Abstract. Microvascular pathology is one of the major problems associated with prolonged diabetes mellitus. The purpose of the present study was to determine if anatomical cellular pathology of the cerebral cortical microvessels could be detected very early after the onset of a streptozotocin-induced model of diabetes. Male rats at age 14-16 weeks were hyperglycemic (> 250 mg/dl) for 4 weeks prior to scanning and transmission electron microscopic analysis of the external and internal cell and vessel wall morphology of the arterioles. Scanning electron microscopic studies indicated that many processes of vascular smooth muscle cells changed their normal spindle shape to a branched or stellate configuration. The internal cellular changes included swollen mitochondria and cisternae of the endoplasmic reticulum and reduced cytoplasmic staining. Necrosis of arteriolar endothelial cells was evident in virtually every vessel section studied. These data indicate that vascular smooth muscle and endothelial cellular degeneration of cerebral cortical arterioles begins in the very early stages of the streptozotocin model of diabetes.
The present study details a new method for the exposure and viewing of individual microvessels located within the small intestine of rats. This procedure will selectively and consistently remove the outer muscle layers and underlying submucosa of the intestinal wall and thereby expose a variety of arterioles in their normal location within the tissue, with their normal relationship to each other undisturbed. The small intestine of the rat was initially fixed by vascular perfusion with 2.5% glutaraldehyde in 0.1 M cacodylate/HCL buffer, reinfused with heparinized whole blood, removed from the animal, and secured to a dissecting petri dish for further fixation. Subsequently, the external muscularis was dissected from the sample which exposed the submucosa. In order to remove the connective tissue elements from this layer and uncover the submucosal vasculature, the samples were first transferred to a solution of 30% potassium hydroxide for 2-5 minutes and then to a final digesting solution containing collagenase. Thereafter, the samples were routinely processed for light microscopy and for scanning (SEM) or transmission (TEM) electron microscopy. Examination of the samples revealed excellent preservation of the three-dimensional organization of the arteriolar wall with minimal membrane damage. This new technique now makes it possible to visualize the shape and position of individual smooth muscle cells along arterioles of differing size and branching order.
Accurate three-dimensional data on the structure of vascular smooth muscle cells is essential for understanding the microvascular system in both normal or disease conditions. The laborious serial reconstruction methods have limited the amount of data collected on the structure of individual vascular smooth muscle (VSM) cells. The circumferential viewing of whole vessel segments via scanning electron microscopy provides an alternative approach, but even this technique is highly specialized and tedious. This study presents a simplified method to determine the average cell length and width of individual VSM cells by using only one view of a microvessel (single view). The vessels do not have to be isolated for circumferential viewing and can be left in their host tissue if desired. Values for the average VSM cell length and width were obtained by both circumferential- and single-view approach on the same vessels. The average cell length and width obtained from the single-view method (using one-third circumference) duplicated the mean length and width measurements obtained by circumferential viewing.
With five rumen-fistulated Holstein steers in a Latin square design, we determined the effect of dietary concentrate (0, 20, 40, 60, or 80% cracked corn) on kinetic characteristics influencing forage fiber digestion in vivo. Rate and potential extent of neutral detergent fiber degradation were determined for fescue hay in situ by nylon bag technique. Rate of fiber passage from the rumen was measured by fecal excretion of chromium-mordanted fescue cell walls. Apparent extent of forage fiber digestion was predicted by a model in which fiber disappearance from the rumen is conceptualized as the sum of two competing first-order processes, digestion and passage, modified further by a discrete lag time during which fiber passes from the rumen before digestion commences. Stepwise multiple regression analysis revealed that potential extent of fiber degradation in situ was the primary determinant of depression of fiber digestibility as dietary concentrate increased. Rate of digestion, rate of passage, and lag effects collectively accounted for a small portion of the depression of fiber digestibility.
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