The development of perirenal fat depots in obese and lean pig fetuses.

The differentiation of perirenal adipose tissue was ascertained in fetuses from Ossabaw (wild and obese) and cross-bred lean dams at 70, 90 and 110 days gestation and from domestic lean and obese dams (USDA) at 110 days gestation. Condensation of presumptive adipocyte clusters was more apparent in Ossabaw sections than in cross-bred (lean) sections at 90 and 110 days gestation. Enzyme and lipid histochemistry showed fat cell cluster development to be largely independent of fetal strain (Ossabaw vs crossbred). However, adipocytes in Ossabaw fetuses were larger (110 days) and more reactive for esterase activity (all three ages) than were adipocytes from crossbred fetuses. Fetuses from USDA-obese dams had larger fat cell diameters (P less than 0.01), a higher percentage of lipoprotein lipase (LPL) positive cells than did fetuses from USDA-lean dams. Perirenal fat pad weights, percent depot lipid, percentages of glucose-6-phosphate dehydrogenase (G6PDH) and succinate dehydrogenase (SDH) positive cells were independent of fetal strain (USDA, lean vs obese). Fat cell cluster development was independent of fetal strain but large cellular condensations of presumptive cells were only present in sections from lean fetuses. Immature capillary beds (devoid of adipocytes) were demonstrable in lean sections but were not observed in obese sections. Morphological and histochemical results from both studies provide no evidence for brown adipocyte-like cells in fetal perirenal tissues.