Control of the rat angiotensin I converting enzyme gene by CRE-like sequences

We characterized the role of potential cAMP-responsive elements (CRE) in basal and in induced angiotensin converting enzyme (ACE) gene promoter activity in order to shed light on the regulation of somatic ACE expression. We identified stimulators and repressors of basal expression between 122 and 288 bp and between 415 and 1303 bp upstream from the transcription start site, respectively, using a rabbit endothelial cell (REC) line. These regions also contained elements associated with the response to 8BrcAMP. When screening for CRE motifs we found pCRE, a proximal sequence between 209 and 222 bp. dCRE, a distal tandem of two CRE-like sequences conserved between rats, mice and humans, was detected between 834 and 846 bp. Gel retardation analysis of nuclear extracts of REC indicated that pCRE and dCRE bind to the same protein complexes as bound by a canonical CRE. Mutation of pCRE and dCRE in REC established the former as a positive element and the latter as a negative element. In 293 cells, a renal cell line, pCRE and dCRE are negative regulators. Co-transfection of ATF-2 or ATF-2 plus c-Jun repressed ACE promoter activity, suggesting that the ACE gene is controlled by cellular stress. Although mapping of cAMP responsiveness was consistent with roles for pCRE and dCRE, mutation analysis indicated that they were not required for cAMP responsiveness. We conclude that the basal activity of the somatic ACE promoter is controlled by proximal and distal CREs that can act as enhancers or repressors depending on the cell context.

Acute blood volume expansion delays the gastrointestinal transit of a charcoal meal in awake rats

The present study evaluates the effect of blood volume expansion on the gastrointestinal transit of a charchoal meal (2.5 ml of an aqueous suspension consisting of 5 percent charcoal and 5 percent gum arabic) in awake male Wistar rats (200-270 g). On the day before the experiments, the rats were anesthetized with ether, submitted to left jugular vein cannulation and fasted with water ad libitum until 2 h before the gastrointestinal transit measurement. Blood volume expansion by iv infusion of 1 ml/min Ringer bicarbonate in volumes of 3, 4 or 5 percent body weight delayed gastrointestinal transit at 10 min after test meal administration by 21.3-26.7 percent (P<0.05), but no effect was observed after 1 or 2 percent body weight expansion. The effect of blood volume expansion (up to 5 por cento body weight) on gastrointestinal transit lasted for at least 60 min (P<0.05). Mean arterial pressure increased transiently and central venous pressure increased and hematocrit decreased (P<0.05). Subdiaphragmatic vagotomy and yohimbine (3 mg/kg) prevented the delay caused by expansion on gastrointestinal transit, while atropine (0.5 mg/kg), L-NAME (2 mg/kg), hexamethonium (10 mg/kg), prazosin (1 mg/kg) or propranolol (2 mg/kg) were ineffective. These data show that blood volume expansion delays the gastrointestinal transit of a charcoal meal and that vagal and yohimbine-sensitive pathways appear to be involved in this phenomenon. The delay in gastrointestinal transit observed here, taken together with the modifications of gastrointestinal permeability to salt and water reported by others, may be part of the mechanisms involved in liquid excess management

Gastroduodenal resistance and neural mechanisms involved in saline flow decrease elicited by acute blood volume expansion in anesthetized rats

We have previously demonstrated that blood volume (BV) expansion decreases saline flow through the gastroduodenal (GD) segment in anesthetized rats (Xavier-Neto J, dos Santos AA & Rola FH (1990) Gut, 31: 1006-1010). The present study attempts to identify the site(s) of resistance and neural mechanisms involved in this phenomenon. Male Wistar rats (N = 97,200-300 g) were surgically manipulated to create four gut circuits: GD, gastric, pyloric and duodenal. These circuits were perfused under barostatically controlled pressure (4 cmH2O). Steadysate changes in flow were taken to reflect modifications in circuit resistances during three periods of time: normovolemic control (20 min), expansion (10-15 min), and expanded (30 min). Perfusion flow rates did not change in normovolemic control animals over a period of 60 min. BV expansion (Ringer bicarbonate, 1 ml/min up to 5 percent body weight) significantly (p<0.05) reduced perfusion flow in the GD (10.3 + 0.5 to 7.6 + 0.6 ml/min), pyloric (9.0 + 0.6 to 5.6 + 1.2 ml/min) and duodenal (10.8 + 0.4 to 9.0 + 0.6 ml/min) circuits, but not in the gastric circuit (11.9 + 0.4 to 10.4 + 0.6 ml/min). Prazosin (1 mg/kg) and yohimbine (3 mg/kg) prevented the expansion effect on the duodenal but not on the pyloric circuit. Bilateral cervical vagotomy prevented the expansion effect on the pylorus during the expansion but not during the expanded period and had no effect on the duodenum. Atropine (0.5 mg/kg), hexamethonium (10 mg/kg) and propranolol (2 mg/kg) were ineffective on both circuits. These results indicate that 1) BV expansion increases the GD resistance to liquid flow, 2) pylorus and duodenum are important sites of resistance, and 3) yohimbine and prazosin prevented the increase in duodenal resistance and vagotomy prevented it partially in the pylorus.

Effects of acute volemic changes on jejunal compliance in dogs

1. Jejunal compliance (deltaV/deltaP) was calculated from the intraluminal pressures measured in anesthetized dogs in an in situ upper jejunal pouch (40-50-ml capcity) with intraluminal volumes of 10, 20, 30, 40 and 50 ml of fisotonic saline. 2. Measurements were made in the same animal during and after acute sequential alterations of the extracellular fluid (ECF) volume obtained by: a) acute intravenous (iv) infusion of isotonic saline, b) acute hemorrhage, and c) reinfusion of isotonic saline. 3. Expansion of the ECF volume caused a significant, reversible downward shift of the compliance curve, i.e., the jejunal pouch became less receptive to liquid distension. After saline infusion was discontinued, complicance gradually returned to control levels. 4. Acute loss a substantial volume of blood after ECF expansion gradually shifted the complicance curve upwards to levels significantly diferent from control, indicating that retraction of the ECF volume made the jejunal pouch more receptive to liquid distension. 5. Reinfusion of bled animals with saline rather than autologous blood also induced a significant decrease in jejunal complicance to below control levels. 6. The jejunal pouch as a suitable preparation for monitoring in vivo modifications of compliance induced by acute changes in ECF volume, especially when it was nearly "half-full" (i.e., filled with 20 ml), suggesting a critical relationship between the volume capacity of the pouch and its fluid content. 7. These results suggest that the modulation of the jejunal portion os small intestine compliance is involved in the processes that balance the ECF volume during acute life-threatening situations such as accidental hyperhydration or hemorrhage

Acute changes in extracellular fluid volume modify the antroduodenal flow of saline in dogs: a possible physiological role

The antroduodenal (AD) flow of saline was measured in anesthetized dogs following two different protocols of acute changes in extracellular fluid (ECF) volume, ECF expansion by in infusion of saline before or after hemorrhage decreased the AD flow; conversely, hemorrhage before or after expansion increased flow. These alternating modifications in the AD flow are independent of the sequence of volemic changes and may constitue part of the homeostatic responses of the gut to confront life-thratening situations such as accidental hyperhydration or hemorrhage