Bone changes in 6-mo-old rats after head-down suspension and a reambulation period

Area of Science:

• Physiology
• Bone Biology
• Spaceflight Analog Research

Background:

• Head-down suspension is a common model for simulating microgravity effects on bone.
• Understanding bone loss mechanisms is crucial for astronaut health and terrestrial conditions.

Purpose of the Study:

• To investigate the impact of 14-day head-down suspension and subsequent reambulation on rat bone morphometry, bone mineral content (BMC), and bone mineral density (BMD).
• To assess the reversibility of suspension-induced bone alterations.

Main Methods:

• Mature rats underwent 14-day head-down suspension or suspension followed by 28-day reambulation.
• Hindlimb long bones, humerus, and skull were analyzed for morphometry, BMC, BMD (using dual-energy X-ray absorptiometry), dry/ash weights, and calcium content.
• Control groups were included for comparison at different time points.

Main Results:

• Suspension led to decreased calcium content, ash weight, BMC, and BMD in the tibia and femur.
• No significant changes were observed in the humerus.
• Unexpectedly, skull BMC, ash, and dry weights decreased post-suspension.
• Bone alterations showed incomplete reversibility after reambulation, with persistent decreases in tibia BMC and BMD.

Conclusions:

• Head-down suspension induces significant bone loss in rat hindlimbs, with limited recovery.
• The unexpected skull bone changes highlight the importance of fluid shifts during desuspension.
• Dual-energy X-ray absorptiometry is a sensitive method for detecting suspension-induced bone changes.