Take a Swipe at Actinide Bioavailability: Application of a New In Vitro Method

ABSTRACT

Filter swipe tests are used for routine analyses of actinides in nuclear industrial, research, and weapon facilities as well as following accidental release. Actinide physicochemical properties will determine in part bioavailability and internal contamination levels. The aim of this work was to develop and validate a new approach to predict actinide bioavailability recovered by filter swipe tests. As proof of concept and to simulate a routine or an accidental situation, filter swipes were obtained from a nuclear research facility glove box. A recently-developed biomimetic assay for prediction of actinide bioavailability was adapted for bioavailability measurements using material obtained from these filter swipes. In addition, the efficacy of the clinically-used chelator, diethylenetriamine pentaacetate (Ca-DTPA), to enhance transportability was determined. This report shows that it is possible to evaluate physicochemical properties and to predict bioavailability of filter swipe-associated actinides.

Actinide-contaminated Skin: Comparing Decontamination Efficacy of Water, Cleansing Gels, and DTPA Gels

Skin contamination by alpha-emitting actinides is a risk to workers during nuclear fuel production and reactor decommissioning. Also, the list of items for potential use in radiological dispersal devices includes plutonium and americium. The actinide chemical form is important and solvents such as tributyl phosphate, used to extract plutonium, can influence plutonium behavior. This study investigated skin fixation and efficacy of decontamination products for these actinide forms using viable pig skin in the Franz cell diffusion system. Commonly used or recommended decontamination products such as water, cleansing gel, diethylenetriamine pentaacetic acid, or octadentate hydroxypyridinone compound 3,4,3-LI(1,2-HOPO), as well as diethylenetriamine pentaacetic acid hydrogel formulations, were tested after a 2-h contact time with the contaminant. Analysis of skin samples demonstrated that more plutonium nitrate is bound to skin as compared to plutonium-tributyl phosphate, and fixation of americium to skin was also significant. The data show that for plutonium-tributyl phosphate all the products are effective ranging from 80 to 90% removal of this contaminant. This may be associated with damage to the skin by this complex and suggests a mechanical/wash-out action rather than chelation. For removal of americium and plutonium, both Trait Rouge cleansing gel and diethylenetriamine pentaacetic acid are better than water, and diethylenetriamine pentaacetic acid hydrogel is better than Osmogel. The different treatments, however, did not significantly affect the activity in deeper skin layers, which suggests a need for further improvement of decontamination procedures. The new diethylenetriamine pentaacetic acid hydrogel preparation was effective in removing americium, plutonium, and plutonium-tributyl phosphate from skin; such a formulation offers advantages and thus merits further assessment.

Forecasting the In Vivo Behavior of Radiocontaminants of Unknown Physicochemical Properties Using a Simple In Vitro Test

An understanding of the "bioavailability" of disseminated radiocontaminants is a necessary adjunct in order to tailor treatment and to calculate dose. A simple test has been designed to predict the bioavailability of different actinide forms likely to be found after dissemination of radioactive elements by dispersal devices or nuclear reactor incidents. Plutonium (Pu) or Americium (Am) nitrate or MOX (U,PuO2) are immobilized in culture wells using a static gel phase simulating biological compartments (lung, wound, etc.). Gels are incubated in a fluid phase representing physiological media (plasma, sweat, etc.). Transfer of radionuclide from static to fluid phase reflects contaminant bioavailability. After 48 h of incubation in physiological saline, Am transfer from static to fluid phase was greater than for Pu (70% vs. 15% of initial activity). Transfer of Pu or Am was markedly less from the oxide form of the two elements (1% Am and 0.05% Pu transferred). Medium representing intracellular lysosomal fluid (pH 4) increased transfer of Pu and Am, whereas culture medium including serum reduced actinide transfer. Actinide transfer was also reduced by elements of the extracellular matrix present in the static gel phase. Increasing DTPA concentrations (5 to 500 μM) to the fluid phase significantly enhanced transfer of Pu and Am. Although this agarose gel cannot fully represent in vivo complexity, this simple test can be used to investigate and predict the behavior in vivo of radiocontaminants to support medical treatments and medical forensic investigations.

Penetration and decontamination of americium-241 ex vivo using fresh and frozen pig skin

Skin contamination is one of the most probable risks following major nuclear or radiological incidents. However, accidents involving skin contamination with radionuclides may occur in the nuclear industry, in research laboratories and in nuclear medicine departments. This work aims to measure the penetration of the radiological contaminant Americium (²⁴¹Am) in fresh and frozen skin and to evaluate the distribution of the contamination in the skin. Decontamination tests were performed using water, Fuller's earth and diethylene triamine pentaacetic acid (DTPA), which is the recommended treatment in case of skin contamination with actinides such as plutonium or americium. To assess these parameters, we used the Franz cell diffusion system with full-thickness skin obtained from pigs' ears, representative of human skin. Solutions of ²⁴¹Am were deposited on the skin samples. The radioactivity content in each compartment and skin layers was measured after 24 h by liquid scintillation counting and alpha spectrophotometry. The Am cutaneous penetration to the receiver compartment is almost negligible in fresh and frozen skin. Multiple washings with water and DTPA recovered about 90% of the initial activity. The rest remains fixed mainly in the stratum corneum. Traces of activity were detected within the epidermis and dermis which is fixed and not accessible to the decontamination.

Internal contamination by actinides after wounding: a robust rodent model for assessment of local and distant actinide retention

Internal contamination by actinides following wounding may occur in nuclear fuel industry workers or subsequent to terrorist activities, causing dissemination of radioactive elements. Contamination by alpha particle emitting actinides can result in pathological effects, either local or distant from the site of entry. The objective of the present study was to develop a robust experimental approach in the rat for short- and long- term actinide contamination following wounding by incision of the skin and muscles of the hind limb. Anesthetized rats were contaminated with Mixed OXide (MOX, uranium, plutonium oxides containing 7.1% plutonium) or plutonium nitrate (Pu nitrate) following wounding by deep incision of the hind leg. Actinide excretion and tissue levels were measured as well as histological changes from 2 h to 3 mo. Humid swabs were used for rapid evaluation of contamination levels and proved to be an initial guide for contamination levels. Although the activity transferred from wound to blood is higher after contamination with a moderately soluble form of plutonium (nitrate), at 7 d most of the MOX (98%) or Pu nitrate (87%) was retained at the wound site. Rapid actinide retention in liver and bone was observed within 24 h, which increased up to 3 mo. After MOX contamination, a more rapid initial urinary excretion of americium was observed compared with plutonium. At 3 mo, around 95% of activity remained at the wound site, and excretion of Pu and Am was extremely low. This experimental approach could be applied to other situations involving contamination following wounding including rupture of the dermal, vascular, and muscle barriers.

Late-occurring pulmonary pathologies following inhalation of mixed oxide (uranium + plutonium oxide) aerosol in the rat

Accidental exposure by inhalation to alpha-emitting particles from mixed oxide (MOX: uranium and plutonium oxide) fuels is a potential long-term health risk to workers in nuclear fuel fabrication plants. For MOX fuels, the risk of lung cancer development may be different from that assigned to individual components (plutonium, uranium) given different physico-chemical characteristics. The objective of this study was to investigate late effects in rat lungs following inhalation of MOX aerosols of similar particle size containing 2.5 or 7.1% plutonium. Conscious rats were exposed to MOX aerosols and kept for their entire lifespan. Different initial lung burdens (ILBs) were obtained using different amounts of MOX. Lung total alpha activity was determined by external counting and at autopsy for total lung dose calculation. Fixed lung tissue was used for anatomopathological, autoradiographical, and immunohistochemical analyses. Inhalation of MOX at ILBs ranging from 1-20 kBq resulted in lung pathologies (90% of rats) including fibrosis (70%) and malignant lung tumors (45%). High ILBs (4-20 kBq) resulted in reduced survival time (N = 102; p < 0.05) frequently associated with lung fibrosis. Malignant tumor incidence increased linearly with dose (up to 60 Gy) with a risk of 1-1.6% Gy for MOX, similar to results for industrial plutonium oxide alone (1.9% Gy). Staining with antibodies against Surfactant Protein-C, Thyroid Transcription Factor-1, or Oct-4 showed differential labeling of tumor types. In conclusion, late effects following MOX inhalation result in similar risk for development of lung tumors as compared with industrial plutonium oxide.

Persistence of altered 5-hydroxytryptamine turnover following hemibody X-irradiation in the rat distal colon

PURPOSE

Acute gastrointestinal responses to ionizing radiation exposure include a role for 5-hydroxytryptamine (5-HT), but it is not known whether involvement of 5-HT persists and contributes to late effects. The aim was to investigate the acute and later effects of lower hemibody irradiation on 5-HT turnover and the biological effect in the rat distal colon.

MATERIALS AND METHODS

Rats were exposed to 10 Gy lower hemibody X-radiation. 5-HT and 5-hydroxyindole acetic acid tissue levels were measured in the distal colon along with the serotonin re-uptake transporter and tryptophan hydroxylase mRNA. 5-HT-containing cells and crypt cell numbers were estimated in addition to 5-HT-stimulated short-circuit current responses in isolated mucosa. Studies were performed from 3 days to 3 months post-exposure.

RESULTS

During the acute phase, at 3 days post-irradiation, reductions in cell number, tissue resistance, serotonin re-uptake transporter expression and secretory responses to 5-HT were observed. However, at later times when secretory responses were normal, 5-HT tissue levels and enterochromaffin cell numbers were increased.

CONCLUSIONS

The results provide evidence that after 10 Gy hemibody irradiation, modifications persist past the acute phase. In particular, 5-HT turnover in the distal colon is altered during a longer period.

Functional and structural alterations of epithelial barrier properties of rat ileum following X-irradiation

Irradiation of the digestive system leads to alterations of the small intestine. We have characterized the disruption of the barrier integrity in rat ileum from 1 to 14 days following irradiation ranging from 6 to 12 Gy. The intestinal permeability to 14C-mannitol and 3H-dextran 70 000 was measured in vitro in Ussing chambers. In parallel to these functional studies, immunohistochemical analyses of junctional proteins (ZO-1 and beta-catenin) of ileal epithelium were performed by confocal microscopy. Irradiation with 10 Gy induced a marked decrease in epithelial tissue resistance at three days and a fivefold increase in mannitol permeability, without modifications of dextran permeability. A disorganization of the localization for ZO-1 and beta-catenin was also observed. At 7 days after irradiation, we observed a recovery of the organization of junctional proteins in parallel to a return of intestinal permeability to control value. In addition to these time-dependent effects, a gradual effect on epithelial integrity of the radiation doses was observed 3 days after irradiation. This study shows a disruption of the integrity of the intestinal barrier in rat ileum following abdominal X-irradiation, depending on the time postirradiation and on the delivered dose. The loss of barrier integrity was characterized by a disorganization of proteins of tight and adherent junctions, leading to increased intestinal permeability to mannitol.

Differential qualitative and temporal changes in the response of the hypothalamus-pituitary-adrenal axis in rats after localized or total-body irradiation

Stress such as exposure to ionizing radiation is able to activate the hypothalamus-pituitary-adrenal axis. The present study sought to examine the effects of different configurations of a 10-Gy gamma irradiation in rats on the hypothalamus-pituitary-adrenal axis to understand the mechanism of negative feedback by glucocorticoids induced by ionizing radiation. Specifically, we determined adrenocorticotropin and corticosterone levels in plasma as well as corticotrophin-releasing factor expression in the paraventricular nucleus of the hypothalamus by in situ hybridization from 6 h to 4 days after total-body, abdominal or head irradiation. In this study, we found an activation of the hypothalamus-pituitary-adrenal axis after radiation exposure. Plasma adrenocorticotropin and corticosterone levels were significantly increased after total-body and abdominal irradiation 3 days after exposure, in parallel with decreased labeling of corticotrophin-releasing factor mRNA in the parvocellular region of the paraventricular nucleus of the hypothalamus. Our results suggest that ionizing radiation activates the neuroendocrine system to protect the organism from the occurrence of radiation-induced inflammation.

Screening of a large panel of gastrointestinal peptide plasma levels is not adapted for the evaluation of digestive damage following irradiation

The aim of this study was to assess the potential of gastrointestinal peptide plasma levels as biomarkers of radiation-induced digestive tract damage. To this end, plasma levels of substance P, GRP, motilin, PYY, somatostatin-28, gastrin, and neurotensin were followed for up to 5 days in pigs after a 16-Gy whole-body X-irradiation, completed by a histopathological study performed at 5 days. Each peptide gave a specific response to irradiation. The plasma levels of GRP and substance P were not modified by irradiation exposure; neither were those of motilin and PYY. Concerning gastrin, a 2-3-fold increase of plasma concentration was observed in pig, which presented the most important histological alterations of the stomach. The plasma levels of somatostatin, unchanged from 1 to 4 days after irradiation, was also increased by 130% at 5 days. In contrast, a diminution of neurotensin plasma levels was noted, firstly at 1 day (-88%), and from 3 days after exposure (-50%). The present study suggested that changes in gastrin and neurotensin plasma levels were associated with structural alterations of the stomach and ileum, respectively, indicating that they may be relevant biological indicators of radiation-induced digestive damage to these segments.

Alteration of the enterohepatic recirculation of bile acids in rats after exposure to ionizing radiation

The aim of this work was to study acute alterations of the enterohepatic recirculation (EHR) of bile acids 3 days after an 8-Gy radiation exposure in vivo in the rat by a washout technique. Using this technique in association with HPLC analysis, the EHR of the major individual bile acids was determined in control and irradiated animals. Ex vivo ileal taurocholate absorption was also studied in Ussing chambers. Major hepatic enzyme activities involved in bile acid synthesis were also measured. Measurements of bile acid intestinal content and intestinal absorption efficiency calculation from washout showed reduced intestinal absorption with significant differences from one bile acid to another: absorption of taurocholate and tauromuricholate was decreased, whereas absorption of the more hydrophobic taurochenodeoxycholate was increased, suggesting that intestinal passive diffusion was enhanced, whereas ileal active transport might be reduced. Basal hepatic secretion was increased only for taurocholate, in accordance with the marked increase of CYP8B1 activity in the liver. The results are clearly demonstrate that concomitantly with radiation-induced intestinal bile acid malabsorption, hepatic bile acid synthesis and secretion are also changed. A current working model for pathophysiological changes in enterohepatic recycling after irradiation is thus proposed.Key words: irradiation, bile acids, intestine, liver, enterohepatic recycling.

Effect of radiation on cAMP, cGMP and Ca(2+)(i) pathways and their interactions in rat distal colon

The secretory response implicated in the intestinal response to luminal attack is altered by radiation. The cAMP, cGMP and Ca(2+)(i) pathways leading to secretion as well as the interactions between the cAMP pathway and the cGMP or Ca(2+)(i) pathway were studied in the rat distal colon 4 days after a 9-Gy abdominal X irradiation, when modifications mainly occurred. The secretory response in Ussing chambers and cAMP and cGMP accumulation in single isolated crypts were measured. The muscarinic receptor characteristics were determined in mucosal membrane preparations. The secretory response by the cAMP pathway (stimulated by vasoactive intestinal peptide or forskolin) and the cAMP accumulation in crypts were decreased (P < 0.05) after irradiation. The weak secretory response induced by the cGMP pathway (stimulated by nitric oxide or guanylin) was unaltered by radiation, and the small amount of cGMP determined in isolated crypts from the control group became undetectable in the irradiated group. Inducible NOS was not involved in the hyporesponsiveness to VIP after irradiation (there was no effect of an iNOS inhibitor). The secretory response by the Ca(2+)(i) pathway (stimulated by carbachol) was unaffected despite a decreased number and increased affinity of muscarinic receptors. The non-additivity of VIP and carbachol co-stimulated responses was unmodified. In contrast, VIP and SNP co-stimulation showed that NO enhanced the radiation-induced hyporesponsiveness to VIP through a reduced accumulation of cAMP in crypts. This study provides further understanding of the effect of ionizing radiation on the intracellular signaling pathways.

'In-field' and 'out-of-field' functional impairment during subacute and chronic phases of experimental radiation enteropathy in the rat

PURPOSE

To investigate subacute and chronic functional consequences of localized irradiation of rat small intestine on exposed and shielded segments (proximal and distal).

MATERIALS AND METHODS

The surgical model of a scrotal hernia was used. The ileal loop was exposed to single doses of 18, 21 or 29.6 Gy X-irradiation. Epithelial structure and transport capacity were followed 2 and 26 weeks post-exposure.

RESULTS

Irradiated segments showed mucosal ulceration followed by transmural fibrosis. Transport capacity was impaired from 2 to 26 weeks. Subacute functional impairment was noticed in the proximal segment, without either morphological alteration or neutrophil influx. At 26 weeks, both proximal and distal segments showed impaired epithelial transport capacity, with neutrophil influx in the submucosa in cases of 21-Gy exposure and in the submucosa and muscularis propria after 29.6 Gy.

CONCLUSIONS

Radiation enteritis was characterized by functional impairment, within as well as outside, the irradiation field. During the subacute phase, the irradiated segment may be a source of mediators which might influence intestinal function outside the site of injury via the blood stream and/or enteric nervous system. The development of an intestinal occlusion syndrome during the chronic phase might be responsible for intestinal dysfunction but it does not rule out a possible inflammatory process developing in the shielded parts of the small intestine.

Alterations in water and electrolyte absorption in the rat colon following neutron irradiation: influence of neutron component and irradiation dose

PURPOSE

To study the absorptive function of rat colon following whole-body exposure to neutron irradiation, either to the same total dose with varying proportion of neutrons or to the same neutron proportion with an increasing irradiation dose.

MATERIALS AND METHODS

Different proportions of neutron irradiation were produced from the reactor SILENE using a fissile solution of uranium nitrate (8, 47 and 87% neutron). Water and electrolyte fluxes were measured in the rat in vivo under anaesthesia by insertion into the descending colon of an agarose gel cylinder simulating the faeces. Functional studies were completed by histological analyses. In the first set of experiments, rats received 3.8 Gy with various neutron percentages and were studied from 1 to 14 days after exposure. In the second set of experiments, rats were exposed to increasing doses of irradiation (1-4Gy) with a high neutron percentage (87%n) and were studied at 4 days after exposure.

RESULTS AND CONCLUSIONS

The absorptive capacity of rat colon was diminished by irradiation at 3-5 days, with a nadir at 4 days. The results demonstrate that an increase in the neutron proportion is associated with an amplification of the effects. Furthermore, a delay in the re-establishment of normal absorption was observed with the high neutron proportion (87%n). A dose-dependent reduction of water absorption by rat colon was also observed following neutron irradiation (87%n), with a 50% reduction at 3 Gy. Comparison of this dose-effect curve with the curve obtained following gamma (60)Co-irradiation indicates an RBE of 2.2 for absorptive colonic function in rat calculated at 4 days after exposure.

Potential role of the membrane in the development of intestinal cellular damage after whole-body gamma irradiation of the rat

Our study emphasizes the effect of gamma irradiation on intestinal cell membrane fluidity and addresses the potential relationships existing between radiation-induced lipoperoxidation, membrane fluidity, and changes in membrane protein activities. Male Wistar rats were exposed to an 8-Gy total body irradiation (60Co source) and studied 1, 4, and 7 days after irradiation (D1, D4, and D7). Membrane enzyme activities and fluorescence anisotropy were determined on small intestinal crude membrane preparations. The supernatants of membrane preparations as well as plasma were used for malonedialdehyde (MDA) quantification. The effect of carbamylcholine on electrical parameters was estimated on distal ileum placed in Ussing chambers. We observed a decrease in fluorescence anisotropy for at least 7 days, an increase in membrane production of MDA at D4, a decrease in membrane enzyme activities at D4, but an amplification of carbamylcholine-induced increase in short-circuit current at D4 and D7. Furthermore, correlations were observed between the 1,6-diphenyl-1,3,5-hexatriene anisotropy coefficient and sucrase activity and between MDA levels and leucine aminopeptidase activity. Thus, total body irradiation induces changes in intestinal membrane fluidity and an increase in lipoperoxidation. These modifications may have an impact on the activity of membrane proteins involved in intestinal function.

Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation

Ionizing radiation induces hyporesponsiveness of rat colonic mucosa to vasoactive intestinal peptide (VIP). Possible mechanisms responsible for this hyporesponsiveness of the cAMP communication pathway in rat colon were investigated. VIP- and forskolin-stimulated short-circuit current (I(sc)) responses were studied after a 10-Gy abdominal irradiation in Ussing chambers as well as in single, isolated crypts. Adenylyl cyclase (AC) activity and VIP receptor characteristics were determined in mucosal membrane preparations. In addition, alterations in crypt morphology were studied. Impaired secretory responses to VIP and forskolin were observed 4 days after irradiation (decrease of 80%). cAMP analog-stimulated I(sc) responses were unchanged. In isolated crypts, VIP- and forskolin-stimulated cAMP accumulation was markedly reduced by 80 and 50%, respectively. VIP-stimulated AC activity and VIP receptor number were decreased in membrane preparations. No major change of cellularity was associated with these functional alterations. In conclusion, the decreased secretory responses to VIP of rat colon are associated with reduced cAMP accumulation, decreased AC activity, and diminution of VIP receptor numbers without a marked decrease of crypt cell number.

Effect of granisetron on radiation-induced alterations of colonic motility and fluid absorption in rats

BACKGROUND

Radiation-induced diarrhoea is attributed to both mucosal injury and alterations of intestinal motility. Previous reports have indicated that 5-hydroxytryptamine is released following irradiation, which may contribute to these changes.

AIMS

To investigate the effects of granisetron (5-hydroxytryptamine type-3 receptor antagonist) on colonic motility, fluid absorption and 5-hydroxytryptamine colonic content following abdominal irradiation (10 Gy) in rats.

METHODS

In vivo measurements of motility and fluid absorption in the proximal and distal colon, respectively, diarrhoea score and 5-hydroxytryptamine tissue levels were performed 3 and 7 days after abdominal irradiation. The effects of post-irradiation granisetron (0.3 mg/kg subcutaneously) were also evaluated.

RESULTS

Colonic motility and fluid/Na(+) absorption were reduced 3 and 7 days after irradiation. All rats developed diarrhoea (3 days) concomitant with increased colonic mucosal 5-hydroxytryptamine levels. Granisetron prevented diarrhoea, attenuated decreased colonic motility and reduced 5-hydroxytryptamine levels on day 3, although fluid absorption was only slightly improved. On day 7, colonic motility and fluid/Na(+) absorption were restored in granisetron-dosed animals.

CONCLUSIONS

These results indicate that radiation-induced diarrhoea involves alterations of both colonic motility and fluid/Na(+) absorption. 5-Hydroxytryptamine could be one of the mediators implicated in these alterations, as post-irradiation dosage with a 5-hydroxytryptamine type-3 receptor antagonist improved colonic motility and prevented diarrhoea on day 3.

Characterization of altered absorptive and secretory functions in the rat colon after abdominal irradiation: comparison with the effects of total-body irradiation

The aim of this work was to determine the alterations in the absorptive and secretory functions of the rat colon after abdominal irradiation and to compare the effects of abdominal and whole-body irradiation. Rats received an abdominal irradiation with 8 to 12 Gy and were studied at 1, 4 and 7 days after exposure. Water and electrolyte absorption was measured in vivo by insertion of an agarose cylinder into the colons of anesthetized rats. In vitro measurements of potential difference, short-circuit current and tissue conductance were performed in Ussing chambers under basal and agonist-stimulated conditions. Most of the changes appeared at 4 days after abdominal irradiation. At this time, a decrease in water and electrolyte absorption in the colon was observed for radiation doses > or = 9 Gy. The response to secretagogues (VIP, 5-HT and forskolin) was attenuated after 10 and 12 Gy. Epithelial integrity, estimated by potential difference and tissue conductance, was altered from 1 to 7 days after 12 Gy abdominal irradiation. These results show that the function of the colon was affected by abdominal irradiation. Comparison with earlier results for total-body irradiation demonstrated a difference of 2 Gy in the radiation dose needed to induce changes in the function of the colon.

Dose dependence effects of ionizing radiation on bile acid metabolism in the rat

PURPOSE

To study radiation dose-related changes of individual or total bile acids in various physiological fluids in order to identify potential bio-indicators of radiation-induced gastrointestinal injuries.

MATERIALS AND METHODS

Wistar rats were sham- or whole-body gamma irradiated (1-12Gy). Total and individual bile acids were quantified, 3 days after exposure, in bile collected after catheterization of the bile duct. Total bile acid concentrations were also measured in plasma and colonic contents 1, 2 and 3 days after irradiation. These concentrations were determined by an enzymatic method whereas individual bile acids were quantified by HPLC.

RESULTS

In bile, whereas total bile acid concentration remained unchanged after irradiation whatever the dose, the proportion of dihydroxy bile acids in the pool of total bile acids was gradually increased with the irradiation dose, especially from 8 Gy. In plasma samples, total bile acid concentrations fell for doses higher than 10 Gy. In colonic contents, bile acid concentrations increased progressively with time (from 1 to 3 days) and with irradiation dose (from 1 to 12Gy), reaching a plateau 3 days after exposure for doses higher than 10 Gy.

CONCLUSIONS

These results show that changes in colonic bile acid concentrations which are reflected in faeces are perhaps a useful parameter to improve diagnosis and prognosis of radiation-induced gastrointestinal damage since it probably reflects directly intestinal bile acid malabsorption.

The example of gastrointestinal damage induced by ionising radiation: are there accessible markers?

Ionising radiation exposure occurs during radiotherapy, diagnostic tests or by accident. In all cases the gastrointestinal tract, which is highly sensitive to radiation, may be at risk. Each region may respond differently to radiation exposure which to some extent is reflected by clinical symptoms. The evaluation of injury, whether acute or chronic, depends on the utilization of a variety of techniques. It appears that no definitive tests exist and that a multiparametric analysis should be undertaken. This review addresses the question of accessible markers associated with radiation-induced intestinal pathologies. Several approaches are discussed which include clinical observations, measurement of faecal parameters, changes in inflammatory mediators and possible applications of imaging techniques.

Absence of protective role of afferent nerves in early intestinal mucosal alterations induced by abdominal irradiation in rats

PURPOSE

To assess the early effects of primary afferent nerve suppression by systemic treatment with the neurotoxin capsaicin in an acute model of abdominal irradiation in rats (10Gy, gamma).

MATERIALS AND METHODS

Changes in myeloperoxidase (MPO) activity, calcitonin gene-related peptide (CGRP) tissue content, number of mast cells and apoptotic cells were determined in jejunum and ileum in four groups of rat male Wistar (vehicle sham-irradiated, vehicle irradiated, capsaicin sham-irradiated and capsaicin irradiated) at 1 and 3 days post-irradiation.

RESULTS

In vehicle irradiated rats, CGRP was significantly increased from the first day after irradiation in jejunal mucosa; MPO activity increased in both segments at day 3 but not at day 1 after irradiation; the number of detectable mucosal mast cells dropped to nearly zero on days 1 and 3, while the apoptotic cells in the intestinal mucosa were significantly increased at day 1. Similar results were obtained for mast cells and apoptosis in capsaicin irradiated rats as compared to capsaicin sham-irradiated rats, while MPO activity was significantly increased and CGRP concentration in jejunal mucosa significantly decreased from the first day in these rats in comparison with capsaicin sham-irradiated rats.

CONCLUSIONS

Intestinal sensory innervation seems not to have a major protective role against a radiation-induced intestinal inflammatory reaction.

Intestinal and colonic motor alterations associated with irradiation-induced diarrhoea in rats

Localized application of ionizing radiation to the gastrointestinal tract frequently elicits responses, which include diarrhoea. The origin of this symptom is not clear but has been attributed to loss of epithelial integrity, together with alterations in motility and increased secretion. The purpose of this study was to examine whether a 10 Gy abdominal gamma irradiation leads to an inflammatory reaction, and to compare intestinal and colonic motility in controls and abdominally irradiated rats 1, 3 and 7 days after irradiation, using an electromyographic technique. The motility parameters analysed were the frequency and velocity of propagation of migrating myoelectric complexes (MMC) in the jejunum and colonic spike activity (long spike bursts; LSB) per 10 min in fasted rats. The MMC frequency was significantly reduced on days 1 and 7 after irradiation and the MMC pattern was markedly disrupted on day 3. The frequency of colonic LSB was significantly reduced on days 1, 3 and 7. Mouth to anus transit was significantly accelerated on day 3 only and diarrhoea was observed at this time. Myeloperoxidase activity in the jejunum and colon was also increased on this day only. It is concluded that irradiation-induced diarrhoea occurs contemporaneously with disruption of MMC in the small intestine.

Radiation induced cytochrome c release causes loss of rat colonic fluid absorption by damage to crypts and pericryptal myofibroblasts

BACKGROUND

Therapeutic or accidental exposure to radiation commonly causes gastrointestinal disturbances, including diarrhoea. Rats subjected to whole body ionising radiation at a dose of 8 Gy lose their capacity to absorb fluid via the descending colon after four days. After seven days, fluid absorption recovers to control levels.

AIMS

To investigate the effect of ionising radiation on colonic permeability together with its effect on mitochondria dependent apoptotic signals and intercellular adhesion molecules.

METHODS

Rats were irradiated with doses of 0-12 Gy. Colonic permeability was measured by accumulation of fluorescein isothiocyanate (FITC) dextran in crypt lumens. Changes in levels of cytochrome c, caspase 3, E and OB cadherin, beta-catenin smooth muscle actin, and collagen IV were assessed using immunocytochemistry with confocal microscopy.

RESULTS

Cytosolic cytochrome c increased after 8 Gy (t(1/2) 1.4 (0.6) hours) and peaked at approximately six hours. Caspase 3 increased more slowly, particularly in crypt epithelial cells (t(1/2) 57 (14.5) hours). Pericryptal myofibroblasts disintegrated within 24 hours as was evident from loss of OB cadherin and smooth muscle actin. This coincided with increased crypt permeability to dextran. Intercellular adhesion between crypt luminal cells was not lost until day 4 when both beta-catenin and E-cadherin were minimal. The half maximal dose-response for these effects was in the range 2-4 Gy. Recovery of colonic transport was concurrent with recovery of pericryptal smooth muscle actin and OB cadherin. The pan caspase inhibitor Z-Val-Ala-Asp.fluoromethylketone (1 mg/kg per day) had a small effect in conserving the pericryptal sheath myofibroblasts and sheath permeability but had no systemic therapeutic effects.

CONCLUSIONS

These data suggest that radiation damage to the colon may be initiated by mitochondrial events. Loss of crypt fluid absorption and increased permeability coincided with decreased intercellular adhesion between crypt epithelial cells and loss of pericryptal sheath barrier function.

Functional changes in the rat distal colon after whole-body irradiation: dose-response and temporal relationships

The aim of this study was to determine the acute radiation response of the rat distal colon by in vivo and in vitro measurements of the functions of the colon over a range of radiation doses. Rats received a whole-body irradiation of 2 to 12 Gy and were studied from 1 to 7 days after exposure. In vivo water and electrolyte absorption was measured by insertion of an agarose cylinder in the colon of anesthetized rats. In vitro transepithelial electrical parameters (potential difference, short-circuit current, transepithelial conductance) were measured in Ussing chambers in basal and agonist-stimulated conditions. In vivo and in vitro functional studies were completed by standard histological analyses. The majority of functional modifications appeared at 4 days after exposure. At this time, a dose-dependent decrease in absorption of water and sodium/chloride ions in the colon was noted. In contrast, a twofold increase in potassium secretion was observed for every radiation dose studied. The response to secretagogues was attenuated at doses >8 Gy. Modifications of basal transepithelial electrical parameters together with marked histological alterations were observed at 4 days with the higher doses (>/=10 Gy). In conclusion, these results show that functions of the colon are affected by irradiation and may contribute to diarrhea induced by ionizing radiation.

Changes in 5-HT-mediated pathways in radiation-induced attenuation and recovery of ion transport in rat colon

Whole body exposure to high doses of ionizing radiation is associated with small intestinal and colonic dysfunction, the etiology of which remains unknown. In this study, we investigated the role of both neural and nonneural 5-hydroxytryptamine (5-HT)-mediated pathways in radiation-induced attenuation and recovery of colonic secretory function. Rats were exposed to whole body 10-Gy gamma irradiation, and distal colonic tissues were studied in Ussing chambers 1, 3, and 7 days after exposure. Tissue responses to exogenously added 5-HT (nonneural pathway) and electrical field stimulation (EFS; neural pathway) were performed, and 5-HT receptor subtypes implicated in both responses were determined using three different 5-HT receptor antagonists: methysergide (5-HT(2/1C)), granisetron (5-HT(3)), and SDZ-205,557 (5-HT(4)). Maximal responses to exogenously added 5-HT were decreased at 1 and 3 days and returned to control values at 7 days. Responses to exogenous 5-HT were insensitive to both 5-HT(2/1C) and 5-HT(3) antagonists and to TTX but were totally inhibited by SDZ-205, 557 in both control and irradiated tissues. Responses to EFS were decreased 1 and 3 days after exposure and returned to control values at 7 days. In control tissues and 1 and 3 days after exposure, EFS responses were insensitive to both 5-HT(2/1C) and 5-HT(4) antagonists but reduced by granisetron in control (51%) and at 1 (64%) and 3 days (58%) after exposure. Granisetron was more effective at 7 days (73% inhibition), which was concomitant with the appearance of a 5-HT(4) antagonist-sensitive pathway (40% inhibition). In conclusion, neural and nonneural 5-HT-mediated pathways involve 5-HT(3) and 5-HT(4) receptors, respectively, in control as well as in irradiated tissues 1 and 3 days after exposure. Conversely, the recovery of colonic transport is associated with additional 5-HT(3)-mediated pathways, probably in combination with 5-HT(4) receptors.

Modified absorptive and secretory processes in the rat distal colon after neutron irradiation: in vivo and in vitro studies

Impaired fluid and electrolyte transport in the intestine is a well-recognized characteristic of radiation-induced pathologies in the gastrointestinal tract. The aim of this study was to investigate the responsiveness of the epithelium of the colon of the rat to electrical and pharmacological (serotonin, carbachol) stimulation concomitantly with in vivo assessment of the absorptive capacity of the colon at 1, 3, 5 and 7 days after 3.8 Gy whole-body exposure to neutrons. The responsiveness of rat colon in vitro to electrical stimulation and the number of mast cells were measured to examine the role of neuroimmune networks in radiation-induced dysfunction. Animals showed an impaired capacity of the colon to absorb water and sodium from 3 to 5 days after irradiation together with decreased responsiveness to electrical and pharmacological stimulation. The time course of decreased responsiveness to neural stimulation was similar to that of impaired absorption observed in vivo, but it was not correlated with variations in mast cell numbers. Histological (mast cells) and biochemical analyses (myeloperoxidase and NO synthase activities) did not find evidence of a marked infiltration and/or activation of inflammatory cells. Thus the impaired absorptive capacity of the colon observed after irradiation occurs concomitantly with decreased neural influence, and is possibly related to reduced epithelial functional capacity but not to decreased mast cell numbers.

Modified bile acid profiles in mixed neutron and gamma-irradiated pigs

PURPOSE

To determine the effect of mixed neutron and gamma-irradiation on the bile acid pool, which may be a key factor in radiation-induced diarrhoea.

MATERIALS AND METHODS

The bile duct of pigs was catheterized to derive bile over several experimental weeks, both before and after a 5.9 Gy neutron and gamma-irradiation. After measurement of the volume and sampling, bile was returned to the pig via a duodenal catheter. Samples of bile were analysed by HPLC for their individual and total bile acid content. Blood samples were also collected for total bile acid determination.

RESULTS

Bile flow was significantly decreased during the first 24h and after the fifth day post-irradiation. Whereas total bile acid concentration in bile was not altered, profiles of individual bile acids were significantly altered as early as the first post-irradiation day. Such modifications in these profiles resulted in a change of the properties of the bile acid pool. An increased proportion of dihydroxylated bile acids known to be more deleterious for the intestine was observed.

CONCLUSIONS

Neutron and gamma-irradiation leads to modifications of bile acid profiles, which may partly explain radiation-induced diarrhoea by a coherent physiopathological mechanism.

Long-term effects of X-irradiation on gastrointestinal function and regulatory peptides in monkeys

PURPOSE

To investigate the long-term effects of X-irradiation on different aspects of gastrointestinal function in the non-human primate (Macaca mulatta).

MATERIALS AND METHODS

Animals were exposed to X-radiation (5 or 6 Gy) or not (sham) and gastrointestinal function was investigated 4-6 years after exposure. Basal and agonist-stimulated short circuit current (Isc) responses were measured in isolated jejunum. Intestinal tissue was taken for histological analysis as well as for determination of mucosal marker enzyme activities and gastrointestinal regulatory peptide levels. Vasoactive intestinal peptide receptor characteristics were determined as well as VIP-stimulated Isc responses. GI peptides were also measured in plasma.

RESULTS

Few differences were seen in basal electrical parameters or tissue morphology but there was a tendency for reduced basolateral membrane enzyme activity. VIP-stimulated Isc responses were reduced in irradiated animals as were VIP-stimulated adenylate cyclase responses. Plasma and tissue (ileal and colonic muscle layers) gastrin releasing peptide levels were increased in irradiated animals. In contrast circulating gastrin levels were lower.

CONCLUSIONS

Late effects of total-body irradiation on GI function in monkeys showed altered circulating and tissue levels of some GI peptides. In addition the biological effects of vasoactive intestinal peptide were modified.

Ionizing radiation stimulates muscarinic regulation of rat intestinal mucosal function

The aim of this study was to determine whether ionizing radiation modifies muscarinic regulation of intestinal mucosal function. Rats exposed to total body 8-Gy gamma-irradiation or sham irradiated were studied up to 21 days after irradiation. Basal and carbachol-stimulated short-circuit current (Isc) and transepithelial conductance (Gt) of stripped ileum were determined in Ussing chambers. Muscarinic receptor characteristics using the muscarinic antagonist [3H]quinuclidinyl benzilate and three unlabeled antagonists were measured in small intestinal plasma membranes together with two marker enzyme activities (sucrase, Na+-K+-ATPase). Enzyme activities were decreased 4 days after irradiation (day 4). Basal electrical parameters were unchanged. Maximal carbachol-induced changes in Isc and Gt were increased at day 4 (maximal DeltaIsc = 195.8 +/- 14.7 microA/cm2, n = 19, vs. 115.4 +/- 8.2 microA/cm2, n = 63, for control rats) and unchanged at day 7. Dissociation constant was decreased at day 4 (0.73 +/- 0.29 nM, n = 10, vs. 2.14 +/- 0.39 nM, n = 13, for control rats) but unchanged at day 7, without change in binding site number. Thus total body irradiation induces a temporary stimulation of cholinergic regulation of mucosal intestinal function that may result in radiation-induced diarrhea.

A substance P receptor antagonist (FK 888) modifies gut alterations induced by ionizing radiation

PURPOSE

We previously reported disturbances of ileal substance P (SP) levels and of characteristics of specific receptors after ionizing radiation associated with disorders of intestinal motility. The aim of this study was to investigate the effect of a SP receptor blockade by FK 888 on gut SP levels and contractile properties after rat irradiation.

MATERIALS AND METHODS

Rats were exposed to 6 Gy whole-body gamma-irradiation and injected 1 h post-irradiation with FK 888 for 3 days (0.1 mg/kg/day). Plasma and ileal SP concentrations, ileal muscle SP receptor binding and SP-induced contractions in isolated ileum were investigated 3 and 14 days post-irradiation and FK 888 treatment.

RESULTS

Irradiation induced an increase of total SP binding site number at day 3 (1.3-fold) and day 14 (1.6-fold). FK 888 had no effect on SP receptor characteristics in irradiated animals. In contrast, FK 888 treatment caused a reduction of endogenous ileal SP level in mucosal (-29%) and muscularis (-40%) layers at day 3 and these decreases were greater at day 14, -88% in mucosal and -61% in muscularis layers. FK 888 treatment decreased efficacy of ileal contraction in both the control and irradiated rat but surprisingly it increased potency at day 3 and decreased it at day 14 in the irradiated rat.

CONCLUSIONS

The findings demonstrate that a SP receptor antagonist could be effective on intestine contractility alteration induced several days after ionizing radiation exposure but not at 3 days after irradiation.

GR-205171 (Glaxo Wellcome plc)

Glaxo Wellcome is developing the NK1 antagonist GR-205171 for the potential treatment of chemotherapy- and radiotherapy-induced emesis, post-operative nausea and emesis, and migraine. Phase II trials have commenced for both these indications. GR-205171 has a similar affinity for the NK1 receptor as CP-99994 [176071,193105]. Glaxo anticipates NDA and MAA filings in 2000 [244813]. A trial of GR-205171 in combination with ondansetron demonstrated the combination to be highly effective in the prevention of acute cisplatin-induced emesis. Complete responses were seen in all patients receiving high-dose GR-205171 plus ondansetron. The combination provided complete control of nausea in 16 h in 10 out of 12 patients [289484]. The compound has an ED90 value of 0.03 mg/kg against radiation-induced emesis in the ferret [207316]. GR-205171 is also active against adjuvant-induced inflammatory pain in the rat and may be of potential use in the treatment of chronic inflammatory pain.

Exposure to ionizing radiation modifies circulating gastrin levels and gastrointestinal endocrine cell densities in the rat

PURPOSE

Gastrointestinal functions, controlled partly by gut peptides, are disturbed by ionizing radiation exposure. The effect of whole-body irradiation on circulating gastrin levels, densities of gastrointestinal endocrine cells and gastric acid secretion was investigated.

MATERIALS AND METHODS

Rats were exposed to 2 or 6 Gy gamma-radiation. They were killed 3 or 7 days later and compared with shams. Plasma gastrin and basal acid output were measured. Endocrine cells were identified by argyrophilia or immunohistochemistry and their densities estimated.

RESULTS

Radiation exposure significantly increased gastrinaemia and gastric acid output at the times studied (p<0.05-p<0.001). Endocrine cells displayed different sensitivities to irradiation. In the gastric mucosa, a 6 Gy dose induced a decrease in fundic argyrophil cell, antral gastrin and somatostatin cell densities, always accentuated 7 days after irradiation, while in the intestinal mucosa it induced an increase, with highest values often at 7 days post-irradiation (p<0.01-p<0.001). This was true for neurotensin cells in the jejunum and ileum, substance P cells in ileum and enteroglucagon cells in the descending colon.

CONCLUSIONS

Whole-body irradiation in rats significantly alters plasma gastrin levels, and several gut endocrine cell densities. This has repercussions on hormonal function, such as that exerted on acid secretion, and may explain gastrointestinal dysfunction observed following radiation exposure.

In vivo alterations of fluid and electrolyte fluxes in rat colon by gamma irradiation

Colonic function in rats was investigated up to 14 days following exposure to whole-body gamma irradiation (8 Gy) using a combination of in vivo and in vitro approaches. Water and electrolyte fluxes were measured in vivo under anesthesia by insertion of an agarose cylinder into the descending colon. Short-circuit current responses (Isc; basal, agonist-stimulated) of distal colon were measured in vitro as were mannitol and sodium fluxes. Water and electrolyte absorption (Na, Cl) was markedly reduced at four days after irradiation but returned to normal at seven days. Potassium secretion was increased from one to seven days after exposure. There were no differences in basal Isc, Na, or mannitol fluxes at four days but responses to secretagogues (5-hydroxytryptamine, forskolin, carbachol) were attenuated. No morphological alterations were associated with these functional modifications.

Exposure to ionizing radiation modifies neurally-evoked electrolyte transport and some inflammatory responses in rat colon in vitro

PURPOSE

To characterize the responsiveness of the colon to neural stimulation following acute exposure of rats to gamma-radiation and to correlate observed changes to a number of parameters.

MATERIALS AND METHODS

Rats were exposed to 5 or 10 Gy 137Cs gamma-radiation or not (sham-irradiated) and studied at 1, 3 and 7 days after irradiation. Stripped segments of colon were mounted in Ussing chambers for measurements of neurally-evoked electrolyte transport (electrical field stimulation). Colonic tissue was also taken for biochemical (tissue 5-hydroxytryptamine, histamine, leukotriene B4, nitric oxide synthase) and histological analyses (mast cells).

RESULTS

In irradiated rats both proximal and distal colon were hyporesponsive to electrical field stimulation at 1 and 3 days, but had recovered by 7 days. In the distal colon, carbachol responses were attenuated 1 day after 10 Gy. Mast cells, tissue histamine and leukotriene B4 synthesis were significantly reduced at all time points but no changes were seen in 5-HT or inducible NOS activity.

CONCLUSIONS

Rat colon becomes hyporesponsive to neural stimuli post-irradiation. The response initially (1 and 3 days) correlates with decreased mast cells and histamine, but not at 7 days.

Whole-body gamma irradiation modifies bile composition in the pig

The effects of 6 Gy whole-body 60Co gamma irradiation on bile composition in pigs were studied to determine possible alterations in the quality of the bile, which may be a determining factor in diarrhea as well as nutrient malabsorption, which classically occurs after irradiation. The bile duct of pigs was catheterized to allow a total and continuous deviation of bile over several weeks, before and after irradiation. After measurement of the volume and sampling, bile was returned to the animal via a duodenal catheter. Bile samples were then analyzed for cholesterol, phospholipid and total bile acid content. Individual bile acids were quantified by HPLC analysis. Bile flow was significantly decreased during the first 24 h and after the fifth day postirradiation. Whereas cholesterol, phospholipid and total bile acid concentrations were not altered, profiles of individual bile acids were modified significantly as early as the first day postirradiation. Moreover, the change of these profiles with time was specific for each bile acid. Such modifications in bile acid profiles resulted in a change in the properties of the bile acid pool in an increased proportion of dihydroxylated bile acids known to interfere with gut functions, and it is reasonable to suggest that radiation-induced changes in bile acid profiles may be involved in radiation-induced gastrointestinal disorders.

Changes in gut neurotensin and modified colonic motility following whole-body irradiation in rat

Exposure to ionizing radiation induces gastrointestinal dysfunction often associated with disorders of intestinal motility. Neurotensin is one of the mediators involved in the control of intestinal muscle activity. The aim of this study was to relate neurotensin tissue content and specific receptor binding with contractile effect of neurotensin in rat colon after irradiation. Rats were exposed to whole-body gamma-irradiation (60Co; 6 Gy). Intestinal (caecum, colon) neurotensin-like immunoreactivity, colonic muscle neurotensin receptor binding and neurotensin-induced contractions in isolated colon were investigated 3 and 7 days after irradiation. Irradiation produced a marked increase in the intestinal muscle content of neurotensin-like immunoreactivity (2.5-fold in caecum, 5-fold in colon) 3 days post-irradiation. At 7 days, the intestinal neurotensin content was close to that of the control values. Three days after irradiation, neurotensin receptors in colonic muscle were characterized by the appearance of a transient second class of sites of low affinity-high capacity. A three-fold increase in the total number of sites was observed. In addition, effects of neurotensin on isolated colon preparations showed an increase (37%) of potency but a decrease (7-fold) of efficacy. Seven days after irradiation, the efficacy was close to the control. Modifications of intestinal neurotensin content and specific receptor characteristics induced by irradiation can influence the colonic contractile activity.

Exposure to either gamma or a mixed neutron/gamma field irradiation modifies vasoactive intestinal peptide receptor characteristics in membranes isolated from pig jejunum

The effect of acute whole body exposure to ionizing radiation was investigated on intestinal vasoactive intestinal peptide (VIP) receptors and adenylate cyclase activity in membranes isolated from pig jejunum. Pigs under light anaesthesia were exposed to a single dose (6 Gy) of gamma (gamma) or to mixed neutron/gamma field (ratio 1:1; neutron/gamma) irradiation. Seven days after irradiation, plasma-membranes were prepared from post mortem jejunal mucosal scrapings. Marker enzyme activities (sucrase, leucine aminopeptidase (LAP), Na,K-ATPase) were measured in each preparation. The characteristics (KD, Bmax) of VIP receptors were determined using 125I-labelled VIP. In addition VIP-sensitive adenylate cyclase activity was measured. Results showed that enzyme activities were reduced following both gamma (sucrase 67%; LAP 53%; Na/K-ATPase 29%; N = 7) and neutron/gamma (sucrase 53%; LAP 59%; Na/K-ATPase 68%; N = 5) compared with control values (N = 5). VIP receptor affinity was decreased following either type of irradiation (gamma or neutron/gamma P < 0.01) and receptor numbers increased. Both VIP- and forskolin-stimulated adenylate cyclase activities were reduced but the sensitivity of the enzyme remained the same for VIP (EC50 values (nmol dm-3)-control-1.27 +/- 0.35; gamma-2.18 +/- 0.41; neutron/gamma-1.91 +/- 0.28). In conclusion, exposure to either gamma or neutron/gamma irradiation attenuates intestinal enzyme activities and VIP receptor affinity but increases VIP receptor numbers.

Active intestinal secretion of the fluoroquinolone antibacterials ciprofloxacin, norfloxacin and pefloxacin; a common secretory pathway?

The transepithelial transport of three fluoroquinolones, norfloxacin, ciprofloxacin and pefloxacin has been compared by using cultured human intestinal Caco-2 cell-layers. Absorptive (apical-basal) fluxes of ciprofloxacin and norfloxacin are small relative to basal to apical fluxes. Norfloxacin and ciprofloxacin are thus subject to active transepithelial secretion. Active net secretion of norfloxacin displays saturation kinetics with Vmax and Km values of 36.2 +/- 6.9 nmol.cm-2.hr-1 and 1.42 +/- 0.79 mM. In contrast, transepithelial pefloxacin fluxes are large, show marked saturation while the direction of net flux is variable and small relative to transepithelial fluxes. Norfloxacin, pefloxacin and ciprofloxacin are all subject to accumulative transport across the basal surface of Caco-2 cell layers. A number of 4-quinolones and fluoroquinolones are capable of inhibition of both net secretion of ciprofloxacin and cellular accumulation across the basal-lateral cell surface. Cinoxacin, a 4-quinolone may selectively inhibit exit from the cell across the apical membrane. Cross-competition studies suggest that fluoroquinolones may compete for a common carrier at the basal-lateral membrane. It is likely that the mechanism of transepithelial secretion involves a common accumulative transport at the basal-lateral membrane followed by facilitated exist across the apical membrane. Pefloxacin may interact with a brush-border carrier for which norfloxacin and ciprofloxacin are poor substrates, enhancing the absorptive flux of this fluoroquinolone.

Active secretion of the fluoroquinolone ciprofloxacin by human intestinal epithelial Caco-2 cell layers

The bidirectional transepithelial fluxes of ciprofloxacin, an antibacterial fluoroquinolone, across the human intestinal epithelial Caco-2 cell-line show marked asymmetry. Basal-to-apical flux of ciprofloxacin (10 microM) exceeds apical-to-basal flux indicating net secretion. Net ciprofloxacin secretion is abolished by azide/2-deoxy-D-glucose treatment, displays saturation kinetics (Km = 0.89 +/- 0.23 mM, Vmax 44.3 +/- 4.9 nmol cm-2.h) and competition by other fluoroquinolones. A specific, active secretion in Caco-2 epithelia may explain the transintestinal elimination of ciprofloxacin observed in pharmacokinetic studies in man.

Effect of prostaglandin E2 on agonist-stimulated cAMP accumulation in the distal convoluted tubule isolated from the rabbit kidney

The effects of calcitonin, vasoactive intestinal peptide (VIP), parathyroid hormone (PTH) and isoprenaline on intracellular cAMP accumulation were determined in the distal tubule (DCT) microdissected from collagenase-treated rabbit kidney. In DCTb (the initial "bright" portion) calcitonin (10 ng/ml) elicited a highly reproducible response 203.7 +/- 19.1 fmol cAMP mm-1 4 min-1 (SE,N = 13) whereas VIP-induced cAMP accumulation was less and more variable from one experiment to another (1 microM, 97.2 +/- 17.8 fmol mm-1 4 min-1, SE, N = 12). When used in combination, these two agonists were non-additive, indicating stimulation of a single pool of cAMP in DCTb. In DCTg, ("granular") which consists of at least two cell types, PTH (100 nM) elicited a marked, reproducible accumulation of cAMP (154.3 +/- 27.0 fmol mm-1 4 min-1; SE, N = 5). Isoprenaline (1 microM) and VIP (1 microM) induced much smaller increases in cAMP levels 20.9 +/- 2.7 and 29.4 +/- 4.1 fmol mm-1 4 min-1 (SE, N = 5) respectively, and, when used in combination, were non-additive, demonstrating that VIP and isoprenaline are active on the same cell type. In DCTb, prostaglandin E2 (PGE2) inhibited both calcitonin- and VIP-stimulated cAMP accumulation (calcitonin 57.8 +/- 2.7% inhibition, SE, N = 16; VIP, 80.6 +/- 2.1% inhibition, SE, N = 5). The EC50 values for calcitonin were 1.21 +/- 0.33 ng/ml and 1.83 +/- 0.25 ng/ml (SD, N = 3) in the absence and presence of PGE2 (300 nM) respectively with an IC50 for PGE2 of 26.3 +/- 6.3 nM (SE, N = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

On the ecophysiology of the Clusiaceae in Trinidad: expression of CAM in Clusia minor L. during the transition from wet to dry season and characterization of three endemic species

A study was made of photosynthesis and expression of crassulacean acid metabolism (CAM) in naturally exposed and shaded populations of Clusia minor L. during the transition from wet to dry season in Trinidad (mid-February to mid-April, 1990). At the start of the dry season, plants from exposed and shaded habitats showed a capacity for CAM either through the fixation of external or internal (respiratory) CO₂ . Exposed plants showed continuous uptake of CO₂ over 24 h although dark fixation accounted for only a small proportion of CO₂ fixed over the day. The expression of CAM was considerably enhanced as the dry season progressed with substantial increases in the overnight accumulation of titratable acidity, particularly in leaves of exposed plants. This was accompanied by a reduction in day-time photosynthesis and an increase in dark fixation, with shaded plants showing only night-time fixation of CO₂ . The magnitude of CAM in C. minor was substantial with a maximum ΔH⁺ of 1410 mol m^-3 measured in leaves from exposed branches. Both malic and citric acids were accumulated overnight. The highest citric:malic acid ratios were found in young leaves from exposed plants with 250 mol m^-3 malic and 125 mol m^-3 citric acid accumulated near the time of maximum CAM activity. Photosynthetic efficiency, measured as light responses of O₂ evolution, also varied on a daily basis dependent on the incident photosynthetic photon flux density (PPFD). Apparent quantum yield and photosynthetic capacity showed marked reductions depending on the degree of exposure, suggesting that photoinhibitory responses are important under natural conditions. An analysis of three members of the Clusiaceae endemic to Trinidad showed that each had the capacity to induce CAM activity, despite being found in a narrow range of habitats which have higher rainfall than those of C. minor. However, despite the variable expression of CAM activity, carbon isotope composition suggested that when integrated throughout the year, carbon accumulation is predominantly mediated via the C₃ pathway in all the species studied.

Discrepancy between the short and long term effects of ouabain on the sodium pumps of human cells grown in culture

1. Human cells (HeLa) were cultured for periods up to 48 h in growth medium in the absence or presence of a range of concentrations of cardiac glycosides. In some experiments the potassium concentration of the medium was varied between 0.3 mM and the usual 5 mM. 2. For periods up to 2 h in ouabain the association and dissociation rate constants were measured and the equilibrium binding constant (KD) calculated; the apparent equilibrium binding constant (K'D) was measured after 1-2 days growth in ouabain. 3. Ouabain had a K'D after 2 days of 2-6 nM in 5 mM K+ growth medium, a 4 fold greater blocking effect on sodium pumps after 2 days than expected from the association and dissociation rate constants measured in untreated or previously ouabain-treated cells. 4. This effect was: (a) approximately the same over a range of external potassium concentrations from 0.3 to 5 mM, although the absolute effect of ouabain over this range of potassium was much different; (b) probably not due to different isoforms of pumps in cells grown in ouabain compared to untreated cells; (c) apparently not a consequence of internalisation of pump-glycoside complexes. 5. We conclude that ouabain has only a limited access to sodium pumps in whole cells; this could be because sodium pumps cycle continuously through an inaccessible region of the plasma membrane. This effect needs to be considered both in the assessment of the magnitude of the long term effects of cardiac glycosides on cells, and in the measurement of the glycoside affinities of various isoforms of the pump.

Vasoactive intestinal peptide stimulation of adenylate cyclase activity in isolated rabbit renal arterial microvessels

Vasoactive intestinal peptide (VIP) at a concentration of 1 microM stimulates adenylate cyclase (AC) in isolated rabbit renal preglomerular arterial vessels by 3.9 +/- 1.3 fold (n = 6) over basal values. A comparable stimulation of AC was observed with prostaglandin E1. Half-maximal VIP-stimulated activity was observed at 7.2 +/- 3.5 nM (n = 6), which was increased to 17.4 +/- 4.4 nM by 10 microM-(4Cl-D-Phe6,Leu17)VIP, a VIP-receptor antagonist.

Localisation and characterisation of functional vasoactive intestinal peptide receptors in feline kidney

Specific 125I-labelled vasoactive intestinal peptide (VIP) binding was determined in feline renal cortical and medullary plasma membranes. For the cortex, Scatchard analysis of the data resulted in a curvilinear plot with a high-affinity site K0.5 of 8.4 +/- 2.6 nmol l-1 (SE, n = 6) and a second low-affinity site K0.5 204 +/- 16 nmol l-1 with binding site concentrations (Bmax) of 385 +/- 44.5 and 2710 +/- 181.3 fmol mg protein-1 respectively. Conversely a similar analysis of the results obtained for outer medullary membranes gave a single site with a K0.5 of 1.2 +/- 0.2 nmol l-1 (SE, n = 4) and Bmax of 157.8 +/- 24.7 fmol mg-1. Inner medullary membrane binding data. Gave a single site of lower affinity (K0.5 = 62.5 +/- 21.6 nmol l-1; n = 3). Structurally related peptides, glucagon and secretin, were ineffective (up to 1 mumol l-1) in displacing VIP from specific sites in both cortex and medulla. Porcine PHI 1-27 (a peptide having N-terminal histidine and C-terminal isoleucine) and a VIP antagonist [4-Cl-D-Phe6Leu17]VIP both displaced 125I-VIP from cortical and medullary membrane binding sites with IC50 values of 43.0 nmol l-1 and 1.3 mumol l-1 (cortex) and 132.0 nmol l-1 and 1.5 mumol l-1 (medulla) respectively. The localisation of specific VIP binding sites in feline kidney was investigated further by in vitro autoradiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoactive intestinal peptide stimulation of renal adenylate cyclase and antagonism by (4Cl-D-Phe6Leu17)VIP

The effect of vasoactive intestinal peptide (VIP) and related peptides [glucagon, secretin, PHI 1-27 (peptide with N-terminal histidine and C-terminal isoleucine)] on renal adenylate cyclase (AC) has been determined in several species. The largest stimulation (4.1 +/- 0.5-fold basal) of AC by 1 mumol.l-1 VIP was observed in feline cortical plasma membranes. In rabbit and guinea-pig, VIP increased AC activity 1.5 +/- 0.3- and 1.8 +/- 0.3-fold respectively but glucagon had no such action. Conversely in the rat glucagon stimulated AC some 3-fold over basal activity whereas VIP had little effect. In dog, cat and mouse both peptides were effective in increasing AC activity. For cat, half-maximal stimulation of cortical plasma membrane AC by VIP was seen at 27.0 +/- 9.0 nmol.l-1 (SE N = 9 animals). VIP also increased AC activity in both outer (red) and inner (white) medulla. In feline cortical membranes VIP and PTH (parathyroid hormone) when added in combination were fully additive. However for VIP and glucagon in combination there was no cumulative increase in AC activity, indeed the resultant activity was less than that attained by VIP alone. The VIP analogue (4Cl-D-Phe6Leu17)VIP at 10 mumol.l-1 produced a right shift in the VIP-dose response curve and increased the EC50 from 17.2 +/- 5.8 nmol.l-1 to 132.0 +/- 22.2 nmol..-1 VIP (SE N = 4). There was no reduction in the maximum response elicited by VIP consistent with a competitive type of antagonism by this analogue. PHI-stimulated AC was also reduced by (4Cl-D-Phe6Leu17)VIP resulting in a similar right shift in the dose response curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoactive intestinal peptide control of renal adenylate cyclase: in vitro studies of canine renal membranes and cultured canine renal epithelial (MDCK) cells

Vasoactive intestinal peptide (VIP) has been shown to stimulate adenylate cyclase activity in plasma membranes isolated from canine renal cortex, outer and inner medulla in vitro. Though related hormones such as glucagon also stimulate adenylate cyclase in these membrane preparations, it is likely that VIP interacts with specific VIP receptors since the VIP receptor antagonist, (4Cl-D-Phe6, Leu17)-VIP, is capable of reducing the response to VIP, but not that to glucagon. Also binding of 125I-VIP to cortical renal plasma membranes shows competition by unlabelled VIP, but not by glucagon. Strain 1 (and clone CL(8)1b cells derived from the established cultured dog kidney cell line, MDCK, have been shown also to respond selectively to VIP by an increase in adenylate cyclase activity and cyclic AMP accumulation in intact cells. A physiological correlate of VIP activation of adenylate cyclase has been sought by addition of VIP to reconstituted epithelial monolayers of strain 1 MDCK cells clamped in Ussing chambers. VIP addition to the basal-lateral cell aspects generates an inward short-circuit current that is sensitive to replacement of medium Cl- by NO3-, and to inhibition by the Cl- channel blocker, 3-nitro-2(3-phenylpropylamino)-benzoic acid, consistent with VIP stimulation of transepithelial Cl- secretion.

Distribution of vasoactive intestinal peptide-sensitive adenylate cyclase activity along the rabbit nephron

The effect of vasoactive intestinal peptide (VIP) upon adenylate cyclase (AC) activity has been determined in defined microdissected renal tubules isolated from collagenase-treated rabbit kidneys. In the presence of 10 microM GTP, 1 microM VIP gave marked stimulations of AC over basal values in the bright portion of the distal convoluted tubule (DCTb) (10.1-fold), and in the collecting tubule isolated from the inner stripe of the outer medulla (OMCTi, 7.8-fold). Less pronounced effects of VIP were found in the medullary collecting tubule isolated from the outer stripe (2.5-fold) and in the granular portion of the distal convoluted tubule (2.0-fold). VIP stimulation of AC activity in these segments amounted to 25 to 40% of the effect elicited by other agonists (arginine vasopressin, calcitonin or parathyroid hormone) in their respective target segments. A low response to VIP was observed in the cortical thick ascending limb (1.8-fold) which represented less than 5% of the calcitonin-stimulated AC activity. In the thin descending limb VIP produced a slight and variable stimulation of AC. VIP was without effect upon AC in the convoluted and straight portions of the proximal tubule, the medullary thick ascending limb and the cortical collecting tubule. Half-maximal stimulation of AC by VIP was observed at 26 +/- 10 nM (n = 3) in OMCTi and at 19 nM (n = 2) in DCTb. Related peptides glucagon, secretin and PHI gave lower stimulations of AC compared to VIP in OMCTi. Conversely for rat OMCTi, under identical conditions, glucagon was much more effective than VIP.

Attribution of [3H]bumetanide binding to the Na+K+Cl 'co-transporter' in rabbit renal cortical plasma membranes: a caveat

The 3H-labelled loop diuretic bumetanide has been used to investigate loop diuretic binding to purified plasma membranes from rabbit kidney cortex (and outer medulla). Bumetanide binding to partially purified cortical plasma membranes in the range 0-10 microM, in a buffer containing principally Na, K and Cl ions, consists of a linear non-saturable component as assessed by 100 microM unlabelled bumetanide, and a saturable component consisting of high- and low-affinity binding sites, half-maximal binding being observed at 1.3 and 220 microM, respectively. The high-affinity site was found to be present in a fraction enriched in basolateral membrane markers when plasma membranes were further purified on a continuous Percoll gradient, whilst bumetanide binding to fractions enriched in brush-border or mitochondrial membrane markers was of lower affinity. Several features of bumetanide binding to basolateral membrane marker-enriched fractions are consistent with binding to the Na+K+Cl 'co-transporter' inhibited by loop diuretics: half-maximal binding was observed at 1.8 microM, with a finite maximal binding capacity of 78 pmol/mg. The relative efficacy of several loop diuretics for displacement of [3H]bumetanide was bumetanide greater than piretanide greater than furosemide = ethacrynic acid. Binding of loop diuretic was found to be dependent upon the medium ionic composition, Na, K and Cl being required to give maximal binding. The ability of probenecid and 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS) to compete with [3H]bumetanide was tested since these compounds are known inhibitors of anion secretion in the proximal nephron. Both DIDS and probenecid were able to effectively compete with [3H]bumetanide binding. A test of the ability of these compounds to inhibit 'co-transport' flux was made in intact MDCK cells using the ouabain-insensitive 86Rb (K) influx. Probenecid, at the concentrations seen to displace [3H]bumetanide binding to renal plasma membranes, was an effective inhibitor of 'co-transport' whereas DIDS was not. The adequacy of present criteria as to the identification of the 'co-transporter' in renal membranes using [3H]bumetanide binding are discussed in the light of this evidence.