Table 2.

Summary of cortical histomorphometric structural parameters from femur mid-diaphysis cross-sections collected from female C57BL/6J mice (77-days-old at euthanasia). Mice were assigned to one of five groups (n=12/group): Baseline, Ground Control (GC) with Vehicle (VEH; phosphate-buffered saline), GC with Osteoprotegerin (OPG-Fc; 20 mg/kg), Spaceflight (SF) with VEH, and SF with OPG-Fc. The duration of microgravity exposure during SF was 12 days. Mice received an injection of the bone label calcein (20 mg/kg) approximately 22 hours prior to the start of the study.

		Ground Control		Spaceflight
	Baseline	Vehicle	OPG-Fc	Vehicle	OPG-Fc	2-Way ANOVA
BV (mm³⁾	0.65 ± 0.01	0.70 ± 0.01	0.71 ± 0.01	0.65 ± 0.01^L	0.67 ± 0.01^L	SF<GC
TV (mm³⁾	1.54 ± 0.02	1.59 ± 0.01	1.61 ± 0.01	1.56 ± 0.02	1.56 ± 0.02^L	SF<GC
Med.V (mm³⁾	0.90 ± 0.01	0.89 ± 0.01	0.90 ± 0.01	0.91 ± 0.01	0.88 ± 0.01	-
Av.Ct.Th (μm)	170 ± 6	194 ± 5	189 ± 6	173 ± 7^L	188 ±6^D	SF<GC
Ec.ES/BS (%)	-	24.5 ± 2.3	14.6 ± 3.3^D	24.8 ± 1.8	17.1 ± 2.3^D	OPG-Fc<VEH

Data are presented at mean ± SEM. 2-way-ANOVA differences are presented in the right-most column. Significant differences within Loading (GC vs. SF) or Drug (VEH vs. OPG-Fc) were tested by a Tukey follow-up test (significance set at P<0.05). Loading (L) indicates a significant difference between SF and GC within VEH or OPG-Fc; Drug (D) indicates a significant difference between OPG-Fc and VEH within GC or SF.