Female reproductive biology of the bluemouth Helicolenus dactylopterus dactylopterus: spawning and fecundity

The bluemouth Helicolenus dactylopterus dactylopterus is a zygoparous species that spawns multiple batches of embryos enclosed within a gelatinous matrix. Oocyte development is asynchronous, and the recruitment of secondary growth oocytes occurs continuously during the developing phase, but stops before the start of the first spawning (i.e. fecundity is determinate). The number of developing oocytes can be estimated as a function of the total length of the fish, its ovary mass and its gonado-somatic index. Only at the onset of spawning, when potential fecundity is determined, does condition also have a significant effect. The low levels of atresia detected during most of the spawning season show that this mechanism does not substantially affect the process. There is variability both in the spawning interval (with a mean of 2 days) and in the number of embryos comprising every single batch (up to 37,000). Expected effect of fisheries on the reproductive traits of this deep-sea species is also discussed.

Agonistic sounds in the skunk clownfish Amphiprion akallopisos: size-related variation in acoustic features

Fourteen individuals of the skunk clownfish Amphiprion akallopisos of different sizes and of different sexual status (non-breeder, male or female) were analysed for four acoustic features. Dominant frequency and pulse duration were highly correlated with standard length (r = 0.97), and were not related to sex. Both the dominant frequency and pulse duration were signals conveying information related to the size of the emitter, which implies that these sound characteristics could be useful in assessing size of conspecifics.

Tepoxalin inhibits inflammation and microvascular dysfunction induced by abdominal irradiation in rats

BACKGROUND

Inflammatory cells contribute to the acute and sub-acute sequelae of radiation therapy. Tepoxalin, an inhibitor of cyclooxygenase and 5-lipoxygenase that suppresses NF-kappaB activation, has potent anti-inflammatory activity.

AIMS

To assess the effects of tepoxalin on radiation-induced inflammatory damage, and determine its mechanisms of action.

METHODS

Leucocyte rolling, adhesion and emigration, and albumin leakage were determined by intra-vital microscopy in rat mesenteric venules. NF-kappaB activation was measured by electrophoretic mobility shift assays, and endothelial intercellular adhesion molecule-1 expression by the radiolabelled antibody technique. Groups of irradiated rats were treated with tepoxalin, N-acetyl-L-cysteine, zileuton (lipoxygenase inhibitor), or vehicle.

RESULTS

Irradiated animals had a marked increase in the number of rolling, adherent and emigrated leucocytes in mesenteric venules, and in microvascular permeability. Tepoxalin prevented leucocyte adhesion and the increase in permeability after radiation. Tepoxalin did not inhibit radiation-induced NF-kappaB activation or intercellular adhesion molecule-1 up-regulation, while N-acetyl-L-cysteine, which attenuated NF-kappaB activation, had no effect on leucocyte recruitment. In contrast, tepoxalin inhibited the increase in leukotriene B4 levels after radiation, and the anti-inflammatory effects of the drug were mimicked by zileuton.

CONCLUSIONS

Tepoxalin affords significant protection against radiation-induced inflammation and microvascular dysfunction in splanchnic organs through a mechanism dependent on leukotriene synthesis inhibition.

Chromium(VI)-mediated DNA damage: oxidative pathways resulting in the formation of DNA breaks and abasic sites

Inside cells chromium(VI) is activated to its ultimate carcinogenic form by reducing agents including glutathione (GSH) and ascorbate (AsA). The precise mechanism by which DNA damaging species are formed is unclear. In earlier in vitro work with isolated DNA we have shown that chromium(VI) in combination with GSH or AsA is able to induce similar numbers of single strand breaks and apurinic/apyrimidinic sites (AP-sites). Moreover, the formation of both lesions followed a similar temporal pattern. It is conceivable that the two forms of DNA damage arise from a common precursor lesion (e.g. hydrogen abstraction at C4' of the DNA sugar moiety) with a partitioning along two pathways, one yielding an AP-site, the other a single strand break (SSB) and a base propenal. The present study is intended to test this hypothesis by analysing whether oxidation products of deoxyribose can be formed in the presence of chromium(VI) and GSH or AsA. It was found that mixtures of chromium(VI) and GSH or AsA were able to oxidise 2-deoxyribose to yield malondialdehyde, which was detected by reaction with thiobarbituric acid. The characteristic pink chromogen, which forms upon reaction with thiobarbituric acid, was also observed with calf thymus DNA as the substrate. In both experimental systems the addition of catalase prevented the formation of deoxyribose breakdown products. Hydroxyl radicals did not seem to be important for the generation of DNA damage as the characteristic modified DNA bases could not be detected by using gas chromatography-mass spectrometry. These results lead us to conclude that the formation of SSB during the reductive conversion of chromium(VI) proceeds primarily via hydrogen abstraction from C4'. The observation that Fenton chemistry is not involved in these processes is intriguing and necessitates further research into the ways in which chromium can activate molecular oxygen to form DNA damaging species.

Influence of dose-rate on inflammatory damage and adhesion molecule expression after abdominal radiation in the rat

PURPOSE

The goal of this study was to assess the effects of two clinically relevant radiation dose-rates on endothelial adhesion molecule expression, inflammatory response, and microvascular dysfunction.

METHODS AND MATERIALS

Rats were irradiated with 10 Gy at low (0.9 Gy/min) or high (3 Gy/min) dose-rates. Control animals received sham irradiation. Leukocyte rolling, adhesion, emigration, and microvascular permeability were assessed in mesenteric venules by intravital microscopy 6 hours after irradiation. P-selectin and intercellular adhesion molecule-1 (ICAM-1) expression were measured using radiolabeled monoclonal antibodies.

RESULTS

Low dose-rate (LDR) abdominal irradiation increased leukocyte adhesion compared with sham-irradiated animals, whereas high dose-rate (HDR) irradiation resulted in enhanced leukocyte rolling, adhesion, and emigration, compared with the LDR or with sham-irradiated rats. Both dose-rates increased microvascular permeability, although this effect was significantly greater after radiation with the high (8-fold) than the low (5-fold) dose-rate. HDR radiation induced significantly larger increments in P-selectin expression in splanchnic organs than LDR, whereas in most organs ICAM-1 expression was only upregulated by the HDR. Blockade of ICAM-1, but not P-selectin, abrogated leukocyte adhesion at both dose-rates.

CONCLUSIONS

The magnitude of upregulation of endothelial adhesion molecules, leukocyte recruitment, and endothelial barrier dysfunction elicited by radiation therapy is dependent on the dose-rate at which the radiation is delivered.

Impaired mesenteric leukocyte recruitment in experimental portal hypertension in the rat

Increased incidence of septic complications in human and experimental portal hypertension has been documented. Because development of an inflammatory response is essential in defense against infectious agents, the aim of this study was to assess leukocyte-endothelial cell interactions in an experimental model of portal hypertension. Intravital microscopy studies showed that under baseline conditions, leukocyte rolling, adhesion, and emigration in mesenteric venules were similar in control, sham operated (SO), and partial portal vein ligated (PPVL) rats. Compared with either control or SO rats, PPVL animals exhibited a markedly reduced recruitment of rolling, adherent, and emigrated leukocytes in response to leukotriene B(4) (LTB(4)) stimulation. Similarly, platelet-activating factor (PAF) superfusion, which induced a large increment in leukocyte rolling and adherence in control and SO rats, was without any effect in PPVL animals. Endothelial P-selectin expression in control rats, as measured by the double radio-labeled monoclonal antibody (mAb) technique, was not modified by LTB(4), but significantly increased in response to PAF. PPVL rats had a significantly lower expression of P-selectin after stimulation with PAF. Neutrophils isolated from PPVL rats exhibited increased L-selectin shedding and CD11b up-regulation in response to PAF and LTB(4), compared with neutrophils isolated from SO rats. These observations indicate that portal hypertension is associated with a defective inflammatory response, which is manifested as a decreased recruitment of rolling leukocytes, and subsequently reduced adhesion/emigration. This defect appears to result from a reduced endothelial P-selectin up-regulation and increased L-selectin shedding.

Mechanisms underlying the anti-inflammatory actions of central corticotropin-releasing factor

Immune activation of hypothalamic corticotropin-releasing factor (CRF) provides a negative feedback mechanism to modulate peripheral inflammatory responses. We investigated whether central CRF attenuates endothelial expression of intercellular adhesion molecule 1 (ICAM-1) and leukocyte recruitment during endotoxemia in rats and determined its mechanisms of action. As measured by intravital microscopy, lipopolysaccharide (LPS) induced a dose-dependent increase in leukocyte rolling, adhesion, and emigration in mesenteric venules, which was associated with upregulation of endothelial ICAM-1 expression. Intracisternal injection of CRF abrogated both the increased expression of ICAM-1 and leukocyte recruitment. Intravenous injection of the specific CRF receptor antagonist astressin did not modify leukocyte-endothelial cell interactions induced by a high dose of LPS but enhanced leukocyte adhesion induced by a low dose. Blockade of endogenous glucocorticoids but not alpha-melanocyte-stimulating hormone (alpha-MSH) receptors reversed the inhibitory action of CRF on leukocyte-endothelial cell interactions during endotoxemia. In conclusion, cerebral CRF blunts endothelial upregulation of ICAM-1 and attenuates the recruitment of leukocytes during endotoxemia. The anti-inflammatory effects of CRF are mediated by adrenocortical activation and additional mechanisms independent of alpha-MSH.

Mechanisms responsible for enhanced inflammatory response to ischemia-reperfusion in diabetes

The objective of the present study was to assess the role of lipid mediators and adhesion molecule expression in exacerbation of ischemia-reperfusion-induced inflammatory response in diabetes. Leukocyte-endothelial cell interactions were studied in mesenteric venules by intravital microscopy. Endothelial expression of intercellular adhesion molecule (ICAM)-1 was measured by the double-radiolabeled monoclonal antibody technique, and beta2-integrin expression was measured by flow cytometry. Ischemia-reperfusion elicited significantly larger increases in leukocyte adhesion and emigration in diabetic rats that were prevented by a platelet-activating factor (PAF)-receptor antagonist or a leukotriene synthesis inhibitor. Leukotriene B4 (LTB4) superfusion induced similar leukocyte recruitment in diabetic and control rats, whereas PAF elicited larger increases in diabetic rats. CD11a, but not CD11b, expression was higher in leukocytes from diabetic animals. Endothelial ICAM-1 in mesentery and in intestine did not differ between diabetic and control rats. These results indicate that diabetes is associated with an enhanced response to ischemia-reperfusion that depends on both PAF and leukotrienes. An increased sensitivity to PAF, along with an increased CD11a expression, may account for the exaggerated inflammatory response to ischemia-reperfusion in diabetes.

Effect of redox conditions on the DNA-binding efficiency of the retinoic acid receptor zinc-finger

Retinoic acid and its derivatives are involved in many important biological processes. In the present study, we have shown that the DNA binding domain of the retinoic acid receptor, which contains two zinc fingers with the Zn(II) tetrahedrally coordinated by four Cys, is susceptible to intracellularly relevant oxidizing agents. In the presence of hydrogen peroxide or hypochlorite, the zinc-finger DNA binding activity was abolished in a concentration dependent manner. The loss of DNA binding activity was correlated with the release of Zn(II) from the zinc-finger motif as a consequence of Zn(II)-thiolate bond oxidation. A combination of glutathione and Zn(II) was able to restore the activity, suggesting that oxidation of the zinc-finger by hydrogen peroxide or hypochlorite resulted in the formation of disulfide bonds between the Cys present in the Zn(II)-binding motif. Our results indicate that in situations of oxidative-stress zinc-finger containing transcription factors may be particularly susceptible to oxidation, resulting in the disruption of control and regulation of gene expression.

Gastric mucosal blood flow regulation in response to different stimuli

We compared changes in gastric mucosal blood flow (GMBF) and left gastric artery blood flow (LGABF) in response to pharmacological, physiological, and pathological stimuli. GMBF and LGABF were measured by the hydrogen gas clearance and perivascular ultrasonic transit time techniques, respectively, under baseline conditions and following intravenous infusion of vasopressin or pentagastrin, isovolemic hemodilution, or gastric perfusion with HCl-taurocholate. Blood flow changes following vasopressin or hemodilution were significantly larger in the left gastric artery than in the gastric mucosa. In contrast, the increment in blood flow associated with pentagastrin-stimulated acid secretion was significantly greater in the gastric mucosa than in the extramural artery. Barrier disruption with acid-taurocholate induced similar changes in both measurement sites. The gastric hyperemia induced by either mechanism was significantly attenuated by blockade of NO synthesis. These data demonstrate that although functional changes in GMBF are primarily supported by changes in blood flow at the extramural gastric arteries, the gastric mucosal microvasculature is also under the influence of independent local control mechanisms.

Platelet activation In mice and human Helicobacter pylori infection

Extracts of Helicobacter pylori (HP) have been shown to induce leukocyte adhesion in mesenteric venules, but the effects of HP infection on gastric microvessels are unknown. Inflammatory cell interactions in the gastric microcirculation were studied by intravital videomicroscopy in mice inoculated with either saline or fresh isolates of HP. Platelet aggregates were detected and quantified in murine portal blood, while endothelial P-selectin expression was determined using the dual radiolabeled mAb technique. Platelet activation and aggregation were studied in HP-infected patients and controls by measuring the platelet-aggregate ratio and platelet P-selectin expression. HP infection induced a marked increase in the flux of rolling leukocytes and the appearance of platelet and leukocyte- platelet aggregates in murine gastric venules. The HP-induced rolling and platelet aggregate formation was abrogated by mAbs against L- or P-, but not E- selectin. Endothelial cell expression of P-selectin was not altered, but platelet P-selectin expression was enhanced in HP-infected mice. Circulating platelet aggregates and activated platelets were also detected in HP-infected patients. These findings indicate that platelet activation and aggregation contribute to the microvascular dysfunction and inflammatory cell recruitment associated with HP infections.

Anemia worsens hyperdynamic circulation of patients with cirrhosis and portal hypertension

This retrospective cohort study was aimed at investigating the effects of anemia on the hemodynamic disturbances associated with portal hypertension. In all, 202 consecutive nontreated portal-hypertensive patients referred for evaluation to our Hepatic Hemodynamic Laboratory were included. Compared to the nonanemic patients, anemic cirrhotic patients had an increased cardiac output (7.9 +/- 1.9 vs 7.1 +/- 2 liters/min, P < 0.01), and a decreased mean arterial blood pressure (82 +/- 11 vs 94 +/- 13 mm Hg, P < 0.0001) and systemic vascular resistance (838 +/- 235 vs 1102 +/- 356 dyn/sec/cm5, P < 0.0001). Similar results were obtained when Child A or Child B-C patients were analyzed separately. Multivariate logistic regression disclosed that hemoglobin concentration, in addition to age, sex azygos blood flow, and albumin concentration, was an independent factor influencing the degree of systemic vasodilation in cirrhotic portal-hypertensive patients. This study discloses that anemia worsens the hyperdynamic circulation associated with portal hypertension. Since hemoglobin concentration may change with time, this parameter should be taken into account when evaluating hemodynamics in portal-hypertensive patients.

[Chronic anemia protects against gastric damage by alcohol and aspirin. The role of the toxic radicals and lipid peroxidation]

The effects of chronic anemia on gastric damage induced by ethanol or aspirin have been investigated in rats. The role of free radicals and lipid peroxidation in that circumstance was also assessed. Chronic anemia was induced by replacement of 1.5 ml of blood by a plasma expander during 5 days. Under anesthesia, the stomach was perfused with 100% ethanol or acidified aspirin during 30 minutes. Thereafter, the rats were sacrificed, the stomachs removed and analyzed planimetrically for macroscopic damage. In addition, gastric tissue was collected and homogenized for assessment of toxic free radicals generation by chemoluminicense and lipid peroxidation by measuring reactive species of thiobarbituric acid (TBA-RS). Chronic anemia significantly protected against damage induced by ethanol or aspirin. The rate of toxic free radicals and the TBA-RS in the gastric mucosa was significantly reduced by anemia, either under ethanol or aspirin injury. It is concluded that anemia offers a general protection against gastric mucosal damage and that this protection is in part mediated by limitations on lipid peroxidation and toxic free radicals generation.

A role for molecular oxygen in the formation of DNA damage during the reduction of the carcinogen chromium (VI) by glutathione

Although well-established as carcinogens, the way in which chromium (VI) compounds exert their carcinogenic, mutagenic, and DNA-damaging potential remains obscure. It is clear that inside cells chromium(VI) is activated to its ultimate carcinogenic form by reducing agents including glutathione (GSH). The present study is intended to clarify if Fenton mechanisms are likely to be important in the formation of DNA lesions by chromium(VI) in combination with GSH. In buffer solutions which were treated to remove Fenton-active metal ions as well as in those not further purified, chromate and GSH induced similar numbers of single-strand breaks (SSB) in isolated PM2 DNA. Molecular oxygen was found to be essential for the formation of SSB, but chromium(V) species arising from chromate/GSH, unless activated by oxygen, appeared to be unreactive toward DNA. Upon addition of Mn(II) to solutions of chromium(VI) and GSH a diminution of Mn(II) ESR signals was observed, good evidence for the presence of chromium(IV) species. Using gas chromatography/mass spectrometry in selective ion-monitoring mode and high-performance liquid chromatography with electrochemical detection, we were able to show that Cr(VI)/GSH failed to induce base modifications typical of hydroxyl radical attack on DNA. Experimental conditions which readily induced SSB gave rise to the formation of chromium-DNA adducts, clearly demonstrating that the generation of these two DNA lesions is not mutually exclusive. We conclude that models which ascribe the induction of chromium-DNA adducts to chromium(V) and the generation of oxidative DNA damage including SSB to hydrogen peroxide are oversimplistic. It is not necessary to invoke a mechanism requiring the presence of added hydrogen peroxide to account for the ability of Cr(VI)/GSH to cause SSB. Our findings suggest that the combination of GSH, molecular oxygen, and chromium(VI) can damage DNA via non-Fenton pathways.

Acute and chronic cyclooxygenase blockage in portal-hypertensive rats: influence in nitric oxide biosynthesis

BACKGROUND & AIMS

Prostacyclin and nitric oxide have been involved in the hyperkinetic syndrome in portal hypertension. The aim of this study was to investigate the relative contribution and possible interaction between prostacyclin and NO in this circulatory abnormality.

METHODS

Portal vein-ligated and sham-operated rats received indomethacin and vehicle either on a short-term (5 mg/kg subcutaneously) or long-term basis (5 mk.kg-1.day-1, continuous 7-day infusion with an osmotic minipump). Measurements of arterial pressure and superior mesenteric arterial flow (mL.min-1.kg-1, ultrasonic flow probe) were then performed before and after NG-nitro-L-arginine methyl ester (L-NAME) injection (13 mg/kg intravenously).

RESULTS

Short-term or long-term indomethacin treatment had no effect in sham-operated rats but significantly decreased mesenteric arterial flow in portal-hypertensive rats. Mesenteric flow remained higher after long-term than after short-term indomethacin treatment (54.5 +/- 2 vs. 46.1 +/- 2; P = 0.01). This blunted response to long-term indomethacin treatment was associated with an enhanced response to L-NAME, shown by greater increments in arterial pressure (29% +/- 3%) and mesenteric arterial resistance (209 +/- 22%) in indomethacin-treated rats than in rats receiving vehicle (19% +/- 2% and 130% +/- 20%; P < 0.05).

CONCLUSIONS

Both prostacyclin and NO contributed to splanchnic hyperemia in portal-hypertensive rats. There was an enhanced release of NO after long-term prostacyclin inhibition, suggesting that both vasodilatory systems interact, promoting splanchnic hyperemia in portal hypertension.

Role of prostaglandins and nitric oxide in gastrointestinal hyperemia of diabetic rats

The aim of the study was to characterize the gastric and mesenteric vascular changes induced by diabetes and the implication of endothelial [nitric oxide (NO) and prostaglandins] and humoral (glucagon) factors in such changes. Diabetes was induced in rats by a single streptozotocin injection. Four weeks later, gastric mucosa, left gastric artery, and superior mesenteric artery blood flows were measured using hydrogen gas clearance and perivascular ultrasonic flowmeter techniques, respectively, in anesthetized and fasted diabetic and control rats. Blood pressure, hematocrit, blood volume, and blood viscosity were also measured. Left gastric (41 +/- 6 vs. 25 +/- 4 ml.min-1.100 g-1) and superior mesenteric artery blood flows (83 +/- 8 vs. 65 +/- 4 ml.min-1.100 g-1) were significantly higher in diabetic than in control rats. The increased blood flow in the left gastric artery was distributed to a hypertrophic mucosa in diabetic rats; therefore, the blood flow per 100 g tissue in the gastric mucosa was not significantly different in diabetic compared with control rats. Pretreatment with indomethacin reduced both increase gastric and mesenteric flows of the diabetic rats to the same levels as in control rats. NG-nitro-L-arginine methyl ester decreased gastric blood flow in a dose-dependent manner and to a similar extent in diabetic and control rats. In contrast, an increased sensitivity to the higher doses of the NO inhibitor was observed in the mesenteric vascular bed of diabetic rats. Glucagon reduction achieved by somatostatin infusion did not influence either gastric or mesenteric blood flow in diabetic rats. In summary, the present study revealed an increase in gastric and mesenteric arterial blood flows in streptozotocin-induced diabetic rats. The gastrointestinal hyperemia seems to be due, at least in part, to the increased demand of a hypertrophic mucosa and is mediated primarily by endogenous prostaglandins. Increased vascular sensitivity to NO may also contribute to the mesenteric vasodilation.

Increased blood hemoglobin attenuates splanchnic vasodilation in portal-hypertensive rats by nitric oxide inactivation

BACKGROUND & AIMS

Nitric oxide, which is quenched by hemoglobin, has been implicated in the pathogenesis of portal hypertension. The aim of this study was to investigate the effects of increasing blood hemoglobin concentration by erythropoietin treatment on the gastrointestinal vasodilation associated with portal hypertension.

METHODS

Portal-hypertensive and sham-operated rats treated with erythropoietin were studied 2 weeks after surgery. Hemodynamic and rheological parameters were measured in baseline conditions and after N(G)-nitro-L-arginine methyl ester (L-NAME) or sodium nitroprusside treatment.

RESULTS

In portal-hypertensive rats, erythropoietin attenuated the increase in gastric mucosal and superior mesenteric artery blood flows and the decrease in arterial blood pressure and splanchnic vascular resistances. Those parameters were not affected by erythropoietin in sham-operated rats. A direct vascular effect of erythropoietin was ruled out by the lack of changes in blood pressure or mesenteric blood flow after intravenous erythropoietin administration and by a similar in vitro relaxation to acetylcholine in mesenteric artery rings. In portal-hypertensive rats, erythropoietin blunted the blood pressure response to sodium nitroprusside and attenuated the gastric and mesenteric blood flow response to L-NAME.

CONCLUSIONS

Gastrointestinal vasodilation associated with portal hypertension can be attenuated by increasing blood hemoglobin concentration. Inactivation of overproduced NO by hemoglobin may account for this effect.

The reductive conversion of the carcinogen chromium (VI) and its role in the formation of DNA lesions

The potential of Cr(VI), in combination with glutathione (GSH) or ascorbate (AsA) to induce apurinic/apyrimidinic sites (AP-sites) and single strand breaks (SSB) in isolated deoxyribonucleic acid (DNA) was investigated. The observation that both lesions were formed with equal probability and followed a similar time course suggests that they might arise from attack of a reactive species at C4' of the DNA sugar moeity. This idea is further substantiated by the finding that malondialdehyde-like products are released in chromate/GSH- and chromate/AsA-treated DNA. The generation of AP-sites and SSB was dependent on molecular oxygen and could be suppressed by the addition of catalase. Our results rule out hydroxyl radicals as the DNA damaging species. Furthermore, Cr(V), an intermediate formed during reaction with GSH or AsA, is not directly involved in the generation of DNA damage, unless activated by molecular oxygen. Our findings indicate that a superoxo- or peroxo-complex involving Cr(V) or Cr(IV) might be the species responsible for DNA damage. Evidence is presented that the DNA lesions arising from chromate/AsA have the potential to cause gene mutations.

Time-course changes in gastric mucosal blood perfusion following portal vein constriction in rats

BACKGROUND/AIMS

Gastric mucosal blood flow is increased in all experimental models of chronic portal hypertension, when portosystemic shunting and the hyperdynamic circulation are fully developed. However, some controversy exists concerning the time course of this event. This study was undertaken to investigate the chronological changes in gastric mucosal blood perfusion during the first 7 days after partial portal vein constriction.

METHODS

Portal hypertensive and sham operated animals were studied. Gastric mucosal blood flow was measured by hydrogen-gas clearance and gastric oxygen and hemoglobin content by reflectance spectrophotometry, prior to and immediately after partial portal vein constriction, and 1, 2, 7 and 15 days after induction of portal hypertension.

RESULTS

Immediately after partial portal vein constriction, gastric mucosal blood flow and gastric oxygen were significantly decreased by 27% and 32% respectively, and gastric hemoglobin significantly increased by 19%. On day 1, gastric mucosal blood flow was increased in both portal hypertensive and sham operated rats. However, while this parameter returned to normal in sham operated rats, it remained high on days 2, 7 and 15 in portal hypertensive rats. In portal hypertensive rats, gastric oxygen values were not significantly different from those in sham operated animals, but hemoglobin tended to increase with development of portal hypertension, being significantly higher than in sham operated rats at days 2 and 7. Similar results were obtained when analyzing gastric mucosal blood perfusion 2 and 7 days after two-staged total portal vein constriction.

CONCLUSIONS

Increased gastric mucosal blood perfusion is present in portal hypertensive rats from the first day after partial portal vein constriction. The lack of significant differences in all parameters on day 1 between portal hypertensive and sham operated rats is probably related to an increased mucosal blood perfusion related to surgery.

Evidence against a role for inducible nitric oxide synthase in the hyperdynamic circulation of portal-hypertensive rats

BACKGROUND/AIMS

Excessive nitric oxide biosynthesis caused by expression of inducible NO synthase has been implicated in the hyperdynamic circulation of portal hypertension. The aim of the study was to investigate whether inducible NO synthase is expressed in portal hypertension an accounts for the hyperdynamic circulation.

METHODS

In study 1, NO synthase activities were measured by the conversion of L-arginine to citrulline in tissues from portal-hypertensive, cirrhotic, and sham-operated rats and from normal rats pretreated with endotoxin and after long-term administration of dexamethasone, which inhibits the expression of inducible NO synthase. In study 2, systemic and splanchnic hemodynamics (radiolabeled microspheres) and gastric blood flow (hydrogen gas clearance and reflectance spectrophotometry) were measured in portal-hypertensive rats after long-term administration of dexamethasone (0.25 mg.kg-1.day-1) or vehicle.

RESULTS

In study 1, constitutive and inducible NO synthase activities in portal-hypertensive or cirrhotic rats were similar to those observed in sham-operated rats. The significant increase in the inducible activity observed after endotoxin injection was prevented when rats received long-term treatment with dexamethasone. In study 2, cardiac index, portal-pressure, portal venous inflow, and gastric blood flow were similar in dexamethasone-or vehicle-treated portal-hypertensive rats.

CONCLUSIONS

These results to not support a role for an increased expression of the inducible NO synthase in the hyperdynamic circulation of portal hypertension.

The formation of both apurinic/apyrimidinic sites and single-strand breaks by chromate and glutathione arises from attack by the same single reactive species and is dependent on molecular oxygen

The induction of apurinic/apyrimidinic sites (AP sites) and DNA single-strand breaks (SSB) by chromate and glutathione in isolated DNA was investigated using agents that cleave the DNA at AP sites (putrescine and exonuclease III). It was found that chromate/glutathione-induced AP sites contain free aldehyde groups, as cleavage by putrescine could be prevented by treatment with sodium borohydride. The formation of AP sites and SSB followed a very similar temporal pattern, suggesting that both lesions arise from attack by the same single reactive species deriving from chromate and glutathione. Furthermore, the induction of both lesions was found to be dependent on the presence of molecular oxygen.

Neonatal capsaicin treatment does not prevent splanchnic vasodilatation in portal-hypertensive rats

It has been suggested that the peripheral sensory neurons are involved in the splanchnic hemodynamic changes of portal hypertension. Therefore the influence of permanent ablation of sensory neurons by neonatal capsaicin pretreatment (50 mg/kg, subcutaneously) on the development of the hyperdynamic splanchnic circulation in portal-hypertensive rats was studied. In adulthood, portal hypertension was induced with partial portal vein ligation. In study 1, systemic and splanchnic hemodynamics were measured by means of a radiolabeled-microsphere technique in portal-hypertensive rats, under ketamine anesthesia, pretreated with capsaicin or vehicle. Mean arterial pressure, heart rate, cardiac index, systemic and splanchnic vascular resistance, portal pressure, portal venous inflow, portal-collateral resistance and portal-systemic shunting were not significantly different between capsaicin-pretreated and vehicle-pretreated rats. In study 2, gastric mucosal blood flow, measured by means of hydrogen gas clearance, and the hemoglobin and oxygen content of the gastric mucosa, as assessed with reflectance spectrophotometry, were not significantly different in the two groups of anesthetized portal-hypertensive rats pretreated with capsaicin or vehicle. In study 3, we confirmed the effectiveness of neonatal capsaicin pretreatment by measuring calcitonin gene-related peptide content of the gastric corpus wall. Capsaicin pretreatment caused a depletion of calcitonin gene-related peptide by at least 98% compared with that in vehicle-pretreated rats. These results do not support a role of capsaicin-sensitive sensory neurons that innervate the gastrointestinal tract in the development of the splanchnic vasodilatation characteristically observed in chronic portal hypertension.

Gastric microcirculatory changes of portal-hypertensive rats can be attenuated by long-term estrogen-progestagen treatment

It has been suggested that estrogen-progestagen therapy may be useful in preventing bleeding from gastric angiodysplasia, a vascular lesion similar to that described in portal-hypertensive gastropathy. In this study we assessed the effects of estrogen-progestagen therapy on gastric microcirculation and systemic and splanchnic hemodynamics in portal-hypertensive and sham-operated rats. One week after the surgical procedure (partial portal vein ligation or sham surgery), animals were given an intramuscular injection of a slow-release preparation of estrogen-progestagen or its vehicle. Two weeks later, gastric mucosal blood flow was measured by means of hydrogen gas clearance, a morphometrical analysis of gastric mucosal blood vessels was performed and systemic and splanchnic hemodynamics were evaluated with a radiolabeled-microspheres technique. In portal-hypertensive rats, estrogen-progestagen therapy induced a significant reduction in gastric mucosal blood flow, number of blood vessels and relative area of vessels. Similar changes, although of lesser magnitude, were achieved with estrogen or progestagen given separately and with the low dose of combined estrogen-progestagen. Estrogen-progestagen treatment also induced significant reductions in portal pressure and porto-collateral resistance without changing systemic or splanchnic hemodynamics. In contrast, estrogen-progestagen treatment did not induce changes in any of the parameters studied in sham-operated rats. We conclude that long-term estrogen-progestagen therapy reduces the gastric hyperemia, increased mucosal vessel density and portal pressure in portal-hypertensive rats.

Acute normovolaemic anaemia prevents ethanol-induced gastric damage in rats through a blood flow related mechanism

The aim of the study was to assess whether changes in gastric mucosal blood flow induced by acute normovolaemic anaemia influence the susceptibility of the gastric mucosa to ethanol-induced damage, and the relationship of these changes with nitric oxide biosynthesis. Acute normovolaemic anaemia, promoted by exchanging 3 ml of blood by a plasma expander, induced a significant increase in gastric mucosal blood flow measured by hydrogen gas clearance, without changes in arterial blood pressure. After intragastric 60% ethanol administration, gastric blood flow was still significantly higher in anaemic than in control rats, and this was associated with a lower macroscopic and microscopic gastric damage. Following ethanol administration, anaemic rats pretreated with an inhibitor of nitric oxide biosynthesis (L-NMMA, 50 mg/kg, i.v.) had a lower gastric blood flow and a higher macroscopic gastric damage than anaemic rats without pretreatment. Anaemic rats pretreated with vasopressin also had after ethanol administration a lower gastric blood flow and a higher macroscopic gastric damage. It is concluded that acute normovolaemic anaemia protects the gastric mucosa against damage induced by intragastric ethanol. The inhibition of nitric oxide biosynthesis reverts in part this protective effect, and this seems to be related with the capability of nitric oxide to increase gastric mucosal blood flow, since vasoconstriction by a nitric oxide-independent mechanism causes a similar effect.

Effect of bolus injection and continuous infusion of somatostatin on gastric perfusion in cirrhotic patients with portal-hypertensive gastropathy

Gastric perfusion has been found to be increased in cirrhotic patients with portal-hypertensive gastropathy. This phenomenon may contribute to gastric bleeding from these lesions. Therefore drugs reducing gastric mucosal perfusion may be beneficial in the treatment of bleeding portal-hypertensive gastropathy. In this study, gastric mucosal perfusion was assessed, by means of laser-Doppler flowmetry and reflectance spectrophotometry, in 36 cirrhotic patients with portal-hypertensive gastropathy in basal conditions and after double-blind administration of placebo or somatostatin. Intravenous bolus injection of 250 micrograms somatostatin induced a rapid, marked decrease in gastric perfusion (-31.6% +/- 7.9%, p < 0.05), as assessed on laser-Doppler flowmetry, that lasted for only 6 min. Changes in the hemoglobin content of the gastric mucosa paralleled those of laser-Doppler signal. The oxygen content of the gastric mucosa was mildly reduced (-6.9% +/- 1.1%, p < 0.05). When the bolus injection was followed by a continuous infusion of somatostatin, the reduction in gastric perfusion, as assessed by means of laser-Doppler flowmetry, was maintained, although the magnitude of the reduction (-17% +/- 7%) was significantly lower than that observed immediately after the bolus (p < 0.05); the hemoglobin content of the gastric mucosa was also significantly reduced (-8% +/- 1%), but no changes were observed in the oxygen content. Placebo administration had no effect on any of these parameters. We conclude that the increased gastric perfusion in cirrhotic patients with portal-hypertensive gastropathy can be effectively decreased by somatostatin administration.

Effects of chronic normovolemic anemia on gastric microcirculation and ethanol-induced gastric damage in rats

The effects of chronic normovolemic anemia on gastric microcirculation and gastric mucosal susceptibility to ethanol-induced gastric damage were investigated in anesthetized rats. Blood exchange by a plasma expander during four consecutive days rendered the animals anemic with a 34% decrease in the baseline hematocrit but without affecting blood volume. Chronic anemia induced a decrease in whole blood viscosity, an increase in gastric mucosal blood flow measured by hydrogen gas clearance, a decrease in gastric vascular resistance, and a decrease in gastric hemoglobin content without changes in the gastric oxygen content, the latter two parameters being measured by reflectance spectrophotometry. Gastric mucosal blood flow was lowered by intragastric administration of 100% ethanol in both anemic and control rats, but the final blood flow was significantly higher in anemic than in control animals. Macroscopic gastric damage induced by ethanol administration was significantly lower in anemic than in control rats. We conclude that chronic normovolemic anemia increases gastric mucosal blood flow and leads a protecting mechanism against gastric mucosal damage induced by absolute ethanol.

The generation of apurinic/apyrimidinic sites in isolated DNA during the reduction of chromate by glutathione

We have obtained evidence for the induction of apurinic/apyrimidinic sites (AP-sites) in isolated DNA treated with chromate and glutathione using agents that cleave the DNA phosphate backbone at AP-sites (putrescine, Lys-Trp-Lys and exonuclease III). In the presence of glutathione (5 mM) the level of AP-sites rose with increasing concentrations of chromate (75-200 microM). Neither chromate nor glutathione alone nor the final product of the reaction between chromate and glutathione were capable of inducing the lesion. Thus, an intermediate species generated during the reduction process seems to be the cause of the damage. In view of the known mutagenicity of AP-sites our findings might be of some importance in relation to the mechanisms involved in chromate carcinogenicity.

Involvement of nitric oxide and prostaglandins in gastric mucosal hyperemia of portal-hypertensive anesthetized rats

This study investigates the effects of inhibition of nitric oxide synthesis by NG-nitro-L-arginine methyl ester (L-NAME), the inhibition of prostaglandin synthesis with indomethacin and the combined effects on gastric mucosal hyperemia of ketamine-anesthetized rats with portal hypertension induced by partial portal vein ligation. The hydrogen gas-clearance technique was used for measurement of gastric mucosal blood flow. Blood pressure increased with L-NAME administration in a similar manner in portal-hypertensive and sham-operated rats. Low doses of L-NAME (1 and 3 mg/kg, intravenously) caused a significant and dose-dependent reduction in gastric mucosal blood flow in portal-hypertensive rats but had no effect on sham-operated animals. With a higher dose of L-NAME (13 mg/kg, intravenously), a significant decrease in gastric mucosal blood flow was observed in both portal-hypertensive and sham-operated rats. Indomethacin pretreatment (5 mg/kg, subcutaneously) caused a significant decrease in basal gastric mucosal blood flow of portal-hypertensive rats but did not modify this parameter in sham-operated animals. In sham-operated rats pretreated with indomethacin, the lower dose of L-NAME (3 mg/kg) did not significantly modify basal gastric mucosal blood flow. Likewise, pretreatment with indomethacin in sham-operated rats did not augment the significant reduction in gastric mucosal blood flow produced by the higher dose of L-NAME. In portal-hypertensive rats the significant dose-dependent reduction in gastric mucosal blood flow induced by L-NAME (3 and 13 mg/kg) was not significantly altered by pretreatment with indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased gastric mucosal perfusion in cirrhotic patients with portal hypertensive gastropathy

To characterize gastric mucosal perfusion in cirrhotic patients with portal hypertensive gastropathy, 34 cirrhotics with this lesion and 24 noncirrhotics were studied by reflectance spectrophotometry and laser-Doppler flowmetry during endoscopy. A significant correlation was observed between the hemoglobin content of the gastric mucosa, measured by reflectance spectrophotometry, and the serum hemoglobin concentration both in cirrhotics (r = 0.72) and in noncirrhotics (r = 0.87). IHb ratio (hemoglobin content of gastric mucosa divided by blood hemoglobin concentration) was higher in cirrhotics with portal hypertensive gastropathy than in noncirrhotics (P < 0.001), whereas the oxygen content of the gastric mucosa was similar in both groups. This pattern indicates that cirrhotics with portal hypertensive gastropathy have increased gastric perfusion without congestion. Gastric blood flow estimated by laser-Doppler was significantly higher in cirrhotics with portal hypertensive gastropathy than in noncirrhotics (P < 0.001). In cirrhotic patients, gastric areas with cherry red spots showed a significantly higher IHb ratio than areas with a mosaic or scarlatina pattern (P < 0.05). The magnitude of changes in gastric perfusion and the endoscopic severity of portal hypertensive gastropathy had no relationship with the degree of portal hypertension or the azygos blood flow.

Limitations of laser-Doppler velocimetry and reflectance spectrophotometry in estimating gastric mucosal blood flow

This study investigated the accuracy of laser-Doppler flowmetry (LDV) and reflectance spectrophotometry (RS) measurements as an index of blood flow in the gastric mucosa of the rat, in experimental conditions such as pharmacologically induced vasoconstriction, hypoxia, hyperoxia, and acute normovolemic anemia. Hydrogen gas clearance was used as a reference method. After vasopressin infusion, LDV signal and indexes of hemoglobin (IHb) and oxygen (ISO2) content in the gastric mucosa estimated by RS significantly decreased in parallel with the reduction of gastric mucosal blood flow (GMBF). Neither hypoxia (5% O2 administration) nor hyperoxia (100% O2) affected GMBF or LDV signal. However, both IHb and ISO2 significantly decreased or increased after hypoxia or hyperoxia, respectively. Acute normovolemic anemia induced a significant increase in GMBF, while LDV signal and ISO2 remained unchanged. IHb significantly decreased in linear relationship with the decrements in the hematocrit. It is concluded that 1) in pharmacologically induced GMBF changes, LDV and RS correlate with GMBF; 2) when changes in hemoglobin saturation are induced, LDV but not RS reflects GMBF; and 3) in acute normovolemic anemia, neither LDV nor RS reflects changes in GMBF.

Effects of acute normovolemic anemia on gastric mucosal blood flow in rats: role of nitric oxide

The present study investigates the effects of acute normovolemic anemia induced by isovolemic hemodilution on gastric mucosal blood flow (GMBF), measured by hydrogen gas clearance, and on the oxygen and hemoglobin content in the gastric mucosa, estimated by reflectance spectrophotometry. GMBF significantly increased after 3 and 6 mL of isovolemic hemodilution (from 50 +/- 5 to 70 +/- 7 and 77 +/- 6 mL.min-1.100 g-1, respectively; P less than 0.05) compared with basal values (50 +/- 5.mL-1.min-1.100 g-1; P less than 0.05). Oxygen content remained unchanged, whereas hemoglobin concentration decreased in parallel with the decrease in hematocrit. In a second set of experiments, the role of endogenous nitric oxide (NO) as a possible mediator of the gastric vascular changes induced by hemodilution was investigated by using the specific inhibitor of NO biosynthesis, NG-monomethyl-L-arginine (L-NMMA). The increase in GMBF induced by 3 mL of isovolemic hemodilution (delta 23 +/- 7 mL.min-1.100 g-1) was attenuated in a dose-related manner with L-NMMA, 6.25 mg/kg IV (delta 15 +/- 4 mL.min-1.100 g-1) or 50 mg/kg IV (delta 5 +/- 2 mL.min-1.100 g-1 g; P less than 0.05). The concurrent administration of L-arginine (the precursor of NO biosynthesis) abolished the effects of L-NMMA on GMBF changes. The current findings show that acute normovolemic anemia causes an increase in GMBF that is dependent on the endogenous formation of NO.