Katsutoshi Yamakawa

Nitric Oxide Contributes to the Progression of Myocardial Damage in Experimental Autoimmune Myocarditis in Rats

BACKGROUND Excess amounts of NO produced by an inducible NO synthase (iNOS) in response to cytokines may be cytotoxic and can be destructive to tissue. We investigated the role of NO in the development of myocardial damage and the effects of aminoguanidine (AG), an inhibitor of iNOS, on experimental autoimmune myocarditis in rats. METHODS AND RESULTS Autoimmune myocarditis was induced in 20 Lewis rats by injection of porcine cardiac myosin. Ten of the 20 rats were administered AG. The severity of myocarditis was evaluated by measuring the size of myocarditic lesion and serum levels of CK-MB. Serum NO levels were determined using the Cd/Cu method. Tissue specimens were immunohistochemically examined for iNOS and nitrotyrosine. Histopathological study revealed extensive myocardial destruction and massive inflammatory cell infiltration in AG-untreated rats but only focal mononuclear cell infiltration in AG-treated rats. The mean percent areas of inflammatory lesions in the untreated and treated rats were 56 +/- 13% and 3 +/- 2%, respectively (P < .001). NO levels were 102 +/- 23 and 25 +/- 9 IU/L, respectively (P < .01). CK-MB levels were 68 +/- 13 and 16 +/- 13 nmol/L, respectively (P < .01). Superoxide production as measured with an ex vivo monitoring system was also significantly decreased in the treated rats. Nitrotyrosine relating to the generation of peroxynitrite was detected through immunostaining in the inflammatory lesions of untreated rats but not in those of treated rats. CONCLUSIONS Excess amounts of NO produced by iNOS appear to contribute to the progression of myocardial damage in myocarditis. AG may prove to be useful in the treatment of myocarditis.

Influence of Aortic Impedance on the Development of Pressure-Overload Left Ventricular Hypertrophy in Rats

BACKGROUND Aortic input impedance, which represents LV afterload, is considered to be a major determinant for the development of pressure-overload left ventricular (LV) hypertrophy. METHODS AND RESULTS To test whether the sustained change in aortic input impedance might affect the mode of development of LV hypertrophy, coarctation of either the ascending aorta (G1, n = 13) or suprarenal abdominal aorta (G2, n = 12) was performed over 4 weeks in 6-weeks-old Wistar rats. Although peak LV pressure and total systemic resistance were increased similarly in G1 and G2, time to peak LV pressure was decreased by 24% (P < .01) in G1 compared with G2. The aortic input impedance spectra revealed that the early systolic loading in G1 was characterized by an increase in characteristic impedance, whereas the late systolic loading in G2 was by an augmented arterial wave reflection. G1 showed a smaller increase (P < .01) in either the ratio of LV weight (mg) to body weight (g) or LV wall thickness than G2 after aortic banding. Myocyte diameter was also smaller (P < .05) in G1 (14.3 +/- 0.7 mm) than in G2 (16.1 +/- 1.2 mm). The ex vivo passive pressure-volume relation had a rightward shift in G1 compared with G2, suggesting less concentric LV hypertrophy in G1. CONCLUSIONS The sustained early systolic loading due to the increase in characteristic impedance was accompanied by less concentric, reduced hypertrophy, whereas the sustained late systolic loading due to the augmented arterial wave reflection was accompanied by concentric, adequate hypertrophy.

Cloning of the cDNA encoding human nonmuscle myosin heavy chain-B and analysis of human tissues with isoform-specific antibodies

SummaryPreviously, we reported the sequence of cDNA clones encoding amino acids 63 through 723 of the human nonmuscle myosin heavy chain-B isoform. In this paper, we present the derived sequence of the remaining 1303 amino acids along with 5′ and 3′ untranslated sequences. We made use of the differences between the derived nonmuscle myosin heavy chain-A and-B amino acid sequences to raise isoform-specific antibodies. Immunoblot analysis reveals a differential expression of both myosin heavy chain isoforms in a variety of human adult and foetal tissues and cells. When extracts of human adult aorta were subjected to gel electrophoresis, two distinct Coomassie Blue-stained bands and a fused band were seen migrating at approximately 200 kDa. These bands can be detected with four different specific antibodies recognizing the two different smooth muscle myosin heavy chain isoforms (204 kDa and 200 kDa) and the two different nonmuscle myosin heavy chain isoforms (A and B). Using immunohistochemistry, we confirmed the presence of the four different isoforms in adult and foetal aortas.