Updated: 5:19 p.m.

Rep. Dan Boren (D-Okla.) will not seek re-election in 2012, providing House Republicans with a prime pickup opportunity in the Sooner State.

Boren, 37, will retire instead of seeking a fifth term, according to a source close to the Congressman — marking the first House Member this cycle to announce he is leaving at the end of this Congress without running for another office.

“I have made the decision not to seek re-election next year for another term in Congress,” Boren said in a statement. “This is not an easy decision for me. It was based on the demands of constant campaigning, and most importantly spending too much time away from my family which includes two very young children.”

The Oklahoman first reported Boren’s retirement, which he announced at 3 p.m. EST in his hometown of Muskogee.

Republicans welcomed the news. Although Boren won re-election with 57 percent of the vote in his mostly-rural eastern Oklahoma district in 2010, Sen. John McCain (R-Ariz.) carried it with 66 percent in 2008. The National Republican Congressional Committee had already indicated that it planned to target Boren in 2012, launching a round of automated phone calls into his district criticizing the Congressman Tuesday morning — hours before Boren was expected to announce his retirement.

“With Dan Boren’s announcement today, conservatives in Eastern Oklahoma will have the opportunity to elect a Republican who will go to Washington and vote the Oklahoma way, not the Obama way,” Oklahoma Republican Party Chairman Matt Pinnell said in a statement following Boren’s news conference. “This is an opportunity, and one that the OKGOP is already working hard to make a reality next November.”

However, Republicans were mostly mum thus far on potential candidates to challenge Boren, whom they failed to recruit top candidates to run against in previous cycles. Oklahoma sources mentioned state Sen. Josh Brecheen (R) as a potential candidate in the open-seat race, but his office did not immediately return an email request for comment.

Former Rep. Brad Carson (D), Boren’s predecessor, was the first to announce his candidacy for the seat just hours before Boren’s official announcement. Carson lost by 12 points to now-Sen. Tom Coburn (R) in 2004.

“I have no doubt it will be very competitive, and you don’t take anything for granted,” Carson told Roll Call in a telephone interview. “A formal announcement will be some months away, but we have every intention to get the campaign up and running sooner rather than later.”

A professor at the University of Tulsa, Carson said his “good friend” Boren called him Tuesday morning to tell him he wasn’t running for re-election, and he then decided immediately he would pursue his former seat. Carson said he has $40,000 left in his campaign account from his failed Senate bid, which he plans to roll over into a new House campaign account.

At least two other Democrats have been mentioned as possible candidates for the seat. Former state Sen. Kenneth Corn, the Democratic nominee for lieutenant governor last year, is also likely to run “no matter who else is in the race,” according to one of his aides. State Sen. Jim Wilson challenged Boren in the Democratic primary in 2010 but only garnered 24 percent of the vote.

“I’ve been surprised by his announcement and it is premature to make a decision,” Wilson said in a statement. “I did run against him in the last cycle because I didn’t believe he had the progressive values needed in CD 2.”

Boren’s announcement came as a surprise to many in Oklahoma and Washington, D.C. The four-term Congressman was actively fundraising for his campaign and reported having almost $1.04 million in the bank at the end of March.

The Democrat had also just finished working with state lawmakers to pass a new Congressional map last month and personally signed off on the changes to what many believed would be his future district.

“I was at a D.C. fundraiser for him just a couple of weeks ago and he sounded like he was full steam ahead,” one Oklahoma insider said. “This has been held close to the vest. In fact, I haven’t even heard any rumors to this effect.”

Carson said he was surprised at first when Boren told him that he wouldn’t run again, but looking back at some of their recent conversations, “it makes sense to me that this was something he was thinking about.”

“He’s got a couple of young children and he thought it was time to do something else with his life,” Carson said. “His lifestyle, I know, is a very grueling one. … You’re under a lot of pressure as a Democrat from Oklahoma, on both sides.”