ATP shows more potential as a urinary biomarker than acetylcholine and PGE2 but its concentration in urine is not a simple function of dilution

Aims
To determine whether the amount of ATP, prostaglandin E2 (PGE2), and acetylcholine (ACh) in voided urine are influenced enough by that released within the lower urinary tract (LUT) for them to be useful biomarkers of bladder function.

Methods
Participants without LUT symptoms collected total urine voids at 15, 30, 60, and 120 min (20 males/23 females) and 240 min (18 males/26 females) following the previous void. Aliquots of urine were immediately frozen at −20°C and later used to measure ATP (luciferin‐luciferase), PGE2 (enzyme‐linked immunosorbent assay), ACh (mass spectrometry), creatinine (colorimetric), and lactose dehydrogenase (colorimetric).

Results
The amount of ATP in voided urine correlated strongly with the rate of urine production, suggesting that the majority, if not all, the ATP in voided urine has an LUT, and likely bladder, origin. In contrast, there appeared to be no significant net LUTs release of creatinine or ACh into the urine. PGE2 was intermediate with an LUT component that increased with urine production rate and contributed about 25% of the total at 1 ml/min in women but a smaller fraction in men.

Conclusion
Whereas the majority of the ATP measured within the voided urine originates in the LUT, ACh reflects that extracted from the plasma in the kidneys and PGE2 is a mixture of both sources. ATP has the most potential as a biomarker of benign bladder disorders. Expressing urinary ATP concentration relative to creatinine concentration is questioned in light of these results.