PORTLAND – The president and chief executive officer of Maine Medical Center is stepping down after 11 years, but the reason for the departure is a mystery.

Vincent Conti’s office reported that he was not responding to media interview requests Wednesday, a day after the hospital’s trustees announced that Conti will step down on June 15.

In a prepared statement, the board on Tuesday praised Conti for his service. Richard Petersen, Maine Med’s chief operating officer, will serve as interim CEO and president, the board said.

“Vince has accomplished a great deal during his tenure, and Maine Medical Center is stronger than ever,” the statement said.