Pryor, who took the hospital system's leadership position in 2013, has been under pressure since last summer, following community concerns over the hospital's research on the sedative ketamine. It's unclear if that factored into his departure.

Reached for comment Tuesday, Pryor confirmed he's resigning, but deferred to the hospital board as to the explanation. Hennepin Healthcare System board chairwoman Sheila Riggs declined to answer questions about Pryor's resignation.

"It's just been a wonderful organization to work for, and I just love our employees and I love the people we take care of," Pryor said.

"This is the right time for me to make a transition to the next chapter of my life," Pryor wrote in an internal e-mail to colleagues. "Hennepin Healthcare is on the right path, but there is work still to be done. I regret that I won't be part of it, but I am confident that the right people and plans are in place. Later this week you will hear more about the next steps."

The board will meet Wednesday to consider Dr. John Cumming as the interim replacement.

"We are grateful to Dr. Pryor for leading us through this period of growth," Riggs said in a written statement. "He is an innovator who helped the organization reconnect with the community and Hennepin Healthcare System is stronger today because of his leadership."

Hennepin Healthcare operates HCMC, the largest safety-net hospital in the Twin Cities. In a statement, the hospital credited Pryor's leadership for expanding the health system's reach by opening clinics in new markets and renovating and expanding existing clinics. The system also opened a six-story Clinic & Specialty Center that combined many of its downtown clinics into a new facility.

The hospital faces financial challenges. County Commissioner Jan Callison said it ran a deficit in 2018 and she expects a deficit this year as well.

Callison praised Pryor as "a dedicated leader who put the interest of the institution at the forefront of his work."

Pryor is trained as a urologist and has published articles in medical journals on men's health issues. From 2001 to 2006 he was chair of the University of Minnesota's Department of Urologic Surgery. He graduated with an MBA from the Kellogg School of Management at Northwestern University. He also worked previously as CEO of the physicians group at the Medical College of Wisconsin.

Since last summer, the hospital has been embroiled in investigations into its use of the sedative ketamine on patients by paramedics in the field. Two politicians called the hospital's research "unconscionable and unethical" after the Star Tribune reported on a ketamine study that didn't require prior consent from patients.

Hennepin County Commissioner Mike Opat called out Pryor for failing to adequately keep the board updated. Pryor disputed Opat's claims, saying the hospital had regularly provided updates to the board.

Opat also criticized Pryor for a proposal to arm hospital security guards after cutting its contract with the Hennepin County Sheriff, which Opat likened to arming teachers to stave off school shootings.

"The need for new leadership at the hospital has been clear to me," Opat said Tuesday. "Financial performance has not been acceptable and community confidence has waned."

"I'm looking forward to a new CEO who will inspire the confidence of the County Board."

Late Tuesday, Hennepin County Board Chairwoman Marion Greene said "Dr. Pryor can best answer questions about why he has resigned" and added "he has led the organization with passion and commitment."

Last month, Hennepin Healthcare released the results of several examinations it commissioned to evaluate its research processes related to the sedation studies. The reports recommended changes to research protocols, including better outreach to the public, but concluded the paramedics and researchers followed protocols in line with national standards.

Staff writer David Chanen contributed to this report.

Andy Mannix • 612-673-4036