Perivascular Adipose Tissue: Quantitative analysis by morphometry and stereology in rodents

The perivascular adipose tissue (PVAT) provides mechanical support to blood vessels and modulates vascular physiology in obesity. Our goal is to provide a reproductive protocol using morphometric and stereological tools to assess PVAT morphology. The thoracic aorta from male Wistar rats (n=6) and C57BL/6 mice (n=7) underwent routine histological procedures, and two independent observers analyzed the same set of digital images. Agreement and reproducibility were assessed. Both observers showed that the diameter of rat brown adipocytes is larger than mice (P<0.002) as expected, and that the number density (QA) of brown adipocytes is smaller in rats compared to mice (P<0.01). Considering lipid droplets, observer #1 reported that in rats they were larger (P<0.005) and had a higher volume density (VV) than mice (P=0.035), but observer #2 found the opposite for lipid droplet diameter (P=0.001). White adipocytes were not found in the PVAT. Bland-Altman plots demonstrated agreement and reproducibility between observers since the means are close to the main difference (bias) and within the 95% limits of agreement. In conclusion, the methodology proposed can quantify morphological aspects of the aorta PVAT in rodents. It is reproducible and can be performed by both expert and inexperienced researchers, once they know how to recognize the structures of interest to be measured.