MANIPULATION OF ADULT BODY-COMPOSITION BY TREATMENT OF THE NEONATAL RAT WITH GROWTH-HORMONE AND PROLACTIN

Previous studies involving fetal decapitation or hypophysectomy, and t he treatment of neonates with hormones or antibodies, have suggested t hat changes in pituitary hormone status during the perinatal period ma y influence later body composition. In the present study, rats were tr eated for the first 21 days of life with twice daily subcutaneous inje ctions of saline, recombinant bovine growth hormone (bGH) or pituitary ovine prolactin (oPRL). The bGH and oPRL were administered at doses o f 0.2 or 0.4 mu g/g bodyweight/day. One-third of the rats in each trea tment group were slaughtered at each of days 21, 60 and 120 of life an d measurements made of: length and weight of the body; weights of bone s and muscle groups in the hindlimb; weights of four fat depots (120-d ay group only); and the content of nitrogen (N) and fat in the carcass , bGH, but not oPRL, treatment increased weight of the femur and humer us (across ages) but neither treatment had marked effects on weights o f muscle groups, carcass weight or carcass N content at any age. Both bGH and oPRL treatment significantly reduced weight of the subcutaneou s scapular fat depot and reduced carcass fat content, but only in anim als aged 120 days (i.e. 99 days after the cessation of treatment), It is concluded that treatment of rats with bGH and oPRL during the immed iate postnatal period specifically retards the ability of animals to d eposit body fat in later life by mechanisms which differ from those in volved in the classical lipolytic/antilipogenic effects of bGH.