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

Abstract

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 postpuberty 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 35-42) 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 Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptBone. Author manuscript; available in PMC 2007 April 10. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript 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 number of trabecula 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.

Delayed pubertal development by hypothalamic suppression causes an increase in periosteal modeling but a reduction in bone strength in growing female rats

“…Significant reductions in cortical area related to body weight and periosteal circumference related to body weight were found. We have previously reported a transient decrease in bone strength at a low dosage of GnRH-a and long term effects on trabecular architecture measured by wavelet analysis (15,23,34). The current data illustrate that an increase in GnRH-a dose, modeling an increase in the severity of the delay in puberty, results in decreased strength values compared to the Low dose.…”

“…Animal models using ovariectomy represent only the most extreme condition of delayed reproductive development with the complete cessation of estrogen. However, gonadotropin releasing hormone antagonists (GnRH-a) have successfully delayed the onset of puberty in female rats as determined by delayed vaginal opening, lower ovarian weights and lower serum estradiol levels (15,(23)(24)(25). Furthermore, the withdrawal of GnRH antagonists restores normal hypothalamic-pituitary function allowing control of estrogen levels for a finite (transient) period of time.…”

Lack of sexual dimorphism in femora of the eusocial and hypogonadic naked mole-rat: A novel animal model for the study of delayed puberty on the skeletal system

“…In mice and rats, a delay in pubertal onset has also been shown to reduce trabecular number, increase trabecular separation, and reduce femoral length and strength [5, 53, 59-61]. Subordinate NMRs circumvent the observed detrimental effects of hypogonadism on the skeletal system that are evident in humans, rats and mice.…”

Hypothalamic Suppression Decreases Bone Strength Before and After Puberty in a Rat Model

“…Animal models that use ovariectomy represent the most extreme condition of delayed reproductive development with the complete cessation of estrogen. However, GnRH-a injections have successfully delayed the onset of puberty in female rats as determined by delayed vaginal opening, lower ovarian and uterine weights, and lower serum estradiol levels [22, 25, 45, 46]. Furthermore, the withdrawal of GnRH-a injections restores normal hypothalamic–pituitary function, allowing control of estrogen levels for a finite (transient) period of time.…”