Incorrect nutrient balance affects normal growth and adipose tissue development in mammals. Adipose tissue first appears around mid-gestation and increases through late gestation, as a mixture of white (WAT) and brown adipose tissue (BAT). BAT is essential for thermoregulation and contributes to energy expenditure with the secretion of the thermogenic uncoupling protein 1 (UCP1). WAT is involved in energy metabolism and inflammation with the secretion of adipokines.
Marsupials deliver highly altricial young that are totally dependent on milk for their growth and development. Milk composition changes dramatically throughout the whole of lactation. Fostering marsupials from one mother to another that is secreting milk for a much older young has provided novel information on the growth hormone axis and the control of post-natal growth. However, as yet no studies have been conducted on the effects of altered nutrition on adipose tissue development and function. Furthermore, the presence of BAT and uncoupling protein 1 (UCP1) in marsupial pouch young and adults is controversial.
To determine the effects of over-nutrition on growth and adiposity, young were transferred to a foster mother at a later lactational stage (fostering “forward”). For under-nutrition, young of primiparous/lower weight females versus older heavier females were measured and compared. Dual-energy X-ray absorptiometry (DEXA) was used to measure fat mass content in normal and nutritionally altered pouch young and adults, and presence of BAT was determined using simple histological techniques. In normal pouch young, retroperitoneal fat was positively correlated to body weight and there were no differences in fat mass content between normal and undernourished pouch young, or between heavier v/s smaller adult females. In contrast, fostered forward pouch young had excessive deposits of retroperitoneal fat. No differences were found between retro-peritoneal fat and axillary fat in adults. Thus post-natal overfeeding has dramatic effects on the adiposity of marsupial young.