Cellular and vascular development in immature rat adipose tissue.

Techniques that allow the study of immature subcutaneous depots in newborn and young rats were developed utilizing a histological and histochemical approach. The temporal and spatial relationship between blood vessel development and adipocyte hypertrophy was examined in rats from large and small litters. Large numbers of small (9.8 +/- 1 micron diameter) multilocular adipocytes were present in subcutaneous depots of newborn animals. These adipocytes were intimately associated with capillaries that had lumen diameters of 4-10 microns. Adipocytes rapidly increased in size up to 30-40 microns in diameter. The development of small capillaries (2-4 microns lumen diameters) was associated with this cell hypertrophy. Lipoprotein lipase (LPL) histochemistry and ultrastructural analysis indicated that the larger capillaries may potentiate LPL-mediated cell hypertrophy. Similar analysis indicated that the development of the narrow lumen capillaries may slow the rate of LPL-mediated hypertrophy. These studies indicate that the adipose tissue capillary may play an important role in adipocyte hypertrophy and metabolism.