SUMMARY. 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. (Circ Res 53: 424-429, 1983)

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SUMMARY 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. (Hypertension 7: 483-490, 1985)

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.

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