Quantitative measurements of periosteal and cortical-endosteal bone formation and resorption in the midshaft of male rat femur.

Morphologic and modeling parameters have been studied in the femoral diaphysis of male rats between 60 days and 840 days of age. The modeling rates were measured by use of a vital labeling technique with calcein. The mathematical bone model that was developed for the midshaft of female rats was used also for male rats. The two ellipses, defined by four time-dependent functions of the radii, and one drift function that describes the movement of the whole diaphysis in the transverse direction have been adapted to the new data sets obtained for male rats. With increasing age the apposition(MF), forming(BF), and resorbing(BR) rates decrease continuously from 5.4 mm/year(MF), 960%/year(BF), and 540%/year(BR) at age 60 days to 0.038 mm/year(MF), 8.4%/year(BF), and 6.3%/year(BR) at age 850 days, whereas the endosteal and periosteal diameters increase. Between age 60 days and 550 days, formation rate, resorption rate, apposition rate, and the growth rate of the bone volume and body weight are greater in male than in female rats, but after this age they are comparable. The average cumulative radiation dose near bone surfaces after contamination with alpha-emitting bone surface-seeking radionuclides is greater in the diaphysis of female rats than in the corresponding male rats. In young animals it is greater initially on the cortical-endosteal surfaces, but after age 250 days the dose on the periosteal surface becomes predominant.