(CNN) Donald Trump's nominee to lead the Department of Health and Human Services, Rep. Tom Price, defended himself from accusations of inappropriate financial investments Wednesday in a fiery four-hour hearing that exposed the congressman's political vulnerabilities.

"Everything that we have done has been above-board, transparent, ethical and legal," Price told the Senate Health committee as Democrats grilled him over stock purchases that they said appeared to show that Price made financial gains from his work as a legislator.

Price, an orthopedic surgeon, made his name in Washington as an ardent critic of Obamacare and authored among the most detailed legislation to dismantle President Barack Obama's landmark health care law. If confirmed, Price could play an outsized role in efforts to roll back major parts of the law -- a top legislative priority for Republicans under the Trump administration.

But while Price fielded plenty of questions Wednesday about his views on reforming the health care system, it was his actions as an investor that sparked the tensest exchanges and seemed at times to leave the veteran lawmaker flustered.

Right off the bat, Sen. Patty Murray, the top Democrat on the Health Committee, grilled Price on whether he purchased stocks in a company called Innate Immunotherapeutics after receiving a "stock tip" from a fellow member of the House, GOP Rep. Chris Collins.

"Do you believe it is appropriate for a senior member of Congress, actively involved in policymaking in the health center, to repeatedly personally invest in a drug company that could benefit from those actions?" Murray asked.

"That's not what happened," said Price, who insisted repeatedly that he never received information that could be considered stock tip.

Murray shot back: "I believe it's inappropriate. And we need answers to this."

Later in the hearing, Price also said he has "no idea" what stocks he owns when Sen. Al Franken brought up congressman's prior holdings in tobacco companies.

"How do you square reaping personal financial gains from sales of an addictive product that kills millions of Americans every decade with also voting against measures to reduce the death toll inflicted by tobacco?" Franken asked.

The question was among the most antagonistic and personally hitting for Price, who had said earlier that his father had been a "Lucky Strike smoker from World War II" who died from emphysema.

"I have no idea what stocks I held in the '90s or the 2000s or even now," Price said. "All of these decisions for all of us I suspect, are through mutual funds and through pension funds."

One specific ethics concern raised during the hearing was Price's investment last year in a medical device manufacturer called Zimmer Biomet. CNN reported on Monday that after buying shares in the company, Price introduced legislation that would have directed benefited the firm.

Democratic Sen. Elizabeth Warren said it was hard to believe that Price's broker was simply someone "you pay to handle the paperwork."

"This is someone who buys stock at your direction. This is someone who buys and sells the stocks you want them to buy and sell," Warren said.

"Not true. That's not true senator," Price responded.

"Just because you decide not to tell them? Wink, wink, nod, nod and we're all just supposed to believe that?"

When Warren pressed Price further on whether he took deliberate action as a lawmaker to help the company, Price shot back that he was "offended by the insinuation."

But while Price said he didn't know what stocks he previously owned, he maintained that he has divulged his and his wife's holdings every year and has updated it if there were any changes.

"There isn't a single bit of information that's out here that I didn't reveal to the public in a transparent process," he said.

Ethics office role

Price also praised the Office of Government Ethics and the "diligence" of its review of cabinet nominees' holdings and assets. He noted that the office puts very specific recommendations online that the public can review.

"We have agreed to every single recommendation that they've made to divest of whatever holdings we have that might even give the appearance of a possible conflict," Price said.

Price was likely referring to the fact that Zimmer Biomet Holdings is listed in his financial disclosure and his ethics agreement as an asset for him to divest if confirmed to run HHS.

The Office of Government Ethics, however, is tasked with reviewing Price's potential conflicts for his administration post, not his previous conduct.

"The Office of Government ethics reviews his current situation for potential conflicts of interest and negotiates an agreement with how he should handle (divestment) in the future," Larry Noble, general counsel at the Campaign Legal Center, said about Price's testimony. "It does not look at his past activity."

The ethics office also weighed, sending out a series of tweets soon after Price's testimony and clarifying its role:

"OGE oversees the executive branch #ethics program, while Congress & the Courts have their own ethics programs....

OGE does not handle complaints of misconduct. Please learn where & how to report #fed employee misconduct," the agency wrote.

Obamacare repeal

Price, expected to be a key player in the GOP's effort to repeal and replace the Affordable Care Act, said Trump and Republicans must reassure the American people that "Nobody's interested in pulling the rug out from under anybody."

"We believe that it's absolutely imperative that individuals that have healthcare be able to keep health coverage and move hopefully to greater choices and opportunities for them to gain the kind of coverage that they want," Price said. "There's been a lot of talk about individuals losing health coverage. That is not our goal, nor is it our desire nor is it our plan."

Asked by Sen. Lamar Alexander, R-Tennessee, chairman of the health committee, about Trump's recent comments that repeal and replace should happen simultaneously, Price said he believes "that's fair."

Price, however, has been kept out of the loop on Trump's Obamacare proposal so that he doesn't have to answer questions about the specifics of that plan, according to a Trump transition official.

In his opening statement, Price emphasized his upbringing and professional background, including his 20 years as a practicing physician that he said helped him learn about "not just treating patients but about he broader health care system and where it intersects with government."

But he did not mention his legislation to undo Obamacare during those introductory remarks, speaking instead in broad strokes about the country's health care system. Price said he believes in these six principles of health care: "Affordability, accessibility, quality, responsiveness, innovation and choices."

GOP Sen. Orrin Hatch, along with other Republican senators, strongly defended his fellow lawmaker. Hatch called the accusations leveled against Price "nothing more than a hypocritical attack on your good character. And I personally resent it."

This will be the first of two hearings for Price. He will also face the Senate Finance Committee on January 24.