Renal Study: Captopril

Overview

Significant renal artery stenosis (60-75%) decreases afferent arteriolar blood pressure, which stimulates renin secretion by the juxtaglomerular apparatus. Renin effects the production of angiotensin I, which is acted on by ACE to yield angiotensin II. Angiotensin II induces vasoconstriction of the efferent arterioles, which restores glomerular filtration pressure and rate. ACE inhibitors, such as captopril and enalapril, prevent the production of angiotensin II, so that in patients with renal artery stenosis and compensated renal function, preglomerular filtration pressures are no longer maintained.

Indications

  • Diagnosis of renovascular hypertension.
  • Diagnosis of renal artery stenosis.

Study Description

After an IV is started, the partient is positioned on the imaging table with the camera detector adjusted to image from the posterior projection. The radiopharmaceutical will be administered and a dynamic study (a rapid series of short duration images) will immediately be acquired to assess the blood flow to the kidney. Following this, a series of dynamic (continous) images will be taken immediately for 30 minutes.

After the picture is obtained, the patient will be set in a designated waiting area and a baseline blood pressure will be taken. (If the baseline blood pressure is less than 140/70, consult the physician or radiologist about continuing the exam).

After the baseline blood pressure is taken, the patient will receive an oral Captopril. Sitting blood pressures should be taken at 15 minute intervals for one hour. The patient is then taken for another image just like the one that was previously acquired for 30 minutes.

Examination Time

  • Approximately 3 1/4Hours

Patient Preparation

  • Ensure the patient is not pregnant or breastfeeding.
  • No solid food 4 hours prior to exam
  • Well hydrated prior to exam
  • Off ACE inhibitors and Angiotensin II receptor blockers (ARB’s) for 3 to 7 days prior to study (longer half-life drugs discontinued for 7 days)
    Examples:
    • Off Captopril 3 days
    • Off of Lisinopril, Benzapril, Enalapril, Irbesartan, Candesartan, Losartan, or Valsartan for 5 days
  • Off diuretics for 3 to 5 days prior to study
  • Off other Antihypertensive drugs (beta blockers & calcium channel blockers) the night before the exam
  • The patient should void before beginning the study