Abstract: AIM To investigate the relationship between impaired vasoconstriction of renal artery and altered Rho-associated protein kinase (ROCK) induced by simulated microgravity in rats. METHODSFour-week hindlimb unweighting (HU) rats were adopted as animal models. Isometric force was measured by isolated tissue bath with or without Y-27632, a specific ROCK inhibitor. Protein expression and activity of ROCK were examined by Western blot and ROCK activity assay. RESULTSCompared with those in the control group, phenylephrine (PE)- and KCl-induced contractions were significantly decreased in the HU group (P<0.05) and inhibition of ROCK with Y-27632 significantly reduced the decrement of vasoconstriction between the control group and the HU group (P<0.05). The protein expression of ROCK was up-regulated (P<0.05), whereas ROCK activity was decreased (P<0.05) in renal arteries of the HU group. CONCLUSIONRenal artery vasoconstriction is decreased under simulated microgravity. Inhibition of ROCK may diminish the vasoconstrictive difference between control and simulated microgravity rats. The reduced activity of ROCK may be an important mechanism accounting for the impaired vasoconstriction in renal arteries induced by simulated microgravity in rats.