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PubMed1990

Organ culture of ixodid-tick salivary glands.

This work describes an organ-culture method for isolated salivary glands of the ixodid tick Amblyomma hebraeum Koch. The support medium is a TC 199-1% agarose gel with no hormonal or undefined supplements. I used a fluid-transport assay for measuring viability of salivary glands. When cultured at 26 degrees C, female glands secreted fluid at 65% on day 2, 59% on day 4 and 42% on day 6 post-culture compared to glands tested on day 0. Fluid secretory rates in culture were higher than rates of glands from partially fed ticks (about 180-250 mg) on days 2, 4 or 6 post-removal from the host. Salivary glands from fed males cultured for 4 days lost only 5% of their fluid secretory competence, whereas glands dissected from males 4 days post-removal lost 63% of their fluid secretory competence.

Animals↗
PubMed1984

Comparison of gastric and intestinal antisecretory and protective effects of prostacyclin and its stable thia-imino-analogue (Hoe 892) in conscious rats.

The effects of prostacyclin (PGI2) and its stable thia-thimo-analogue (Hoe 892) on gastric and intestinal secretions and gastric mucosal lesions have been determined in conscious rats. Both PGI2 and Hoe 892 given subcutaneously (s.c.) reduced dose-dependent gastric acid secretion, the ID50 (dose producing 50% inhibition) being about 48.6 and 11.8 micrograms/kg, respectively. In contrast, intragastric (i.g.) PGI2 and Hoe 892 did not cause any change in gastric acid secretion at doses ranging from 1 to 100 micrograms/kg. Both PGI2 and Hoe 892 reduced significantly intestinal fluid secretion (antienteropooling activity). PGI2 and Hoe 892 given i.g. or s.c. reduced dose-dependent gastric ulcer formation induced by acidified aspirin (ASA), Hoe 892 being somewhat less potent than PGI2. Both PGI2 and Hoe 892 were equally effective against gastric mucosal necrosis induced by absolute ethanol and this effect was observed both after i.g. and s.c. administration of these agents. We conclude that stable thia-imino-PGI2 analogue, Hoe 892, has similar gastric and intestinal antisecretory and protective activity as PGI2 and may be useful in the prevention of gastric damage by various noxious agents.

16,16-Dimethylprostaglandin E2↗
PubMed2004

Stimulation of distal airspace fluid clearance in guinea pigs involves bumetanide-sensitive ion transport.

OBJECTIVE: This study was undertaken to test the hypothesis that beta-adrenoceptor stimulation of fetal lung fluid absorption in near-term guinea pig fetuses involves bumetanide-sensitive ion transport. STUDY DESIGN: Fetuses were obtained from timed-pregnant guinea pigs at 61 to 69 days' gestation with and without oxytocin-induced preterm labor. The fetuses were placed on continuous positive airway pressure oxygenation, and an isosmolar 5% albumin solution was instilled into the lungs. Distal airspace fluid clearance was measured over 1 hour from the increase in distal airspace protein concentration as fluid was reabsorbed with and without the Cl(-) transport inhibitor bumetanide. RESULTS: Fetal lungs began to absorb distal airspace fluid at 64 to 66 days' gestation, and at birth, distal airspace fluid clearance rapidly quadrupled. Labor induction by oxytocin stimulated distal airspace fluid clearance. Distal airspace fluid clearance, when present, was sensitive to propranolol-inhibition and depended on beta-adrenoceptor stimulation. Fluid secretion at 61 days' gestation was reduced by bumetanide instillation. Bumetanide addition was only inhibitory when distal airspace fluid clearance was propranolol-sensitive. CONCLUSION: Beta-adrenoceptor stimulation from endogenous fetal epinephrine increased fetal distal airspace fluid clearance and involved bumetanide-sensitive ion transport.

Absorption↗
PubMed1983

Fallopian tube microvasculature in the rabbit.

The microvascular architecture of rabbit Fallopian tube isthmic, ampullary and fimbrial regions was examined by the corrosion vascular cast-scanning electron microscope method. The aorta and inferior vena cava of virgin adult female rabbits (2.5-3.5 kg) were cannulated; after blood wash out, methacrylate casting medium was infused via the aorta. After plastic hardening, Fallopian tubes were excised, tissues corroded and casts prepared for scanning electron microscopy. The isthmic myosalpinx is encircled subserosally by an interlocking venous plexus. We suggest that a rise in pelvic venous pressure could lead to a decrease in isthmic luminal diameter and thus act as a sphincter contributing to the known delay in ovum transport at the ampullary isthmic junction. Stereo pairs of photomicrographs showed that isthmic plicae are supplied by arterioles which change little in diameter passing through the tubal wall. Near the apex of a fold, these arterioles terminate in a subepithelial capillary plexus which drains to deep mucosal and plical core venules. In contrast, the ampulla is supplied by smaller and less frequent arterioles. Frequent large venules extending high into the plicae drain the subepithelial capillary plexus. Based on this microvascular architecture, we suggest that the subepithelial capillary plexus of the apical region of the plicae probably contains high pressure blood in the isthmus and lower pressure blood in the ampulla. Therefore, plicae in these regions may be specialised for net luminal fluid secretion and absorption respectively, implying a role for the microvasculature in tubal transport by initiation or modification of fluid flow along the lumen.

Animals↗
PubMed1981

The action of loperamide in inhibiting prostaglandin-induced intestinal secretion in the rat.

1 The mechanisms by which loperamide inhibits the intestinal secretion induced by prostaglandin E2 were investigated in rat jejunum. 2 In vivo loperamide prevented prostaglandin-induced fluid secretion but did not reduce the associated rise in the transintestinal potential difference. 3 In intestinal sheets the electrical response to prostaglandin E2 was enhanced in the presence of loperamide. 4 The ionic basis of these changes was determined by measuring Na+ and Cl- fluxes across intestinal sheets. Loperamide did not reduce the prostaglandin-induced increase in net Cl- secretion, although it prevented the inhibition of mucosal-to-serosal Na+ movement. 5 Loperamide does not alter cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels by a direct action at the enterocyte, since in isolated enterocytes neither basal nor prostaglandin-stimulated cyclic AMP levels were affected by the drug.

Animals↗
PubMed1994

Somatostatin and somatostatin analogues: pharmacokinetics and pharmacodynamic effects.

Somatostatin is a 14 amino acid peptide that inhibits pancreatic exocrine and endocrine secretion. Its clinical application has been limited by its very short half life, necessitating continuous intravenous infusion. Octreotide is an 8 amino acid synthetic analogue of somatostatin that possesses similar pharmacological effects. It has a much longer duration of action, however, and can be given subcutaneously. Both the intravenous and subcutaneous routes of injection of octreotide are well tolerated. Peak serum concentrations occur within 30 minutes after subcutaneous administration and within four minutes of a three minute intravenous infusion. Serum concentration increases linearly with dose. Octreotide is distributed rapidly, mainly in the plasma, where it is 65% protein bound. The elimination half life is about 1.5 hours and about 32% of a subcutaneous dose is excreted in the urine as unchanged octreotide. Octreotide inhibits gastroenteropancreatic secretion, especially of insulin, glucagon, pancreatic polypeptide, gastric inhibitory polypeptide, and gastrin. It also inhibits both release of thyroid stimulating hormone and growth hormone secretion in response to exercise, insulin induced hypoglycaemia, and argenine stimulation. Octreotide reduces splanchnic blood flow in healthy volunteers and hepatic venous pressure in cirrhotic patients. It can accelerate or delay gastric emptying, prolong transit time at moderate to high doses, stimulate motility at low doses, and inhibit gall bladder emptying. Octreotide considerably inhibits pentagastrin stimulated gastric acid secretion and significantly diminishes exocrine pancreatic function (amylase, trypsin, lipase). Octreotide increases intestinal transit time and decreases endogenous fluid secretion in the jejunum and ileum, thus increasing the absorption of water and electrolytes. These pharmacological effects of the analogue point to its therapeutic role in a variety of endocrine and gastrointestinal disorders.

Amino Acid Sequence↗
PubMed1988

Studies on the mechanism of non-visualization of diseased human gallbladders during oral cholecystography.

Oral cholecystography is a well established method for studying the human gallbladder and radiological non-visualization of the gallbladder has been shown to correlate highly with the presence of disease. The exact mechanism by which diseased gallbladders fail to visualize is unclear, but may be due to a failure of the gallbladder to concentrate the luminal contents. Concentration of gallbladder contents is achieved by the reabsorption of water, the driving force for which is active sodium (Na+) absorption. Therefore Na+ transport was studied by measuring the flux of Na22 across isolated human gallbladder mucosa (obtained at cholecystectomy) and compared with the results of oral cholecystography and histological grading. In 27 gallbladders studied, 59% absorbed Na+, whilst the remainder secreted Na+. Comparison with histological grading showed that as gallbladders became more diseased they absorbed less Na+ and were more likely to secrete Na+. In addition, gallbladders that absorbed Na+ were significantly more likely to visualize on cholecystography than those that secreted Na+. These results indicate that some diseased human gallbladders secrete, rather than absorb, Na+ and suggest that the mechanism for radiological non-visualization is failure of fluid absorption and the development of active fluid secretion.

Cholecystography↗
PubMed1988

The effect of oleate on pancreatic and bile secretion in the conscious rat.

The effects of sodium oleate infused into either the duodenum or the terminal ileum on bile and pancreatic secretion were examined in the conscious rat. Rats were prepared with cannulae draining pure bile and pancreatic juice separately, and with an ileal and two duodenal cannulae. A 40 mM taurocholate solution containing 7 mg/ml bovine trypsin was infused into the duodenum throughout the experiment to replace diverted bile-pancreatic juice to maintain the normal regulation of pancreatic secretion. The intraduodenal infusion of sodium oleate significantly increased pancreatic juice flow, protein, and bicarbonate outputs, whereas it did not affect bile secretion. Intravenous infusion of proglumide (300 mg/kg/hr) did not inhibit pancreatic secretion stimulated by intraduodenal infusion of sodium oleate. An intravenous infusion of atropine (100 micrograms/kg/hr) attenuated protein and fluid secretions but not that of bicarbonate in response to intraduodenal oleate. In contrast, the intraileal infusion of oleate had no effect on pancreatic secretion, whereas it decreased bile flow, bicarbonate, and bile salt outputs. In conclusion, sodium oleate introduced in the duodenum stimulates pancreatic secretion but oleate in the terminal ileum inhibits bile secretion.

Animals↗
PubMed1996

Molecular and biochemical characterization of a heat-labile cytotonic enterotoxin from Aeromonas hydrophila.

We report herein the DNA sequence analysis of the heat-labile cytotonic enterotoxin gene (alt) from Aeromonas hydrophila and the biological function of the purified hyperproduced toxin (Alt). One large open-reading frame (ORF), comprised of 1104 bp, was detected at positions 804 to 1907 bp on a 4.0-kb Sa/l DNA fragment from Aeromonas. This ORF encodes for a protein having 368 amino acids (aa) with a computed molecular weight of 38 kDa. The aa sequence of the first 15 NH2-terminal residues of the mature native Alt from A. hydrophila matched with the DNA-derived aa sequence of the alt gene expressed in E. coli starting at position 19, which was leucine. The first 18aa residues of the Alt represented a putative signal sequence with alanine at its carboxy terminus. A BLAST search of the entire database showed 45-51% identity of the Alt, starting at position 158 with the carboxy half of the phospholipase C (PLC) and lipase from A. hydrophila; however, the purified Alt had no lipase/PLC activity. The alt gene was hyperexpressed using gene fusion expression vector systems, and the recombinant Alt exhibited a size of 35-40 kDa. The pure recombinant Alt elongated Chinese hamster ovary cells and elicited fluid secretion in rats ligated intestinal loops, indicating its enterotoxicity. Immunization of mice with recombinant Alt resulted in a reduced fluid secretory response when challenged with Aeromonas. The biological activity of the recombinant Alt in E. coli was about 10-fold less, compared to native Alt from Aeromonas, indicating differential processing of the toxin. The antibodies to native Alt neutralized the biological activity of the recombinant toxin, and these antibodies reacted with the same specificity to the native and recombinant Alt in immunoblots. The role of cyclic adenosine monophosphate and prostaglandins in causing a fluid secretory response by Alt also was demonstrated.

Aeromonas hydrophila↗
PubMed1984

Inhibition by loperamide of deoxycholic acid induced intestinal secretion.

The effect of loperamide on deoxycholic acid (DOC)-induced secretion was studied in ligated loops of the rat jejunum and colon in vivo. In controls, loperamide slightly augmented fluid absorption. 3 mmol DOC caused net fluid secretion. Loperamide reduced this secretion in the colon and reversed it to absorption in the jejunum. Na-K-ATPase specific activity and cAMP levels were measured in the jejunum, and [14C]erythritol clearance as an index of mucosal permeability in the colon. In the jejunum this opiate analogue affected neither basal or DOC-depressed Na-K-ATPase, nor mucosal cAMP. In the colon it reduced a large increase of the erythritol clearance caused by DOC. It is suggested that loperamide interferes with DOC-induced intestinal secretion in part by lowering mucosal permeability.

Animals↗
PubMed1979

Differentiation in human amniotic fluid cell cultures: chorionic gonadotropin production.

Two of the distinguishable cell classes subcultured from human amniotic fluid were examined for their capability to produce human chorionic gonadotropin (hCG) as determined by radioimmunoassay. The class that predominates in most cultures used for prenatal genetic diagnosis, previously termed AF (for amniotic fluid), secretes hCG into the culture medium. Dermal fibroblasts do not, nor does another type of cultured cell from amniotic fluid, previously termed F because of a resemblance to fibroblasts. Primary AF cultures produce more hCG than do subcultures. Evidence that this hormone is intact hCG is provided by its immunoreactivity with antisera raised against the beta-subunit and against the intact molecule of hCG. Furthermore, a dose-response curve for hormone in culture medium is parallel to that of highly purified intact hCG. It is postulated that AF cultures are derived from fetal membranes and retain properties of trophoblast.

Amniotic Fluid↗
PubMed1994

Regulation of chloride secretion in mammalian colon.

A number of procedures or interventions which activate electrogenic ion transport in mammalian intestine are reviewed. Using in vitro models it is possible to demonstrate direct or indirect pathways to stimulate chloride secretion. Such activation, in vivo, would change the gut from a state of net water absorption to one of fluid secretion. The movement of water is driven by electrical and osmotic gradients set up as a consequence of opening regulated ion channels in epithelial cells. Secretagogues may govern epithelial intracellular second messenger pathways to regulate ion channel activity directly or by activation of membrane bound receptors on the surface of epithelial cells. In health or disease secretagogues may be derived from cells within the attendant lamina propria of the intestinal mucosa. Pharmacological techniques may be employed to determine which mediators contribute to indirect stimulation of electrogenic ion transport by activation of neurons or of immunocytes (mast cells or phagocytes). Dissection and reconstruction of models of intestinal hypersensitivity reactions show that neuro-immune networks which regulate intestinal ion transport appear to be complex, functionally integrated systems. Analysis of such interactions may identify cellular or humoral targets with which to examine novel diagnostic, preventative or therapeutic strategies with regard to intestinal diseases.

Animals↗
PubMed2005

Expression and subcellular localization of the AQP8 and AQP1 water channels in the mouse gall-bladder epithelium.

BACKGROUND INFORMATION: Transepithelial transport of water is one of the most distinctive functions by which the gall-bladder rearranges its bile content. Water is reabsorbed from the gall-bladder lumen during fasting, whereas it is secreted into the lumen following meal ingestion. Nevertheless, the molecular mechanism by which water is transported across the gall-bladder epithelium remains mostly unclear. RESULTS: In the present study, we investigate the presence and subcellular localization of AQP (aquaporin) water channels in the mouse gall-bladder epithelium. Considerable AQP8 mRNA was detected in the gall-bladder epithelium of mouse, calf, rabbit, guinea pig and man. Studies of subcellular localization were then addressed to the mouse gall-bladder where the transcript of a second AQP, AQP1, was also detected. Immunoblotting experiments confirmed the presence of AQP8 and AQP1 at a protein level. Immunohistochemistry showed intense expression of AQP8 and AQP1 in the gall-bladder epithelial cells where AQP8 was localized in the apical membrane, whereas AQP1 was seen both in the apical and basolateral membranes, and in vesicles located in the subapical cytoplasm. CONCLUSIONS: The pattern of subcellular distribution of AQP8 and AQP1 strongly corroborates the hypothesis of a transcellular route for the movement of water across the gall-bladder epithelium. Osmotic water would cross the apical membrane through AQP8 and AQP1, although AQP1 would be the facilitated pathway for the movement of water across the basolateral membrane. The presence of two distinct AQPs in the apical membrane is an unusual finding and may relate to the membrane's ability both to absorb and secrete fluid. It is tempting to hypothesize that AQP1 is hormonally translocated to the gall-bladder apical membrane to secrete water as in the bile duct epithelium, a functional homologue of the gall-bladder epithelium, whereas apical AQP8 may account for the absorption of water from gall-bladder bile.

Amino Acid Sequence↗
PubMed1996

Apical secretion of rat submandibular tissue kallikrein continues in the absence of external stimulation: evidence for a constitutive secretory pathway.

Sequential samples of saliva evoked by low frequency parasympathetic nerve stimulation were collected from cannulated submandibular ducts of anaesthetized rats following periods of varying length without stimulation. After such rest periods the first samples of saliva were found to contain much higher levels of tissue kallikrein (rK1) activity and protein than the ensuing samples from the same stimulation period and the latter contained levels similar to those found previously in parasympathetically-evoked saliva. rK1 activity in first samples increased with the length of the preceding interval, indicating that a continuous secretion of rK1 occurs from ductal cells into glandular lumina and accumulates there in the absence of stimulation or fluid secretion. The protein secretory pattern following rest pauses was unaffected by alpha-adrenergic receptor blockade and a high percentage of the proteinase activity was resistant to soya bean trypsin inhibitor, showing that the secretion was not caused by exocytosis of storage granules from ductal cells and therefore was likely to be a result of a constitutive secretion of newly synthesized enzyme. The pattern of continuous secretion into lumina detected for total protein in the absence of stimulation, suggests that other secretory proteins may also be secreted similarly but at different rates.

Animals↗
PubMed1996

Apical secretion of rat submandibular tissue kallikrein continues in the absence of external stimulation: evidence for a constitutive secretory pathway.

Sequential samples of saliva evoked by low frequency parasympathetic nerve stimulation were collected from cannulated submandibular ducts of anaesthetized rats following periods of varying length without stimulation. After such rest periods the first samples of saliva were found to contain much higher levels of tissue kallikrein (rK1) activity and protein than the ensuing samples from the same stimulation period and the latter contained levels similar to those found previously in parasympathetically evoked saliva rK1 activity in first samples increased with the length of the preceding interval, indicating that a continuous secretion of rK1 occurs from ductal cells into glandular lumina and accumulates there in the absence of stimulation or fluid secretion. The protein secretory pattern following rest pauses was unaffected by alpha-adrenergic receptor blockade and a high percentage of the proteinase activity was resistant to soya bean trypsin inhibitor, showing that the secretion was not caused by exocytosis of storage granules from ductal cells and therefore was likely to be a result of a constitutive secretion of newly synthesized enzyme. The pattern of continuous secretion into lumina detected for total protein in the absence of stimulation, suggests that other secretory proteins may also be secreted similarly but at different rates.

Animals↗
PubMed1969

Metabolism, sperm and fluid production of the isolated perfused testis of the sheep and goat.

1. A total of nineteen ram and three goat testes have been perfused in isolation at 34-35 degrees C for 3(1/2)-9 hr with heparinized blood and an added 5-HT antagonist (bromolysergic acid diethylamide) and their function compared with that of the normal ram testes in vivo.2. The metabolism of the perfused testes and the testes in vivo was similar but blood flow through the perfused testes was two to three times normal.3. Vasoconstriction was produced by adrenaline and noradrenaline (10-20 mug I.A.) and by electrical stimulation of nerves in the spermatic cord or of the lumbar sympathetic chain; these responses were abolished or reduced by phenoxybenzamine.4. Flow of fluid from the rete testis continued only if ischaemia was reduced to a minimum and glucose concentration in the blood perfusing the testis was kept above about 25 mg/100 ml.; the fluid secreted during perfusion was of normal composition.5. The perfused testis showed no evidence of autoregulation and the flow of fluid was not affected by changes in perfusion pressure.6. When the temperature of three testes was raised to 40 degrees C for 2 hr, metabolism increased but blood flow was unaltered; the flow of fluid and the concentration of spermatozoa decreased during heating.7. The testes perfused at normal scrotal temperatures (34-35 degrees C) were histologically normal but some abnormalities were observed in the heated testes.

Animals↗
PubMed2006

Ion and fluid transport properties of small airways in cystic fibrosis.

RATIONALE: Small airways constitute a major site of pathology in cystic fibrosis (CF) and provide most of the surface area of the conducting airways of the lung. Little is known, however, about the impact of CF on ion and fluid transport in small (bronchiolar) airways. OBJECTIVES: To describe the ion and fluid transport properties of CF bronchiolar epithelium. METHODS: Primary cultures of human bronchial and bronchiolar (non-CF and CF) epithelial cells were obtained. The bioelectric properties were studied in Ussing chambers and the airway surface liquid (ASL) height was measured with confocal microscopy. MAIN RESULTS: Primary cultures of DeltaF508 CF bronchiolar epithelial cells displayed higher transepithelial resistance than non-CF cultures, whereas baseline short circuit current and amiloride-inhibitable short circuit current were similar in both preparations. The ASL height was significantly smaller in CF compared with non-CF preparations. In the presence of amiloride, addition of forskolin increased short circuit current in non-CF but not in CF bronchiolar cultures, and the ATP-induced increase in short circuit current was lower in CF than in non-CF cultures. Non-CF bronchiolar preparations displayed larger short circuit current and fluid secretion in responses to forskolin than non-CF bronchial preparations, suggesting that CFTR-dependent Cl(-) transport may play a more important role in the regulation of fluid transport in small airways than in large airways. CONCLUSION: In CF small airways, defective Cl(-) secretion combined with unregulated (persistent) Na(+) absorption results in ASLdepletion.

Body Water↗
PubMed2006

Pentagastrin-induced nitric oxide-dependent protein secretion from the parotid gland of the anaesthetized rat.

Infusion of pentagastrin (20 microg kg(-1) h(-1), i.v.) for 10 min evokes protein output but no overt fluid secretion from the parotid gland of the rat, as revealed by increased protein concentration in a subsequent wash-out flow of saliva in response to a bolus injection of methacholine (5 microg kg(-1), i.v.) 10 min later. Using this experimental set-up, the contribution of nitric oxide (NO) generation to the protein and amylase response evoked by pentagastrin was investigated. Neither the neuronal type NO synthase inhibitor N(omega)-propyl-L-arginine (N-PLA; 30 mg kg(-1), i.v.) nor the non-selective NO synthase inhibitor L-NAME (30 mg kg(-1), i.v.) as such affected the methacholine-evoked volume response or the outputs of protein and amylase. However, when preceeded by the pentagastrin infusion, the expected increases in concentrations of protein (145%) and amylase activity (127%) of the methacholine-evoked response (compared to a pre-infusion methacholine response) were reduced to 68 and 74%, respectively, in the presence of N-PLA, and to 70 and 63%, respectively, in the presence of L-NAME. Thus, NO generation resulting from the activity of the neuronal type NO synthase, most probably of parenchymal origin, plays an important role in the pentagastrin-induced protein and amylase secretion of the rat parotid gland.

Amylases↗