Sex and strain differences in whole skeletal development in the rat

The dry weight and calcium content of whole skeletons was determined in both male and female weanling, adolescent, and mature rats of the spontaneously hypertensive (SHR), Wistar Kyoto (WKY), and Sprague-Dawley (SD) rat strains. Dry skeletal mass, calculated as percent of body mass (%BM), increased with maturity in each strain. In adolescent and mature animals, skeletal development (%BM) was greater in female rats. SHR showed greater skeletal development (%BM) than normotensive rat strains and this difference was detectable even in weanling animals. Despite these age, strain, and gender-related differences in skeletal development, the calcium content per unit skeletal mass was identical among the various groups examined. Regression analysis of the plot of skeletal mass as a function of body mass indicated that only a portion of mature skeletal development was related to body mass. The results show that skeletal mass developed in the rat is only partially determined by structural support demands.