Variations in rat mesenteric tissue thickness due to microvasculature

Abstract

Studies of microvascular, tissue and lymphatic transport using microphotometric and microfluorometric techniques are potentially subject to artifact due to variations in tissue specimen thickness. Absorbance techniques utilize the Lambert-Beer law in which A = log I0/I = act, where A is absorbance, I0 is incident light intensity, I is transmitted intensity, a is an absorbance coefficient, c is concentration of substance, and t is path length. If differences in t are known to be present, then inferences of changes in c from changes in A become suspect. In microfluorometry the amount of light gathered is proportional to the number of fluorochromes in the effective cuvette, which is determined by the microscope's numerical aperture and the sample thickness. If variations in thickness are known to occur, the effective cuvette volume may be changing; therefore, inferences of changes in fluorochrome concentration from changes in intensity become suspect. Existing data suggest that rat mesentery is 15-30 microns thick, but variation over a tissue region is unknown. Our goals are to determine thickness variation in avascular, fat-free mesenteric tissue regions; thickness variation near blood vessels; and average tissue thickness. Sprague-Dawley rats were anesthetized with Inactin. Mesenteric tissue from a loop of small intestine was draped over a platform for observation; thickness was measured with an oblique microscope and a microgravimetric technique. The average variation in avascular fat-free tissue was 1.1 micron/100-microns distance, and average thickness was 17.4 microns. There was a significant increase in thickness over the microvasculature.

Po2profiles near arterioles and tissue oxygen consumption in rat mesentery

“…27,38,46). In the work of Yaegashi et al (49), the most probable source of the discrepancy with our results was the separation of the probe membrane and the mesentery by an estimated 38-m fluid layer [approximately the equivalent thickness of rat mesentery in avascular, adipocyte-free regions (17.4 -58.6 m) (2,15,49)], which could cause a substantial bypass for oxygen diffusion ultimately resulting in a three times higher rate of diffusion (DO 2 in water at 37°C is 3.3 ϫ 10 Ϫ5 cm 2 /s; Refs. 1, 49).…”

“…These factors limit the radial distance from arterioles that can be used for PO 2 profile analysis with the homogeneous one-dimensional model of oxygen diffusion, combined with zero-order consumption kinetics. According to the anatomic data reported previously (2,15), application of this model may be limited to a distance of ϳ100 m from a vessel. In the present study, this interval contains four experimental points (5-60 m) that have a good parabolic fit and can be used to calculate the rate of oxygen consumption by the mesentery for comparison with previously reported values of V O 2 in different tissues (see Fig.…”

Mast Cell-Directed Recruitment of MHC Class II Positive Cells and Eosinophils Towards Mesenteric Lymphatic Vessels in Adulthood and Elderly

“…Thus all our cell counts were automatically normalized to 8.75 lm of tissue thickness representing at least one half of mesenteric tissue volume, whereas average thickness of rat mesentery has been reported as 17.4 lm. 37 Statistical differences were determined by oneway ANOVA and Student's unpaired t-test ( JMP software version 9.0.0. for Windows) as appropriate and considered significant at p £ 0.05. A minimum of four animals was used for each given type of treatment for each animal age/strain.…”

Advances in small animal mesentery models for in vivo flow cytometry, dynamic microscopy, and drug screening

“…Mesentery consists of thin (8-15 µm), relatively transparent, duplex connective tissue, which is divided into triangular, relatively transparent windows by arteries (400-500 µm in diameter) and veins (600-700 µm in diameter) obscured by adipose tissue ( Figure 3D) [3,[89][90][91] . The smaller branches of these vessels leave the adipose regions and pass into the microvascular net ( Figure 3E), which spreads out into transparent areas.…”