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Biomedical subjects

T A Twietmeyer

Publications and source records attributed to T A Twietmeyer.

9 recordsLinked to original sources
PubMed1985

Transcytosis of ferritin and increased production of subendothelial matrix components by aortic endothelial cells during the development of hypertension.

The aortic intima of the Spontaneously Hypertensive Rat underwent dramatic structural alterations with respect to the subendothelial space coincident with the rise in arterial pressure. This space became increasingly widened from four to 24 weeks, and exhibited a dense accumulation of granular material, resembling a complex reticular basement membrane. To determine if this alteration was due to an abnormality in endothelial transcytosis, rats of four, ten and 24 weeks of age were studied using ferritin as a tracer. In the SHR, vesicular transport of injected ferritin was significantly increased at all ages studied compared to the WKY, but decreased to prehypertensive levels by 24 weeks of age. This occurred without a change in the density of vesicles and caveolae within the cells. Despite the decrease in transcytosis from 10 to 24 weeks the alterations of the subendothelial space continued indicating that the endothelium may play a role in the synthesis and deposition of the dense extracellular matrix.

Animals↗
PubMed1984

Intramembrane particle distribution and junction morphology in rapidly frozen aortic endothelial cells.

The morphology of unfixed plasma membranes of aortic endothelial cells from adult Sprague-Dawley rats was investigated using the Polaron E7200 quick freeze unit. Intramembrane particle distributions were determined from replicas of rapidly frozen samples and compared with counts from both aldehyde fixed, conventionaly frozen and rapidly frozen aortic samples. Aldehyde fixed cells prepared by either of the freezing methods revealed a significantly greater number of particles associated with the protoplasmic face of the membrane compared to the exoplasmic face. In contrast, those cells fixed by rapid freezing showed a nearly equal number of particles on both faces. In both fixation methods tight junctions partitioned with the exoplasmic half of the membrane, exhibiting more of a particulate morphology in rapidly frozen cells. These findings suggest that aldehydes strongly influence the morphological appearance of endothelial membranes and membrane associated structures, and that functional implications based on images of aldehyde fixed cells may be subject to errors.

Animals↗
PubMed1984

Skeletal muscle capillarity during recovery from chronic hypoxic exposure.

Young male Sprague-Dawley rats were randomly assigned to one of three groups (Chronically Hypoxic, N = 15; Age-Control, N = 15; Weight-Control, N = 15) and studied immediately following a 36-day exposure at a simulated altitude of 5846m or after recovery periods of one, three or seven days. Following preincubation at pH 3.8, cross-sections of soleus muscle were stained by the calcium ATPase method and analyzed for six indices of skeletal muscle capillarity: capillary density (CD), fiber density, number of capillaries around each fiber (CAF), Capillary/fiber ratio (C:F), fiber cross-sectional area (FCSA), and fiber diameter. No differences in skeletal muscle capillarity were observed in chronically hypoxic rats at the termination of exposure or during the seven day recovery period. The Chronically Hypoxics differed significantly (p less than or equal to .05) from both control groups in three different measures of physiologic stress, but showed a definite trend toward recovery in the post-exposure period. This recovery was most apparent in body weight comparisons. The Chronically Hypoxics weighed less than the Age-Controls immediately following the exposure period but gained rapidly during the first three days post-exposure. These rapid body weight increases in rats recovering from chronic exposure to hypoxia suggest that age-controls should not be excluded in favor of weight-controls in similar studies.

Age Factors↗
PubMed1983

Morphology of rapidly frozen aortic endothelial cells. Glutaraldehyde fixation increases the number of caveolae.

Using a Polaron E7200 quick freeze unit, we investigated the distribution of vesicles (caveolae) bound to the plasma membrane of aortic endothelial cells from adult Sprague-Dawley rats. Counts of caveolae from replicas of rapidly frozen, unfixed samples were made and compared with counts from both aldehyde-fixed, conventionally frozen, and rapidly frozen aortic samples. Aldehyde-fixed samples prepared for freeze fracture by either of the freezing methods revealed a significantly greater number of caveolae than did unfixed, rapidly frozen samples. These findings suggest that the relative number of caveolae is artifactually increased by exposure to aldehyde fixatives. We conclude that previous estimates of the rates of pinocytotic activity in vascular endothelial cells may contain substantial errors based on overestimates of caveolae and underestimates of subplasmalemmal "free" vesicles.

Aldehydes↗
PubMed1983

Quantitative aspects of arterial endothelium in the adult Sprague-Dawley rat.

Ultrastructural features of aortic and carotid artery endothelium were investigated using transmission electron microscopy and freeze-fracture methodologies. Morphometric analysis was conducted to quantitate the pinocytotic vesicle population within endothelial cells. A significantly greater volume fraction of vesicles and vesicles/micrometer 3 was found in the carotid artery. The membrane-bound vesicles in the endothelium of the aorta and carotid artery exhibited a greater fractional area than has been reported for capillary endothelium. These findings may indicate a specialized function of the vesicles in large arteries for increasing the total plasma membrane surface area in response to high transmural pressures.

Animals↗
PubMed1979

Localization of acid and alkaline phosphatase activities in the blood vessels of normotensive and hypertensive rats.

Samples of aortae and caudal arteries from normotensive and hypertensive rats were studied for cytochemical and biochemical determinations of acid and alkaline phosphatase activities. Cytochemical examination revealed an increased amount of acid phosphatase reaction product in hypertensive samples, with extensive localization to the extracellular matrix. Alkaline phosphatase activity was localized to the plasma membrane of fibroblasts and vascular smooth muscle cells and to the extracellular matrix. Biochemical assays of enzyme activities supported the cytochemical findings, showing increased activity in aortae from hypertensive rats.

Acid Phosphatase↗
PubMedDate not supplied

Aortic endothelial junctions in developing hypertension.

The morphology of the intercellular pathway of aortic endothelium was investigated in spontaneously hypertensive rats (SHR) at three different stages in the hypertensive process. Aortic endothelial cells of the SHR, in contrast to those of the normotensive Wistar-Kyoto rats exhibited an increased length and complexity of tight junctions, at all ages studied. That this finding was seen in young SHR, before the elevation of arterial pressure, suggests that other factors (genetic, humoral, neurogenic) may be influencing the morphology of aortic endothelium in the SHR. The area of lateral endothelial membrane occupied by gap junctions also was increased in the SHR, especially at 10 weeks of age, and corresponded to the greatest increase in tight junction strand length and the most rapid and dramatic rise in arterial pressure. The results indicate that aortic endothelium of the SHR can anticipate or respond, and partially adapt, to the abnormal influence of elevated arterial pressure.

Aging↗