Cellular and Enzyme-Histochemical Aspects of Adipose Tissue Development in Obese (Ossabaw) and Lean (Crossbred) Pig Fetuses: An Ontogeny Study

Abstract

The cellular and enzyme-histochemical differentiation of subcutaneous adipose tissue was studied in lean and obese pig fetuses at several ages. Positive reactions for a variety of cytosolic and organellar enzyme markers indicate metabolic competence of fetal adipocytes despite their small size (12 to 15 microns). Reactions for several enzymes decreased with fetal age and may be associated with a qualitative change in activity of adipocyte organelles. Age-associated increases in two lipogenic enzymes were observed in obese adipocytes. Observations on developing cells around hair follicles in the younger fetuses indicated significant temporal lags between the appearance of detectable enzyme activities in adipocytes. Enzyme activities in order of appearance were: dehydrogenases (cytosolic and mitochondrial), lipoprotein lipase and esterase. Esterase activity and several other enzymes were never observed in lipid positive cells that were not spherical. A proportion of hair follicle associated adipocytes in 110-d-old lean fetuses were histochemically and morphologically similar to brown adipocytes in the young rat. There was no evidence for brown adipocyte like cells in obese fetuses. Finally, comparison of the enzyme-histochemical differentiation of lean and obese fetal adipocytes indicates that fetal adipocytes become sensitive to external stimuli between 70 and 90 d of gestation.

C/EBPα identifies differentiating preadipocytes around hair follicles in foetal and neonatal rat and mouse skin

“…A close association between hair follicles and the appearance of subcutaneous lipid has been described in series of studies in rat and pig skin (1–4). In all species studied, the fat cells consistently appear around established hair follicles in the lower dermis.…”

Development of the Mouse Dermal Adipose Layer Occurs Independently of Subcutaneous Adipose Tissue and Is Marked by Restricted Early Expression of FABP4

“…Seminal investigations of the development of skin adipose tissues have been carried out by Hausman and colleagues, particularly in pigs e.g. [11],[12],[13],[14],[15]. These animals develop multiple layers of subcutaneous adipose tissue [16], and the extensive studies from the Hausman laboratory have pointed to three important recurring features: the close association between development of the outermost adipose layers and developing hair follicles; differences between this outer layer of adipose tissue and other subcutaneous adipose tissue at the histochemical level; and the spatio-temporal correlation between adipogenesis and blood vessel formation [9],[12].…”

Ontogeny of the Response to Thyroxine (T4) in the Porcine Fetus: Interrelationships Between Serum T4, Serum Insulin‐Like Growth Factor‐1 (IGF‐1) and Differentiation of Skin and Several Adipose Tissues

“…Fetal adipocytes grouped around hair follicles or "hair follicle adipose lobules" are linked developmentaIIy to hair follicle growth, develop later (>70 days) than outer and inner SQ adipocytes and are morphologically and metabolically distinct from outer SQ cells (6,11,12).…”