Preglomerular resistance is regulated by calcium influx- and mobilization-dependent mechanisms; however, the role of Rho-kinase in calcium sensitization in the intact kidney has not been carefully examined. Experiments were performed to test the hypothesis that Rho-kinase inhibition blunts pressure-mediated afferent arteriolar autoregulatory behavior and vasoconstrictor responses evoked by angiotensin II and P2X₁ receptor activation. Rat kidneys were studied in vitro using the blood perfused juxtamedullary nephron technique. Autoregulatory behavior was assessed before and during Rho-kinase inhibition with Y-27632 (1.0 µM; n=5). Control diameter averaged 14.3 ± 0.8 µm and increased to 18.1 ± 0.9 µm (P<0.05) during Y-27632 treatment. In the continued presence of Y-27632, reducing perfusion pressure to 65 mmHg slightly increased diameter to 18.7 ± 1.0 µm. Subsequent pressure increases to 130 and 160 mmHg yielded afferent arteriolar diameters of 17.5 ± 0.8 and 16.6 ± 0.6 µm (P<0.05). This 11% decline in diameter is significantly smaller than the 40% decrease obtained in untreated kidneys. The inhibitory effects of Y-27632 on autoregulatory behavior were concentration dependent. Angiotensin II responses were blunted by Y-27632. Angiotensin II (1.0 nM) reduced afferent diameter by 17 ± 1% µm in untreated arterioles and by 6 ± 2% during exposure to Y-27632. The P2X₁ receptor agonist, , -methylene ATP, reduced afferent arteriolar diameter by 8 ± 1% but this response was eliminated during exposure to Y-27632. Western blot analysis confirms expression of the Rho-kinase signaling pathway. Thus, Rho-kinase may be important in pressure-mediated autoregulatory adjustments in preglomerular resistance and responsiveness to angiotensin II and autoregulatory P2X₁ receptor agonists.