Masamitsu Hasegawa

Change in the static rheological properties of the aorta in Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits with progress of atherosclerosis

The rheological properties of the arterial wall have intimate connections with the fine structure of the wall. Alteration in fine structure due to cardiovascular disease, such as atherosclerosis, could affect the rheological characteristics of the wall. The present study was designed to investigate changes in the static rheological properties of the aorta in Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits aged 10-12, 22-24 and 34-36 months in relation to histological alteration of the wall due to progression of atherosclerosis with age. Circumferential wall strips were excised from the ascending, proximal descending thoracic and proximal abdominal aortas and their stress/strain relationship was recorded. Tensile force of the wall showed a slight but insignificant decrease in the KHC rabbit group aged 10-12 months compared to that in the age-matched control group in the proximal thoracic aorta and increased significantly with ageing in the KHC rabbits in these aortic regions mainly at medium and high strain ranges. Wall stress was significantly smaller in the 10-12 months old KHC rabbit group than in the age-matched control group in the proximal thoracic and proximal abdominal aortas and increased significantly with ageing in the KHC rabbit groups chiefly at medium and high strain ranges. Incremental elastic modulus determined at 50% stretching of the initial length of the wall strip was also significantly lower in the KHC rabbit group aged 10-12 months in comparison to that in the age-matched control group and increased significantly with ageing in the KHC rabbit group. The intima thickened severely with abundant foam cells in the KHC rabbits aged 10-12 months. With increasing age, collagen and elastin fibres showed signs of gradual proliferation among the foam cells. The aortic wall in KHC rabbits was viscoelastic in the relatively early stage of atherosclerosis due to abundant foam cells, and thereafter increased in stiffness gradually with fibrous proliferation and calcification. We can conclude that the static rheological properties of the atherosclerotic aortic wall changed in association with alteration in the microstructure of the wall with progression of atherosclerosis.

Region dependency of pulse wave velocity in the atherosclerotic aorta of the Kurosawa and Kusanagi-hypercholesterolemic (KHC) rabbit

Abstract We investigated the relation of regional foot-to-foot pulse wave velocity (PWV) along the atherosclerotic aorta to the fractional lesioned area at various aortic regions in Kurosawa and Kusanagi-Hypercholesterolemic (KHC) rabbits aged 10–12 months. The PWV was determined at 8 positions in the aorta and iliac artery from the time delay between two pulse waves and the distance between two micromanometers in situ. The fractional lesioned area was calculated in 7 aortic regions sectioned at 7 positions in which pulse waves were recorded. The PWV increased with passage through the aortic arch and with increasing distance from the heart, decreased in the thoracic aorta, and moderately increased again in the abdominal aorta. The fractional lesioned area was maximal in the aortic arch, reduced in the thoracic aorta, and moderately increased again in the proximal abdominal aorta. In the middle and distal abdominal aorta, the fractional lesioned area was markedly reduced, to below 10% compared with the entire area of the aortic segment. We conclude that the regional PWV in the atherosclerotic aorta is dependent on the extent of the lesioned area at the different aortic segments through which the pulse wave is propagated.

Spaceflight Affects Postnatal Development of the Aortic Wall in Rats

We investigated effect of microgravity environment during spaceflight on postnatal development of the rheological properties of the aorta in rats. The neonate rats were randomly divided at 7 days of age into the spaceflight, asynchronous ground control, and vivarium control groups (8 pups for one dam). The spaceflight group rats at 9 days of age were exposed to microgravity environment for 16 days. A longitudinal wall strip of the proximal descending thoracic aorta was subjected to stress-strain and stress-relaxation tests. Wall tensile force was significantly smaller in the spaceflight group than in the two control groups, whereas there were no significant differences in wall stress or incremental elastic modulus at each strain among the three groups. Wall thickness and number of smooth muscle fibers were significantly smaller in the spaceflight group than in the two control groups, but there were no significant differences in amounts of either the elastin or collagen fibers among the three groups. The decreased thickness was mainly caused by the decreased number of smooth muscle cells. Plastic deformation was observed only in the spaceflight group in the stress-strain test. A microgravity environment during spaceflight could affect postnatal development of the morphological and rheological properties of the aorta.