Biomedical subjects

V A Davis

Publications and source records attributed to V A Davis.

4 recordsLinked to original sources

PubMed1996

Morphology of the normal human lens.

PURPOSE: To provide a quantitative, morphologic description of differentiated lens fiber cells in all regions of aged normal human lenses. METHODS: Transparent normal human lenses (age range, 44 to 71 years) were examined with correlative transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Vibratome sections allowed examination of internal structures, whereas dissected whole lenses revealed surface characteristics. Additionally, image analysis was used to measure cross-sectional areas of fiber cells. RESULTS: Approximate regional dimensions (percentage of diameter and thickness, respectively) were determined for whole lenses: cortex 16%, 17%; adult nucleus 24%, 21%; juvenile nucleus 12%, 9%; fetal nucleus 45%, 49%; and embryonic nucleus 3%, 4%. Cortical cells were irregularly hexagonal, and the average cross-sectional area measured 24 +/- 9 microns2. Adult nuclear cells were flattened with intricate membranous interdigitations and an area of 7 +/- 2 microns2. Juvenile nuclear cells had an area of 14 +/- 5 microns2. Fetal nuclear cells were rounded with an area of 35 +/- 22 microns2. Embryonic nuclear cells also were rounded and had a variable area of 80 +/- 68 microns2. Fiber cell cytoplasm in all lens regions appeared smooth in texture and homogeneous in staining density. CONCLUSIONS: Both TEM and SEM are necessary to obtain a complete description of fiber cells. Cross-sections of fibers give new insights into the lamellar organization of the lens, indicating that each region has characteristic cell shapes and sizes. Furthermore, average dimensions were used to demonstrate that the number of cells and approximate growth rates vary significantly between adjacent regions.

Adult↗

PubMed1995

Localization of aortic disease is associated with intrinsic differences in aortic structure.

PURPOSE: While localization of atherosclerosis and aneurysms to the infrarenal aorta has been attributed, in part, to hemodynamic factors, anatomic differences between the proximal and the distal aorta may also be important. Our purpose was to determine the changes in content and organization of major structural proteins (elastin and collagen) throughout the normal human aorta. METHODS: Biochemical analysis for desmosine-isodesmosine (elastin) and hydroxyproline (collagen) content was done by HPLC on complete 1-cm transverse rings removed from the ascending and descending thoracic aorta and abdominal supraceliac, suprarenal, and midinfrarenal aorta. Elastin and collagen content was normalized to lumenal surface area and compared by ANOVA: Light microscopy and optical micrometry were used to determine changes in intimal, medial, and adventitial thickness and number of elastin lamellae at each level. RESULTS: Both collagen/cm2 and elastin/cm2 decrease from the proximal to distal aorta. Collagen content did not differ among the three abdominal segments, but there was a 58% decrease in elastin between the suprarenal and the infrarenal aorta. The proportion of elastin and collagen does not differ throughout the aorta except in the infrarenal aorta where there is decreased elastin relative to collagen. CONCLUSION: Collagen and elastin in the distal aorta bear an increased load as compared to the proximal aorta. The infrarenal aorta differs biochemically and histologically from the remainder of the aorta. A decrease in infrarenal elastin without a corresponding decrease in collagen may effect the compliance and integrity of the distal aorta. These anatomic differences may be important in predisposing the infrarenal aorta to atherosclerosis and aneurysm formation.

Adult↗

PubMed1994

Elastin is increased in abdominal aortic aneurysms.

The decrease in elastin concentration in abdominal aortic aneurysm (AAA) has been ascribed to elastolysis. The discordant response of the elastin and collagen genes in AAA suggests a different explanation: dilution of elastin because of higher levels of synthesis of collagen and other matrix proteins. The purpose of this study was to determine circumferential content of elastin, collagen, and total protein in aneurysmal (AAA), atherosclerotic, and normal (NL) infrarenal aorta. Standard serial extraction techniques of complete 1-cm rings of midinfrarenal aortic tissue were used to remove soluble protein, calcium, and lipids. Hydroxyproline (collagen), desmosine/isodesmosine (elastin), and total amino acid (total protein) content were determined by amino acid analysis. Means values (+/- SEM) were compared by ANOVA. Circumferential content of desmosine/isodesmosine was increased 2.5-fold in AAA compared to NL (P < 0.05). Collagen and total protein were increased 5.7- and 4.7-fold, respectively (P < 0.05). There was a high degree of correlation between circumference and collagen content (r = 0.89). These data demonstrate that significant synthesis of matrix proteins accompanies aortic dilatation. While both elastin and collagen are increased, there is a much greater increase in circumferential collagen content than elastin content. These data do not preclude proteolysis as a factor in AAA but suggest that the decrease in elastin concentration results from dilution of elastin by a greater increase in the synthesis of other matrix proteins and that synthesis is an important factor in AAA formation.

Adult↗

PubMed1994

Abdominal aortic aneurysms are associated with altered matrix proteins of the nonaneurysmal aortic segments.

PURPOSE: Abdominal aortic aneurysms (AAA) are associated with diffuse arteriomegaly and peripheral aneurysms, suggesting a generalized process. Elastin and collagen are the key structural proteins of the aorta, and their relative content is markedly altered in tissue from AAA. Our purpose was to investigate elastin and collagen content in the proximal, nonaneurysmal segments of aortas with infrarenal AAA. METHODS: After extraction of lipid, calcium, and soluble proteins, hydroxyproline (collagen) and desmosine-isodesmosine (elastin) contents were determined by high-performance liquid chromatography in the ascending and descending thoracic, supraceliac, and suprarenal aorta. By repeated measures of analysis of covariance, collagen was found to be increased throughout the aorta in AAA as compared with normal aorta or aorta with atherosclerotic occlusive disease. This difference remained significant when adjustments were made for group differences in age and degree of atherosclerosis. This increase in collagen content results in a dilutional decrease in elastin concentration. These data demonstrate that the same matrix protein alterations found in AAA tissue occur throughout the aorta, differing only in magnitude in the aneurysmal and nonaneurysmal segments. These data suggest that aneurysm formation may related to alterations in the regulation of elastin and collagen.

Adult↗