List seven causes of a persistent nephrogram on IVP.

1. Ureteral obstruction (unilateral)
2. Hypotension (bilateral)
3. Ischemia (bilateral)
4. Acute renal failure (bilateral)
5. Glomerulonephritis (bilateral)
6. Acute tubular necrosis (bilateral)
7. Renal vein thrombosis (either)