Development of an experimental rat model of hyperammonemic encephalopathy and evaluation of the effects of rifaximin.

Hepatic encephalopathy (HE) is a neuropsychiatric syndrome associated with hepatic dysfunction. However, the precise mechanism of HE is unclear. To elucidate the mechanism, we developed a new rat model of HE with coma using a combination of subcutaneous splenic transposition, partial hepatectomy and portal vein stenosis. In this model, blood ammonia levels increase in the postcaval vein over time and markedly increase in the cerebrospinal fluid (CSF). The distribution of ammonia in the various blood vessels in the HE model suggests that the origin of peripheral blood and CSF ammonia is the mesenteric veins that drain blood from the gastrointestinal tract. Behavioral analysis revealed decreased pain response, increased passivity, and decreased pinna and corneal reflexes, followed by the development of coma. The development of coma in this model was frequent and reproducible. Increased S100 calcium-binding protein B (S100B: a biomarker for brain injury) in venous blood, as well as damaged brain tissue, increased intracranial pressure and cerebral edema were observed in rats with coma. A very high correlation was observed between the blood ammonia concentration in the postcaval vein and the onset of coma. Rifaximin, a poorly absorbed antibiotic that targets gut flora, significantly improved symptoms of HE. Based on these results, our rat model appears to reflect the pathological state of HE associated with acute liver failure and may be a useful model for analysis of hyperammonemic encephalopathy.

Spleen-specific development of germinal centers in rats treated with antithyroid drugs.

The antithyroid drugs (ATDs) methimazole (MMI) and propylthiouracil (PTU) have been used for treatment of hyperthyroidism for more than several decades, despite the fact that they are associated with adverse drug reactions that are thought to be autoimmune mediated. We therefore examined histopathologic responses in the immune system in male and female rats given MMI (2, 20 and 200 mg/kg/day, p.o., in experiment 1; 200 mg/kg/day, p.o., in experiment 3) or PTU (25 and 250 mg/kg/day, p.o., in experiment 2; 200 mg/kg/day, p.o., in experiment 3) for two weeks. In experiments 1 and 2, highest doses of MMI and PTU induced histopathologic changes in the spleen consistent with those in experiment 3 without any changes in the other peripheral lymphoid organs and tissues. In experiment 3, histopathological evaluation of the spleen along with hematological and bone marrow examinations were performed. In both male and female rats, MMI or PTU induced histopathological changes in the spleen characterized by development of germinal centers and an increase in the number of IgG-positive plasma cells in the red pulp; these changes were most prevalent in the MMI-treated female rats. Total red and white blood cell counts were decreased in the MMI-treated male and female rats; lymphocytes and monocytes were lower in male and female rats, respectively. Bone marrow nucleated cells were significantly lower in the MMI-treated males. This is the first study to demonstrate that ATDs induce spleen specific B-cell reactions in rats.

Histopathological and immunocytochemical studies of chlormadinone acetate on the rat prostate.

In order to confirm the relationship between glutathione-peroxidase (GSH-PO) and testosterone action in rat ventral prostate, we have studied the immunocytochemical localization of GSH-PO in glandular epithelial cells of rat ventral prostate after chlormadinone acetate CMA) as antiandrogen. In the control rat ventral prostate, GSH-PO was predominantly observed in the glandular epithelial cells and intracellular localization of GSH-PO was exclusively observed in the cytoplasmic matrix near the rough endoplasmic reticulum and it was occasionally noted as small granular structure. In CMA-administered rats, the glandular epithelial cells of the ventral prostate were markedly atrophic. The intensity of GSH-PO staining in the glandular epithelial cells was markedly decreased. Immunoelectron microscopically, GSH-PO-positive granules were hardly seen in the atrophic glandular epithelial cells. These findings strongly suggest that loss of GSH-PO staining in the glandular epithelial cells of the rat ventral prostate treated with CMA a s antiandrogen is thought to be caused by inhibition of testosterone action, and that its staining pattern is useful for the effect of antiandrogens or antiprostatic agents on prostate.

Immunohistochemical and biochemical studies in 4-aminopyrazolopyrimidine (4-APP)-induced fatty liver.

Four-aminopyrazolopyrimidine (4-APP)-induced fatty livers were studied immunohistochemically and biochemically. Immunohistochemical localization of glutathione-peroxidase (GSH-PO) in control rat liver was predominantly observed in the hepatocytes of portal zones of the hepatic lobules. After 3 days of 4-APP administration, the intensity of GSH-PO staining was weaker than that of control. Especially, this tendency was predominantly observed in portal zones of the hepatic lobules. Biochemcally, lipid peroxide levels measured by thiobarbituric acid method in the liver homogenates were markedly increased following 4-APP administration. However, glutathione-peroxidase (GSH-PO) activity in the same homogenates was decreased. Based on our data, we strongly suggested that pathogenesis of 4-APP induced-fatty liver may be due to uncontrolled free radical formation, peroxidation of lipids, and an associated lipid accumulation in the liver.