Response of Pericytes to Thermal Lesion in the Inguinal Fat Pad of 10-Day-Old Rats

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Abstract
The response of capillary pericytes to thermal lesion in the inguinal fat pad of 10-day-old rats was observed with the light and electron microscope. Samples were taken from the necrotic area and the immediately surrounding tissue at various time intervals from 1 h to 10 days post-lesion. The initial physical disruption and swelling of the capillary resulted in the liberation of some pericytes near the necrotic zone. Most pericytes remained, however, in the basal lamina and went through a period of activation that peaked at 48 h. Pericyte activation consisted of a noticeable increase in rough endoplasmic reticulum with the cisternae containing granular, electron-opaque material. There was evidence of migration of these activated cells from the capillary basal lamina between 24 and 72 h. By 72 h, fibroblast-like cells possessing different nuclear and cytoplasmic morphology were oriented along distinct bands of extracellular fibrin and necrotic tissue. These cells produced limited amounts of collagen. Differentiation into immature adipocytes occurred 5 days after the lesion. Small, unilocular adipocytes were located in the necrotic zone by 7 days. Complete restoration of the lesion area was accomplished by 10 days. It is proposed that pericytes act as a reserve cell in the recovery of the rat inguinal fat pad after thermal lesion.