QUANTITATIVE DEVELOPMENT OF ADIPOSE-TISSUE IN FETAL SHEEP

The development of lipid stores in fetal sheep was examined using quantitative dissection and chloroform extraction. The accumulation of extractable lipid commenced prior to the 50th day of fetal age. Growth of dissectible perirenal-abdominal adipose tissue and other non-subcutaneous depots (all brown fat) commenced at about day 70, while growth of the subcutaneous adipose tissue (white fat) commenced 2-3 wk later. The subcutaneous fat regressed markedly from about day 115 and virtually disappeared by full term. There was consistent trends (not all statistically significant) in various indices of lipid status indicating that the rate of lipid accumulation was declining near term. These indices include percentage of lipid in adipose tissue, in the body as a whole and in skeletal muscle and the rate of growth of the perirenal-abdominal adipose depot. The involution of subcutaneous adipose tissue appeared to be hastened by maternal nutritional restriction but was not prevented by feeding the ewes ad lib on a high-energy diet. There were also consistently lower values of the indices of lipid status in fetuses from nutritionally restricted ewes than in fetuses from ewes fed ad lib. The early regression of the white subcutaneous adipose tissue suggests that the normal fetal lamb may be in a state of undernutrition during the last 5 or so wk of pregnancy. Hypophysectomized fetuses, full term or post-term, were comparatively obese, with a thick layer of subcutaneous fat, a high proportion of other adipose tissue depots in the body and a high content of chloroform-extractable lipid.