UK pharmaceutical giant AstraZeneca pulled out all the stops to fend off a hostile takeover from Pfizer earlier this year, refusing to release certain financial statements and stirring up opposition from British politicians.

Behind the scenes, the company also targeted Washington. AstraZeneca hired Wall Street advisers with close ties to the Obama administration: Thomas Nides of Morgan Stanley and Roger Altman of Evercore Partners. Messrs. Nides and Altman made previously undisclosed calls in May, people familiar with the calls said, telling senior administration officials they should clamp down on a merger technique, known as a corporate inversion, that Pfizer wanted to use to make its proposed deal more lucrative.