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Biomedical subjects

Y Kagaya

Publications and source records attributed to Y Kagaya.

41 records · Page 3Linked to original sources
PubMed1992

Endothelial modulation of porcine coronary microcirculation perfused via immature collaterals.

Porcine hearts have relatively few native collateral vessels and lack the propensity to develop normal perfusion to the collateral-dependent myocardium. To examine microvascular responses in the collateral-dependent region, collateral vessels were stimulated in pigs by the Ameroid constrictor technique. After 4-7 wk, isolated microarterial vessels (90-170 microns ID) were studied in a pressurized (40 mmHg), no-flow state. Microvessels from noninstrumented pigs were used as controls for vascular studies. Although myocardium in the collateral-dependent region showed minimal evidence of infarction, percent systolic shortening was reduced at rest and after pacing compared with myocardium in the normally perfused region. Relaxations to the receptor-mediated endothelium-dependent agents ADP and bradykinin were impaired in collateral-dependent coronary microvessels. Relaxations to the calcium ionophore A23187, which acts through a non-receptor-mediated mechanism, were similar in control and Ameroid microvessels. Relaxations to the endothelium-independent agent sodium nitroprusside were markedly enhanced in microvessels from the collateral-dependent region compared with microvessels from control hearts. In conclusion, receptor-mediated endothelium-dependent relaxation is impaired and endothelium-independent relaxation to sodium nitroprusside is enhanced in microvessels from myocardium perfused by immature collateral vessels.

Animals↗
PubMed1990

Effects of long-term pressure overload on regional myocardial glucose and free fatty acid uptake in rats. A quantitative autoradiographic study.

To investigate the effects of long-term pressure overload on regional myocardial substrate use, we performed quantitative autoradiography using 2-deoxy-D-[U-14C]glucose (14C-DG) and beta-methyl[1-14C]heptadecanoic acid (14C-BMHDA) in conscious rats with a 10-week ascending aortic constriction. Heart weight/body weight ratio increased by 27% in aortic-constricted rats as compared with sham-operated rats (p less than 0.01). Myocardial 14C-DG uptake increased (258 +/- 63 vs. 144 +/- 41 nCi/g, p less than 0.01, n = 6 for each group); however, 14C-BMHDA extraction decreased (251 +/- 69 vs. 342 +/- 75 nCi/g, p less than 0.05, n = 7 for each group) in aortic-constricted rats as compared with sham-operated rats. In sham-operated rats, both 14C-DG and 14C-BMHDA uptakes were higher in the left ventricular anterior and lateral walls as compared with the posterior wall or the interventricular septum. In aortic-constricted rats, 14C-DG uptake also increased in the interventricular septum, as well as in the left ventricular anterior and lateral walls, as compared with the posterior wall. There was, however, no regional difference in 14C-BMHDA extraction among these four regions. Myocardial blood flow distribution determined by 4-[N-methyl-14C]iodoantipyrine or myocyte width showed no regional variations among the four regions, either in aortic-constricted or sham-operated rats. Regional interstitial fibrosis was small in either group. The present study suggests that myocardial substrate uptake is altered nonhomogeneously, and that the nonhomogeneity is not because of regional variations in blood flow distribution, myocyte hypertrophy, or interstitial fibrosis. The results of angiotensin II-induced acute pressure overloading in other sham-operated rats, in which a remarkable increase in myocardial 14C-BMHDA extraction (n = 3, p less than 0.01) and no difference in 14C-DG uptake (n = 3) as compared with normotensive sham-operated rats were elicited, suggest that the findings in aortic-constricted rats are not direct responses to increased left ventricular pressure itself but rather should be explained by still unknown factors related to prolonged pressure overload.

Acute Disease↗
PubMed1987

Myocardial imaging using 11C-CoQ10 with positron emission tomography.

The potential of 11C-labeled coenzyme Q10(CoQ10) as a myocardial imaging tracer was explored with positron emission tomography (PET). Serial myocardial imaging studies were performed using 11C-CoQ10, 45Ti-diethylenetriaminepentaacetic acid (45Ti-DTPA), and 2-deoxy-2-[18F]fluoro-D-mannose (18FDM) in the same dog. Cross sectional images of the heart with 11C-CoQ10 showed relatively high radioactivity in the blood pool, when compared with images taken with 18FDM. However, when the blood spillover of radioactivity is adequately corrected with 45Ti-DTPA data, it was found that 11C-CoQ10 accumulated in the myocardium with time.

Animals↗
PubMedDate not supplied

Interaction between sarcomere and mitochondrial length in normoxic and hypoxic rat ventricular papillary muscles.

We hypothesized that the mitochondrial length may be altered according to changes in the sarcomere length, and that this relationship may be affected by exposure to hypoxia. Rat ventricular papillary muscles were isolated and immersed in normoxic or hypoxic solutions for 10 min. Sarcomeres of various lengths were obtained by fixing the papillary muscles in a slack or stretched state, or after exposure to a contracture solution containing saponin and CaCl(2). The mitochondrial length measured using electron microscopy significantly correlated to the length of the adjacent sarcomere in both the normoxic (n=767) and hypoxic (n=1145) groups (P<.0001). The slope of the regression line, however, was significantly less steep, and its intercept was significantly larger in the hypoxic group than in the normoxic group (analysis of covariance). When we analyzed the mitochondrial lengths among the three sarcomere-length subgroups (<1.5, 1.5-2.0, and >2.0 microm), the mitochondrial length was significantly shorter in the hypoxic condition than in the normoxic condition at sarcomere lengths greater than 2.0 microm. Staining for desmin, the major muscle-type intermediate filament, the longitudinal system of which connects the mitochondria with the Z bands of sarcomeres, showed a clear cross-striation pattern in both papillary muscles with and without the exposure to hypoxia, suggesting that desmin was preserved after the exposure to hypoxia. These data indicate that the mitochondrial length changes according to changes in the sarcomere length, suggesting the possible role of mitochondria as an internal load against myocyte contraction. It is also suggested that mitochondria exposed to hypoxia may be more resistive to both compression and stretch in a longitudinal direction than those in the normoxic condition.

Animals↗