SCANNING ELECTRON-MICROSCOPY OF VASCULAR SMOOTH-MUSCLE CELLS FROM SPONTANEOUSLY HYPERTENSIVE RATS

The fine structure of vascular smooth muscle cells from large mesenter ic arteries of adult (28 weeks) spontaneously hypertensive rats and Wi star-Kyoto rats was studied using scanning electron microscopy (SEM). The effect of the digestion method for SEM on tissue size and smooth m uscle cell size was also studied using morphometric analysis. A signif icant reduction in cell size (42-43%) was present after critical point drying, based on the reduction in volume to surface ratio of smooth m uscle cells. However, percent change of volume density and volume to s urface ratio of smooth muscle cells after digestion and after critical point drying, was similar between the hypertensives and normotensives . Most of the tissue shrinkage occurred during the digestion process t o remove the connective tissue. Overall tissue shrinkage due to the di gestion method involving OsO4/HCl and subsequent processing for SEM, b ased on changes in the thickness of the medial wall, was similar betwe en arteries from hyper-tensive (34.7%) and normotensive (31.4%). After compensating for the shrinkage, vascular smooth muscle cells from hyp ertensive animals were found to have a wider somal region (5.94 mum) t han those from the normotensives (5.46 mum), suggesting cellular hyper trophy. We conclude that a significant reduction in size of tissue and smooth muscle cells took place when arteries were processed for SEM. For comparative study of vascular changes in hypertension involving SE M, cellular shrinkage due to processing should be included in the calc ulations in order to provide a reasonable estimate of the alterations.