Bicarbonate Response Research Articles

Functional expression and ligand identification of homo- and heteromeric Drosophila melanogaster CO2 receptors in the Xenopus laevis oocyte system.

Carbon dioxide (CO2) is an important olfactory cue in Drosophila melanogaster and can elicit both attractive and aversive behaviors. It is detected by gustatory receptors, Gr21a and Gr63a, found in the ab1C neuron in basiconic sensilla on the third antennal segment. Volatile substances that modulate the receptors' function are of interest for pest control. While several substances block ab1C neurons or mimic the activating effect of carbon dioxide, it is not known if these substances are indeed ligands of the CO2 receptor or might act on other proteins in the receptor neuron. In this study, we used the recombinant Xenopus laevis expression system and two-electrode voltage-clamp technology to investigate the receptor function. We found that application of sodium bicarbonate evokes large inward currents in oocytes co-expressing Gr21a and Gr63a. The receptors most likely form hetromultimeric complexes. Homomultimeric receptors of Gr21a or Gr63a are sufficient for receptor functionality, although oocytes gave significantly lower current responses compared to the probable heteromultimeric receptor. We screened for putative blockers of the sodium bicarbonate response and confirmed that some of the substances identified by spike recordings of olfactory receptor neurons, such as 1-hexanol, are also blockers in the Xenopus oocyte system. We also identified a new blocking substance, citronellol, which is related to insect repellents. Many substances that activate receptor neurons were inactive in the Xenopus oocyte system, indicating that they may not be ligands for the receptor, but may act on other proteins. However, methyl pyruvate and n-hexylamine were found to be activators of the recombinant Gr21a/Gr63a receptor.

Neuropeptide S reduces duodenal bicarbonate secretion and ethanol-induced increases in duodenal motility in rats

Alcohol disrupts the intestinal mucosal barrier by inducing metabolic and functional changes in epithelial cells. Recently, we showed that neuropeptide S (NPS) decreases duodenal motility and increases mucosal paracellular permeability, suggesting a role of NPS in the pathogenesis of disorders and dysfunctions in the small intestine. The aim of the present study was to investigate the effects of NPS on ethanol- and HCl-induced changes of duodenal mucosal barrier function and motility. Rats were anaesthetized with thiobarbiturate, and a 30-mm segment of the proximal duodenum with an intact blood supply was perfused in situ. The effects on duodenal bicarbonate secretion, the blood-to-lumen clearance of 51Cr-EDTA, motility and transepithelial net fluid flux were investigated. Intravenous (i.v.) administration of NPS significantly reduced duodenal mucosal bicarbonate secretion and stimulated mucosal transepithelial fluid absorption, mechanisms dependent on nitrergic signaling. NPS dose-dependently reduced ethanol-induced increases in duodenal motility. NPS (83 pmol·kg-1·min-1, i.v.) reduced the bicarbonate and fluid secretory response to luminal ethanol, whereas a 10-fold higher dose stimulated fluid secretion but did not influence bicarbonate secretion. In NPS-treated animals, duodenal perfusion of acid (pH 3) induced greater bicarbonate secretory rates than in controls. Pre-treating animals with Nω-nitro-L-arginine methyl ester (L-NAME) inhibited the effect of NPS on bicarbonate secretion. In response to luminal acid, NPS-treated animals had significantly higher paracellular permeability compared to controls, an effect that was abolished by L-NAME. Our findings demonstrate that NPS reduces basal and ethanol-induced increases in duodenal motility. In addition, NPS increases luminal alkalinization and mucosal permeability in response to luminal acid via mechanisms that are dependent on nitric oxide signaling. The data support a role for NPS in neurohumoral regulation of duodenal mucosal barrier function and motility.

Bicarbonate Induced Redox Proteome Changes in Arabidopsis Suspension Cells.

Climate change as a result of increasing atmospheric CO2 affects plant growth and productivity. CO2 is not only a carbon donor for photosynthesis but also an environmental signal that can perturb cellular redox homeostasis and lead to modifications of redox-sensitive proteins. Although redox regulation of protein functions has emerged as an important mechanism in several biological processes, protein redox modifications and how they function in plant CO2 response remain unclear. Here a new iodoTMTRAQ proteomics technology was employed to analyze changes in protein redox modifications in Arabidopsis thaliana suspension cells in response to bicarbonate (mimic of elevated CO2) in a time-course study. A total of 47 potential redox-regulated proteins were identified with functions in carbohydrate and energy metabolism, transport, ROS scavenging, cell structure modulation and protein turnover. This inventory of previously unknown redox responsive proteins in Arabidopsis bicarbonate responses lays a foundation for future research toward understanding the molecular mechanisms underlying plant CO2 responses.

Dose-Response of Sodium Bicarbonate Ingestion Highlights Individuality in Time Course of Blood Analyte Responses.

To defend against hydrogen cation accumulation and muscle fatigue during exercise, sodium bicarbonate (NaHCO3) ingestion is commonplace. The individualized dose-response relationship between NaHCO3 ingestion and blood biochemistry is unclear. The present study investigated the bicarbonate, pH, base excess and sodium responses to NaHCO3 ingestion. Sixteen healthy males (23 ± 2 years; 78.6 ± 15.1 kg) attended three randomized order-balanced, nonblinded sessions, ingesting a single dose of either 0.1, 0.2 or 0.3 g·kg-1BM of NaHCO3 (Intralabs, UK). Fingertip capillary blood was obtained at baseline and every 10 min for 1 hr, then every 15 min for a further 2 hr. There was a significant main effect of both time and condition for all assessed blood analytes (p ≤ .001). Blood analyte responses were significantly lower following 0.1 g·kg-1BM compared with 0.2 g·kg-1BM; bicarbonate concentrations and base excess were highest following ingestion of 0.3 g·kg-1BM (p ≤ .01). Bicarbonate concentrations and pH significantly increased from baseline following all doses; the higher the dose the greater the increase. Large interindividual variability was shown in the magnitude of the increase in bicarbonate concentrations following each dose (+2.0-5; +5.1-8.1; and +6.0-12.3 mmol·L-1 for 0.1, 0.2 and 0.3 g·kg-1BM) and in the range of time to peak concentrations (30-150; 40-165; and 75-180 min for 0.1, 0.2 and 0.3 g·kg-1BM). The variability in bicarbonate responses was not affected by normalization to body mass. These results challenge current practices relating to NaHCO3 supplementation and clearly show the need for athletes to individualize their ingestion protocol and trial varying dosages before competition.

Cluster analysis reveals a binary effect of storage on boar sperm motility function.

Storage of liquid-preserved boar spermatozoa is associated with a loss of fertilising ability of the preserved spermatozoa, which standard semen parameters barely reflect. Monitoring responses to molecular effectors of sperm function (e.g. bicarbonate) has proven to be a more sensitive approach to investigating storage effects. Bicarbonate not only initiates capacitation in spermatozoa, but also induces motility activation. This occurs at ejaculation, but also happens throughout passage through the oviduct. In the present study we tested whether the specific response of boar sperm subpopulations to bicarbonate, as assessed by motility activation, is altered with the duration of storage in vitro. Three ejaculates from each of seven boars were diluted in Beltsville thawing solution and stored at 17°C. Only minor changes in the parameters of diluted semen were revealed over a period of 72h storage. For assessment of bicarbonate responses, subsamples of diluted spermatozoa were centrifuged through a discontinuous Percoll gradient after 12, 24 and 72h storage. Subsequently, spermatozoa were incubated in two Ca2+-free variants of Tyrode's medium either without (TyrControl) or with (TyrBic) 15mM bicarbonate, and computer-aided sperm analysis motility measurements were made. Cluster analysis of imaging data from motile spermatozoa revealed the presence of five major sperm subpopulations with distinct motility characteristics, differing between TyrBic and TyrControl at any given time (P<0.001). Although there was an increasing loss of motility function in both media, bicarbonate induced an increase in a 'fast linear' cohort of spermatozoa in TyrBic regardless of storage (66.4% at 12h and 63.9% at 72h). These results imply a binary pattern in response of sperm motility function descriptors to storage: although the quantitative descriptor (percentage of motile spermatozoa) declines in washed semen samples, the qualitative descriptor (percentage of spermatozoa stimulated into fast linear motion by bicarbonate) is sustained independent of the duration of storage.

Population pharmacodynamic model of bicarbonate response to acetazolamide in mechanically ventilated chronic obstructive pulmonary disease patients

IntroductionAcetazolamide is commonly given to chronic obstructive pulmonary disease (COPD) patients with metabolic alkalosis. Little is known of the pharmacodynamics of acetazolamide in the critically ill. We undertook the pharmacodynamic modeling of bicarbonate response to acetazolamide in COPD patients under mechanical ventilation.MethodsThis observational, retrospective study included 68 invasively ventilated COPD patients who received one or multiple doses of 250 or 500 mg of acetazolamide during the weaning period. Among the 68 investigated patients, 207 time-serum bicarbonate observations were available for analysis. Population pharmacodynamics was modeled using a nonlinear mixedeffect model. The main covariates of interest were baseline demographic data, Simplified Acute Physiology Score II (SAPS II) at ICU admission, cause of respiratory failure, co-prescription of drugs interfering with the acid-base equilibrium, and serum concentrations of protein, creatinin, potassium and chloride. The effect of acetazolamide on serum bicarbonate levels at different doses and in different clinical conditions was subsequently simulated in silico.ResultsThe main covariates interacting with acetazolamide pharmacodynamics were SAPS II at ICU admission (P = 0.01), serum chloride (P < 0.001) and concomitant administration of corticosteroids (P = 0.02). Co-administration of furosemide significantly decreased bicarbonate elimination. Acetazolamide induced a decrease in serum bicarbonate with a dose-response relationship. The amount of acetazolamide inducing 50% of the putative maximum effect was 117 ± 21 mg. According to our model, an acetazolamide dosage > 500 mg twice daily is required to reduce serum bicarbonate concentrations > 5 mmol/L in the presence of high serum chloride levels or coadministration of systemic corticosteroids or furosemide.ConclusionsThis study identified several covariates that influenced acetazolamide pharmacodynamics and could allow a better individualization of acetazolamide dosing when treating COPD patients with metabolic alkalosis.

After Damage of Large Bile Ducts by Gamma-Aminobutyric Acid, Small Ducts Replenish the Biliary Tree by Amplification of Calcium-Dependent Signaling and de Novo Acquisition of Large Cholangiocyte Phenotypes

Large cholangiocytes secrete bicarbonate in response to secretin and proliferate after bile duct ligation by activation of cyclic adenosine 3', 5'-monophosphate signaling. The Ca(2+)-dependent adenylyl cyclase 8 (AC8, expressed by large cholangiocytes) regulates secretin-induced choleresis. Ca(2+)-dependent protein kinase C (PKC) regulates small cholangiocyte function. Because gamma-aminobutyric acid (GABA) affects cell functions by activation of both Ca(2+) signaling and inhibition of AC, we sought to develop an in vivo model characterized by large cholangiocyte damage and proliferation of small ducts. Bile duct ligation rats were treated with GABA for one week, and we evaluated: GABA(A), GABA(B), and GABA(C) receptor expression; intrahepatic bile duct mass (IBDM) and the percentage of apoptotic cholangiocytes; secretin-stimulated choleresis; and extracellular signal-regulated kinase1/2 (ERK1/2) phosphorylation and activation of Ca(2+-)dependent PKC isoforms and AC8 expression. We found that both small and large cholangiocytes expressed GABA receptors. GABA: (i) induced apoptosis of large cholangiocytes and reduced large IBDM; (ii) decreased secretin-stimulated choleresis; and (iii) reduced ERK1/2 phosphorylation and AC8 expression in large cholangiocytes. Small cholangiocytes: (i) proliferated leading to increased IBDM; (ii) displayed activation of PKCbetaII; and (iii) de novo expressed secretin receptor, cystic fibrosis transmembrane regulator, Cl(-)/HCO(3)(-) anion exchanger 2 and AC8, and responded to secretin. Therefore, in pathologies of large ducts, small ducts replenish the biliary epithelium by amplification of Ca(2+)-dependent signaling and acquisition of large cholangiocyte phenotypes.

Is Peptic Ulceration a Hormonal Deficiency Disease?

TO THE EDITOR: There is evidence that Helicobacter pylori (H. pylori) infection may cause a deficiency of the hormone secretin that allows peptic ulcer disease to develop by impairing the body's defenses to gastric acid. Secretin is released into the circulation from the S cells of the duodenal crypts in response to gastric acid entering the duodenum. Once in the circulation, secretin has five well-documented effects that protect the upper intestine from gastric acid: it stimulates secretion of bicarbonate rich exocrine pancreatic juice, it stimulates secretion of alkaline bile, it stimulates secretion of alkaline mucus from the duodenal submucosal glands of Brunner, it inhibits the humoral phase of gastric secretion, and it inhibits gastric motility, thereby delaying gastric emptying (1). Impaired secretin release and reduced duodenal S cells have been documented in peptic ulcer patients compared to control patients (2,3). The clinical evidence that patients with H. pylori infection and peptic ulceration have increased gastric secretion (4) and decreased duodenal bicarbonate response to gastric acid (5), which normalize after eradication of the infection, could be explained by reversible impairment of the secretin mechanism (Table 1). Gastric metaplasia in the duodenum with H. pylori infection is known to reduce the S-cell population (6). The fact that not all patients with H. pylori infection develop peptic ulceration suggests that degree of secretin deficiency, determined by extent of the infection, must reach a critical level for peptic ulceration to occur (7). Peptic ulceration may be a hormonal deficiency disease, a result of secretin deficiency caused by H. pylori infection. It may be the first example of a specific hormonal deficiency disease caused by a specific bacterial infection.

Angiotensin II Activates H+-ATPase in Type A Intercalated Cells

We reported previously that angiotensin II (AngII) increases net Cl(-) absorption in mouse cortical collecting duct (CCD) by transcellular transport across type B intercalated cells (IC) via an H(+)-ATPase-and pendrin-dependent mechanism. Because intracellular trafficking regulates both pendrin and H(+)-ATPase, we hypothesized that AngII induces the subcellular redistribution of one or both of these exchangers. To answer this question, CCD from furosemide-treated mice were perfused in vitro, and the subcellular distributions of pendrin and the H(+)-ATPase were quantified using immunogold cytochemistry and morphometric analysis. Addition of AngII in vitro did not change the distribution of pendrin or H(+)-ATPase within type B IC but within type A IC increased the ratio of apical plasma membrane to cytoplasmic H(+)-ATPase three-fold. Moreover, CCDs secreted bicarbonate under basal conditions but absorbed bicarbonate in response to AngII. In summary, angiotensin II stimulates H(+) secretion into the lumen, which drives Cl(-) absorption mediated by apical Cl(-)/HCO(3)(-) exchange as well as generates more favorable electrochemical gradient for ENaC-mediated Na(+) absorption.

Peptic ulceration may be a hormonal deficiency disease

Evidence is reviewed that Helicobacter pylori infection may cause a deficiency of the hormone secretin that allows peptic ulcer disease to develop by impairing the body's defenses to gastric acid. Secretin is released into the circulation from the S-cells of the duodenal crypts in response to gastric acid entering the duodenum. Once in the circulation, secretin has five well-documented effects that protect the upper intestine from gastric acid: it stimulates secretion of bicarbonate rich exocrine pancreatic juice; it stimulates secretion of alkaline bile; it stimulates secretion of alkaline mucus from the duodenal submucosal glands of Brunner; it inhibits the humoral phase of gastric secretion; and it inhibits gastric motility, thereby delaying gastric emptying. Impaired secretin release and reduced duodenal S-cells have been documented in peptic ulcer patients compared with control patients. Clinical evidence that patients with H. pylori infection and peptic ulceration have increased gastric secretion and motility and decreased duodenal bicarbonate response to gastric acid, all of which normalize after eradication of the infection, could be explained by reversible impairment of the secretin mechanism. Gastric metaplasia in the duodenum with H. pylori infection is known to reduce the S-cell population. The fact that not all patients with H. pylori infection develop peptic ulceration suggests that degree of secretin deficiency determined by extent of the infection must reach a critical level for peptic ulceration to occur. Peptic ulceration may be a hormonal deficiency disease, a result of secretin deficiency caused by H. pylori infection. It may be the first example of a specific hormonal deficiency disease caused by a specific bacterial infection.

Heat-stable enterotoxin ofEscherichia colistimulates a non-CFTR-mediated duodenal bicarbonate secretory pathway

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) is an important pathway for duodenal mucosal bicarbonate secretion. Duodenal biopsies from CF patients secrete bicarbonate in response to heat-stable enterotoxin from Escherichia coli (STa) but not cAMP. To explore the mechanism of STa-induced bicarbonate secretion in CF more fully, we examined the role of CFTR in STa-stimulated duodenal bicarbonate secretion in mice. In vivo, the duodenum of CFTR (-/-) or control mice was perfused with forskolin (10(-4) M), STa (10(-7) M), uroguanylin (10(-7) M), 8-bromoguanosine 3',5'-cGMP (8-Br-cGMP) (10(-3) M), genistein (10(-6) M) plus STa, or herbimycin A (10(-6) M) plus STa. In vitro, duodenal mucosae were voltage-clamped in Ussing chambers, and bicarbonate secretion was measured by pH-stat. The effect of genistein, DIDS (10(-4) M), and chloride removal was also studied in vitro. Control, but not CF, mice produced a significant increase in duodenal bicarbonate secretion after perfusion with forskolin, uroguanylin, or 8-Br-cGMP. However, both control and CF animals responded to STa with significant increases in bicarbonate output. Genistein and herbimycin A abolished this response in CF mice but not in controls. In vitro, STa-stimulated bicarbonate secretion in CF tissues was inhibited by genistein, DIDS, and chloride-free conditions, whereas bicarbonate secretion persisted in control mice. In the CF duodenum, STa can stimulate bicarbonate secretion via tyrosine kinase activity resulting in apical Cl(-)/HCO(3)(-) exchange. Further studies elucidating the intracellular mechanisms responsible for such non-CFTR mediated bicarbonate secretion may lead to important therapies for CF.

Bicarbonate and its role in mammalian sperm function

This paper deals with the effects of bicarbonate induced signaling pathways on plasma membrane lipid organization and downstream protein signaling, and their role in sperm–egg interactions. It also provides an overview of results that indicate that bicarbonate responses are not related to cell death or apoptosis. The information presented shows that only those sperm cells that have functionally completed maturation in the epididymis are sensitive to bicarbonate whereas immature sperm fail to respond to this physiological challenge. Therefore, it is important to selectively analyze the responsive sperm subpopulations when studying sperm capacitation. Moreover, bicarbonate induced signaling responses differ within the diverse sperm structures (e.g. the tail versus the head). Consequently, dissecting sperm structures and signaling areas from each other deserves more attention in sperm capacitation research. The information discussed was obtained from a variety of mammalian species but the basic bicarbonate-mediated sperm responses are similar in most Eutherian species despite some species to species variations (most notably in kinetics rather than the sequence of events). The objective of the paper is to provide a comparative experimental overview of bicarbonate mediated sperm capacitation in the hope that this information will lead to a better understanding of the complex biochemical nature of the involvement of bicarbonate in mammalian sperm capacitation.

Bicarbonate and its role in mammalian sperm function

This paper deals with the effects of bicarbonate induced signaling pathways on plasma membrane lipid organization and downstream protein signaling, and their role in sperm–egg interactions. It also provides an overview of results that indicate that bicarbonate responses are not related to cell death or apoptosis. The information presented shows that only those sperm cells that have functionally completed maturation in the epididymis are sensitive to bicarbonate whereas immature sperm fail to respond to this physiological challenge. Therefore, it is important to selectively analyze the responsive sperm subpopulations when studying sperm capacitation. Moreover, bicarbonate induced signaling responses differ within the diverse sperm structures (e.g. the tail versus the head). Consequently, dissecting sperm structures and signaling areas from each other deserves more attention in sperm capacitation research. The information discussed was obtained from a variety of mammalian species but the basic bicarbonate-mediated sperm responses are similar in most Eutherian species despite some species to species variations (most notably in kinetics rather than the sequence of events). The objective of the paper is to provide a comparative experimental overview of bicarbonate mediated sperm capacitation in the hope that this information will lead to a better understanding of the complex biochemical nature of the involvement of bicarbonate in mammalian sperm capacitation.

Dietary Amino Acid and Sodium Bicarbonate Responses in Broilers Reared in Hot Environmental Temperatures

Better environmentally controlled broiler houses have resulted in many integrated broiler operations using the same dietary feed formulations in winter and summer months due to only minor differences in environmental temperature in the broiler house. Much research has addressed broiler nutrient needs in thermoneutral vs. hot temperature conditions, but research evaluating nutrient needs of broilers during moderate temperature conditions (tunnel-ventilated houses during summer months) is lacking. This study evaluates the impact of increasing dietary Lys and other essential amino acids, and the addition of dietary sodium bicarbonate in high and moderate temperature conditions. Experiment 1 was conducted in batteries and evaluated broiler nutritional responses (d 20 to 40) in hot-cyclic temperature conditions (26 to 34°C). Experiment 2 was conducted in floor pens and evaluated broiler nutritional responses (d 37 to 49) in environmental temperature ranges that mimic a tunnel-ventilated broiler house during summer months (26 to 31°C). In both experiments, dietary treatments had minimal impact on live performance and breast meat yield. Lower mortality (P < 0.06), however, was observed in broilers fed the low CP diet in the hot temperature environment.

ELECTROPHYSIOLOGIC EVALUATION OF RETINAL PIGMENT EPITHELIAL DAMAGE INDUCED BY PHOTIC EXPOSURE

To evaluate the retinal pigment epithelial damage induced by light exposure. One eye of 20 rabbits was exposed to xenon light for 2 hours at an irradiance of 140 mW/cm2 at the surface of the cornea. The contralateral eye served as a control. Forty-eight hours after the light exposure, corneal direct-coupled electroretinograms and the 7% NaHCO3 (bicarbonate) responses of the standing potential were recorded. The amplitudes of the a-, b-, and c-waves of the electroretinograms were significantly reduced in the light-exposed eyes, with the c-waves more reduced than the a- and b-waves. The bicarbonate response was also significantly reduced in the irradiated eyes. The decrease of the bicarbonate response of the standing potential indicated that significant functional damage of the retinal pigment epithelium was induced by the light exposure.

Role of endogenous nitric oxide and prostaglandin in duodenal bicarbonate response induced by mucosal acidification in rats.

Duodenal HCO3- secretion increases in response to mucosal acidification by luminal acid. Although this process is known to be mediated by endogenous prostaglandins (PGs), the role of nitric oxide (NO) in this response has been little studied. We examined the effects of indomethacin and N(G)-nitro-L-arginine methyl ester (L-NAME) on the acid-induced HCO3- secretion in the rat duodenum, together with those on PGE2 generation as well as luminal release of NO metabolites (NOx). A proximal duodenal loop was perfused with saline, and the HCO3- secretion was measured at pH 7.0 using a pH-stat method and by adding 10 mM HCl. Mucosal acidification was performed by exposing the loop to 10 or 100 mM HCl for 10 min. Acidification of the duodenal mucosa stimulated the HCO3- secretion, with concomitant increase of mucosal PGE2 contents and luminal release of NOx, the response being much greater in case of 100 mM HCl. Indomethacin significantly inhibited the acid-induced HCO3- secretion as well as the PGE2 biosynthetic response, without influence on the NOx release. Pretreatment of the animals with L-NAME attenuated both the increase of mucosal PGE2 contents and luminal release of NOx following the acidification, resulting in a marked inhibition of the acid-induced HCO3- response, and these effects were significantly antagonized by coadministration of L-arginine. Duodenal HCO3- secretion was also increased by mucosal exposure to NOR-3 (a NO donor), with concomitant increase of PGE2 generation, but these effects were mitigated in the presence of indomethacin. In addition, the duodenal damage caused by mucosal perfusion with 100 mM HCl for 4 hr was markedly aggravated by pretreatment with L-NAME as well as indomethacin. These results suggest that both endogenous NO and PGs are involved in the mechanism for the acid-induced duodenal HCO3- secretion, and that NO may increase the HCO3- secretion by stimulating PG generation.

Role of endogenous nitric oxide in duodenal bicarbonate response induced by mucosal acidification in rats: Interaction with prostaglandins

Background & Aim. The circulating peptide leptin produced by the fat cells, acts on central receptors to control food intake and body weight homeostasis. Contrary to initial reports, leptin expression has also been detected in the human placenta, the muscles and recently rat gastric chief cells. Here we investigate the possible presence of leptin and leptin receptor in human stomach. Methods. Immunohistochemistry, reverse transcriptase (RT-PCR) and western blot analysis on biopsy samples from 24 normal individuals was used to investigate leptin and leptin receptor expressions. These individuals were randomly selected from the files of our Gastroenterology Department. They included 15 healthy volunteers and 9 patients with non-ulcer dyspepsia (n=24) who gave informed consent for upper endoscopy and gastric secretory tests. Secretory studies upon pentagastrin (6J,Lg/kg/hr) or secretin (3Ul/kg.hr) infusions, available for 22 subjects (mean age 46.7::':: 3.lyears; range 15-67,9 women, l3 men) were analyzed. At the time of study, all had normal endoscopy and normal gastric mucosa on histological examination. Plasma, gastric juice and fundic mucosa leptin were determined by radioimmunoassay. Results. In fundic biopsies from normal individuals, immunoreactive leptin cells were found in the lower half of the fundic glands at the site of chief cells. mRNA encoding ob-protein was detected in the corpus of human stomach. The amount of fundic content of leptin was 10.4 ::':: 3.7 ng leptin/g mucosa as determined by radioimmunoassay. Intravenous infusions of pentagastrin or secretin caused an increase in circulating leptin levels and leptin release into the gastric juice from 24.5 ::'::.3.5 in basal condition to 109 ::':: 26 ng/h under pentagastrin and 1556 ::':: 107 ng/hr under secretin. Gel filtration of leptin incubated with stimulated gastric juice at pH 2 showed an only limited degradation of this peptide. Immunohistochemistry and immunoblotting detected leptin receptor protein and mRNA encoding Ob-RL in the corpus and the antrum. Conclusion. These data provide the first evidence for the presence of leptin and leptin receptors in human stomach. We suggest that gastric epithelial cells be direct targets of leptin. However, the physiological and/or pathophysiological meanings of these findings remain so far unknown.

Pancreatic secretory response to intraileal amino acids: studies in dogs with an in situ neurally isolated ileum.

Intraileal carbohydrates and lipids affect the pancreatic exocrine secretion, but the effect of intraileal amino acids and the role of the extrinsic nerves of the ileum as mediators of the pancreatic bicarbonate and enzyme output are unknown. Four dogs underwent total extrinsic denervation of the entire ileum. Thomas-like cannulas were placed into the stomach, duodenum (to collect pure pancreatic juice), and at the jejuno-ileal junction. Eight neurally intact control dogs received only the three fistulas. After recovery, in both sets of dogs, dose-response studies of the pancreatic secretory response to intraileal infusion with graded loads of tryptophan (0.12-10.0 mmol/h) were performed, given against an intravenous (iv) background of secretin (20.5 pmol/kg/h) and cerulein (29.6 pmol/kg/h). On separate days, control experiments with intraileal infusion of 0.15 M NaCl were performed. In both sets of dogs, iv secretin plus cerulein significantly (p < 0.05) increased pancreatic bicarbonate and protein output above basal. Intraileal tryptophan caused a dose-dependent decrease in the pancreatic bicarbonate and protein response to secretin plus cerulein. In the dogs with denervated ileum, this inhibition was significantly stronger than in the intact animals. In both sets of dogs, the 225-min integrated bicarbonate (IBR) and protein response (IPR) to all loads of tryptophan were significantly lower than in control experiments. Both IBR and IPR were significantly lower in the denervated as compared with the intact animals. 1) Extrinsic denervation of the entire ileum is a valuable preparation to study the role of nerves in the control of pancreatic exocrine secretion; 2) both in the intact and denervated animals the amino acid tryptophan induces an "ileal brake" of the hormonally stimulated pancreatic bicarbonate and protein output; 3) the extrinsic nerves of the ileum are probably not the dominant mediators of the inhibitory action of intraileal tryptophan but rather counteract this effect.

Modulation of external pancreatic secretion by endogenous norepinephrine: study with a norepinephrine uptake blocker in the rat.

The effect of endogenous catecholamines on pancreatic secretion was analyzed with nisoxetine, a specific norepinephrine uptake blocker, and specific adrenoceptor antagonists in anesthetized acute fistula rats. Nisoxetine was administered alone or with alpha-1 (prazosin), alpha-2 (idazoxan or yohimbine), or beta (propranolol) adrenoceptor antagonists. Pancreatic secretion was measured in basal conditions or after stimulation by 2-deoxy-D-glucose (2DG), electrical vagal stimulation, or acetylcholine. (a) Basal. Nisoxetine alone had no effect. Associated with idazoxan or yohimbine, nisoxetine produced a dose-related stimulation (p < 0.01) of water and electrolyte without changing protein output. Addition of propranolol abolished this stimulation. (b) 2DG. Nisoxetine inhibited 2DG-induced secretion (p < 0.01). Idazoxan or yohimbine suppressed the nisoxetine inhibition of water and electrolyte output (p < 0.01) but had no effect on protein output, which was restored only by adding a mixture of idazoxan, prazosin, and propranolol. (c) Electrical stimulation. Nisoxetine did not modify water and electrolyte but inhibited protein response by 75%. Adding idazoxan to nisoxetine significantly increased (p < 0.01) water and bicarbonate response and partly restored protein response. Water and bicarbonate response was restored by propranolol, whereas protein response was only restored by adding a mixture of idazoxan, prazosin, and propranolol. (d) Nisoxetine did not modify pancreatic response to acetylcholine. In conclusion, endogenous norepinephrine affects the response to vagally mediated effects through several subtypes of adrenoceptors, without changing basal or acetylcholine stimulated secretion.

Effects of bicarbonate ion on chick retinal pigment epithelium: membrane potentials and light-evoked responses.

The purpose of this study was to determine how changes in [HCO3-] alter the electrical properties of the retinal pigment epithelium (RPE). Experiments were conducted on the isolated chick retina-RPE-choroid preparation. The chamber holding the preparation allowed independent perfusion of the retinal and the choroidal surfaces. The light-evoked trans-tissue potential (TTP), the trans-epithelial potential (TEP), the trans-retinal potentials, and the intracellularly-recorded apical and basal membrane potentials were studied. Increasing the [HCO3-]0 in the choroidal bath from 25 to 40 mEq/1 led to an increase in the TTP and TEP. The same change in the retinal bath decreased the TTP because of a biphasic change of the RPE membrane potentials. There was also an increase in the amplitudes of the TEP, the c-wave and the slow PIII. The light-evoked subretinal K+ decrease was greater which is consistent with an increase in the photoreceptor light response. These observations indicated that the decrease of TTP resulted from a basal membrane hyperpolarization followed by an apical membrane depolarization induced by an increase in retinal [HCO3-]0. The relationship of these potential changes to the human bicarbonate responses is discussed.