190. A 68-year-old woman comes to the office because of a 3-month history of increased daytime and nighttime urination and pain of her low back. She had cervical cancer 15 years ago, at which time she underwent hysterectomy with bilateral salpingo-oophorectomy. She also received external beam radiation to the pelvis. Physical examination shows no palpable abdominalnasses. Laboratory studies show increased serum concentrations of urea nitrogen and creatinine and decreased urine osmolality. Renal ultrasonography shows bilateral hydronephrosis and hydroureter, with distal ureteral narrowing bilaterally. Which of the following best explains the polyuria and nocturia in this patient? A) Decreased estradiol secretion B) Decreased glomerular filtration C) Failure to concentrate the urine D) Increased renal plasma flow E) Osmotic diuresis

190. A 68-year-old woman comes to the office because of a 3-month history of increased daytime and nighttime urination and pain of her low back. She had cervical cancer 15 years ago, at which time she underwent hysterectomy with bilateral salpingo-oophorectomy. She also received external beam radiation to the pelvis. Physical examination shows no palpable abdominalnasses. Laboratory studies show increased serum concentrations of urea nitrogen and creatinine and decreased urine osmolality. Renal ultrasonography shows bilateral hydronephrosis and hydroureter, with distal ureteral narrowing bilaterally. Which of the following best explains the polyuria and nocturia in this patient? A) Decreased estradiol secretion B) Decreased glomerular filtration C) Failure to concentrate the urine D) Increased renal plasma flow E) Osmotic diuresis