Maternal exercise during pregnancy affects the rat musculoskeletal system and indices of energy metabolism : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatū, New Zealand

Abstract

The developmental origins of health and disease hypothesis postulates that

environmental cues perceived by the developing organism during early life program long-term health outcomes. A series of studies were undertaken to examine the developmental programming effects of maternal exercise during pregnancy on offspring musculoskeletal health and energy metabolism using a rat model. Firstly, an exercise that did not cause a potentially confounding stress response in the exercising animal was identified. Secondly, pregnant dams then performed this exercise and its effects on fetal growth and the maternal stress response were quantified. Finally, the offspring of dams that exercised throughout pregnancy were allowed to grow to maturity, and the effects of maternal exercise on their musculoskeletal health and energy metabolism were assessed. Throughout these experiments, body composition was assessed by dual- energy X-ray absorptiometry, and tibial parameters were measured using peripheral quantitative computed tomography. Maternal stress was quantified by measurement of faecal corticoid metabolites. Serum concentrations of the fully and undercarboxylated forms of the bone-derived hormone osteocalcin, and expression of genes related to osteocalcin carboxylation, were measured to explore their role in the response of offspring bone and energy metabolism to maternal exercise. Two exercise types, rising to an erect bipedal stance and tower climbing, were initially tested in non-pregnant rats. Both rapidly caused changes in the tibias of exercised animals without inducing stress. In pregnant rats, both exercises increased fetal growth relative to controls, and neither caused a physiological stress response in the dams. Since rising to an erect bipedal stance had the greater effect on fetal growth, it was selected for use in the final study in which the offspring were grown to maturity. Maternal exercise throughout pregnancy was associated with sex-dependent changes in

the bone and body composition of the mature offspring. Male offspring of exercised dams had increased adiposity and serum undercarboxylated osteocalcin concentrations, while offspring of both genders had lower volumetric bone mineral density at the tibial diaphysis, relative to controls. These results suggest that maternal exercise has long- term effects on the musculoskeletal system and energy metabolism, and that undercarboxylated osteocalcin may play a role in these effects.