Nitric oxide in the kidney; direct measurements of bioavailable renal nitric oxide

Increasing efforts have been directed towards investigating the involvement of nitric oxide (NO) for normal kidney function. Recently, a crucial role of NO in the development of progressive renal dysfunction has been reported during diabetes and hypertension. Indirect estimation of renal NO production include urinary nitrite/nitrate measurements, but there are several disadvantages of indirect methods since production and bioavailability of NO rarely coincide. Thus, direct measurement of in vivo NO bioavailability is preferred, although these methods are more time consuming and require highly specialized equipment and knowledge. This review focuses on two techniques for in vivo measurement of bioavailable NO in the kidney. We have applied Whalen-type recessed NO microsensors for measurement of NO in the kidney cortex, whereas the hemoglobin-trapping technique seems to be more suitable for NO measurement in the renal medulla. Both methods are robust and reliable, and we discuss advantages and shortcomings of each method.