Electron microscopical studies on the genesis of white adipocytes: differentiation of immature pericytes into adipocytes in transplanted preadipose tissue.

In order to clarify the relationships between perivascular cells, capillaries and fat cells, with a special reference to the origin of fat cells, we have made a light and electron microscopical study on the developing epididymal adipose tissue of newborn to 5-week-old rats, and also on the differentiating, transplanted epididymal preadipose tissue from 6-day-old rats. Development of epididymal preadipose tissue progressed rapidly 6 or 7 days after birth. The preadipose tissue on the 5th day after transplantation consisted of differentiated areas with many mature fat cells, and of undifferentiated areas in which these cells were scanty. In the differentiated areas of developing epididymal preadipose tissue, both in situ and transplanted, many fat cells seemed to develop in the area immediately adjacent to growing capillaries, but cells intermediate between perivascular cells and preadipocytes were seldom observed. However, in undifferentiated areas of transplanted tissue, we found ultrastructural evidence that immature pericytes of capillaries can differentiate into preadipocytes.