Anatomical and enzyme histochemical differentiation of adipose tissue.

Temporal and spatial patterns of lipid deposition, vascularization and collagen deposition were described for subcutaneous adipose tissue in the fetal pig. Enzyme cytochemical changes were reported as they relate to the morphological differentiation of the subcutaneous depot. There are distinct temporal lags between the appearance of specific enzymes in adipocytes. For example, NADH-tetrazolium reductase activity appeared earliest whereas esterase activity appeared before lipoprotein lipase (LPL) activity. Adipose tissue primordia has been localized around specific tissue components in rat and pig tissues. These tissue components include hair follicles, sweat glands, large nerves, large blood vessels and mammary gland ducts. Lipid and enzyme cytochemistry demonstrates physical continuity between primordial cells and differentiated fat cell clusters. Alterations in maternal and/or fetal endocrine or metabolic profiles result in specific changes in fetal subcutaneous adipocytes. For example, maternal diabetes significantly increases cell size whereas genetic obesity has little effect on cell size but increases cellular LPL activity significantly. A comparison of subcutaneous and perirenal depots in the pig fetus indicated several depot specific anatomical and enzyme histochemical traits. Blood vessel architecture and vascular alkaline phosphatase activity clearly demarcated perirenal and subcutaneous depots in the fetus. These data indicate that site to site variations of adipose tissue characteristics may be reflecting intrinsic stromal-vascular aspects of specific locations.