Intravital intestinal videomicroscopy: techniques and experiences.

Intravital videomicroscopy (IVM) of the gastrointestinal (GI) tract is a sophisticated and powerful technique to directly observe the neurologically intact microvasculature of rats in naive and pathological conditions. We combine IVM with other techniques (i.e., vascular ring tension analysis and colorimetric microsphere determination of whole organ blood flow) to develop a strategy for the systematic analysis of the regulation of GI blood flow in healthy animals and in models of systemic sepsis and resuscitated hemorrhagic shock. We also study the molecular biology of the GI tract (enzyme- or radio-linked immunosorbent assays, fluorescent Greiss assay, and immunoblots) to correlate expression and levels of vascular mediators in tissue and arterial, venous, and portal blood with functional activity of the GI microvascular tree. When combined, these techniques develop a picture of gut pathophysiology at the level of the endothelium, vascular smooth muscle cells, and blood cells in the microcirculation. Our work led us to the general hypothesis that altered microcirculatory function in disease states lies primarily at the level of the interface between vascular and tissue physiology, i.e., the endothelial cell. This review focuses on methods and techniques for studying microvascular function, and concludes with focused reviews of pertinent findings. a 2005 Wiley-Liss, Inc. Microsurgery 25:247y257, 2005. The health of the gastrointestinal (GI) tract is prerequisite for the health of the individual. Numerous studies linked altered or impaired function in the microcirculation of the intestinal tract to pathophysiological conditions that can spiral into disease states like multiple system organ failure and death. 1 Intravital videomicroscopy (IVM) of the GI tract is a sophisticated and powerful technique that allows for direct observation and study of the intestinal microvasculature in naive and pathological states. Regulation of intestinal blood flow is complex, as outlined in Table 1, which shows some of the proposed mediators of intestinal microvascular tone in the rat. 2 Over the last 20+ years, we utilized several techniques such as vascular ring tension measurements, IVM, and colorimetric microsphere determination of whole organ blood flow to examine intestinal microvascular function in healthy Sprague-Dawley rats as well as in rat models of systemic sepsis and resuscitated hemorrhagic shock. We correlated these microvascular studies with molecular biology techniques such as enzyme- or radio-linked immunosorbent assays (ELISA and RIA, respectively), fluorescent Greiss assay, and various immunoblot techniques to measure the vascular mediators in tissue and in arterial, venous, and portal blood. 3,4 When combined, these techniques develop a picture of the pathophysiology of the gut at the level of the endothelium, vascular smooth muscle cells, and blood cells in the microcirculation. Our studies and the work of many other investigators led us to the generalized hypothesis that altered microcirculatory function in disease states lies primarily at the level of the interface between vascular and tissue physiology, specifically in deranged endothelial cell function, as shown in Figure 1. 5 This review focuses on methods and techniques for studying microvascular function, and concludes with focused reviews of pertinent findings in septic shock and resuscitated hemorrhagic shock from our laboratory.