Contractile responses of thoracic aorta to hindlimb unloading in rat

Hindlimb Unloading (HLU) is used to simulate microgravity in rats and has been shown to decrease contractile response in the abdominal aorta. The aim of present study was to investigate the contractile responses of smooth muscle of thoracic aorta following acute and chronic microgravity treatment. Male adult rats (Wistar) were subjected to HLU for 3 and 20 days to establish ground-based-model of microgravity. The thoracic aortas were dissected and suspended in Krebs-Henseleit solution less than 1 g resting tension. Concentration response curves to cumulative doses of phenylephrine (PHE) and KCL were obtained in endothelium-denuded rings from control and HLU groups. Statistical analysis was carried out using analysis of two-way ANOVA and post hoc Bonferroni test. Contractile response of 20-day HLU-treated tissues with phenylephrine and KCL were increased in endothelium-denuded rings versus control group (3. 01±0. 058 vs. 2. 23±0. 034 g at max (phenylephrine)، HLU-20 vs. control; 2. 71±0. 043 vs. 2. 06±0. 040 g at max (KCl)، HLU-20 vs. control). There was no difference in vasoresponsiveness between control and 3-day HLU rings. Results of this study suggest that chronic HLU increase smooth muscle contracting in the thoracic aorta. It is proposed that these effects may be related to the fluid shifts in microgravity condition. Briefly، studies of vascular function are of particular importance in elucidating the mechanisms underlying vascular adaptation to microgravity and its gravity based countermeasure.