The Role of Tooth-brushing and Diet in the Maintenance of Periodontal Health in Dogs

Tooth-brushing every other day did not maintain clinically healthy gingivae in dogs. The daily addition of a dental hygiene chew to a regimen of tooth brushing every other day reduced the gingivitis scores and reduced the accumulation of dental deposits (plaque, calculus and stain). Daily tooth-brushing should be the recommendation to the dog owner irrespective of dietary regimen. Providing a dental hygiene chew daily seems to give an added health benefit when tooth-brushing is less frequent, and provides the pet owner with a useful adjunct for homecare.

Metabolic determinants of body weight after cats were fed a low-carbohydrate high-protein diet or a high-carbohydrate low-protein diet ad libitum for 8 wk

Overweight and obese conditions are common in cats and are associated with the development of a number of diseases. Knowledge of metabolic determinants and predictors of weight gain may enable better preventative strategies for obesity in cats. Lean, healthy cats were fed either a low-carbohydrate high-protein diet (n 16) or a high-carbohydrate low-protein (n 16) diet ad libitum for 8 wk. Potential determinants and predictors of final body weight assessed were body fat and lean masses, energy required for maintenance, energy requirements above maintenance for each kilogram of weight gain, insulin sensitivity index, fasting, mean 24-h and peak plasma glucose, insulin, and leptin concentrations, and fasting and mean 24-h serum adiponectin concentrations. In cats fed the low-carbohydrate high-protein diet, after adjusting for initial body weight, those with higher energy requirements for weight gain and higher fasting glucose concentration had higher final body weights (P ≤ 0.01). Predicted final body weights using initial body weight, fasting glucose and mean 24-h insulin concentrations (partial R(2) 37.3%) were imprecise. An equation using just initial body weight and fasting glucose concentration would be of more practical value, but was marginally less precise. In cats fed the high-carbohydrate low-protein diet, those with lower fasting leptin concentration initially had higher final body weights (P = 0.01). Predicted final body weights using initial body weight, energy requirements for maintenance, total body fat percentage and fasting leptin concentration (partial R(2) 39.2%) were reasonably precise. Further studies are warranted to confirm these findings and to improve the precision of predicted final body weights.

Fat mass, and not diet, has a large effect on postprandial leptin but not on adiponectin concentrations in cats

Leptin and adiponectin play important roles in carbohydrate and lipid metabolism in different species. Information is limited on the effects of diet, weight gain, and fat mass on their concentrations in cats. This study compared fasting and postprandial blood leptin and total adiponectin concentrations before and after 8 wk of ad libitum feeding to promote weight gain in adult cats (n = 32) fed either a low-carbohydrate, high-protein (23% and 47% ME) or a high-carbohydrate, low-protein (51% and 21% ME) diet. There were significant effects of total, abdominal, and nonabdominal fat mass, but not diet or body weight, on mean 24-h and peak leptin (P < 0.01); observed increases in mean and peak leptin were greatest for abdominal fat mass (50% and 56% increase for every extra 100 g, respectively). After weight gain, postprandial leptin concentration increased markedly relative to when cats were lean, and the duration of the increase was longer after a mean weight gain of 37% with the low-carbohydrate, high-protein diet group compared with 17% with the high-carbohydrate, low-protein group (P ≤ 0.01). Adiponectin was lower than fasting at some time points during the postprandial period in both groups (P ≤ 0.05). For both fasting and mean 24-h adiponectin, there was no significant diet effect (P ≥ 0.19) or changes in weight gain relative to when cats were lean (P ≥ 0.29). In conclusion, fat mass, and not diet, has a large effect on postprandial leptin but not adiponectin concentrations in cats.

Is the fish embryo toxicity test (FET) with the zebrafish (Danio rerio) a potential alternative for the fish acute toxicity test?

The fish acute toxicity test is a mandatory component in the base set of data requirements for ecotoxicity testing. The fish acute toxicity test is not compatible with most current animal welfare legislation because mortality is the primary endpoint and it is often hypothesized that fish suffer distress and perhaps pain. Animal alternative considerations have also been incorporated into new European REACH regulations through strong advocacy for the reduction of testing with live animals. One of the most promising alternative approaches to classical acute fish toxicity testing with live fish is the fish embryo toxicity (FET) test. The FET has been a mandatory component in routine whole effluent testing in Germany since 2005 and has already been standardized at the international level. In order to analyze the applicability of the FET also in chemical testing, a comparative re-evaluation of both fish and fish embryo toxicity data was carried out for a total of 143 substances, and statistical approaches were developed to evaluate the correlation between fish and fish embryo toxicity data. Results confirm that fish embryo tests are neither better nor worse than acute fish toxicity tests and provide strong scientific support for the FET as a surrogate for the acute fish toxicity test.

Characterisation of long term cat placental explant cultures: uptake of taurine by system β

Dietary taurine is essential for cats and deficiency during pregnancy may lead to abortion, growth restriction or impaired neurological function of kittens. We previously described Na(+)- and Cl(-)-dependent taurine transport by system beta in fragments of freshly isolated cat placenta [Champion EE, Bailey SJ, Glazier JD, Jones CJP, Mann SJ, Rawlings JM, et al. Taurine uptake into cat placental tissue fragments. Placenta 2001;22:A.42]. Here we evaluate long term culture of cat placental explants as a model for the future study of chronic nutrient regulation of amino acid transport in this species. The cat placental explants displayed (i) Na(+)-dependent [(3)H]taurine uptake and (ii) taurine transporter protein on day 7 of culture, as observed in fresh cat placental fragments. The explants had preserved the ability to secrete PGF(2alpha) hormone until day 11 of culture and remained morphologically largely intact until day 7 of culture. This model of placental explant culture will provide an important in vitro method for the study of chronic regulation of amino acid transport in the cat.

Ultrastructural Aspects of Long-term Cat Placental Explant Culture

Changes in tissue architecture and ultrastructure in the cat placenta during long-term explant culture have been examined over an 11-day period. Pieces of cat placenta, dissected from the lamellar region, were cultured in CMRL-1066 medium and tissue was fixed for electron microscopy at 2, 5, 7, and 11 days' culture, as well as before culture was initiated (day 0). Four samples were examined at each time point. After two days, the trophoblast basal lamina and attached cytotrophoblast cells had begun to separate from the syncytium and the cytotrophoblasts were spreading over the surface of the exposed fetal stromal compartment, and by five days were showing signs of growth. At seven days' culture, cytotrophoblast multilayering was common, and vascular and stromal components were also well preserved with collagen biosynthesis evident. By 11 days, the centre of the culture was compacted and degenerate with loss of tissue architecture, but on the outside polyp-like growths could be seen, with a well-developed covering of trophoblast containing fat and secretory droplets, lining a connective tissue matrix and stromal components. The cat placenta, therefore, like the human, has the capacity for regrowth in explant culture, including both trophoblast and stromal components.

System beta and system A amino acid transporters in the feline endotheliochorial placenta

There is no knowledge of the transport mechanisms by which solutes cross the cat placenta or any other endotheliochorial placenta. Here, we investigated whether the amino acid transport systems beta and A are present in the cat placenta using a placental fragment uptake technique. Data were compared with studies in the human placenta, in which the presence of these two transport systems has been well established. A time course of [(3)H]taurine (substrate for system beta) and [(14)C]MeAIB (nonmetabolizable substrate for system A) uptake was determined in the term cat and human placental fragments in the presence and absence (choline substituted) of Na(+), and further studies were carried out over 15 min. Taurine uptake into both cat and human placenta fragments was found to be Na(+) and Cl(-) dependent, and Na(+)-dependent taurine uptake was blocked by excess beta-alanine. MeAIB uptake was found to be Na(+) dependent, and Na(+)-dependent MeAIB uptake was blocked by excess MeAIB or glycine. Western blotting and immunohistochemistry performed on cat and human placenta showed expression of TAUT and ATA2 (SNAT2), proteins associated with system beta and system A activity, respectively. This study therefore provides the first evidence of the presence of amino acid transport systems beta and A in the cat placenta.

Age-related differences in parameters of feline immune status

In order to assess age-related differences in feline immune status, 101 domestic short haired cats were assigned to two groups, adult (2-5 years, n=50) and senior (10-14 years, n=51). Analyses of leucocyte populations, lymphocyte subsets, complement activity, serum immunoglobulins and acute-phase proteins were undertaken and revealed significant differences between the two groups. The senior group had significantly lower WBC, lymphocyte and eosinophil counts than the adult group. Neutrophil, monocyte and basophil counts did not differ between the groups. Flow cytometry analysis, in combination with differential WBC data, revealed that the absolute values (cells/l) of T-cells, B-cells and natural killer (NK) cells were significantly lower in the older animals. While serum immunoglobulins IgA and IgM were higher in the senior group when compared with the adult group, no significant differences were observed in complement activity or in serum acute-phase proteins. Our findings suggest that age-related changes to parameters of immune status in the feline model are likely to follow a similar pattern to those observed in other long-lived mammalian species.

Insulin-like growth factor-I (IGF-I) and its association with lymphocyte homeostasis in the ageing cat

Ageing affects feline lymphocyte homeostasis in a similar pattern to that observed in other long-lived mammalian species, contributing to increased levels of morbidity and mortality in the ageing cat. Insulin-like growth factor-I (IGF-I) is now recognised as an important endocrine regulator of immunity and has been shown to decline with age in humans and rodent species. Analysis of plasma IGF-I in adult and senior cats confirmed that the older cats had significantly lower circulating levels of IGF-I. In order to determine whether an association existed between lymphocyte subpopulations and IGF-I levels in the cat, each parameter was measured and subjected to regression analysis. A highly significant association was found in vivo between plasma IGF-I and CD4(+) T-cell values in the senior group, but no such association was observed in the adult group. In order that this relationship could be examined further, in vitro studies were undertaken to investigate the effects of physiologically relevant concentrations of recombinant human IGF-I (rhIGF-l) on peripheral blood lymphocyte (PBL) cultures from adult and senior cats. While rhlGF-I induced low-level thymidine incorporation in the lymphocytes isolated from the senior group, it did not enhance the proliferative response to T-cell mitogens, Con A and PHA in either group, nor did it rescue cells from oxidatively induced apoptosis. Furthermore, the proliferative response of PBL from seniors did not attain the magnitude of that from the adults at any concentration of rhIGF-l. We propose that the observed association is not a direct effect of IGF-I on PBL, but may be mediated through an effect of IGF-I on the thymus.

Localization of alkaline phosphatase and Ca2+-ATPase in the cat placenta

We localized alkaline phosphatase and plasma membrane calcium-ATPase (PMCA) in the cat placental syncytiotrophoblast to address their polarized distribution and their potential as markers for specific plasma membrane purification. We used enzyme- (alkaline phosphatase) and immuno- (PMCA) histochemistry and, for alkaline phosphatase, compared data to observations on the human placenta. Alkaline phosphatase activity in the cat was localized to the decidual cell membranes, to within the associated interstitial space and on the subjacent apical (maternal facing) plasma membrane of the syncytiotrophoblast. Occasional maternal capillaries were positive on their basal surface and there was focal staining within the syncytiotrophoblast. This widespread distribution is less specific than in the human placenta where alkaline phosphatase was restricted to the apical and basal plasma syncytiotrophoblast membranes, with much greater density on the apical membrane. Expression of PMCA in the cat was restricted to the basal membrane of the syncytiotrophoblast only. This specific localization of PMCA is identical to the human placenta and all other species in which its placental localization has been studied. We conclude that the plasma membranes of the cat syncytiotrophoblast show a broadly similar functional polarization to the human and that PMCA would prove a useful marker in isolation of the cat syncytiotrophoblast basal plasma membrane.

Bioconcentration and toxicity of dodecylbenzene sulfonate (C12LAS) to aquatic organisms exposed in experimental streams

Fish, mollusks, and crustaceans were caged in the tail pool of streams during a C(12)LAS (dodecyl benzene sulfonate) model ecosystem experimental program. Bioconcentration of total C(12)LAS and individual isomers and acute and chronic toxicity were investigated during this study. Toxicity endpoints were based on water and tissue (i.e., body burden) concentrations at which adverse effects were observed. At 32 days, total C(12)LAS bioconcentration factors (BCFs) for the fathead minnow and three invertebrate species ranged from 9 to 116. In general, bioconcentration was affected by isomer position, exposure concentration, and species. BCF values tended to decrease as isomer position moved from external (e.g., 2-phenyl) to internal (e.g., 5,6-phenyl). BCFs also decreased as exposure concentration increased. Mean acute 4-d LC(50) values ranged from 1.5 to >3.0 mg/L for the six species tested. Lethal body burdens associated with 50% mortality (LBB(50)) varied from 0.21 to 0.60 mmole/kg (wet weight). During the 32-day chronic exposures, the EC(20) values were 0.27 (0.204-0.352), 0.95 (0.597-1.29), and approximately 1.0 mg/L for Corbicula (length), Hyalella (survival), and fathead minnow (survival), respectively. At these EC(20) values, C(12)LAS body burdens were 0.035, 0.23, and 0.19 mmoles/kg wet weight in Corbicula, Hyalella, and fathead minnow, respectively. Fish exposed to wastewater treatment plant effluent had total C(12)LAS tissue concentrations ranging from 0.0005 to 0.0039 mmoles/kg wet weight. These concentrations are approximately 45-360 times below the tissue concentration associated with subtle effects in the model ecosystem stream exposures. Total C(12)LAS body burdens in feral and caged Corbicula exposed to WWTP effluents were approximately 0.0013 mmoles/kg; approximately 25-fold below concentrations associated with effects in stream exposures.

Influence of a high fibre diet on glycaemic control and quality of life in dogs with diabetes mellitus

A study was undertaken to evaluate a high fibre diet used in the management of 10 dogs with naturally occurring insulin-dependent diabetes mellitus. Following baseline measurements of health and glycaemic control, the dogs were fed a canned diet containing a blend of insoluble and soluble dietary fibres and were monitored during the ensuing four months. Switching to the high fibre diet was associated with significantly lower mean 24-hour and postprandial plasma glucose concentrations, which were maintained over the study period. The high fibre diet was also associated with significant reductions in plasma concentrations of fructosamine, glycated haemoglobin, free glycerol and cholesterol, and there were significant improvements in dog activity and demeanour. Bodyweight declined during the fourth month of feeding the diet, which is likely to have resulted from underfeeding relative to increased activity. The results indicate that a high fibre diet can significantly improve glycaemic control and quality of life in dogs with diabetes mellitus.

The use of P-aminobenzoic acid and chromic oxide to confirm complete excreta collection in a carnivore, Felis silvestris catus

Complete excreta collection is a pre-requisite for several protocols in protein metabolism, and lack of confidence in achieving this may be increased when working with carnivores. Recovery of p-aminobenzoic acid (PABA) as a check for complete urine collection and chromic oxide for complete faeces collection were assessed in the cat. A single oral dose of PABA (4 mg/kg BW) was excreted more slowly than has been reported in the human (82% recovery at 6 h). A daily dose of PABA proved a useful method for confirming complete urine collection in the cat, and was 99% excreted in 72 h. Chromic oxide (500 mg/cat) was administered orally and recovery of chromium in the faeces was 90% after 96 h. A HPLC method for the analysis of PABA in cat urine was developed, and from the application of the techniques to a nitrogen balance study, it was concluded that PABA and chromic oxide are useful checks for complete excreta collection in the cat.

Feline hypertension: clinical findings and response to antihypertensive treatment in 30 cases

Systolic hypertension was diagnosed in 30 cats. At diagnosis, 16 of those were found to be in chronic renal failure only, while five were azotaemic and either receiving treatment for hyperthyroidism (four cases) or were untreated hyperthyroid cases (one case). Two cases were untreated hyperthyroid cases with no evidence of azotaemia and the remaining seven cases had no definitive diagnosis of the underlying cause of their hypertension. The successful treatment used for the majority of cases was amlodipine, which lowered systolic blood pressure from 202.5+/-16.8 to 153.2+/-21.6 mmHg (mean+/-SD; n=29) within the first 50 days. Each case was followed for at least three months, or to the end of its natural life, and each cat was re-examined every six to eight weeks. Systolic blood pressure was kept below a target value of 165 mmHg in 58 per cent of cases treated for three months or longer. At the time of writing, 19 of the cases had died or been euthanased with a median treatment time of 203 days, one case was lost to follow-up and 10 cases were still alive, nine of which had been treated for six months or more. Amlodipine can be used for long-term control of feline systemic hypertension.

Survival of cats with naturally occurring chronic renal failure: effect of dietary management

Fifty cats with naturally occurring stable chronic renal failure (CRF) were entered into a prospective study on the effect of feeding a veterinary diet restricted in phosphorus and protein with or without an intestinal phosphate binding agent on their survival from initial diagnosis. Twenty-nine cats accepted the veterinary diet, whereas compliance (due to limited intake by the cats or owner resistance to diet change) was not achieved in the remaining 21. At diagnosis, both groups of cats were matched in terms of age, bodyweight, plasma creatinine, phosphate, potassium and parathyroid hormone (PTH) concentrations, packed cell volume and urine specific gravity. Feeding the veterinary diet was associated with a reduction in plasma phosphate and urea concentrations and prevented the increase in plasma PTH concentrations seen in cats not receiving the diet. Cats fed the veterinary diet survived for longer when compared with those that were not (median survival times of 633 versus 264 days). These data suggest that feeding a diet specifically formulated to meet the needs of cats with CRF, together with phosphate binding drugs if required, controls hyperphosphataemia and secondary renal hyperparathyroidism, and is associated with an increased survival time.

Effect of dietary phosphate restriction on renal secondary hyperparathyroidism in the cat

Twenty-three cats with stable chronic renal failure (CRF) were examined in a prospective study of the effects of feeding a veterinary diet restricted in phosphorus and protein with or without an intestinal phosphate binding agent (aluminium hydroxide) on plasma phosphate and parathyroid hormone (PTH) concentrations. Fifteen cats accepted the veterinary diet; compliance was not achieved in the remaining eight (due to limited intake by the cats or owner resistance to diet change). Feeding the veterinary diet was associated with a significant fall in plasma phosphate and PTH concentrations by five months, with only two cats requiring aluminium hydroxide therapy. The maximum decrease in plasma PTH concentration was not associated with a significant change in plasma 1,25 dihydroxycholecalciferol concentration. Euparathyroidism was achieved in eight cats. Conversely, in cats with CRF fed proprietary diets over the same time period, mean plasma PTH concentrations did not change significantly; indeed, in seven of the eight cats, PTH concentrations increased. Dietary therapy alone or in combination with intestinal phosphate binders does reduce PTH concentrations in cats with CRF and, when effective control of phosphate intake is achieved, plasma PTH can be normalised.

Studies of oral malodor in the dog

We compared currently used methods for assessing oral malodor and found a significant, positive correlation between the concentration of volatile sulfur compounds (VSCs) in breath and the human perception of malodor, but only within a limited range of VSC production. Daily tooth-brushing from an early age maintains a low and consistent level of oral malodor that does not differ significantly throughout the day. In contrast, dogs with elevated concentrations of VSC production suffer from the highest level of malodor early in the morning, prior to feeding and daily activities. Even in older dogs, periodontal therapy can result in a substantial reduction of oral malodor that remains significantly below pre-treatment values for up to 3 months after treatment.

Oral malodor and its relevance to periodontal disease in the dog

Oral malodor has been studied extensively in humans but very little work has been done in dogs where it constitutes a significant problem. In this article we review its causes, methods of detection, and strategies for preventing it. Oral malodor arises from microbial metabolism of exogenous and endogenous proteinaceous substrates in the oral cavity and is exacerbated by periodontal disease and poor oral hygiene. Gram negative bacteria found in plaque, in periodontal pockets, and on the dorsum of the tongue are primarily responsible for odor production. The volatile sulfur compounds (VSCs) hydrogen sulfide and methyl mercaptan, which are produced by these bacteria, are not only primarily responsible for the objectionable odor but have been implicated in the pathogenesis of periodontal disease. Assessment of malodor by portable sulfide monitors correlates well with organoleptic measurements. Reduction of microbial load in the oral cavity due to good oral hygiene practices (such as tooth-brushing) or by the use of appropriate diets or chews may reduce malodor formation.

Effect on canine oral health of adding chlorhexidine to a dental hygiene chew

A study to compare the effect of a dental hygiene chew with or without 0.2% chlorhexidine on the development of gingivitis and the accumulation of dental deposits was performed using 11 small dogs. Confirming previous data, the daily addition of a standard chew to a dry diet resulted in significantly less gingivitis and calculus after 3 weeks compared with feeding the dry diet alone. Addition of chlorhexidine to the chew made no difference to the degree of gingivitis or the amount of calculus that accumulated, but did result in significantly less plaque accumulation after 3 weeks. The abrasiveness of the chew, rather than the antibacterial activity of chlorhexidine, is likely to have contributed the most to the maintenance of oral health in dogs with mild gingivitis.

Effect of two dietary regimens on gingivitis in the dog

The effect of two commercially available dietary regimens on the development of gingivitis and the accumulation of dental plaque, calculus and stain in the dog were studied. One regimen consisted of feeding an oral hygiene chew and a standard dry diet. The other was based on a specifically designed oral care dry main meal. The study was conducted using 15 dogs in a two period, parallel cross-over design. Each period consisted of a one week pretest phase followed by a three week test phase. During the test phase, gingivitis and plaque were measured after one week and gingivitis, calculus, stain and plaque were measured after a further two weeks. Comparison of the two regimens showed that there were equal amounts of gingivitis, plaque and calculus by the end of the study. There was significantly more stain and significant loss in bodyweight when the main meal was fed. The role of dietary modification in the maintenance of periodontal health is discussed.

The role of tooth-brushing and diet in the maintenance of periodontal health in dogs

Tooth-brushing every other day did not maintain clinically healthy gingivae in dogs. The daily addition of a dental hygiene chew to a regimen of tooth brushing every other day reduced the gingivitis scores and reduced the accumulation of dental deposits (plaque, calculus and stain). Daily tooth-brushing should be the recommendation to the dog owner irrespective of dietary regimen. Providing a dental hygiene chew daily seems to give an added health benefit when tooth-brushing is less frequent, and provides the pet owner with a useful adjunct for homecare.

Effect of dosing vehicle on the dermal absorption of fluazifop-butyl and fomesafen in rats in vivo

One important factor which may influence the extent and rate of percutaneous absorption is the dosing vehicle. The purpose of the experiments described was to compare the effect of dosing vehicles of different polarities on the absorption of two herbicides across rat skin in vivo. Rats were dosed dermally with either fluazifop-butyl (logP(oct) 4.5) or fomesafen sodium salt (logP(oct) -1.2) in propylene glycol (PG), octanol (OCT), or ethyl decanoate (ED), and the amount of radioactivity excreted in urine was determined. Absorption rates were estimated from the urinary excretion data and from blood kinetic data derived from intravenously dosed rats. For fluazifop-butyl the average rate of absorption (x10(-2) micrograms/hr-1 +/- SE) was not greatly influenced by the dosing vehicle (OCT, 2.94 +/- 0.08; ED, 3.66 +/- 0.10; PG, 3.95 +/- 0.32) despite relatively large differences in solubility (PG, 38 mg/ml; OCT, and ED, > 600 mg/ml). These results were consistent with the finding that there was at most only a twofold difference in the epidermal membrane:vehicle partition coefficients (km). In contrast, the absorption rate of fomesafen from PG (1.98 +/- 0.04) was approximately half that of ED (3.98 +/- 0.06) and OCT (4.49 +/- 0.08) for the first 30 hr after application and was in keeping with solubility data (PG, 638 mg/ml; OCT, 12 mg/ml; ED, < 10 mg/ml). At later time points the absorption of fomesafen from PG increased; this is discussed in relation to the penetration-enhancing properties of PG.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for redox cycling of diquat in rat small intestine

It has previously been established that acute diquat (1,1'-ethylene, 2,2'-bipyridilium) toxicity in the rat is associated with stimulation of net fluid secretion into the gastrointestinal tract. We have examined the possibility that the mechanism of diquat toxicity in the small intestine involves redox cycling of the bipyridyl leading to a disturbance of biochemical function and oxidative stress. Experiments performed in vitro showed that diquat (10 microM to 1 mM) produced an increase in activity of the pentose phosphate pathway in rat small intestinal tissue slices, suggesting that there was oxidation of NADPH even at concentrations of diquat which do not cause intestinal fluid secretion in anaesthetized rats. When the effect of diquat on pentose phosphate activity was measured in rats in situ at a dose which causes maximal fluid secretion [50 mM diquat dibromide (DQBr2)], production of 14CO2 from [1-14C]-glucose increased by 278 +/- 28% (N = 4) within 1 hr of exposure to diquat. Under these same conditions, the tissue content of NADPH in the proximal small intestine was significantly depleted, though there was no corresponding increase in NADP+ concentration. Diquat had no effect on tissue concentrations of either the reduced or oxidized forms of NAD. It is likely that NADPH oxidation at low diquat concentrations can be adequately compensated for by mechanisms within the tissue which protect against oxidative stress. However, the data also suggest that diquat-induced fluid secretion in the rat small intestine is associated with redox cycling of bipyridyl leading to depletion of NADPH.

Comparison of two methods for determining the toxicokinetics of fluazifop-butyl after intravenous dosing in rats

1. We have described and compared the use of two blood sampling techniques to measure the kinetics of fluazifop-butyl, a selective herbicide. Following intravenous administration of radiolabelled compound, blood samples were collected from female rats either by tail vein puncture or from chronically implanted catheters inserted in tethered rats. Urine samples were also collected from tethered animals. 2. Both techniques indicate that fluazifop-butyl is rapidly eliminated from blood into urine (t(1/2)3-4.5 h) and the overall blood concentration profiles were comparable between the two methods. However, by using cannulated rats, kinetic data were obtained from individual animals, providing evidence of inter-animal variation and allowing compartmental and statistical analysis. 3. The tethered rat technique is relatively simple and reliable. Compared to tail vein bleeding, results obtained from cannulated animals are more informative, providing comprehensive data from a small number of rats. It is therefore the preferred method for our kinetic based research studies using compounds known to exhibit multicompartmental elimination kinetics.

Diquat-induced intestinal secretion in the anaesthetized rat

1. Diquat (1,1'-ethylene-2,2'-bipyridilium) is a non-selective desiccant herbicide which, when administered orally to mammalian species, causes significant secretion of fluid into the lumen of the gastrointestinal tract. In order to characterize this secretory response in more detail the effect of sublethal doses of diquat dibromide (DQBr2) on intestinal secretion was investigated in vivo in the jejunum of anaesthetized rats. 2. Ligated segments of jejunum (10 cm) which were prepared in groups of up to five animals were filled with 500 microliters of isosmotic DQBr2 solutions with concentrations ranging from 1-100 mM and maintained in the anaesthetized rat for 1, 2 or 3 h; in control experiments a solution of 100 mM NaBr was used. 3. It was found that while all of the fluid instilled into the segments was absorbed in the control experiments, there was both a dose- and time-dependent secretory response to DQBr2. Maximal fluid secretion occurred after treatment with 50 mM DQBr2 for 3 h. 4. Histological assessment of the jejunum revealed an increase in cell exfoliation and evidence of luminal distension after incubation with DQBr2. However, no structural damage to the mucosa could be seen to account for the fluid secretion. 5. The model described provides a quantitative means of evaluating intestinal secretion and may be used for elucidating the mechanism by which diquat alters fluid transport processes.

The effect of E. coli STa enterotoxin on the absorption of weakly dissociable anti-malarial drugs from rat intestine in vivo

1. The effect of E. coli heat stable (STa) enterotoxin on the absorption of radiolabelled anti-malarial weak bases and their appearance in peripheral blood was assessed in vivo by a recirculation procedure in rat intestinal loops. 2. Enterotoxin increased the jejunal disappearance of quinine (P less than 0.05), trimethoprim (P less than 0.05), proguanil (P less than 0.05) and chloroquine (P less than 0.001) and left pyrimethamine disappearance unaltered. Peripheral blood levels of trimethoprim (P less than 0.02) and proguanil (P less than 0.05) were higher after STa exposure. 3. In the ileum, enterotoxin increased the luminal disappearance (P less than 0.05) and peripheral blood appearance (P less than 0.001) of chloroquine. The luminal disappearance rate of trimethoprim was reduced (P less than 0.05) and that of pyrimethamine unchanged. 4. The increased jejunal absorption of the anti-malarial drugs occurred despite STa causing a reduction in the amount of net fluid absorption. It seems likely that the enhanced absorption with STa exposure is related to the effect of STa on the microclimate pH. An elevation in the microclimate pH would increase the amount of undissociated weak base available for non-ionic diffusion. 5. The favourable elevation of microclimate pH by STa seemed to be outweighted by the reduced fluid absorption in the ileum. Only chloroquine still showed enhanced absorption in the ileum and this may have been because unlike the other antimalarial drugs, chloroquine has two dissociable groups likely to be affected by the mucosal surface pH changes.

Water permeability of acinar cell membranes in the isolated perfused rabbit mandibular salivary gland

1. The diffusive water permeability of epithelial cell membranes in the perfused rabbit mandibular salivary gland was measured at 37 degrees C by a 1H nuclear magnetic resonance relaxation method using an extracellular relaxation reagent, gadolinium diethylenetriaminepentaacetic acid (Gd(DTPA)). 2. In glands perfused with a HEPES-buffered solution containing 10 mmol l-1 Gd(DTPA), the spin-lattice (T1) relaxation of the water protons showed two exponential components. The water compartment responsible for the slower component corresponded in magnitude to 71 +/- 5% of the wet weight of the gland, and was attributed to the exchangeable intracellular water of the acinar cells. 3. The rate constant for water efflux from the cells was estimated to be 4.1 +/- 0.1 s-1 which would be consistent with a diffusive membrane permeability (Pd) of approximately 3 x 10(-3) cm s-1. Stimulation with acetylcholine (10(-6) mol l-1) did not cause any detectable change in membrane water permeability. 4. Since the basolateral membrane probably provides the main pathway for water efflux, the osmotic water permeability of this barrier (expressed per gland) was estimated to be less than 6.2 cm3 s-1. This would be insufficient to account for the generation of a near-isosmotic fluid at the flow rates observed during secretion, and suggests that a substantial fraction of the flow of water occurs via a paracellular route.

Electrodes for 24 hours pH monitoring--a comparative study

Three pH electrodes in clinical use were examined--(1) antimony electrode with remote reference electrode (Synectics 0011), (2) glass electrode with remote reference electrode (Microelectrodes Inc. MI 506) and (3) combined glass electrode with integral reference electrode (Radiometer GK2801C). In vitro studies showed that both glass electrodes were similar and superior to the antimony electrode with respect to response time, drift, and sensitivity. The effect of the siting of the reference electrode on the recorded pH was examined in five human volunteers. The pH reading using a remote skin reference electrode was higher by a mean of 0.3 pH units (range 0.0-0.6) in the stomach, lower by 0.65 pH units (0.5-0.8) in the duodenum and lower by 0.3 pH units (0.0-0.6) in the oesophagus than that simultaneously obtained with an intraluminal reference electrode. Buccal reference electrodes gave similar readings to skin. Combined reference and glass pH electrodes are recommended for 24-hour ambulatory pH monitoring.

Measurement of jejunal surface pH in situ by plastic pH electrode in patients with coeliac disease

Attaching plastic pH electrodes to a Crosby capsule provides a means of measuring mucosal surface pH in the small intestine during jejunal biopsy. Plastic electrodes, with operating characteristics comparable to glass electrodes within the physiological pH range, were selected because of their mechanical flexibility. The sensing tip can be placed close to the capsule aperture to facilitate contact with the intestinal mucosa. Using this system, the jejunal mucosal surface pH was found to be 5.97 +/- 0.07 in 15 control subjects. In contrast, 13 coeliac patients had a significantly (p less than 0.001) higher jejunal surface pH of 6.73 +/- 0.15, subdivisible into 4 untreated patients with a mean value of 6.95 +/- 0.33 and 9 patients on a gluten-free diet with a mean value of 6.63 +/- 0.15, both higher (p less than 0.01, p less than 0.005) than the control value. An elevated jejunal surface pH in coeliac disease was associated with partial or subtotal villous atrophy and with low brush border enzyme activities. Confirming previous in vitro findings, the elevated surface pH in coeliac jejunum may affect digestive and absorptive processes occurring at the brush border.

Plastic pH electrodes for the measurement of gastrointestinal pH

Plastic electrodes have been developed for measuring pH in the human gastrointestinal tract. The electrodes have a plastic hydrogen ion sensitive membrane sealed to a length of fluid filled PVC tubing. Two recently developed hydrogen ion sensitive ligands have been examined. Their operational characteristics have been described. These electrodes have an electrical response of 52 to 58 mV/pH unit change in the range pH 4-9, with a diminished response outwith this range. They have a low resistance value and a fast response time of one second to reach 90% of their maximum response. The electrodes can be passed down the biopsy channel of an endoscope to obtain mucosal pH readings under direct vision. Readings obtained in this way using plastic electrodes are comparable to those obtained with glass electrodes. Alternatively, these electrodes can be joined to a Crosby capsule, allowing continuous recording of mucosal pH through to the jejunum during jejunal biopsy procedures. These electrodes can be used repeatedly or may be acceptable as inexpensive disposable items for sterile clinical use.