Rapid stimulation of human renal ENaC by cAMP in Xenopus laevis oocytes

Among the compensatory mechanisms restoring circulating blood volume after severe haemorrhage, increased vasopressin secretion enhances water permeability of distal nephron segments and stimulates Na+ reabsorption in cortical collecting tubules via epithelial sodium channels (ENaC). The ability of vasopressin to upregulate ENaC via a cAMP-dependent mechanism in the medium to long term is well established. This study addressed the acute regulatory effect of cAMP on human ENaC (hENaC) and thus the potential role of vasopressin in the initial compensatory responses to haemorrhagic shock. The effects of raising intracellular cAMP (using 5 mmol/L isobutylmethylxanthine (IBMX) and 50 ìmol/L forskolin) on wild-type and Liddle-mutated hENaC activity expressed in Xenopus oocytes and hENaC localisation in oocyte membranes were evaluated by dual-electrode voltage clamping and immunohistochemistry, respectively. After 30 min, IBMX + forskolin had stimulated amiloride-sensitive Na+ current by 52 % and increased the membrane density of Na+ channels in oocytes expressing wild-type hENaC. These responses were prevented by 5 ìmol/L brefeldin A, which blocks antegrade vesicular transport. By contrast, IBMX + forskolin had no effects in oocytes expressing Liddle-mutated hENaC. cAMP stimulated rapid, exocytotic recruitment of wild-type hENaC into Xenopus oocyte membranes, but had no effect on constitutively over-expressed Liddle-mutated hENaC. Extrapolating these findings to the early cAMP-mediated effect of vasopressin on cortical collecting tubule cells, they suggest that vasopressin rapidly mobilises ENaC to the apical membrane of cortical collecting tubule cells, but does not enhance ENaC activity once inserted into the membrane. We speculate that this stimulatory effect on Na+ reabsorption (and hence water absorption) may contribute to the early restoration of extracellular fluid volume following severe haemorrhage (AU)

Rapid stimulation of human renal ENaC by cAMP in Xenopus laevis oocytes.

Among the compensatory mechanisms restoring circulating blood volume after severe haemorrhage, increased vasopressin secretion enhances water permeability of distal nephron segments and stimulates Na(+) reabsorption in cortical collecting tubules via epithelial sodium channels (ENaC). The ability of vasopressin to upregulate ENaC via a cAMP-dependent mechanism in the medium to long term is well established. This study addressed the acute regulatory effect of cAMP on human ENaC (hENaC) and thus the potential role of vasopressin in the initial compensatory responses to haemorrhagic shock. The effects of raising intracellular cAMP (using 5 mmol/L isobutylmethylxanthine (IBMX) and 50 µmol/L forskolin) on wild-type and Liddle-mutated hENaC activity expressed in Xenopus oocytes and hENaC localisation in oocyte membranes were evaluated by dual-electrode voltage clamping and immunohistochemistry, respectively. After 30 min, IBMX + forskolin had stimulated amiloride-sensitive Na(+) current by 52% and increased the membrane density of Na(+) channels in oocytes expressing wild-type hENaC. These responses were prevented by 5 µmol/L brefeldin A, which blocks antegrade vesicular transport. By contrast, IBMX + forskolin had no effects in oocytes expressing Liddle-mutated hENaC. cAMP stimulated rapid, exocytotic recruitment of wild-type hENaC into Xenopus oocyte membranes, but had no effect on constitutively over-expressed Liddle-mutated hENaC. Extrapolating these findings to the early cAMP-mediated effect of vasopressin on cortical collecting tubule cells, they suggest that vasopressin rapidly mobilises ENaC to the apical membrane of cortical collecting tubule cells, but does not enhance ENaC activity once inserted into the membrane. We speculate that this stimulatory effect on Na(+) reabsorption (and hence water absorption) may contribute to the early restoration of extracellular fluid volume following severe haemorrhage.

Evidence of high sugar intake, and low fibre and mineral intake, in the gluten-free diet.

BACKGROUND: The only therapy for coeliac disease (CD) is a long-term gluten-free diet (GFD). Little is known about the detailed composition of such a diet. AIM: To clarify the nutritional composition of a GFD and to compare it with a non-GFD diet in representative non-CD populations. METHODS: A total of 139 consecutive patients with CD were invited to fill in a prospective validated 5-day food diary, of whom data from 93 were analysed. Results were compared with data from the National Diet and Nutrition Survey of Adults and the UK Women's Cohort Study (UKWCS). RESULTS: Individuals consuming a strict GFD generally had similar intakes of energy and nutrients to those of comparison populations, but a higher proportion of carbohydrate intake was obtained from nonmilk extrinsic sugars and intakes of nonstarch polysaccharides were low. Compared with the UKWCS sample, female patients adhering to a GFD had lower intakes of magnesium, iron, zinc, manganese, selenium and folate. In male patients, intakes of magnesium and selenium were particularly low. CONCLUSIONS: This study reinforces the need for clinicians to recognize that avoidance of gluten cannot be the sole focus of a gluten-free diet. Maintenance of adequate intakes of essential nutrients and in particular complex carbohydrates must also be the goal for patients.

Long-term histological follow-up of people with coeliac disease in a UK teaching hospital.

BACKGROUND: Coeliac disease is a relatively common condition which is usually managed by placing patients on a gluten free diet. Follow up biopsies to confirm histological recovery are controversial with a considerable variation in practice observed. AIM: To determine the length of time to histopathological recovery in a group of coeliac disease patients and its associations with clinicopathological data. DESIGN AND METHODS: All patients attending a specialist coeliac disease clinic prior to March 2009 were entered onto a database which recorded various clinicopathological data. The histopathology reports for all duodenal biopsies were reviewed and each biopsy was given a histopathological disease score based on a modified Marsh grade. RESULTS: Two hundred and eighty-four patients underwent index and at least one subsequent biopsy. Two-hundred and twenty-seven (80%) showed histopathological improvement and 100 (35%) returned to normal (median recovery time 1.9 years, inter-quartile range 1.0-4.8 years). Patients with less severe disease at diagnosis were more likely to show a better response (r = 0.281, P < 0.0001). Older patients demonstrated a shorter time to histopathological recovery (r = -0.200, P = 0.001). Compliance with a gluten free diet was correlated with the best biopsy score (r = -0.134, P = 0.040) and degree of histological recovery (r = 0.161, P = 0.014). CONCLUSION: Current guidelines for the timing of repeat biopsy after commencing a gluten free diet are unclear, although 4-6 months has been recommended. This study shows that time to histological recovery is longer than traditionally thought and may need to take into account the patient's age at diagnosis, the initial disease score and the level of compliance with a gluten free diet.

Evaluation of the need for endoscopy to identify low-risk patients presenting with an acute upper gastrointestinal bleed suitable for early discharge.

AIMS: To audit the safety of differing protocol-driven early-discharge policies, from two sites, for low-risk acute upper gastrointestinal (GI) bleeding and determine if default early (<24 h) in-patient endoscopy is necessary. METHODS: All patients with low-risk acute upper GI bleeding presenting to two separate hospital sites in Leeds from August 2002 to March 2005 were identified. Both hospitals operate nurse-led process-driven protocols for discharge within 24 h, but only one includes default endoscopy. Relevant information was obtained from patients' notes, patient administration systems, discharge letters and endoscopy records. RESULTS: 120 patients were admitted to site A and 74 to site B. Median length of stay on the clinical decisions unit was 12.6 h at site A and 9.4 h at site B (p = 0.045). Oesophagogastroduodenoscopy was performed on 89/120 (74%) patients at site A compared with only 7/74 (9%) at site B (p<0.001). Six of 120 (5%) patients from site A were admitted to hospital for further observation compared with 6/74 (8%) from site B (p = 0.38). Of the remaining patients, all were discharged within 24 h, and 8/114 (7%) at site A vs 17/68 (25%) at site B were given hospital clinic follow-up (p<0.001). None of the 194 patients had further bleeding or complications within 30 days. CONCLUSIONS: Patients admitted with a low-risk acute upper GI bleeding can be managed safely by a nurse-led process-driven protocol, based on readily available clinical and laboratory variables, with early discharge <24 h. Avoiding in-patient endoscopy appears to be safe but at the price of greater clinic follow-up.