Medtronic Inc. on Thursday discontinued development in the U.S. on what many considered one of the most promising potential therapies for high blood pressure that cannot be controlled by medication.

The Fridley-based med-tech giant ended a large U.S. trial for its Symplicity renal denervation system, which seeks to control hypertension by burning nerves in the kidneys. The company said the technology was ineffective.

The news puts the future of renal denervation, and what some analysts predicted could become a $3 billion worldwide market, in doubt.

About 1.2 billion people worldwide suffer from high blood pressure and about one-third of them have a kind that doesn’t respond to medications.

Medtronic, St. Jude Medical Inc., Boston Scientific Corp. and dozens of other companies around the world had been racing to take advantage of what was seen as a promising therapy.

In addition to ending the U.S. trial, which involved 535 patients at 87 medical centers, Medtronic also said it would stop recruiting patients for clinical trials in Japan and India. The company added that it will tell medical investigators of its findings and create a panel of independent advisers to make recommendations on what to do next.

“I think there’s a lot of work to do to understand and evaluate what these findings mean,” said Wendy Dougherty, a Medtronic spokeswoman.

Medtronic stock dropped $1.48, or 2.4 percent, on the news. Medtronic said it will continue to make its device available to overseas patients in countries where it had been previously approved for sale.

“We are disappointed that the clinical trial failed to meet its primary efficacy endpoint,” Dr. Rick Kuntz, Medtronic’s chief medical officer, said in a statement. “We believe this course of action is the most prudent and will help us thoroughly evaluate these findings and determine the appropriate next steps.”

Analysts noted that renal denervation is not a big part of Medtronic’s overall portfolio, but the company had been an enthusiastic early proponent of its potential.

Other programs are at risk

“Bottom line: the potential $1 billion market opportunity remains elusive, and we assume competitive programs [St. Jude Medical, Boston Scientific and Covidien] are at risk.” said Joanne Wuensch, an analyst at BMO Capital Markets.

Danielle Antalffy, with Leerink Swann Research, said Medtronic’s news came as a surprise, following positive results from earlier, smaller clinical trials and in Europe.

“The failed Symplicity HTN-3 trial could also have implications for the [renal denervation] market more broadly, bringing into question whether the catheter ablation approach is truly efficacious in reducing hypertension,” she wrote to investors.

Renal denervation involves snaking a catheter through the femoral artery up to the renal arteries, where it uses heat to deactivate the renal nerves and, in theory, lower blood pressure.

Earlier clinical ­trials had been positive and, last year, analysts were saying that global denervation sales could reach $3 billion within 10 years.

Medtronic paid $800 million in 2010 for the Ardian renal denervation product.

St. Jude had dropped trial

Last year, St. Jude Medical announced that its EnligHTN renal denervation system safely and effectively lowered blood pressure at six months. But, in December, St. Jude discontinued its trial, citing recruitment challenges. Spokeswoman Amy Jo Meyer said Thursday that that decision was “not a consequence of a safety or efficacy issue with the device or study.”

Boston Scientific, a Natick, Mass.-based medical device maker with sizable operations in the Twin Cities, last year bought a company that had developed a renal denervation system that had been approved for use in Europe and Australia. On Thursday, Boston Scientific said it has no plans to exit the business.

“We remain confident in the direction and the prospects for our Vessix renal denervation program,” spokesman Ryan Davenport said. “There is a large patient population that is challenged by hypertension on a daily basis. We have a highly differentiated technology that we believe can provide benefits to these patients.”

He added: “Our outlook has not changed.”