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PubMed1996

Leucokinin increases paracellular permeability in insect Malpighian tubules

There are two major transport pathways across epithelia: a transcellular pathway through cells and a paracellular pathway between cells. Previous electrophysiological studies in mosquito Malpighian tubules suggested that the neuropeptide leucokinin-VIII (LK-VIII) increases the chloride permeability of the paracellular pathway. To test the effect of LK-VIII on the paracellular pathway further, we measured transepithelial permeabilities of inulin and sucrose in isolated Malpighian tubules from the mosquito Aedes aegypti. Cell membranes are impermeable to inulin and sucrose, leaving the paracellular pathway as the only route for their transepithelial permeation. LK-VIII (10(-6) mol l-1) significantly increased transepithelial permeability to both inulin (by 73.8 %) and sucrose (by 32.4 %) in parallel with a significant increase in rates of transepithelial fluid secretion (by 75­90 %). Cyclic adenosine monophosphate (cyclic AMP, 10(-4) mol l-1), which is known to stimulate transcellular transport, also increased rates of transepithelial fluid secretion (by 57­59 %), but it did so without increasing the permeability to sucrose and inulin. Thus, LK-VIII increases the permeability of the paracellular pathway whereas cyclic AMP does not.

Journal Article↗
PubMed1983

Vasoactive intestinal peptide evoked secretion of fluid and protein from rat salivary glands and the development of supersensitivity.

Vasoactive intestinal peptide (VIP) injected intravenously was found to induce a flow of saliva from both the parotid and the submaxillary gland in the rat. The secretion was slow in onset. The amount of saliva secreted from the parotid gland was less than that from the submaxillary gland. Parotid saliva was very viscous. VIP-evoked parotid saliva was more protein rich than both submaxillary saliva and saliva secreted in response to other sialagogue drugs including the beta-adrenergic receptor agonist isoprenaline. The effect of VIP was direct; it occurred after removal of the adrenals, after degeneration of intraglandular nerves and in the presence of autonomic blockers. A supersensitivity to VIP was demonstrable. In the parotid and the submaxillary glands the secretory response to VIP was enlarged following parasympathetic denervation and decentralization, respectively, while after sympathetic denervation supersensitivity was only found to develop in the submaxillary gland.

Adrenalectomy↗
PubMed1993

Inflammation as a major cause of fluid losses in small-bowel obstruction.

The importance of inflammation for fluid losses in obstructive ileus was investigated in vivo in the rat. Inflammation was quantified by spectrophotometry of extravasated Evans blue (Eb)-albumin. Net fluid secretion in the obstructed jejunum was measured by a continuous gravimetric technique. The inflammation in the obstructed gut wall was significantly more pronounced than that in the gut distal to the obstruction and the sham-obstructed gut. The inflammation was significantly more pronounced in the serosa and external muscle layer than in the mucosa-submucosa. Acid-base balance in obstructed animals showed a significant metabolic alkalosis, whereas serum albumin and electrolytes were normal. Lumen fluid in obstructed animals showed low levels of albumin and total calcium as compared with serum, whereas fluid from the peritoneal cavity of obstructed rats showed high contents of albumin. Indomethacin and hydrocortisone given intravenously to obstructed animals significantly reduced the degree of extravasated Eb-albumin in the obstructed gut wall. Sham-operated animals showed net fluid absorption, whereas obstructed rats showed net fluid secretion. Secretion in obstructed animals was in all cases reversed into net fluid absorption after intravenous administration of indomethacin and hydrocortisone. These findings suggest that a pronounced inflammation occurs in the wall of the obstructed small intestine and that this inflammation plays an important role in the pathogenesis of the profuse fluid losses of obstructive ileus.

Analysis of Variance↗
PubMed1984

Structural and functional aspects of cells in the nasal mucociliary system.

The regulation of the fluid balance of the mucus is important for a good function of the mucociliary system in the nose. The nasal glands and the goblet cells have been proposed to be the main source of fluid. Microvilli-equipped epithelial cells, ciliated and nonciliated, constituting 70% to 90% of the cells on the turbinates in the nose, are of importance for the regulation of the hydration of the mucus. These cells have the same characteristics as other fluid-secreting cells elsewhere in the body. They have microvilli, a terminal web, folding of the basolateral membrane, and numerous cell organelles. Blockage of the energy supply strongly reduces the fluid secretion.

APUD Cells↗
PubMed2005

In vivo pharmacology and antidiarrheal efficacy of a thiazolidinone CFTR inhibitor in rodents.

A small-molecule inhibitor of the cystic fibrosis transmembrane conductance regulator (CFTR), 3-[(3-trifluoromethyl)phenyl]-5-[(4-carboxyphenyl)methylene]-2-thioxo-4-thiazolidinone (CFTR(inh)-172), reduces enterotoxin-induced intestinal fluid secretion in rodents. Here, we study CFTR(inh)-172 pharmacology and antidiarrheal efficacy in rodents using (14)C-labeled CFTR(inh)-172, liquid chromatography/mass spectrometry, and a closed intestinal loop model of fluid secretion. CFTR(inh)-172 was cleared primarily by renal glomerular filtration without chemical modification. CFTR(inh)-172 accumulated in liver within 5 min after intravenous infusion in mice, and was concentrated fivefold in bile over blood. At 30-240 min, CFTR(inh)-172 was found mainly in liver, intestine, and kidney, with little detectable in the brain, heart, skeletal muscle, or lung. Pharmacokinetic analysis in rats following intravenous bolus infusion showed a distribution volume of 770 mL with redistribution and elimination half-times of 0.14 h and 10.3 h, respectively. CFTR(inh)-172 was stable in hepatic microsomes. Closed-loop studies in mice indicated that a single intraperitoneal injection of 20 microg CFTR(inh)-172 inhibited fluid accumulation at 6 h after cholera toxin by >90% in duodenum and jejunum, approximately 60% in ileum and <10% in colon. No toxicity was seen after high-dose CFTR(inh)-172 administration (3 mg/kg/day in two daily doses) in mice over the first 6 weeks of life. The metabolic stability, enterohepatic recirculation, slow renal elimination, and intestinal accumulation of CFTR(inh)-172 account for its efficacy as an antidiarrheal.

Animals↗
PubMed1987

Pathophysiology of acute obstructive cholecystitis: implications for non-operative management.

Recent research suggests that disturbances in gallbladder mucosal functions are important in the initiation of acute cholecystitis and its progression. Prostaglandins have pathophysiological significance and prostaglandin synthesis inhibitors such as indomethacin inhibit fluid secretion by gallbladder mucosa, reduce distension and relieve pain. Nerves in the gallbladder wall are involved in disturbed mucosal function, and the benefits of opiates may derive from reduction of active fluid secretion in the inflamed and obstructed gallbladder as well as from central analgesic effects.

Acute Disease↗
PubMed1999

Intracellular and luminal pH measurements of Malpighian tubules of the mosquito Aedes aegypti: the effects of cAMP.

In order to understand the critical role that hydrogen ions play in fluid secretion in Malpighian tubules, intracellular and luminal pH and K+ measurements were performed in isolated Malpighian tubules of the yellow fever mosquito (Aedes aegypti). The intracellular pH was 7.03+/-0.05 (n=15 Malpighian tubules (MT)) and the luminal pH was 7.19+/-0.09 (n=99 MT) when bathed in saline at a pH of 7.0. The lumen potential is positive, thus net proton secretion into the lumen is active. The intracellular and the luminal K+ concentrations were 75+/- 9 mM (n=15) and 102+/-13 mM (n=9 MT) respectively. Cyclic AMP analogues accelerated fluid secretion and at the same time acidified the cell without affecting the luminal pH. Both effects were abolished by an isomer of adenosine-3',5' cyclic monophosphothioate (cAMPS), the Rp-cAMPS, known to inhibit protein kinase A. The results suggest that in the presence of cAMP the properties of the cation/H+ exchanger are affected and that this may be a result of phosphorylation of a Na+/2H+ antiporter located on the apical membrane.

Journal Article↗
PubMed2003

Does preejaculatory penile secretion originating from Cowper's gland contain sperm?

PURPOSE: To determine if spermatozoa are present in the preejaculatory penile secretion, originating from Cowper's gland. METHODS DESIGN: Prospective clinical and laboratory study. SETTING: Andrology and Sex Counseling Unit, Department of Obstetrics and Gynecology, Academic Teaching Hospital. PATIENTS: Five patients referred for premature ejaculation, three for excessive fluid secreted during foreplay and four normal healthy volunteers. INTERVENTION: Glass slide smears of preejaculatory Cowper's gland secretion obtained during foreplay from at least two different occasions, and semen samples after masturbation. MAIN OUTCOME MEASURES: Microscopic examination of air-dried smears, and routine semen analyses. RESULTS: None of the preejaculatory samples contained sperm. All the patients had sperm in routine sperm analyses. CONCLUSIONS: Preejaculatory fluid secreted at the tip of the urethra from Cowper's gland during sexual stimulation did not contain sperm and therefore cannot be responsible for pregnancies during coitus interruptus.

Adult↗
PubMed1990

Lack of cholinergic control in feedback regulation of pancreatic secretion in the rat.

The effect of atropine (100 micrograms/kg/h, i.v.) on plasma cholecystokinin and pancreatic secretion during diversion of bile and pancreatic juice from the intestine was studied in 8 conscious rats equipped with jugular vein, pancreatic, biliary, and duodenal cannulas, and with pyloric ligation and gastric drainage. Diversion of bile and pancreatic juice to the exterior for 4 h significantly increased pancreatic protein and fluid secretion. Atropine delayed the pancreatic response to diversion, but during 4 h of diversion, neither total nor incremental pancreatic protein or fluid secretion was inhibited by atropine. Plasma cholecystokinin levels were elevated after diverting bile and pancreatic juice and were not significantly reduced by atropine (23.0 +/- 6.6 pM vs. 16.0 +/- 3.9 pM at 1.5 h and 17.3 +/- 5.4 pM vs. 13.1 +/- 2.9 pM at 4 h after bile and pancreatic juice diversion; atropine-treated vs. controls, respectively). These results indicate that cholinergic nerves play no important role in feedback regulation of cholecystokinin release and that the previously reported suppressive effect of atropine on the pancreatic response to diversion of bile and pancreatic juice from the intestine was secondary to inhibition of gastric secretion.

Animals↗
PubMed1998

Secreted effector proteins of Salmonella dublin act in concert to induce enteritis.

The ability of enteropathogenic salmonellae to recruit inflammatory cells and induce secretory responses in the infected ileum is considered to be a main feature in Salmonella-induced enteritis. Interactions between the pathogen and intestinal epithelial cells result in a variety of cellular responses mediating inflammation and fluid secretion. It is becoming apparent that proteins secreted by the Inv-Spa type III secretion system of Salmonella spp. play a key role in the induction of these responses. We have recently demonstrated that the SopB effector protein is translocated into eukaryotic cells via a Sip-dependent pathway and mediates inflammation and fluid secretion in infected ileal mucosa. However, SopB did not appear to be the only effector involved, as inactivation of the sopB gene only partially impaired enteropathogenicity. We suggested that at least some of such protein effectors are likely to be proteins of the same class as SopB, i.e., secreted effector proteins translocated into eukaroyotic cells via a Sip-dependent pathway. In this work, we identify SopD, another secreted protein belonging to the family of Sop effectors of Salmonella dublin. Using the cya reporter system we showed that SopD is translocated into eukaroyotic cells. We assessed the potential involvement of SopD in enteropathogenicity and found that inactivation of sopD has an additive effect in relation to the sopB mutation.

Amino Acid Sequence↗
PubMed2000

Calcium transport by isolated anterior and posterior Malpighian tubules of Drosophila melanogaster: roles of sequestration and secretion.

Ca(2+) transport was examined in isolated Malpighian tubules (MTs) of adult Drosophila melanogaster. All segments of both anterior and posterior MTs have substantial capacity to transport Ca(2+) and to play a role, therefore, in calcium homeostasis and elimination of excess dietary Ca(2+). Approximately 85% of Ca(2+) which enters the tubule is sequestered, and approximately 15% is secreted in soluble form into the tubule lumen. Tubules secreting fluid at maximal rates can remove an amount of Ca(2+) equal to the whole animal calcium content in approximately 9 h. Distal segments of the pair of anterior MTs can sequester the same amount of Ca(2+) in <2 h. Functional advantages of high Ca(2+) turnover rates are discussed. Transepithelial Ca(2+) secretion is increased by treatments which depolarize the transepithelial potential (thapsigargin, high K(+)), or acidify the secreted fluids (bicarbonate-free salines). The effects of pharmacological reagents and variations in bathing saline ionic composition indicate that the processes of secretion and sequestration are controlled independently, and that diltiazem-sensitive Ca(2+) channels are an important component of sequestration. The contribution of some form of apical Ca(2+) pump is evaluated.

Journal Article↗
PubMed1998

Immunocytochemical localisation and biological activity of diuretic peptides in the housefly, Musca domestica.

The distribution of a CRF-related diuretic peptide (Musca-DP) and the diuretic/myotropic insect myokinins in the central nervous system of larval and adult houseflies was investigated using antisera raised against Locusta-DH and leucokinin-I, respectively. Two separate, small populations of immunoreactive neurons are present in the brain and fused thoracic-abdominal ganglion mass. There is no evidence for these immunoreactivities being colocalised either within single neurons or at neurohaemal release sites. Crude extracts of tissues containing immunoreactive material increase fluid secretion by isolated Malpighian tubules from adult flies. Diuretic activity is highest in tissues containing myokinin-immunoreactive material. Consistent with this observation, myokinin analogues produce a four- to five-fold increase in fluid secretion, which is more than twice the response to Musca-DP. These effects are mimicked by treatments that increase intracellular calcium and cyclic AMP, respectively. When tested at threshold concentrations, the two classes of diuretic peptide act synergistically to accelerate tubule secretion, and their separate localisation may be important for the precise control of diuresis.

Animals↗
PubMed1996

Granulocyte-macrophage colony-stimulating factor: presence in human follicular fluid, protein secretion and mRNA expression by ovarian cells.

In recent years it has become evident that a leukocyte-cytokine network contributes to the paracrine regulation of ovarian function. The objectives of this study were to examine the presence of a potent lympho-haemopoietic cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF), in tissues and fluids from human ovaries. In a prospective study, follicular fluid and plasma were collected from naturally cycling women and women undergoing hyperstimulation for in-vitro fertilization (IVF). Granulosa-lutein cells were collected at the time of oocyte recovery for IVF and corpora lutea were collected at the time of hysterectomy for non-ovarian reasons. Culture supernatants from ovarian cell and tissue cultures were harvested on completion of a 48 h incubation. Immunoactive GM-CSF was measured by enzyme-linked immunosorbent assay, and was found to be present at statistically significantly higher levels in follicular fluid (8.9 +/- 0.7 pg/ml) and plasma (11.3 +/- 0.8 pg/ml) of women undergoing hyperstimulation compared to follicular fluid (5.3 +/- 0.3 pg/ml) and plasma (7.1 +/- 0.5 pg/ml) from naturally cycling women. Immunoactive GM-CSF was also detected in culture supernatants of granulosa-lutein cells (47.6 pg/10(5) cells), early luteal phase corpora lutea (0.52 pg/microgram DNA) and mid-luteal phase corpora lutea (0.98 pg/microgram DNA). Furthermore, transcripts for GM-CSF, and both the alpha and beta subunits of the GM-CSF receptor, were detected by reverse transcription polymerase chain reaction (RT-PCR) in granulosa-lutein cell culture preparations and corpora lutea collected during the early, mid- and late luteal phase of the menstrual cycle. These results show that GM-CSF is expressed and secreted by cells within the human ovary, and, together with the finding of expression of mRNA for GM-CSF receptor, suggest a role for GM-CSF in the local regulation of ovarian events.

Adult↗
PubMed2003

Involvement of enteric nerves in permeability changes due to deoxycholic acid in rat jejunum in vivo.

AIM: Stress and Clostridium difficile toxin A increase epithelial permeability in the small intestine via vagus and visceral afferents, in turn activating mucosal mast cells. Bile acids also increase epithelial permeability but it is not known if nerves or mast cells are involved in this effect in the small intestine. METHOD: In jejunum of anesthetized rats, the effects of hexamethonium and atropine on deoxycholic acid (DCA) induced fluid secretion and increase in epithelial permeability was therefore studied by determining the appearance and disappearance rates of 14C-mannitol and 51Cr-EDTA into and from a perfusion system containing 4 or 8 mm DCA and expressed as clearance. RESULTS: DCA increased net fluid transport and appearance and to a less extent disappearance rates of the probes. Hexamethonium but not atropine, chronic denervation or the NO synthase inhibitor L-NNA did significantly decrease the appearance rate and net fluid secretion. The levels of the mast cell protease II (RMCP II) in perfusate and plasma were not increased by DCA. The clearance ratio Cr-EDTA/mannitol indicates that the plasma clearance of the permeability probes is partly secondary to net fluid transport only at higher DCA concentrations. CONCLUSION: We conclude that the DCA effect on epithelial permeability is to a large part induced by intramural reflex(es) containing nicotinic receptors. The results also suggest that mast cell degranulation and NO release are not involved in the mechanism. This indicates that the nerve effect on intestinal paracellular permeability is not mediated by the mechanisms described for stress or Clostridium difficile toxin A.

Animals↗
PubMed1997

Nitric oxide production during Vibrio cholerae infection.

Vibrio cholerae induces massive intestinal fluid secretion that continues for the life of the stimulated epithelial cells. Enhanced regional blood flow and peristalsis are required to adapt to this obligatory intestinal secretory challenge. Nitric oxide (NO) is a multifunctional molecule that modulates blood flow and peristalsis and possesses both cytotoxic and antibacterial activity. We demonstrate that, compared with those in asymptomatic control subjects, levels of stable NO metabolites (NO2-/NO3-) are significantly increased in sera from acutely ill Peruvian patients with natural cholera infection as well as from symptomatic volunteers from the United States infected experimentally with V. cholerae. In a rabbit ileal loop model in vivo, cholera toxin (CT) elicited fluid secretion and dose-dependent increases in levels of NO2-/NO3- in the fluid (P < 0.01). In contrast, lipopolysaccharide (LPS) elicited no such effects when applied to the intact mucosa. NO synthase (NOS) catalytic activity also increased in toxin-exposed tissues (P < 0.05), predominantly in epithelial cells. The CT-induced NOS activity was Ca2+ dependent and was not suppressed by dexamethasone. In conclusion, symptomatic V. cholerae infection induces NO production in humans. In the related animal model, CT, but not LPS, stimulated significant production of NO in association with increases in local Ca(2+)-dependent NOS activity in the tissues.

Adult↗
PubMed2005

Nitric oxide scavenging by the cobalamin precursor cobinamide.

Nitric oxide (NO) is an important signaling molecule, and a number of NO synthesis inhibitors and scavengers have been developed to allow study of NO functions and to reduce excess NO levels in disease states. We showed previously that cobinamide, a cobalamin (vitamin B12) precursor, binds NO with high affinity, and we now evaluated the potential of cobinamide as a NO scavenger in biologic systems. We found that cobinamide reversed NO-stimulated fluid secretion in Drosophila Malpighian tubules, both when applied in the form of a NO donor and when produced intracellularly by nitricoxide synthase. Moreover, feeding flies cobinamide markedly attenuated subsequent NO-induced increases in tubular fluid secretion. Cobinamide was taken up efficiently by cultured rodent cells and prevented NO-induced phosphorylation of the vasodilator-stimulated phosphoprotein VASP both when NO was provided to the cells and when NO was generated intracellularly. Cobinamide appeared to act via scavenging NO because it reduced nitrite and nitrate concentrations in both the fly and mammalian cell systems, and it did not interfere with cGMP-induced phosphorylation of VASP. In rodent and human cells, cobinamide exhibited toxicity at concentrations > or =50 microM with toxicity completely prevented by providing equimolar amounts of cobalamin. Combining cobalamin with cobinamide had no effect on the ability of cobinamide to scavenge NO. Cobinamide did not inhibit the in vitro activity of either of the two mammalian cobalamin-dependent enzymes, methionine synthase or methylmalonyl-coenzyme A mutase; however, it did inhibit the in vivo activities of the enzymes in the absence, but not presence, of cobalamin, suggesting that cobinamide toxicity was secondary to interference with cobalamin metabolism. As part of these studies, we developed a facile method for producing and purifying cobinamide. We conclude that cobinamide is an effective intra- and extracellular NO scavenger whose modest toxicity can be eliminated by cobalamin.

Animals↗
PubMed1979

Secretory effect of prostaglandins on the rabbit lacrimal gland in vivo.

Fluid secretion from the cannulated excretory duct of the rabbit lacrimal gland was collected in microcapillary pipette at 10 min intervals. Secretion rate and electrolyte concentrations (Na+, K+ and Cl-) in the lacrimal fluid samples were determined before and after injections of small doses of prostaglandins (PGE1, PGE2, PGF1 alpha, PGF2 alpha, 15 epi-PGF2 alpha, PGF2 beta, PGA1 & PGA2) into the external maxillary artery. Only PGE1 had a dose-dependent stimulatory effect on the lacrimal gland secretion. The maximum secretion rate which was induced by PGE1 (25 micrograms/kg) was 7.2 +/- 0.9 microliters/10 min. Na+ concentration in the fluid secretion stimulated by PGE1 was increased; however, K+ and Cl- concentrations were not changed. Pretreatment with atropine (50 micrograms/kg, I.A.) failed to prevent the stimulatory effect of low doses of PGE1. On the other hand, the secretory responses were abolished when propanolol (3 mg/kg, I.A.) was administered prior to PGE1. The results suggest that fluid secretion of the rabbit lacrimal gland in response to PGE1 may be caused by excitation of the sympathetic ganglia and/or by direct action on beta-receptors in the acinar cells.

Animals↗
PubMed1974

The nature of the binding between LSD and a 5-HT receptor: a possible explanation for hallucinogenic activity.

1 (+)-Lysergic acid diethylamide (LSD) mimicked 5-hydroxytryptamine (5-HT) in its ability to stimulate fluid secretion, to change transepithelial and intracellular potentials as well as to increase the cyclic 3',5'-adenosine monophosphate (cyclic AMP) concentrations of isolated salivary glands of Calliphora.2 Unlike 5-HT, LSD disengages slowly from the receptor and fluid secretion continues despite repeated washing.3 Both 5-HT and tryptamine prevented LSD from acting on the glands.4 LSD bound to the receptor was slowly displaced when glands were treated with agonists (tryptamine) or antagonists (gramine).5 The property of LSD which permits it to function as an agonist despite remaining tightly bound to the receptor is discussed as a possible basis for its profound effects within the central nervous system.

Alkaloids↗