Intestinal microvascular patterns during hemorrhagic shock

While injuries due to a hypoxic state commonly appear later in both intesti nal crypts and basal portion of the villi than in the apical portion, a non homogeneous distribution of blood flow in the intestinal mucosa may be supp osed. The presence of two different microvascular plexuses inside the mucos a, corresponding to the cryptal plexus and the villous plexus, supports the above hypothesis. This work studies the intestinal microvasculature in sho cked versus normal rats. Forty-five rats were divided into four groups to s tudy the histological damage and the microvascular bed by ink injection, fl uorescent microsphere infusion, and resin injection for scanning electron m icroscopy (SEM) of vascular corrosion cast (VCC) observations. An infusion pressure of 100 +/- 5 mm Hg was used in control animals, while 30 +/- 5 mm Hg infusion pressure was adopted for controls as well as for shocked animal s to simulate physiological or shock conditions. Hemorrhagic shuck was indu ced by removing blood and maintaining a mean arterial pressure of 30 +/- 5 mm Hg for 45-120 mins. A close connection among the patterns of microvascul ature obtained with VCC and ink injection technique can be appreciated. In normal rats the whole microvasculature was visualized, but in both normal a nd shocked animals injected at low pressure different patterns could be fou nd, generally showing a highly incomplete visualization of the vascular net work. A significant decrease of visualization of both the entire microvascu lature and the villous plexus is present in shocked animals when compared t o unshocked controls, while no difference in the cryptal plexus visualizati on was observed. These observations suggest that the cryptal plexus is perf used preferentially during hemorrhagic shock, as a consequence of its pecul iar microvascular organization. This may explain the relative resistance of the crypts, compared to villi, to hypoxic injuries in order to sustain end ocrine function and the regenerative capability of the mucosa after prolong ed hypoperfusion conditions that can lead to villi,us damage and temporary loss of che intestinal barrier function.