bm1/cagA-positive, whereas all genotypes were well represented in non-Hispanic-Caucasians. By multivariate analysis, H pylori colonization was significantly associated with DU (Adjusted odds ratio [AdjOR] = 3.2 [1.4-7.2]) and nonsteroidal anti-inflammatory drugs (NSAID) use was inversely associated (AdjOR = 0.3 [0.2-0.7]). NSAID use (AdjOR = 4.3 [1.02-18.5]) and African-American ethnicity (AdjOR = 10.9 [2.6-50]) were significantly associated with GU. Smoking and age were not significantly associated with either DU or GU. These data indicate that DU is associated with an antral-dominant gastritis, and H pylori genotype and NSAID use independently contribute to the pathogenesis of PUD. HUM PATHOL 32:264-273. This is a US Government work. There are no restrictions on its use.

Lithium clearance in healthy humans: effects of sodium intake and diuretics.

In summary, our experiments clearly demonstrate that lithium reabsorption occurs by frusemide- and bumetanide-sensitive reabsorption, but we have failed to identify the mechanism(s) responsible for the lower CLi and FELi in salt-depletion. It is possible that some, as yet unknown, factor increases the activity of the Na, K, 2Cl cotransporter and, hence, increases lithium reabsorption in the thick ascending limb in salt-depleted subjects. However, it is equally possible that a fraction of proximal tubular reabsorption is inhibited by frusemide and bumetanide. If this is correct, CLi in humans are reasonable markers of proximal tubular function even in conditions of avid salt retention and in salt depletion, when fractional reabsorption of salt and water in the proximal tubules is enhanced.

A comprehensive review of the natural history of Helicobacter pylori infection in children.

Across populations of children, Helicobacter pylori prevalence ranges from under 10% to over 80%. Low prevalence occurs in the U.S., Canada, and northern and western Europe; high prevalence occurs in India, Africa, Latin America, and eastern Europe. Risk factors include socioeconomic status, household crowding, ethnicity, migration from high prevalence regions, and infection status of family members. H. pylori infection is not associated with specific symptoms in children; however, it is consistently associated with antral gastritis, although its clinical significance is unclear. Duodenal ulcers associated with H. pylori are seldom seen in children under 10 years of age. H. pylori-infected children demonstrate a chronic, macrophagic, and monocytic inflammatory cell infiltrate and a lack of neutrophils, as compared with the response observed in adults. The effect of H. pylori infection on acid secretion in children remains poorly defined. The events that occur during H. pylori colonization in children should be studied more thoroughly and should include urease activity, motility, chemotaxis, adherence, and downregulation of the host response. The importance of virulence determinants described as relevant for disease during H. pylori infection has not been extensively studied in children. Highly sensitive and specific methods for the detection of H. pylori in children are needed, especially in younger pediatric populations in which colonization is in its early phases. Criteria for the use of eradication treatment in H. pylori-infected children need to be established. Multicenter pediatric studies should focus on the identification of risk factors, which can be used as prognostic indicators for the development of gastroduodenal disease later in life.

Helicobacter pylori unmasked--the complete genome sequence.

The publication of the complete genome sequence of Helicobacter pylori and the computer analysis of the genes it contains represents an enormous advance in H. pylori research. Besides providing an overview of H. pylori biology, the genome sequence will aid future research and radically alter the research process. In particular, it will enable a 'top down' approach whereby genes are investigated because of their similarity to genes of known function in other organisms. Other advances in biotechnology will allow all H. pylori genes to be studied simultaneously, proteins to be identified quickly, and potential drug targets to be evaluated efficiently. Progress in H. pylori research should now be rapid, and with the research interest and resources focused on it, H. pylori could become the paradigm for post-genomic research.

Molecular Methods for Detecting Ulcerogenic Strains of H. pylori.

Certain nonconserved genotypic and phenotypic characteristics of H. pylori are associated with increased risk of peptic ulceration in the human host. These characteristics can be divided into two groups: first, those relating to vacuolating cytotoxin activity (1,2), and differences in the gene encoding the cytotoxin, vacA (3); second, those relating to the cytotoxin-associated gene, cagA (4,5).

Glomerular filtration rate and salt and water reabsorption during pregnancy in the conscious rat.

1. Glomerular filtration rate (g.f.r.) and salt and water reabsorption were measured in age-matched conscious virgin rats and rats at different stages of pregnancy that were infused with saline at 40 and 200 microliters min-1. 2. G.f.r. and salt and water reabsorption were significantly higher at all stages of pregnancy irrespective of the the rate of infusion. 3. The similarity in both time course and magnitude, of changes in renal function between conscious and anaesthetized rats at the two infusion rates suggests that the detection of differences in the anaesthetized rat during pregnancy is not dependent on either the anaesthetic/surgery employed or the rate of expansion of the extracellular fluid volume. 4. During the induction of the diuresis in 20-day pregnant rats infused at 40 microliters min-1 urine flow was higher and osmolality lower than in virgin rats and rats at earlier stages of pregnancy, suggesting that late-pregnant rats have an altered ability for elaborating concentrated or dilute urine.