The effect of a short-term delay of puberty on trabecular bone mass and structure in female rats: A texture-based and histomorphometric analysis

Accrual of bone mass and strength during development is imperative in order to reduce the risk of fracture later in life. Although delayed pubertal onset is associated with an increased incidence of stress fracture, evidence supports the concept of "catch up" growth. It remains unclear if deficits in bone mass associated with delayed puberty have long-term effects on trabecular bone structure and strength. The purpose of this study was to use texture-based analysis and histomorphometry to investigate the effect of a delay in puberty on trabecular bone mass and structure immediately post-puberty and at maturity in female rats. Forty-eight female Sprague-Dawley rats (25 days) were randomly assigned to one of four groups; (1) short-term control (C-ST), (2) long-term control (C-LT), (3) short-term GnRH antagonist (G-ST) and (4) long-term GnRH antagonist (G-LT). Injections of either saline or gonadotropin-releasing hormone antagonist (GnRH-a) (100 μg/day) (Cetrotide™, Serono, Inc.) were given intraperitoneally for 18 days (day 25-42) to both ST and LT. The ST groups were sacrificed after the last injection (day 43) and the LT groups at 6 months of age. Pubertal and gonadal development was retarded by the GnRA antagonist injections as indicated by a delay in vaginal opening, lower ovarian and uterine weights and suppressed estradiol levels in the short-term experimental animals (G-ST). Delayed puberty caused a transient reduction in trabecular bone area as assessed by histomorphometry. Specifically, the significant deficit in bone area resulted from a decreased trabecula number and an increase in trabecular separation. Texture analysis, a new method to assess bone density and structural anisotropy, correlated well with the standard histomorphometry and measured significant deficits in the density measure (M_Density) in the G-ST group that remained at maturity (6 months). The texture energy deficit in the G-ST group was primarily in the 0° orientation (- 13.2%), which measures the longitudinal trabeculae in the proximal tibia. However, the deficit in the G-LT group was in the 45° and 135° orientations. These results suggest that any "catch-up" growth following the cessation of the GnRH-antagonist injection protocol may be directed in trabeculae oriented perpendicular to 0° at the expense of trabeculae in other orientations.