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PubMed1976

Role of calcium in exocrine pancreatic secretion. III. Comparison of calcium and magnesium movements in rabbit pancreas.

1. Calcium and magnesium movements in the isolated rabbit pancreas and in rabbit pancreas fragments are compared in a qualitative and quantitative way. 2. At the basal secretion rate calcium and magnesium are present in the secreted fluid in concentrations of about 30% of their concentrations in the bathing medium. 3. Addition of 10(-6) M carbachol to the bathing medium results in enzyme secretion accompanied by calcium and magnesium release, in divalent cation-free medium as well as in a complete medium. 4. The secretion of each divalent cation is the sum of two components: an extracellular flux and a flux of protein-associated cations, the so-called secretory flux. 5. The extracellular flux is proportional to the concentration of the divalent cation in the bathing medium. The secretory flux is not dependent on the presence of the divalent cation in the bathing medium, but is proportional to the amount of protein secreted. About 25 nmol of each cation is secreted per mg protein. 6. Ca2+ and Mg2+ can be nearly completely separated from the digestive enzymes by gel filtration. They equilibrate completely with their radioactive isotopes added to the sample just before elution, indicating that the cations are rapidly exchangeable after secretion. 7. Efflux studies on rabbit pancreas fragments, pre-loaded with 45Ca2+, show a carbachol-stimulated 45Ca2+ efflux (the stimulatory flux) in addition to a release of amylase. Fragments pre-loaded with 28Mg2+ do not show carbachol stimulation of the tracer efflux. 8. These studies indicate that calcium and magnesium behave quite similarly with respect to the extracellular and secretory fluxes. The absence of a stimulatory flux for magnesium, suggests that the increase of the cytoplasmic calcium concentration plays a specific role in the stimulus-secretion coupling of pancreatic enzyme secretion.

Animals↗
PubMed1994

Role of platelet activating factor in the intestinal epithelial secretory and Chinese hamster ovary cell cytoskeletal responses to cholera toxin.

With the recent heightened concern about cholera around the world come new questions about the mechanism by which cholera toxin causes diarrhea. Peterson and Ochoa have suggested that prostaglandin synthesis is key to both the intestinal epithelial secretory and the CHO cell responses to cholera toxin [Peterson, J. W. and Ochoa, G. (1989) Science 245, 857-859]. Because platelet activating factor (PAF) can be a potent stimulus for prostaglandin synthesis, we examined its role in the intestinal and tissue culture effects of cholera toxin. We report that the specific PAF receptor antagonists BN 52021 and SR 27417 inhibit the effects of cholera toxin on intestinal secretion in rabbit ileal loops in vivo and on the cytoskeleton of Chinese hamster ovary cells in vitro. We also show that PAF itself can cause net fluid secretion in the rabbit model and that PAF potentiates the effects of cholera toxin on intestinal secretion. Finally, we demonstrate that cholera toxin stimulates significant PAF production (2.6-fold) in isolated T-84 intestinal epithelial cells. We conclude that cholera toxin stimulates PAF production and that PAF is involved in both the secretory and cytoskeletal responses to cholera toxin. These findings further support the involvement of additional mediators of cholera toxin effects other than mucosal cell cyclic AMP and help explain the effects of cholera toxin on prostaglandin synthesis.

Animals↗
PubMed1989

Gamma-interferon-mediated down-regulation of electrolyte secretion by intestinal epithelial cells: a local immune mechanism?

Active chloride (Cl-) secretion by intestinal crypt enterocytes is the central pathophysiological disturbance in most cases of acute diarrhoea. We examined monolayers of the human intestinal cell line T84 mounted in Ussing chambers to see whether the T-cell lymphokine gamma interferon (IFN-gamma) might affect the Cl- secretory properties of these cells, which morphologically and functionally resemble native crypt enterocytes. Pretreatment of T84 cell layers with IFN-gamma for 24 h (but not for 3 h) markedly decreased the Cl- secretory response to vaso-active intestinal polypeptide (VIP) and to cholera toxin and carbachol without appreciably affecting the overall morphology, electrical resistance, or cyclic AMP response of the T84 cell monolayer. The IFN-gamma treatment, however, did induce subtle changes in the T84 cell membrane protein composition which might have affected ion channels regulating Cl- secretion. Our results may indicate a possible novel 'cell-mediated' immune mechanism through which activated gut T cells could modulate the extent of intestinal electrolyte and fluid secretion in, for example, enteric infections.

Carbachol↗
PubMed1989

The rat distal ileum has a reduced absorptive and secretory capacity compared with proximal ileum--is it to facilitate its chemosensing function?

Compared with the proximal ileum, the distal ileum in rat has a greatly reduced capacity for electrogenic ion secretion induced by secretagogues and for electrogenic, sodium-linked glucose transfer assessed in vitro. Similarly, in vivo, there is a great reduction in distal ileal basal fluid absorption and secretagogue-activated fluid secretion compared with proximal ileal values. This reduced absorptive and secretory capacity of the distal ileum would allow minimal changes in the concentrations of the luminal contents, facilitating its putative role as final chemosensor of the luminal contents of the small intestine.

Acetylcholine↗
PubMed1995

Amniotic fluid and plasma levels of parathyroid hormone-related protein and hormonal modulation of its secretion by amniotic fluid cells.

Parathyroid hormone-related (PTHrP), the major mediator of humoral hypercalcemia of malignancy, may also regulate placental calcium flux, uterine contraction and fetal tissue development. In the present study, we demonstrated that the mean immunoreactive PTHrP concentrations in amniotic fluid at mid-gestation (21.2 +/- 3.7 pmol/l) and at term (19.0 +/- 2.7 pmol/l) were 13-16-fold higher than levels measured in either fetal (1.6 +/- 0.1 pmol/l) or maternal plasma (1.4 +/- 0.3 pmol/l) at term and equal to levels found in plasma of patients with humoral hypercalcemia of malignancy. In vitro studies pointed to three possible sources of PTHrP in amniotic fluid: cultured amniotic fluid cells, cells derived from the amniotic membrane overlying the placenta and placental villous core mesenchymal cells. Treatment of cultured amniotic fluid cells with human prolactin, human placental lactogen (hPL) or human growth hormone (100 micrograms/l) increased PTHrP secretion after 24 h by 43%, 109% and 90%, respectively. Insulin-like growth factors I and II (100 micrograms/l), insulin (100 micrograms/l) and epidermal growth factor (EGF) (10 micrograms/l) increased PTHrP secretion by 53%, 46%, 68% and 118%, respectively. The stimulation of PTHrP secretion by EGF or by hPL was both time- and dose-dependent. In contrast, calcitriol and dexamethasone (10 nmol/l) decreased PTHrP secretion by 32% and 75%, respectively. Estradiol, progesterone, dihydrotestosterone and human chorionic gonadotropin had no effect on PTHrP secretion. These findings support the notion that PTHrP may play a physiological role in the uteroplacental unit and demonstrate that human amniotic fluid cells could be a useful model for studying the regulation of PTHrP production and secretion by hormones and growth factors.

Amniotic Fluid↗
PubMed1979

The influence of follicular fluid on progesterone secretion by porcine granulosa cells in vitro.

Porcine follicular fluid contains at least two factors which can modify porcine granulosa cell function in vitro. One factor, found primarily in fluid from 1--2 mm follicles inhibits LH stimulated cyclic AMP accumulation, basal and LH stimulated progesterone secretion, and morphological luteinization of granulosa cells from medium sized (3--5 mm) and large (6--12 mm) follicles. Following inhibition by the follicular fluid luteinization inhibitor, incubation with both OH and a phosphodiesterase inhibitor partially restores cyclic AMP accumulation and fully restores progesterone secretion. This suggests that the defect induced by the luteinization inhibitor is primarily an alteration of cyclic nucleotide metabolism. Another factor found primarily in fluid from large preovulatory follicles stimulates basal and gonadotrophin stimulated progesterone secretion by granulosa cells from small antral follicles. We hypothesize that it may be necessary for the fluid within an individual follicle to shift from being inhibitory of luteinization to being permissive or stimulatory for the granulosa cells to mature rather than become atretic.

Animals↗
PubMed1998

Nitric oxide and guanosine 3',5'-cyclic monophosphate stimulate bile secretion in isolated rat hepatocyte couplets, but not in isolated bile duct units.

Nitric oxide (NO) and guanosine 3',5'-cyclic monophosphate (cGMP) have recently been shown to stimulate bile acid-independent bile flow in the isolated perfused rat liver (IPRL). However, the cellular origin and mechanisms of this choleresis have not yet been determined. To address these questions, we examined the effects of NO and cGMP on bile secretion in isolated rat hepatocyte couplets (IRHC) and in isolated bile duct units (IBDU), both of which are isolated cell systems in which cell polarity is maintained and secretion can be measured directly. Changes in the area of the canalicular and ductular lumens were determined in IRHC and IBDU, respectively, as indicators of the rate of fluid secretion using video microscopy. In addition, Cl-/HCO3- exchanger activity in IBDU was evaluated by measuring changes in intracellular pH (pHi) after Cl- removal/readmission by microfluorometric methods. In the presence of HCO3-, both the NO donor, S-nitroso-acetyl-penicillamine (SNAP), and the cell-permeant cGMP analogue, dibutyryl cGMP (DBcGMP), stimulated canalicular bile secretion (P <.05), as did the cell-permeant cAMP analogue, dibutyryl cAMP (DBcAMP) (P <.05). Removal of HCO3- from the buffer completely abolished the choleretic effects of DBcGMP, but had no effect on NO-induced choleresis. In contrast, secretion in IBDU was not stimulated following incubations with SNAP or DBcGMP over 30 minutes, whereas DBcAMP and secretin, a cholangiocyte secretagogue and cAMP agonist, both had a marked effect on ductular secretion over this same time interval (P <.05). SNAP also had no effect on Cl-/HCO3- exchanger activity in IBDU, and inhibition of endogenous NO synthesis by NG-monomethyl-L-arginine (L-NMMA) did not alter secretin-induced stimulation of ductular bile secretion and Cl-/HCO3- exchanger activity. In summary, NO and cGMP stimulate bile secretion exclusively at the the level of hepatocytes, whereas cAMP mediates choleresis at both hepatocyte and bile duct levels. These findings may have important implications for the regulation of ductular bile secretion by hormones and neuropeptides, as well as under pathological conditions with increased hepatic NO synthesis.

Animals↗
PubMed1987

Small-bowel colonization alone is a cause of diarrhea.

Bacterial overgrowth in the small bowel is known to occur in patients with persistent diarrhea, but it has been unclear if colonization alone causes fluid secretion. We studied isogenic, nontoxigenic Escherichia coli strains with colonizing factor antigen II (CFA/II) (1392+) and without CFA/II (1392-) in 18-h rabbit ileal loops. Neither strain produced fluid, but quantitative cultures of rabbit ileal loops with the CFA/II-positive strain had a mean of 10(3) more CFU of bacteria per cm2 than did cultures of rabbit ileal loops with the CFA/II-negative strain or a negative control (P less than 0.05). Of 11 rabbits given strain 1392+ via the small bowel in the reversible ileal tie model, 7 became colonized (mean, 10(10.4) +/- 1.6 CFU/cm2) over 72 h, and all 7 developed diarrhea and had gross gut fluid accumulation, versus none of 10 rabbits given strain 1392- (mean, 10(3.6) +/- 1.9 CFU/cm2) (P less than 0.05). Both strains grew equivalently in vitro. The mechanism by which this E. coli strain which colonizes small-bowel mucosa but produces no recognized toxins causes fluid accumulation and diarrhea in a rabbit model at 72 h remains to be elucidated.

Animals↗
PubMed1979

[Water and electrolytes intestinal secretion (author's transl)].

This paper reviews methods used for studying intestinal secretion in man and animals, fasting and post prandial intestinal secretion, as well as that induced by bacterial enterotoxins, hormonal stimuli, some endocrine tumours and various intraluminary agents; finally the possible mechanisms and sites of intestinal secretion are discussed. That the intestine secretes fluid under physiological conditions is not proven but seems very likely. Several mechanisms seem to be involved in the production of fluid by the intestine. The adenylate-cyclase-cyclic adenosine monophosphate (AMPc) system is currently thought to play a major role in endotoxins and some hormone-induced secretions. The site of intestinal secretion remains a matter of discussion: both crypts and villi seem to participate in the secretory process.

Adenylyl Cyclases↗
PubMed1980

Oral rehydration in diarrhoea : applied pathophysiology.

The main danger of acute diarrhoea is the loss of body water and electrolytes. The scientific rationale for oral rehydration therapy depends on the function of the small bowel enterocytes. Recent studies have indicated that active secretion rather than a failure of absorption is the main mechanism for most cases of acute disease. The linked-absorption process of sodium and substrate enhance the assimmlation of replacement fluid and remains intact in most cases of diarrhoea. A suitable rehydration mixture depends on: the physiology of the absorption mechanism, the chemical composition of fluid secreted in the particular type of diarrhoea, and on practical factors relating to the cost and availability of ingredients. Oral rehydration therapy is an appropriate primary health care technique for use in early acute diarrhoea.

Acute Disease↗
PubMed1992

Parasympathetic NANC-secretion of saliva in the mink, and effects of substance P and VIP.

In both parotid and submandibular glands a parasympathetic non-adrenergic, non-cholinergic (NANC) nerve-evoked secretion of saliva was demonstrated. Saliva evoked by exogenous substance P was poor in protein, while saliva evoked by VIP was protein-rich. In a subthreshold dose for fluid secretion VIP released protein and potentiated the responses elicited by substance P, particularly regarding the output of protein. The two neuropeptides may contribute to the parasympathetic NANC secretion of saliva in the mink. Further, agonists responsible for the secretory NANC response are also likely to contribute to the secretory response of the glands to parasympathetic stimulation in the absence of autonomic receptor blockade in this species.

Adrenergic alpha-Antagonists↗
PubMed1989

Evidence for sympathetic regulation of the hydraulic conductance of rat jejunal mucosa in vivo.

The aim of the study was to test the hypothesis that sympathetic nerve stimulation inhibits jejunal fluid secretion by decreasing the hydraulic conductance (Lp) of the mucosa. Jejunal segments of anaesthetized rats were mounted in a specially constructed chamber which makes it possible to measure net fluid transport together with transmural potential difference or short circuit current in vivo. Lp was estimated by measuring the effects on net fluid transport rate elicited by stepwise changes in luminal pressure. Lp was measured in four groups of animals: (1) under control conditions; (2) after hexamethonium administration, to block intramural secretory neurons; (3) during efferent stimulation of the mesenteric nerves, to activate sympathetic neurons, and (4) during mesenteric nerve stimulation (MNS) after pre-treatment with phentolamine, an alpha-adrenergic antagonist, to block the sympathetic effector mechanism. Lp measured at positive luminal pressures in control animals was approximately 4 microliters min-1 cmH2O-1 100 cm-2 serosal surface area. When measured at negative luminal pressures, this value increased approximately threefold. Hexamethonium did not significantly influence Lp. At positive luminal pressures, MNS decreased Lp to a value not significantly different from zero. This effect was abolished by phentolamine. At negative luminal pressures, MNS decreased Lp by approximately 50% and this effect was partly antagonized by phentolamine. The results suggest that a decrease in mucosal hydraulic conductance may contribute to the antisecretory effect of sympathetic nerve stimulation in vivo.

Adrenergic alpha-Antagonists↗
PubMed1990

An emerging role for a cardiac peptide hormone in fish osmoregulation.

It is clear from the extant literature that various fish groups face chronic osmoregulatory problems that depend on the surrounding salinity. Their physiologic and hormonal responses are largely those seen in the mammals, but their terrestrial descendants have lost osmoregulatory structures such as gills and rectal glands and depend primarily on renal function. A data base is now emerging that strongly suggests that a putative atriopeptin plays a role in osmoregulation in fishes. This conclusion is supported by the fact that heterologous AP produces relevant physiologic responses (e.g. natriuresis, vasodilation, stimulation, or inhibition of Na+ secretion by intestine, gills, and rectal gland) in both teleosts and elasmobranchs. Moreover, cardiac and brain extracts from fish can produce similar effects in both fishes and mammals, and these tissues from various fish groups contain immunoreactive AP, as does plasma. Both physiologic and immunologic evidence suggests that the ventricle may be a significant source of AP in fishes, contrary to the situation in mammals. Finally, osmotic perturbations result in a change in plasma and tissue APir levels. The finding that plasma APir levels increase in sea water, and that heterologous AP stimulates salt secretion by the teleost gill and shark rectal gland, and inhibits salt uptake by the teleost intestine, suggests that AP may primarily play a role in salt, rather than fluid, secretion in fishes. The fact that in mammals AP inhibits prolactin secretion, but is itself stimulated by cortisol, supports this conclusion, since prolactin is generally considered to be the dominant osmoregulatory hormone in freshwater fishes, and cortisol serves this function in marine fishes. In addition, if AP inhibits brain AVT release in fishes, as it apparently inhibits vasopressin release in mammals, this also would be adaptive in marine fishes since AVT in fishes is diuretic, rather than antidiuretic. Interactions between AP and these hormones (prolactin, cortisol, and ATV) have not been studied in fishes to date, but these theoretical interactions do lend support to the hypothesis that AP may function primarily in salt homeostasis in fishes. At least one potential hormonal interaction counters this argument, however. Atriopeptin is known to inhibit the production and effects of angiotensin II in mammals, and since this hormone is apparently dipsogenic in fishes, it may play a critical role in osmoregulation in sea water. Finally, it is of some historical interest that in Keys' (67) original description of the eel heart-gill perfusion system in 1931 he commented that gill resistance remained constant for hours only if the heart itself was perfused.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1975

Effect of Klebsiella pneumoniae enterotoxin on intestinal transport in the rat.

The effects on intestinal transport of either a semipurified preparation of enterotoxin elaborated by Klebsiella pneumoniae or similaryly prepared control material were tested by marker perfusion studies in the small intestine of rats. At a concentration of 2 mg/ml, the enterotoxin produced net secretion of water, Na, and Cl in both jejunal and ileal segments; HCO3 transport was not affected. Net secretion was evident within 30 min after intorduction of the toxin and was maximal after 90 min. The addition of 56 mM glucose to the enterotoxin-containing perfusion fluid resulted in reversal of water and Na transport to net absorption in both intestinal segments. The enterotoxin also produced a significant depression of xylose absorption in both the jejunum and ileum but did not affect the absorption of either glucose or L-leucine. Intestinal structure was not altered after perfusion of the toxin but insillation of approximately one-quarter of the total perfusion dose into a ligated jejunal loop for 18 h produced fluid secretion and structural abnormalities. These observations confirm the fact that other species of coliform bacteria in addition to tescherichia coli are capable of elaborating an enterotoxin. Such species commonly contaminate the small intestine of persons with tropical sprue and it is suggested that chronic exposure of the intestinal mucosa to the enterotoxin elaborated by these bacteria may be a factor in the pathogenesis of intestinal abnormalities in thid disorder.

Animals↗
PubMed2004

Secreted and placental membrane forms of folate-binding protein occur sequentially during pregnancy in swine.

The objective was to understand how two forms of folate-binding protein interact to accomplish folate transport during pregnancy in swine. Specific folate binding was measured in uterine flushings during the estrous cycle and early pregnancy and in allantoic fluid (secreted form) and placental membranes (membrane form) throughout later pregnancy. In addition, the localization of the secreted form of folate-binding protein (sFBP) in uterine wall sections was assessed. Uterine flushings were collected on Days 10, 13, and 15 of the estrous cycle and pregnancy. Allantoic fluid and placentas were collected on Days 20, 35, 50, 70, 90, and 105 of pregnancy. Uterine-wall sections were collected on all days of the experiment. Folate binding was measured by incubation of aliquots of uterine flushings, allantoic fluid, or placental microsomal membranes with 0.5-4 nM [(3)H]folate. Uterine-wall sections were incubated with purified anti-FBP IgG or normal rabbit serum IgG to localize sFBP. Folate binding did not differ between early pregnancy and the estrous cycle in uterine flushings, was greatest from Day 50 to 70 of pregnancy in allantoic fluid, and was greatest from Day 50 of pregnancy onward in placental microsomal membranes. Staining for sFBP was present in the endometrial glands from Day 10 to 15 in cyclic gilts and from Day 10 to 20 in pregnant gilts. The pattern of folate binding and sFBP staining supports the concept that sFBP transports folate to the developing conceptus until placentation and then the placental form takes over folate transport.

Allantois↗
PubMed1982

Blood flow and secretion in the submaxillary gland of the rabbit during stimulation of the autonomic nerves.

The excitation of the chorda-tympani nerve caused a marked increase in the blood flow through the gland and in secretion of saliva; both phenomena had a threshold frequency of around 0.3 Hz and reached a maximum at around 20 Hz, where a 6-fold increase in the blood flow and a salivary secretion of at the most 300 microliters/min were seen. Sympathetic excitation severely retarded the blood flow, which almost ceased at frequencies as low as 3-5 Hz; mostly single shocks of sympathetic stimulation reduced the blood flow through the gland. An on-going parasympathetic activation did not alter the effects of sympathetic stimulation on the blood flow and the parasympathetically produced salivary secretion almost stopped. The experiments support previous results, which have suggested electrical excitation of the sympathetic trunk at or above 2 Hz to cause a vasoconstriction which adversely affects the fluid secretion in the rabbit salivary glands.

Animals↗
PubMed1979

Chlorpromazine reverses diarrhea in piglets caused by enterotoxigenic Escherichia coli.

The effect of chlorpromazine (CPZ) on diarrhea caused by enterotoxigenic Escherichia coli was tested in piglets since CPZ has been shown to be a potent antagonist to enterotoxins in vitro in a cell system and in vivo in a mouse model. Experimental diarrhea was induced in three litters of newborn piglets which were infected by mouth with 2 x 10(9)E. coli bacteria, which produce heat-labile (LT) and heat-stable (ST) enterotoxins. Treatment with CPZ given intramuscularly 1 h after the onset of diarrhea reversed fluid secretion in small intestine as well as dehydration, as judged by clinical criteria. A dose of 5 mg of CPZ per kg of body weight completely normalized the intestinal-fluid content measured 4 h after diarrhea developed, whereas 1 to 2 mg of CPZ per kg of body weight was somewhat less effective but still caused significant reduction of fluid (P < 0.001). Studies with radioactive [(35)S]CPZ showed preferential and dose-dependent uptake of (35)S in the intestinal mucosa, the radioactivity being evenly distributed in the membranes of both crypt and villus cells. The enzyme adenylate cyclase, which probably mediates the cellular effects of LT, was shown to have two- to threefold higher activity in the infected than in the uninfected animals. This activation was reduced about 50% by the CPZ treatment (2 mg/kg of body weight). In a preliminary field trial the effect of CPZ was tested in a spontaneous outbreak of diarrhea in piglets due to enterotoxinogenic E. coli. The animals were treated either with oral electrolyte solution and standard antimicrobial agents only (controls) or with 1 mg of CPZ per kg of body weight intramuscularly in addition to this treatment. The mean duration of diarrhea in CPZ-treated animals was significantly shorter, 4.1 h (n = 23), than that in controls, 7.2 h (P < 0.05).

Adenylyl Cyclases↗
PubMed2006

The distribution of intermediate-conductance, calcium-activated, potassium (IK) channels in epithelial cells.

Intermediate-conductance, calcium-activated, potassium (IK) channels were first identified by their roles in cell volume regulation, and were later shown to be involved in control of proliferation of lymphocytes and to provide a K+ current for epithelial secretory activity. Until now, there has been no systematic investigation of IK channel localization within different epithelia. IK channel immunoreactivity was present in most epithelia, where it occurred in surface membranes of epithelial cells. It was found in all stratified epithelia, including skin, cornea, oral mucosa, vaginal mucosa, urothelium and the oesophageal lining. It occurred in the ducts of fluid-secreting glands, the salivary glands, lacrimal glands and pancreas, and in the respiratory epithelium. A low level of expression was seen in serous acinar cells. It was also found in other epithelia with fluid-exchange properties, the choroid plexus epithelium, the ependyma, visceral pleura and peritoneum, bile ducts and intestinal lining epithelium. However, there was little or no expression in vascular endothelial cells, kidney tubules or collecting ducts, lung alveoli, or in sebaceous glands. It is concluded that the channel is present in surface epithelia (e.g. skin) where it has a cell-protective role against osmotic challenge, and in epithelia where there is anion secretion that is facilitated by a K+ current-dependent hyperpolarization. It was also in some epithelial cells where its roles are as yet unknown.

Animals↗