1. Previous data indicate that the loss of estrogen is associated
with an altered balance between bone formation and resorption,
resulting in bone loss. Ovariectomy (OVX) in rats is an
appropriate model to examine the effects of sex-hormone
deficiency on osteoblast and osteoclast activity. Further,
estrogen repletion provides a mechanistic examination of bone
restoration following OVX. The purpose of this study was to
examine bone static properties (i.e., osteoblast and osteoclast
activity) following OVX and estrogen replacement (OVE).
Methods: Female Sprague Dawley rats (~6 mon) underwent
bilateral ovariectomy according to accepted procedures and
were divided into two groups: 1) ovariectomized (OVX; n=5) and
ovariectomized + estrogen replacement (OVE; n=5). At the time
of surgery, a slow-release estrogen pellet was implanted into the
rats of the OVE group. All experimental procedures lasted 2
months. At sacrifice, right femora were dissected, fixed in 10%
formalin and processed for bone histomorphometry for the
examination of bone microarchitectural (i.e., bone volume/total
volume ratio [BV/TV, %], trabecular thickness [Tb.Th, μm],
trabecular number [Tb.N /mm] and trabecular separation [Tb.
Sp, μm]) and bone static (osteoid surface/bone surface [OS/BS,
%], osteoblast surface/bone surface [Ob.S/BS, %], number of
osteoblast per total area [N.Ob/T.Ar], osteoclast surface/bone
surface [Oc.S/BS, %)], and number of osteoclast per total area
[N.Oc/T.Ar]) properties. Results: OVX significantly (p < 0.05)
enhanced body mass vs. OVE rats (233 ± 6g vs. 204 ± 8g,
respectively). As anticipated, estrogen replacement reversed the
declines in bone volume observed with ovariectomy (BV/TV;
OVX = 3±1% vs. OVE = 12±1%; p < 0.05), due to augmented
Tb.Th and Tb.N. Further, osteoblast activity was augmented
with estrogen replacement (N.Ob/T.Ar; OVX = 7.4±1.7% vs.
OVE = 24.4±5.2%; p < 0.05). However, OS/BS was augmented
by 87% in the OVX vs. OVE group, presumably indicating a
delay in bone mineralization. Osteoclast activity did not differ
between groups. Conclusions: Ovariectomy (i.e., loss of
reproductive hormones) markedly reduced bone volume and
presumably reduced bone mineralization in OVX rats;
suggesting reductions in bone mechanical strength. Finally,
bone volume was restored with estrogen replacement via
augmented osteoblast activity.
ABSTRACT
BACKGROUND
RESULTS
Female Sprague Dawley rats (~6 mon) underwent bilateral ovariectomy according
to accepted procedures and were divided into two groups:
1) ovariectomized (OVX; n=5)
2) 2)ovariectomized + estrogen replacement (OVE; n=5).
At the time of surgery, a slow-release estrogen pellet was implanted into the rats of
the OVE group. All experimental procedures lasted 2 months.
Right femora (n=5/group) were analyzed by bone histomorphometry to assess
 Bone Microarchitecture = bone volume to total volume ratio [BV/TV; %],
trabecular thickness [Tb.Th; µm], trabecular number [Tb.N/mm], and
trabecular separation [Tb.S; µm]
 Bone Static Properties = osteoid surface to bone surface [OS/BS;%],
osteoclast surface to bone surface [OcS/BS; %], osteoclast number per total
area [N.Oc/TAr /mm], osteoblast surface to bone surface [Ob.S/BS; %], and
osteoblast number per total area [Ob.N/TAr /mm]
Statistical analysis
One-way ANOVA was used for between group comparisons of body mass, bone
microarchitectural properties and bone static properties.
Enoch Samraj1, Tyler Benson1, Kirk Evanson2, Heidi Kluess3, Rhonda Prisby1
1Bone and Microcirculation Laboratory, Department of Kinesiology, University of Texas Arlington, Arlington TX, 2Department of Health Science, Kinesiology,
Recreation and Dance, University of Arkansas, Fayetteville AR, and 3Department of Kinesiology, Auburn University, Auburn AL
Bone Cellular Activity with Ovariectomy and Estrogen Replacement
Loss of estrogen is associated with an altered balance
between bone formation and resorption, resulting in bone loss.
Ovariectomy (OVX) in rats is an appropriate model to
examine the effects of sex-hormone deficiency on osteoblast
and osteoclast activity.
Further, estrogen repletion provides a mechanistic
examination of bone restoration following OVX.
HYPOTHESIS
METHODS
Bone volume will be lower in OVX vs. OVE rats
Osteoclast activity will be higher in OVX vs. OVE rats
Osteoblast activity will be lower in OVX vs. OVE rats
PURPOSE
The purpose of this study was to examine bone static
properties (i.e., osteoblast and osteoclast activity) following
OVX and estrogen replacement (OVE).
Ovariectomy (i.e., loss of reproductive hormones) markedly reduced bone volume and presumably reduced bone
mineralization in OVX rats; suggesting reductions in bone mechanical strength. Finally, bone volume was
restored with estrogen replacement via augmented osteoblast activity.
CONCLUSION
Values represent mean ± SE. *denotes a significant (p < 0.05)
difference from OVE groups.
204 ± 8233 ± 6*Body Mass (g)
OVEOVX
Table 1. Rat Characteristics
Values represent mean ± SE. *denotes a significant (p < 0.05)
difference from OVE groups.
204 ± 8233 ± 6*Body Mass (g)
OVEOVX
Table 1. Rat Characteristics
Values represent mean ± SE. *denotes a significant (p < 0.05)
difference from OVE groups.
213 ± 381314 ± 516Tb.Sp (µm)
4.6 ± 0.71.2 ± 0.3*Tb.N /mm
29 ± 221 ± 2*Tb.Th (µm)
OVEOVX
Table 2. Bone Microarchitectural Properties
Values represent mean ± SE. *denotes a significant (p < 0.05)
difference from OVE groups.
213 ± 381314 ± 516Tb.Sp (µm)
4.6 ± 0.71.2 ± 0.3*Tb.N /mm
29 ± 221 ± 2*Tb.Th (µm)
OVEOVX
Table 2. Bone Microarchitectural Properties
Values represent mean ± SE.
2.6 ± 0.82.4 ± 1.1N.Oc/T.Ar
0.6 ± 0.20.9 ± 0.3Oc.S/BS (%)
0.8 ± 0.11.5 ± 0.6Ob.S/BS (%)
OVEOVX
Table 3. Bone Static Properties
Values represent mean ± SE.
2.6 ± 0.82.4 ± 1.1N.Oc/T.Ar
0.6 ± 0.20.9 ± 0.3Oc.S/BS (%)
0.8 ± 0.11.5 ± 0.6Ob.S/BS (%)
OVEOVX
Table 3. Bone Static Properties
0
2
4
6
8
10
12
14
16
OVX OVE
BV/TV(%)
*
Figure 1. Bone volume to total volume ratio
(BV/TV). *p < 0.05
0
2
4
6
8
10
12
14
16
OVX OVE
BV/TV(%)
*
Figure 1. Bone volume to total volume ratio
(BV/TV). *p < 0.05
*
Figure 1. Bone volume to total volume ratio
(BV/TV). *p < 0.05
0.0
0.5
1.0
1.5
2.0
OVX OVE
OS/BS(%)
*
Figure 2. Osteoid surface to bone surface
(OS/BS). *p < 0.05
0.0
0.5
1.0
1.5
2.0
OVX OVE
OS/BS(%)
*
Figure 2. Osteoid surface to bone surface
(OS/BS). *p < 0.05
0
5
10
15
20
25
30
35
OVX OVE
N.Ob/T.Ar
*
Figure 3. Number of osteoblast per total area
(N.Ob/T.Ar). *p < 0.05
0
5
10
15
20
25
30
35
OVX OVE
N.Ob/T.Ar
*
Figure 3. Number of osteoblast per total area
(N.Ob/T.Ar). *p < 0.05