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PubMed1996

Metabolic base production and mucosal vulnerability during acid inhibition in a mammalian stomach in vitro.

Acid inhibition increases gastric mucosal susceptibility to damage by luminal acid. This might be due to reduced metabolic CO2 and bicarbonate whereas, during normal acid, secretion cytoprotective CO2/HCO3- production parallels acid production. Metabolic activity and mucosal damage caused by luminal acid perfusion was determined in an in vitro mouse stomach, with and without acid inhibition, and at 0%, 1%, or 5% serosal CO2 supply. Without acid inhibition there was no mucosal damage at any level of serosal CO2/HCO3- supply. Acid inhibition reduced metabolic CO2 production by 29% (P < 0.004) and resulted in microscopic damage to 55% of the mucosal area and perforation in four of five stomachs (P < 0.05). Although, 1% CO2 supply completely replaced the reduction in metabolic CO2, it did not protect against mucosal damage. Overreplacement by 5% serosal CO2/HCO3- was required to prevent damage. There was no correlation between luminal CO2/HCO3- output and mucosal damage. The protection by endogenous or exogenous CO2/HCO3- appears to act intracellularly rather than by intragastric or intercellular neutralization.

Acid-Base Equilibrium↗
PubMed1996

Increased permeability occurs in rat ileum following induction of pan-colitis.

Acetic acid-induced pan colitis in rats leads not only to colonic injury but also to a bystander ileal injury, characterized by decreased fluid and electrolyte absorption without associated histological injury or infiltration of inflammatory cells. To examine the nature of this decreased ileal fluid and electrolyte absorption, we measured effect of acetic acid-induced pancolitis on ileal transmural sodium and chloride transport, as well as on ileal permeability to mannitol and inulin on mucosal sheets mounted in Ussing chambers. In addition, ileal tight junctional morphology was assessed by electron microscopy. In colitic animals, ileal serosal-to-mucosal sodium and chloride transmural fluxes were increased (P<0.05); compatible with the observed decrease in net fluid absorption. Mannitol and inulin ileal serosal-to-mucosal and mucosal-to-serosal ileal fluxes were similarly increased (P<0.05), suggesting that an increase in ileal permeability occurred during acetic acid-induced pancolitis. This increase in ileal permeability was not accompanied by changes in tight junctional ultrastructure. These results suggest that: (1) the decrease in ileal fluid and electrolyte absorption seen during acetic acid-induced rat pancolitis occurred in parallel with a rise in both transcellular and paracellular permeability, and (2) the ileal permeability changes were not accompanied by structural changes.

Animals↗
PubMed1987

Phorbol ester effect on the hydrosmotic response to vasopressin in frog skin.

Serosal preincubation of frog skin with tetradecanoyl phorbol acetate, TPA, an activator of protein kinase C, inhibits the hydrosmotic response elicited by vasopressin (AVP) but not that induced by 8br-cAMP. This proves that serosal TPA primarily influences a pre-cAMP step. The TPA-induced inhibition of AVP response appears to be related to TPA-induced prostaglandin synthesis. The pretreatment with naproxen, in fact, prevents the inhibition induced by serosal TPA on the AVP response. On the contrary, mucosal TPA produces a more marked inhibition of the response to AVP and significantly diminishes the water flow induced by 8br-cAMP; this suggests that mucosal TPA interferes mainly with a post-cAMP step. Furthermore, naproxen is unable to completely prevent the inhibition induced by mucosal TPA on AVP response thus indicating that mucosal TPA may also activate a prostaglandin-independent mechanism able to inhibit one of the last steps of the hydrosmotic response to AVP.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1977

The effect of lipids on taurocholate absorption from intestinal loops in the rat.

The rates of uptake and serosal transfer of [14C]-labelled taurocholate (7.77 mM in bicarbonate buffer, pH 6.5) were determined in situ in ligated segments of rat intestine in the presence of lipids. Oleic acid, monoolein, lecithin, and lysolecithin enhanced taurocholate uptake and transfer in the jejunum, each lipid exhibiting an optimal concentration at which the bile acid fluxes were maximal. The maximal rates of bile acid uptake observed with the various lipids were close to four times the uptake rates found with the lipid-free taurocholate medium, whereas serosal transfer rates under optimal conditions were enhanced about six-fold. The optimal concentrations differed widely among the various lipids, being inversely related to the lipids' polarity. Simultaneous measurement of taurocholate and [3H]-labelled oleic acid showed that under optimal conditions, when the molar concentration of oleic acid was about equal to that of the bile acid, the fatty acid and bile acid also exhibited closely similar rates of absorption. At other fatty acid concentrations, the fractional rate of absorption of the bile acid was much lower than that of the fatty acid. The rates of uptake and serosal transfer of pure taurocholate by the ileum exceeded those of the jejunum by factors of about 7 and 15, respectively, but in the presence of lipids this difference in absorptive capacity for bile acid between the distal and proximal segment largely disappeared.

Animals↗
PubMed2001

Effect of vehicles and enhancers on the in vitro skin penetration of aspalatone and its enzymatic degradation across rat skins.

The feasibility of skin penetration was studied for aspalatone (AM, acetylsalicylic acid maltol ester), a novel antithrombotic agent. In this study, hairless mouse dorsal skins were used as a model to select composition of vehicle and AM. Based on measurements of solubility and partition coefficient, the concentration of PG that showed the highest flux for AM across the hairless mouse skin was found to be 40%. The cumulative amount permeated at 48 h, however, appear inadequate, even when the PG concentration was employed. To identify a suitable absorption enhancer and its optimal concentration for AM, a number of absorption enhancers and a variety of concentration were screened for the increase in transdermal flux of AM. Amongst these, linoleic acid (LOA) at the concentration of 5% was found to have the largest enhancement factor (i.e., 132). However, a further increase in AM flux was not found in the fatty acid concentration greater than 5%, indicating the enhancement effect is in a bell-shaped curve. In a study of the effect of AM concentration on the permeation, there was no difference in the permeation rate between 0.5 and 1% for AM, below its saturated concentration. At the donor concentration of 2%, over the saturated condition, the flux of AM was markedly increased. A considerable degradation of AM was found during permeation studies, and the extent was correlated with protein concentrations in the epidermal and serosal extracts, and skin homogenates. In rat dorsal skins, the protein concentration decreased in the rank order of skin homogenate > serosal extract > epidermal extract. Estimated first order degradation rate constants were 6.1 5 +/- 0.14, 0.57 +/- 0.02 and 0.011 +/- 0.004 h(-1) for skin homogenate, serosal extract and epidermal extract, respectively. Therefore, it appeared that AM was hydrolyzed to some extent into salicylmaltol by esterases in the dermal and subcutaneous tissues of skin. Taken together, our data indicated that transdermal delivery of AM is feasible when the combination of PG and LOA is used as a vehicle. However, since AM is not metabolically stable, acceptable degradation inhibitors may be necessary to fully realize the transdermal delivery of the drug.

Animals↗
PubMed2000

Papillary adenocarcinoma of the stomach.

BACKGROUND: Papillary gastric carcinoma (PGC) is a rare histologic entity among gastric adenocarcinomas. The aim of this study was to clarify the clinicopathologic characteristics of PGC, including the survival rate, recurrence pattern, and factors influencing the prognosis of patients with PGC.METHODS: The clinicopathologic findings of 65 patients with PGC and 566 patients with non-papillary gastric carcinoma (NGC) were examined and compared. The tumor was classified as PGC when more than 50% of the tumor area contained papillary structures. Survival rates were calculated using the Kaplan-Meier method and were assessed by the generalized Wilcoxon test. Prognostic factors were evaluated by univariate analysis, using the chi(2) test and Student's t-test, and confirmed by multivariate analysis, using the Cox proportional hazards model.RESULTS: PGC was characteristically found in patients over 65 years of age (68%), was located in the upper one-third of the stomach (37%), was of grossly localized type (85%), was negative for serosal invasion (86%), and was associated with liver metastasis (14%). The overall 5-year survival rate for patients with PGC was significantly lower than the rate for those with NGC (63% vs 76%) ( P < 0.05). Although the 5-year survival rate for each stage of PGC and NGC did not differ significantly, the death of PGC patients was more frequently associated with liver metastasis (62%) than with peritoneal dissemination (5%). Independent prognostic factors of PGC were liver metastasis, serosal invasion, and lymph node metastasis.CONCLUSION: These results suggest that PGC is characterized by advanced patient age, proximal tumor location, grossly localized type, negative serosal invasion, and frequent liver metastasis. A poor prognosis for patients with PGC is associated with the presence or recurrence of liver metastasis.

Journal Article↗
PubMed2006

Release and permeation of histamine in isolated caecum epithelia of pigs.

OBJECTIVE: The objective was to investigate the role of histamine in the porcine caecum with special regard to its release and permeation. MATERIAL AND METHODS: Caecal epithelia were mounted in Ussing chambers. Mast cells were stimulated by A23187 (1 micromol/l). Permeation and changes in short-circuit current (Isc) were assessed after unilateral application of 3H-labelled histamine (100 micromol/l). Mucosal-to-serosal (ms) and serosal- to-mucosal (sm) flux rates were calculated based on the contralateral appearance of radioactive histamine label (hist-rad; representing histamine plus catabolites) as well as histamine. 14C-mannitol fluxes were measured to assess paracellular permeability. RESULTS: Both A23187 and serosal addition of histamine increased Isc of caecal epithelia. The Isc increase due to A23187 was associated with an elevated histamine release from epithelia. A discrepancy between hist-rad and histamine fluxes (P<0.05) indicated efficient histamine catabolism (ca. 85%), which was decreased by blockage of diamine oxidase through aminoguanidine. Fluxes of histamine were correlated to 14C-mannitol fluxes. Fluxes of hist-rad and histamine were higher in the sm direction. CONCLUSIONS: Histamine can be released from endogenous stores and acts on the epithelium. The absorption of luminal histamine is predominantly restricted by paracellular permeability and catabolism. The latter is only partially catalysed by diamine oxidase.

Animals↗
PubMed2005

Inducible nitric oxide synthase inhibition improves intestinal microcirculatory oxygenation and CO2 balance during endotoxemia in pigs.

OBJECTIVE: We examined whether selective inhibition of inducible nitric oxide synthase (iNOS) promotes intestinal microvascular oxygenation (microPO2) and CO2 off-load after endotoxic shock. DESIGN AND SETTING: Prospective, controlled experimental study in a university animal research laboratory. SUBJECTS: 13 domestic pigs. INTERVENTIONS: After baseline measurements shock was induced by 1 microg kg-1 h-1 endotoxin until mean arterial pressure fell below 60 mmHg. After 30 min in shock the animals were resuscitated with either fluid alone (control, n=6) or fluid and the iNOS inhibitor N-[3-(aminomethyl)benzyl]acetamidine hydrochloride (1400W, n=7). As final experimental intervention all animals received the nonselective NOS inhibitor L-NAME. MEASUREMENTS AND RESULTS: Systemic and regional hemodynamic and oxygenation parameters were measured at baseline, during endotoxemia and shock, hourly for 3 h of 1400W therapy, and 30 min after the final L-NAME administration. microPO2 was assessed by the Pd-porphyrin phosphorescence technique, and the arterial to intestinal PCO2 gap was determined by air tonometry. Endotoxemia and shock resulted in a decrease in ileal mucosal and serosal microPO2 and a rise in PCO2 gap. The combination of 1400W and fluid resuscitation, but not fluid alone, normalized both the serosal microPO2 and the intestinal PCO2 gap. Administration of L-NAME decreased cardiac output and oxygen delivery and intestinal microPO2 and blood flow in both groups. CONCLUSIONS: Partial blockade of NO production by 1400W increased serosal microvascular oxygenation and decreased the intestinal CO2 gap. This findings are consistent with the idea that 1400W corrects pathological flow distribution and regional dysoxia within the intestinal wall following endotoxic shock.

Animals↗
PubMed1997

Fish gill respiratory cells in culture: a new model for Cl(-)-secreting epithelia.

Primary cultures of sea bass gill cells grown on permeable membranes form a confluent, polarized, functional tight epithelium as characterized by electron microscopy and electrophysiological and ion transport studies. Cultured with normal fetal bovine serum (FBS) and mounted in an Ussing chamber, the epithelium presents a small short-circuit current (Isc: 1.4 +/- 0.3 microA/cm2), a transepithelial voltage (Vt) of 12.7 +/- 2.7 mV (serosal positive) and a high transepithelial resistance (Rt: 12302 +/- 2477 omega x cm2). A higher degree of differentiation and increased ion transport capacities are observed with cells cultured with sea bass serum: numerous, organized microridges characteristic of respiratory cells are present on the apical cell surface and there are increased Isc (11.9 +/- 2.5 microA/cm2) and Vt (25.9 +/- 1.7 mV) and reduced Rt (4271 +/- 568 omega x cm2) as compared with FBS-treated cells. Apical amiloride addition (up to 100 microM) had no effect on Isc. The Isc, correlated with an active Cl- secretion measured as the difference between 36Cl- unidirectional fluxes, was partly blocked by serosal ouabain, bumetanide, DIDS or apical DPC or NPPB and stimulated by serosal dB-cAMP. It is concluded that the chloride secretion is mediated by a Na+/K+/2Cl- cotransport and a Cl-/HCO3- exchanger both responsible for Cl- entry through the basolateral membrane and by apical cAMP-sensitive Cl- channels. This study gives evidence of a functional, highly differentiated epithelium in cultures composed of fish gill respiratorylike cells, which could provide a useful preparation for studies on ion transport and their regulation. Furthermore, the chloride secretion through these cultures of respiratorylike cells makes it necessary to reconsider the previously accepted sea water model in which the chloride cells are given the unique role of ion transport through fish gills.

Animals↗
PubMed1997

Osmotic regulation of Na+ transport across A6 epithelium: interactions with prostaglandin E2 and cyclic AMP.

Previous work from this laboratory has shown that apical membrane sodium channel activity is stimulated by serosal hyposmotic solutions (Wills, Millinoff & Crowe, 1991). In the present study, we determined whether this stimulation of sodium transport is additive with the actions of prostaglandin E2 (PGE2) or cyclic AMP (cAMP). Addition of exogenous PGE2 (100 nM; serosal bath) to isosmotic solutions led to large increases in the amiloride-sensitive short-circuit current (Isc) and transepithelial conductance (Gt), whereas no significant effects of PGE2 were observed in hyposmotic serosal solutions. Subsequent addition of mucosal amiloride reduced Isc by approximately 95% and Gt by approximately 60%. Inhibition of endogenous PGE2 production by blockers of phospholipase A2 activity (quinacrine or 3[4-octadecyl]-benzoylacrylic acid; OBBA), or inhibition of cyclooxygenase activity by indomethacin reduced the stimulation of Isc and Gt by hyposmotic solutions. Addition of forskolin (FSK) or 3-Isobutyl-1-methylxanthine (IBMX) also resulted in approximately twofold increases in the amiloride-sensitive Isc and Gt and abolished the effects of subsequent hyposmotic challenge. The effects of forskolin, PGE2, and hyposmotic challenge were diminished by pretreatment with H89, a protein kinase A (PKA) inhibitor. We conclude that osmotic regulation of sodium channel activity interacts with multiple intracellular signaling pathways, specifically the arachidonic acid metabolic pathway and the cAMP/PKA intracellular messenger cascade.

1-Methyl-3-isobutylxanthine↗
PubMed1997

Abdominal calcification in cystic fibrosis with meconium ileus: radiologic-pathologic correlation.

BACKGROUND: There is confusion in the radiological literature as to the site of abdominal calcification in cystic fibrosis (CF) with meconium ileus (MI) in neonates. PURPOSE: To correlate the site of radiographic abdominal calcification with histologic and operative findings. MATERIALS AND METHODS: A review of clinical, radiographic, surgical and histologic data in 58 neonates with CF and MI. RESULTS: Abdominal calcification was identified in 15 (26 %) neonates: on an abdominal radiograph in 8 (13 %), at laparotomy in 3 and histologically in 10 (37 %) of the 27 resected specimens. The radiographic pattern of calcification varied from small specks in three cases to small, better-defined areas in two. In the other three patients, the calcification was more extensive and curvilinear. Histologically, calcification was found to be intramural in ten resected specimens, of which two also had intraluminal and one serosal calcification. The more extensive, curvilinear calcification identified radiographically correlated with histologically proven dystrophic intramural calcification. The less marked flecks or discrete areas of radiographic calcification may represent intramural, serosal or intraluminal calcification. CONCLUSION: Intramural calcification is common microscopically in CF with MI. Extensive radiographic calcification in these patients is more likely to represent intramural rather than serosal or intraluminal calcification.

Calcinosis↗
PubMed2001

Indications for early postoperative intraperitoneal chemotherapy of advanced gastric cancer: results of a prospective randomized trial.

Previous analysis of this prospective randomized trial and meta-analysis of published randomized trials of adjuvant intraperitoneal chemotherapy demonstrated improved survival in patients with advanced gastric cancer. Simple criteria applicable at the time of surgery for patient selection were sought in this analysis. From 1990 to 1995 a series of 248 patients with biopsy-proven gastric cancer were randomized intraoperatively to receive early postoperative intraperitoneal mitomycin C and 5-fluorouracil (125 patients) versus surgery only (123 patients). Gastric resection plus early postoperative intraperitoneal chemotherapy showed improved overall survival compared to surgery only (54% and 38%, respectively; p = 0.0278). There were statistically significant differences in patients with stage III (57% and 23%, respectively; p = 0.0024) and in those with stage IV (28% and 5%, respectively; p = 0.0098) gastric cancer. The improvement in survival rate was statistically significant for the subgroup of patients with gross serosal invasion (52% and 25%, respectively; p = 0.0004) and patients with lymph node metastasis (46% and 22%, respectively; p = 0.0027). The surgeons' impression about lymph node status was unreliable, but assessment of serosal invasion was accurate in 80% of cases. Gross serosal invasion with or without frozen section evaluation of lymph nodes can be used as the major selection criteria for early postoperative intraperitoneal chemotherapy of advanced gastric cancer.

Antibiotics, Antineoplastic↗
PubMed2004

Laparoscopic cholecystectomy: its effect on the prognosis of patients with gallbladder cancer.

Numerous reports suggest more recurrences and a worse prognosis after laparoscopic cholecystectomy (LC) than after open cholecystectomy (OC). The objective of this study was to compare the survival rate of patients undergoing a laparoscopic procedure versus those undergoing an open operation. A series of 24 patients with gallbladder cancer detected after LC were compared with 40 consecutive patients with gallbladder cancer detected after OC. Patients were matched by wall invasion, age, and whether they underwent a reoperation or only cholecystectomy. The series included 2 patients with in situ tumors, 2 with mucosal tumors, 1 with muscular invasion, 13 with subserosal invasion, and 6 with serosal invasion. Recurrences were observed in 4 of the 10 patients with subserosal compromise who underwent reoperation. In contrast, in the OC group of 26 patients with subserosal invasion, 20 of whom were reoperated, only 2 had a recurrence. Of the six patients with serosal infiltration, three in the LC underwent reoperation, all of whom had recurrences that precluded resection. Of the 12 patients in the OC group who presented with serosal invasion, 6 were reoperated and 4 had a recurrence. Overall survival curves did not show differences when patients were compared according to the type of procedure performed. Similarly, the analysis of patients according to the level of wall invasion indicated that there was no significant difference in survival. Although multiple reports have shown a worse prognosis for patients with gallbladder cancer undergoing LC, this study did not show a significant survival difference between the two methods. Although there is a higher but insignificant recurrence rate among the patients who underwent LC, this is not translated into survival.

Aged↗
PubMed2000

Protective effects of prostaglandins in the isolated gastric mucosa of the eel, Anguilla anguilla.

The protective effect of endogenous prostaglandins on the fish gastric mucosa was evaluated by studying the effect of indomethacin and aspirin, known cyclooxigenase inhibitors, on the mucosal ulceration in the isolated gastric sacs of Anguilla anguilla. Gastric sacs devoid of muscle layers were incubated in the presence of indomethacin (10(-4) mol x l(-1)) or aspirin (10(-4) mol x l(-1)) in different experimental conditions. Both the antiinflammatory drugs produced ulcers, but the effects were more severe in the presence of histamine and in the absence of HCO3- in the incubation bath. The effects of prostaglandin E2 (PGE2) on acid secretion rate (J(H)) and on alkaline secretion rate (J(OH)) were evaluated (with the aid of the pH stat method) in isolated gastric mucosa mounted in Ussing chambers. We found that PGE2 (10(-8)-10(-5) mol x l(-1)) increased JH in a dose-dependent manner. In tissues pretreated with luminal omeprazole (10(-4) mol x l(-1)), PGE2 stimulated gastric alkaline secretion. It was nullified by serosal removal of HCO3- or Na+ and by serosal ouabain (10(-4) mol x l(-1)). These results suggested that prostaglandins also exert their protective effects in fish gastric mucosa. This protection seems partially due to a stimulation of exogenous HCO3- transport from the serosal to the mucosal side. It is likely that this transport is an active transcellular mechanism coupled to Na+ transport.

Alkalies↗
PubMed2002

Regulation of urea permeability in frog urinary bladder by prostaglandin E(2).

The present study was performed to investigate the role of prostaglandin E(2) (PGE(2)) in the regulation of urea transport in the frog urinary bladder, which is known to occur via a specialized arginine-vasotocin- (AVT-) regulated urea transporter. The bladders isolated from Rana temporaria L. were filled with amphibian Ringer solution containing 370 Bq/ml (0.01 microCi/ml) of [14C]urea, and urea permeability ( P(urea)) was determined by sampling the serosal and mucosal bathing medium at 30-min intervals for measurement of radioactivity. It was found that, from the serosal side, PGE(2) (10 nM to 1 microM) caused a dose-dependent increase in P(urea) [(7.2+/-1.8)x10(-6) cm/s in the presence of 0.5 microM PGE(2)versus (1.0+/-0.2)x10(-6) cm/s in control, n=9, P<0.001]. As in response to AVT, the PGE(2)-induced P(urea)reached a maximum in 1-1.5 h after the agonist was added. The stimulatory effects of PGE(2) and AVT applied together were not additive. PGE(2)-induced urea transport was strongly inhibited by nearly 75% in the presence of mucosal or serosal phloretin (10(-4) M). P(urea) was enhanced up to (4.7+/-0.8)x10(-6) cm/s (n=12, P<0.001) by butaprost (5 x 10(-6) M), a selective EP(2) receptor agonist, while sulprostone (EP(1)/EP(3) agonist, 10(-6) M) caused no changes in P(urea). PGE(2)dose-dependently increased the content of cAMP in mucosal epithelial cells (control: 18.0+/-1.8; 10(-6) M PGE(2): 74.2+/-9.3 pmol cAMP/mg protein per 30 min, n=7, P<0.001). Phorbol esters did not alter PGE(2)-induced P(urea), whereas H-89 (20 microM), a protein kinase A inhibitor, reduced it by 45.1+/-9.9% ( n=5, P<0.05). PGE(2)did not change the AVT-stimulated P(urea) measured in isoosmotic conditions, but inhibited the last one in the presence of a serosa-to-mucosa osmotic gradient. The data obtained show that, in the frog urinary bladder, PGE(2)is a stimulator of phloretin-inhibitable urea transport. Its effect seems to be mediated by EP(2) receptor-coupled generation of intracellular cAMP.

Algorithms↗
PubMed2002

Paracellular tightness and catabolism restrict histamine permeation in the proximal colon of pigs.

Luminal histamine concentrations can be very high in the intestine without eliciting clinical histaminosis. The intestinal mechanisms that possibly prevent systemic intoxication by luminal histamine were investigated in the present study. Porcine colonic epithelia were mounted in Ussing chambers. After unilateral application of partially (3)H-labelled histamine, mucosal-to-serosal (MS) and serosal-to-mucosal (SM) flux rates were calculated from the contralateral appearance of histamine and the radioactive histamine label (hist-rad; representing histamine plus catabolites). A discrepancy between histamine and hist-rad fluxes was observed in both flux directions, indicating efficient histamine catabolism at all histamine concentrations tested (5, 50 and 100 microM). Catabolism exceeded 65% at 100 microM histamine and reached approximately 100% at 5 microM histamine. Blockade of histamine N-methyltransferase by amodiaquin (100 microM) abolished catabolism completely, whereas blockade of diamine oxidase by aminoguanidine (100 microM) was less effective. MS fluxes of histamine and hist-rad correlated with mannitol fluxes. Mast cell stimulation with the calcium ionophore A23187 (1 microM) induced a twofold larger histamine appearance on the serosal side than the mucosal application of 100 microM histamine. It is concluded that histamine permeation across the porcine proximal colon is restricted by low permeability and sequential catabolism by histamine N-methyltransferase and diamine oxidase.

Amine Oxidase (Copper-Containing)↗
PubMedDate not supplied

AVP-independent high osmotic water permeability of frog urinary bladder and autacoids.

In the isolated frog urinary bladder a 20- to 50-fold increase of the osmotic water permeability has been revealed in the absence of arginine vasopressin (AVP) as a result of several successive changes of the serosal Ringer solution. This increase of the osmotic water permeability was of the same magnitude as that of the effect of 1 nM AVP. Similarly to the effect of AVP, the amount of adenosine 3',5'-cyclic monophosphate (cAMP) in the cells rose, and aggregates of intramembraneous particles were formed in the apical plasma membrane of granular cells (as shown by the freeze-fracture method). Immunocytochemical studies using anti-actin monoclonal antibodies indicated depolymerization of F-actin following the AVP-independent change in water permeability. It was possible to decrease the high level of osmotic permeability to the initial level if 10 microl/ml of frog blood serum or a lipid extract of this blood serum, or 1 microM arachidonic acid or 1 nM prostaglandin E2 was added to the serosal Ringer solution. The rapid restoration of the osmotic water impermeability of the epithelium after the AVP- evoked effect was achieved by the addition to the serosal Ringer solution of Ringer solution in which intact frog urinary bladders had been previously incubated for 1 h. The data obtained indicate that the maintenance of the impermeability to water of the osmoregulating epithelium and the restoration of the initial low level of the osmotic permeability after the effect of AVP are due to participation of prostaglandin E2 and other autacoids as well as, probably, some physiologically active substances of a lipid nature that are present in the blood serum.

Animals↗
PubMed1998

Losartan antagonism of angiotensin-II-induced potassium secretion across rat colon.

The effect of angiotensin II (ANG II) on potassium transport across the short-circuited rat distal colon was investigated using 86Rb+ as a tracer for unidirectional K+ fluxes. The addition of high concentrations of ANG II (>/=10(-6) M) to the serosal bathing solution had no effect on the mucosal to serosal flux of Rb+, but significantly increased the serosal to mucosal flux and abolished the basal net absorptive Rb+ flux. These ANG-II-induced alterations in Rb+ transport were blocked by the AT1 receptor antagonist losartan and its metabolite EXP3174, which is also known to have AT1 receptor antagonistic activity. In contrast, an AT2 receptor antagonist, PD123319, did not prevent the alterations in colonic Rb+ transport induced by ANG II in vitro. At lower bath concentrations (10(-7) M to 10(-10) M ), ANG II had no measurable effects on Rb+ transport across this tissue but ANG II did have a bimodal effect on short-circuit current (Isc), indicating additional effects on the electrogenic transport of other ions. Dose-dependent reductions in Isc were observed between 10(-7) M (DeltaIsc=1.96+/-0.49 microEq.cm-2.h-1, n=6) and 10(-10) M (DeltaIsc=0.16+/-0.19 microEq.cm-2.h-1, n=7) ANG II, whereas Isc was increased at the higher concentrations (DeltaIsc= 3.36+/-0.52 microEq.cm-2.h-1, n=7, at 10(-4) M). The ANG-II-induced increases and decreases in Isc were both blocked by losartan but not by PD123319. These studies are the first to demonstrate an effect of ANG II on K+ transport across rat colon that is independent of aldosterone and mediated by AT1 receptors.

Angiotensin II↗