Biomedical subjects

K Miyanaka

Publications and source records attributed to K Miyanaka.

6 recordsLinked to original sources

PubMed2000

Induction of endothelial nitric-oxide synthase in rat brain astrocytes by systemic lipopolysaccharide treatment.

In the brain, three isoforms of nitric oxide (NO) synthase (NOS), namely neuronal NOS (nNOS, NOS1), inducible NOS (iNOS, NOS2), and endothelial NOS (eNOS, NOS3), have been implicated in biological roles such as neurotransmission, neurotoxicity, immune function, and blood vessel regulation, each isoform exhibiting in part overlapping roles. Previous studies showed that iNOS is induced in the brain by systemic treatment with lipopolysaccharide (LPS), a Gram-negative bacteria-derived stimulant of the innate immune system. Here we found that eNOS mRNA is induced in the rat brain by intraperitoneal injection of LPS of a smaller amount than that required for induction of iNOS mRNA. The induction of eNOS mRNA was followed by an increase in eNOS protein. Immunohistochemical analysis revealed that eNOS is located in astrocytes of both gray and white matters as well as in blood vessels. Induction of eNOS in response to a low dose of LPS, together with its localization in major components of the blood-brain barrier, suggests that brain eNOS is involved in early pathophysiologic response against systemic infection before iNOS is induced with progression of the infection.

Animals↗

PubMed2000

Regulation of genes for inducible nitric oxide synthase and urea cycle enzymes in rat liver in endotoxin shock.

Arginine is an intermediate of the urea cycle in the liver. It is synthesized by the first four enzymes of the cycle, carbamylphosphate synthetase I, ornithine transcarbamylase, argininosuccinate synthetase, and argininosuccinate lyase, and is hydrolyzed to urea and ornithine by arginase I, forming the cycle. In endotoxemia shock, inducible nitric oxide (NO) synthase (iNOS) is induced in hepatocytes and arginine is utilized for NO production. Regulation of the genes for iNOS and the urea cycle enzymes was studied using lipopolysaccharide (LPS)-treated rat livers. When rats were injected intraperitoneally with LPS, iNOS mRNA was markedly induced. Cationic amino acid transporter-2 and C/EBPbeta mRNAs were also highly increased. In contrast, mRNAs for all the urea cycle enzymes except ornithine transcarbamylase were gradually decreased and reached 16-28% of controls at 12 h. However, all these enzymes remained unchanged at protein level up to 24 h. In light of these results, we suggest that synthesis of urea cycle enzymes is downregulated and that the protein synthetic capacity is directed to synthesis of proteins required for defense against endotoxemia.

Amino Acid Transport Systems, Basic↗

PubMed2000

Expression and localization of enzymes of arginine metabolism in the rat eye.

PURPOSE: Production of NO may be regulated by argininosuccinate synthetase and argininosuccinate lyase which recycle citrulline to arginine, and by arginase which hydrolyzes arginine to urea and ornithine. Expression of these and related enzymes in rat eye was studied. METHODS: mRNAs for the enzymes were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). Localization of the enzyme proteins and mRNAs was analyzed by immunohistochemistry and in situ hybridization, respectively. RESULTS: In RT-PCR analysis, arginase II (nonhepatic type) mRNA was detected in retina and weakly in cornea, whereas arginase I (hepatic type) mRNA was not detected in any area. mRNAs for argininosuccinate synthetase, argininosuccinate lyase, ornithine aminotransferase and ornithine decarboxylase were present in all areas. In immunohistochemical analysis, arginase II was stained in cornea, epithelium of iris and ciliary process, inner part of neural retina and retinal pigment epithelium. Immunostaining of ornithine aminotransferase resembled that of arginase II. In in situ hybridization, arginase II and ornithine aminotransferase mRNAs were located much as seen with the enzyme proteins. CONCLUSIONS: These results indicate that arginine recycling activity from citrulline is present widely in ocular tissues, whereas expression of arginase II differs among the tissues. We suggest that NO production may be regulated by these enzymes in the cells where NO synthase is colocalized. Colocalization of arginase II and ornithine aminotransferase suggests a role for arginase II in collagen synthesis in the eye.

Animals↗

PubMed1999

Expression of arginase II and related enzymes in the rat small intestine and kidney.

Arginase, which catalyzes the conversion of arginine to urea and ornithine, and consists of a liver-type (arginase I) and a non-hepatic type (arginase II). Arginine is also used for the synthesis of nitric oxide and creatine phosphate, while ornithine is used for the synthesis of polyamines and proline, and thus collagen. Arginase II mRNA and protein are abundant in the intestine (most abundant in the jejunum and less abundant in the ileum, duodenum, and colon) and kidney of the rat. In the kidney, the levels of arginase II mRNA do not change appreciably from 0 to 8 weeks of age. In contrast, arginase II mRNA and protein in the small intestine are not detectable at birth, appear at 3 weeks of age, the weaning period, and their levels increase up to 8 weeks. On the other hand, mRNAs for ornithine aminotransferase (OAT), ornithine decarboxylase, and ornithine carbamoyltransferase (OCT) are present at birth and their levels do not change much during development. Arginase II is elevated in response to a combination of bacterial lipopolysaccharide, dibutyryl cAMP, and dexamethasone in the kidney, but is not affected by these treatments in the small intestine. Immunohistochemical analysis of arginase II, OAT, and OCT in the jejunum revealed their co-localization in absorptive epithelial cells. These results show that the arginase II gene is regulated differentially in the small intestine and kidney, and suggest different roles of the enzyme in these two tissues. The co-localization of arginase II and the three ornithine-utilizing enzymes in the small intestine suggests that the enzyme is involved in the synthesis of proline, polyamines, and/or citrulline in this tissue.

Animals↗

PubMed1999

[Dimethylamine].

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Dimethylamines↗

PubMed1998

Immunohistochemical localization of arginase II and other enzymes of arginine metabolism in rat kidney and liver.

Arginine is a precursor for the synthesis of urea, polyamines, creatine phosphate, nitric oxide and proteins. It is synthesized from ornithine by argininosuccinate synthetase and argininosuccinate lyase and is degraded by arginase, which consists of a liver-type (arginase I) and a non-hepatic type (arginase II). Recently, cDNAs for human and rat arginase II have been isolated. In this study, immunocytochemical analysis showed that human arginase II expressed in COS-7 cells was localized in the mitochondria. Arginase II mRNA was abundant in the rat small intestine and kidney. In the kidney, argininosuccinate synthetase and lyase were immunostained in the cortex, intensely in proximal tubules and much less intensely in distal tubules. In contrast, arginase II was stained intensely in the outer stripes of the outer medulla, presumably in the proximal straight tubules, and in a subpopulation of the proximal tubules in the cortex. Immunostaining of serial sections of the kidney showed that argininosuccinate synthetase and arginase II were colocalized in a subpopulation of proximal tubules in the cortex, whereas only the synthetase, but not arginase II, was present in another subpopulation of proximal tubules. In the liver, all the enzymes of the urea cycle, i.e. carbamylphosphate synthetase I, ornithine transcarbamylase, argininosuccinate synthetase and lyase and arginase I, showed similar zonation patterns with staining more intense in periportal hepatocytes than in pericentral hepatocytes, although zonation of ornithine transcarbamylase was much less prominent. The implications of these results are discussed.

Animals↗