(1/31) The bioavailability, dispostion kinetics and dosage of sulphadimethoxine in dogs.
The disposition kinetics of sulphadimethoxine were studied in six normal beagle dogs after intravenous injection of a single dose (55 mg/kg). The median (range) distribution and elimination half times of the drug were 2.36 (2.06-3.35) hours and 13.10 (9.71-16.50) hours, respectively. Total body clearance of the drug had a median value of 21.7 ml/kg/h and a mean value of 21.4 ml/kg/h. While the overall tissue to plasma level ratio (k12/k21) of the drug was 0.55 after distribution equilibrium had been attained, analogue computer simulated curves showed that at 24 hours the fractions (percentage) of the dose in the central and tissue compartments were 12 and 11%, respectively. The drug was shown, by equilibrium dialysis method, to be highly bound to plasma proteins (greater than 75%) within the usual therapeutic range (50 to 150 mug/ml) of plasma levels. The systemic availability of sulphadimethoxine from the oral suspension was 32.8% (22.5-80.0). Since the absorption half time, 1.87 (0.86-3.22) hours, was considerably shorter than the half-life, 13.10 (9.71-16.50) hours, of the drug, the rate of absorption would have little influence on the dosage regimen. Based on the experimental data obtained, a satisfactory dosage regimen might consist of a priming dose of 55 mg/kg by the intravenous route and maintenance doses of either 27.5 mg/kg of sulphadimethoxine injection given intravenously or 55 mg/kg of the oral suspension administered at 24 hour intervals. The adequacy and duration of therapy will depend upon the clinical response obtained. (+info)
(2/31) Use of antibacterial agents To elucidate the etiology of juvenile oyster disease (JOD) in Crassostrea virginica and numerical dominance of an alpha-proteobacterium in JOD-affected animals.
Since 1988, juvenile oyster disease (JOD) has resulted in high seasonal losses of cultured Eastern oysters (Crassostrea virginica) in the Northeast. Although the cause of JOD remains unknown, most evidence is consistent with either a bacterial or a protistan etiology. For the purpose of discerning between these hypotheses, the antibacterial antibiotics norfloxacin and sulfadimethoxine-ormetoprim (Romet-B) were tested for the ability to delay the onset of JOD mortality and/or reduce the JOD mortality of cultured juvenile C. virginica. Hatchery-produced C. virginica seed were exposed in triplicate groups of 3,000 animals each to either norfloxacin, sulfadimethoxine-ormetoprim, or filter-sterilized seawater (FSSW) and deployed in floating trays on the Damariscotta River of Maine on 17 July 1997. Each week thereafter, a subset of animals from each group was reexposed to the assigned treatment. Repeated immersion in either a sulfadimethoxine-ormetoprim or a norfloxacin solution resulted in a delay in the onset of JOD mortality in treated animals and reduced weekly mortality rates. Weekly treatments with either norfloxacin or sulfadimethoxine-ormetoprim also resulted in a statistically significant reduction in cumulative mortality (55 and 67% respectively) compared to animals treated weekly with FSSW (81%) or those that had received only a single treatment with either norfloxacin, sulfadimethoxine-ormetoprim, or FSSW (77, 84, and 82%, respectively). Bacteriological analyses revealed a numerically dominant bacterium in those animals with obvious signs of JOD. Sequence analysis of the 16S rRNA gene from these bacteria indicates that they are a previously undescribed species of marine alpha-proteobacteria. (+info)
(3/31) Sequential analysis of development of invasive thyroid follicular cell carcinomas in inflamed capsular regions of rats treated with sulfadimethoxine after N-bis(2-hydroxypropyl)nitrosamine-initiation.
A 2-stage thyroid follicular carcinogenesis model in rats initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN) is widely used to detect modifying effects of chemicals on thyroid carcinogenesis. A number of goitrogens are known to strongly promote carcinogenesis, and the carcinomas often originate adjacent to the thyroid capsule and show invasive growth into the capsule or adjacent tissues. To clarify mechanisms of progression to invasive carcinomas, we sequentially evaluated histopathological and immunohistochemical characteristics of thyroids in male F344 rats treated with sulfadimethoxine (SDM, 0.1% in drinking water) for 0-10 weeks beginning 1 week after DHPN initiation (2800 mg/kg body weight, single s.c. injection). In DHPN-SDM-treated rats, multiple focal hyperplasias and adenomas developed in thyroid follicular parenchyma at weeks 4 to 6. Apart from the proliferative lesions, capsular thickening with inflammatory cell infiltration, mainly consisting of macrophages, and migration of follicular epithelium into the capsule were also observed. Focal hyperplasias/adenomas adjacent to the capsule progressively developed to invasive carcinomas at weeks 6 to 10. In thyroid parenchyma, malignant lesions were seldom observed. With SDM-treatment alone, although no neoplastic lesions were observed, capsular thickening with inflammation and epithelial migration resulted in intracapsular residual follicles. Intracapsular residual follicular cells as well as invasive and intrathyroidal carcinoma cells generally showed increased cell proliferative activity, coincidental with cytoplasmic/nuclear positivity for beta-catenin. These results suggested that beta-catenin activation related to capsular inflammation may play a role in development of invasive carcinomas but is insufficient for tumor formation by itself. Whether this is associated with mutations in the beta-catenin gene remains to be clarified. (+info)
(4/31) Specificity of co-promoting effects of caffeine on thyroid carcinogenesis in rats pretreated with N-bis(2-hydroxypropyl)nitrosamine.
The specificity of copromotion effects of caffeine with known goitrogenic factors on thyroid carcinogenesis was examined in rats pretreated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). Male F344 rats were divided into 8 groups, each consisting of 10 animals, and received a single sc injection of 2,800 mg/kg DHPN. From one week after the DHPN initiation, they were given basal diet, iodine deficiency (ID) diet, 500 ppm phenobarbital (PB) solution or 1,000 ppm sulfadimethoxine (SDM) solution with or without 1,500 ppm caffeine feeding for 12 weeks. The caffeine, PB, SDM, and ID treatments significantly (p < 0.05 or 0.01) increased the relative thyroid weights, and the increases with PB or ID were further (p < 0.05 or 0.01) enhanced in combination with caffeine. SDM drastically promoted thyroid carcinogenesis in association with increased serum TSH levels regardless of the caffeine treatment. Thyroid follicular carcinomas and adenomas were more frequently observed in the additional caffeine groups than in the ID alone groups. The incidence and multiplicity of focal thyroid follicular hyperplasias in the ID-treated groups were significantly (p < 0.05 and 0.01) elevated in the case of combination with caffeine. Increases in serum TSH levels with PB or ID were also further enhanced in combination with caffeine. Serum thyroid hormone levels were significantly (p < 0.01) decreased by SDM but significantly (p < 0.05 or 0.01) increased by caffeine, PB or ID. Our results clearly indicate that dietary caffeine at a high dose of 1,500 ppm interacts with ID, but neither SDM nor PB, to promote rat thyroid carcinogenesis although the combined caffeine + PB treatment somewhat affected thyroid weights as well as thyroid hormone levels. (+info)
(5/31) A multifactorial test of the effects of carotenoid access, food intake and parasite load on the production of ornamental feathers and bill coloration in American goldfinches.
(6/31) Chronic intermittent diarrhea in a 14-month-old Abyssinian cat.
A 14-month-old intact, female Abyssinian cat was presented for chronic intermittent diarrhea and bilateral enlargement of the mammary glands. Gastrointestinal coccidiosis was diagnosed; therapy with sulfadi-methoxine was unsuccessful in the elimination of Isospora felis and clinical signs. Infection with Tritrichomonas foetus was diagnosed by fecal polymerase chain reaction (PCR) and successfully treated with ronidazole and dietary modification. (+info)
(7/31) Role of NKX2-1 in N-bis(2-hydroxypropyl)-nitrosamine-induced thyroid adenoma in mice.
(8/31) Lack of modifying effects of prepubertal exposure to acrylamide (AA) on N-methyl-N-nitrosourea (MNU)-induced multi-organ carcinogenesis in F344 rats.
Acrylamide (AA) has been reported to be formed in fried and baked foods with various concentrations, and exposure levels to AA from cooked foods in children are estimated to be higher than those in adults. In order to evaluate the carcinogenicity of AA exposure during childhood, we conducted a medium-term carcinogenicity study with prepubertal administration of AA followed by treatments of a multi-organ-targeted genotoxic carcinogen and a promoting agent for thyroid carcinogenesis in rats. A total of 36 postpartum F344 rats were given drinking water containing AA at 0, 20, 40 or 80 ppm for 3 weeks during the lactation period, and their weaned offspring received the same AA-containing water for 3 more weeks. Offspring were then injected with N-methyl-N-nitrosourea (MNU; 40 mg/kg body weight, i.p.) once at week 7 after birth. Half the animals of the 0 and 40 ppm groups were additionally treated with the anti-thyroid agent sulfadimethoxine (SDM; 125 ppm) in the drinking water thereafter. Offspring were subjected to complete necropsy at week 50. All the major organs and macroscopic abnormalities were excised and examined histopathologically. There was no significant difference in the incidences of hyperplastic and neoplastic lesions in the target organs of AA and/or MNU, such as the brain, spinal cord, pituitary gland, thyroid, adrenal glands, uterus, mammary glands, clitoral gland and tunica vaginalis. In conclusion, no significant modifying actions of AA on MNU-induced multi-organ carcinogenesis were exhibited in any organs of rats when exposed prepubertally under the present experimental conditions. (+info)