The initial reaction to Ohio Republican Sen. Rob Portman’s shift to supporting gay marriage was mixed on Friday, with leading Republican gay rights groups praising his decision and some social conservatives rejecting the senator's claim that same-sex marriage is a generational issue.

"I'm not too sure the rationale behind what Senator Portman's doing is something that has broad application to the base," former Pennsylvania senator Rick Santorum told CNN. "The fundamental principles that attach to the institution of marriage really haven't changed as a result of that personal story."

Michael Steel, a spokesman for House Speaker John Boehner (R-Ohio), said, "Sen. Portman is a great friend and ally, and the Speaker respects his position, but the Speaker continues to believe that marriage is between a man and a woman."

Anti-tax advocate Grover Norquist, who sits on the board of GOProud, a national conservative gay rights group, said he doesn't know if Portman's decision will mark a turning point in the debate over gay rights, but it's worth watching. Norquist said he doesn't have a position on gay marriage.

"In terms of what will happen, I guess watch on this one," Norquist said in an interview at the Conservative Political Action Conference. "But I think at the end of the day that you're going to have a modern Republican Party that makes it very clear that it's open to participation by everybody, including gays."

“Senator Portman's announcement that he supports marriage equality for gay couples because he wants his gay son to have the same opportunity he and his wife have had for 26 years is an announcement that hits home for many Americans,” added GOProud Executive Director Jimmy LaSalvia.

Gregory T. Angelo, the Executive Director of the Log Cabin Republicans, an LGBT advocacy group, said, “If there was any doubt that the conservative logjam on the issue of civil marriage for committed gay and lesbian couples has broken, Senator Portman's support for the freedom to marry has erased it.”

Portman told reporters that his 21-year-old son came out as gay to him and his wife in February 2011, an event that has affected his thinking about gay marriage.

"With the overwhelming majority of young people in support of allowing gay couples to marry, in some respects the issue has become more generational than partisan," he wrote in the Columbus Dispatch.

Tony Perkins, head of the conservative Christian group Family Research Council, commended Portman for loving his son, but disputed the generational component he cited.

"Senator Portman stated this was a generational issue, with younger Americans more supportive of redefining marriage. However, one of the Senate's youngest senators, [Sen.] Marco Rubio [of Florida] clearly articulated the need for natural marriage and the right of states to preserve it," said Perkins.

Bob Vander Plaats, an Iowa conservative activist who has long opposed gay marriage, said he doesn’t think that Portman’s announcement will shift the debate about it within the GOP.

“I totally recognize Sen. Portman and his love for his son, but at the same time, a love for a son shouldn’t dictate cultural shifting policies for our country that are against god’s design for the family,” said Vander Plaats.

Andrea Lafferty, the head of the conservative Christian group Traditional Values Coalition, likened the influence of Portman's son on the senator's decision to support gay marriage to someone accepting drunk driving after learning their child was a drunk driver.

"I wish no harm to either Senator Portman or his son but they are wrong," said Lafferty.

Veteran Republican strategist Ed Rogers said Portman's decision is a positive step for the Republican Party.

"Who among us doesn’t have gay family and friends that we love and want them to have complete and fulfilled lives," Rogers said. "Good for Rob Portman, and good for the GOP."

Aaron Blake contributed to this post