A surprising discovery inside a laboratory at Mayo Clinic may reshape scientists' understanding of one of the body's most basic survival functions: how the kidneys conserve water.

Researchers have identified a previously unknown pathway that helps the kidneys regulate water balance, a finding that could eventually improve treatment for people living with polycystic kidney disease (PKD), a common inherited condition that often leads to kidney failure. The study, led by kidney specialist Dr Fouad Chebib and published in the Journal of Clinical Investigation, goes against many years of medical teaching that has mainly attributed the control of urine concentration and dehydration prevention to one hormone, vasopressin.

"The kidney's ability to regulate water is one of the most fundamental processes in the body," Dr Chebib said. "It's not every day that you uncover a new way it carries out that function."

The breakthrough emerged from an unexpected laboratory observation. Dr Chebib's team was studying how fluid-filled cysts grow in PKD using lab-grown kidney cell models. Researchers tested several compounds that they believed would worsen the disease by boosting cellular signals linked to cyst growth. One of those compounds was probenecid, a drug introduced in the 1940s to slow the loss of penicillin through urine.

The result stunned the team.

"We thought this drug would make the disease process worse," Dr Chebib said. "Instead, it did the opposite."

After repeating the experiments multiple times to rule out error, the researchers found that probenecid actually slowed cyst growth. Months of follow-up investigations revealed why. The drug altered how kidney cells handled urate, a natural substance best known for its role in gout. Inside kidney cells, urate appeared to act as a signalling molecule, triggering a chain reaction that moved water channels to the cell surface. These channels then allowed the kidneys to reabsorb water and produce more concentrated urine.

In simple terms, the kidneys seemed to possess a backup system for conserving water.

"This represents a distinct pathway from what is described in traditional physiology models," Dr Chebib said. "It demonstrates that the kidney has an additional mechanism to preserve water."

The finding may be particularly important for patients taking tolvaptan, currently the only approved treatment for autosomal dominant polycystic kidney disease. The drug slows cyst growth by blocking vasopressin. However, it often causes patients to produce six to seven litres of urine a day, forcing many to drink constantly and wake repeatedly during the night.

In preclinical studies and a small clinical trial, adding probenecid reduced urine volume by about 30 per cent while maintaining treatment effectiveness. Patients who previously woke several times each night to urinate reported waking only about once. Many also described improvements in daily comfort and quality of life.

The discovery adds to a growing body of research showing that kidney function is more complex than previously believed. Scientists worldwide have spent decades studying vasopressin and water regulation, yet this newly identified pathway suggests important biological mechanisms may still remain hidden.

"The goal is to preserve the therapeutic benefit of tolvaptan while reducing its burden," Dr Chebib said.

Researchers caution that probenecid itself is unlikely to become the long-term answer because the drug affects multiple systems in the body and is not widely used today. Instead, the Mayo Clinic team hopes the discovery will lead to a new generation of targeted medicines designed specifically to activate this newly uncovered pathway.

"Probenecid helped us uncover the mechanism," Dr Chebib said. "Our goal is to take this insight and develop therapies designed specifically for this pathway."

For millions of people living with kidney disease, that insight may one day translate into something simple but life-changing: effective treatment with fewer disruptions to everyday life.