What are the three hemodynamic phases of acute unilateral upper tract urinary obstruction?
In the first phase of unilateral upper tract obstruction (first 1 to 2 hours), intrarenal pressure rises due to obstruction.
In response, tubuloglomerular feedback mechanisms allow for afferent arteriolar vasodilation (mediated by prostaglandin E 2 and nitric oxide), which increases kidney blood flow to maintain glomerular filtration rate (GFR).
In the second phase (lasting 3 to 4 hours), intrarenal pressures remain elevated, but elevated renin released during phase one results in angiotensin II mediated preglomerular vasoconstriction and decreased kidney blood flow.
A third phase (beginning ~5 hours after obstruction) is marked by a further decline in kidney blood flow and GFR mediated by a number of vasoconstrictors (including angiotensin II, thromboxane A 2 , endothelin).