REN and Hypertension: Increases in circulating Ang II concentrations during the first 1–2 weeks of 2K1C hypertension cause systemic effects; however, it has been shown that, after several weeks of stenosis, renal perfusion pressure to the clipped kidney can be re-established, and plasma renin activity and circulating Ang II concentrations tend to return to the normal levels even though the arterial pressure remains elevated.