** Shares of healthcare conglomerate UnitedHealth UNH.N fall 1.53% to $454.4

** U.S. Senator Chuck Grassley launches inquiry into UNH's Medicare billing practices amid reports suggesting the insurer may have leveraged billing rules to its advantage

** Grassley, who heads the Senate Judiciary Committee, demanded the health insurer provide all records relating to the company's compliance program, training manuals and guidance documents to better understand its billing practices

** Over the last several months, the Wall Street Journal has run a series of stories detailing how UnitedHealth profited from using Medicare billing rules to its favor.

** "We welcome the opportunity to share the facts with Senator Grassley, especially given the ongoing misinformation campaign by the WSJ" - UNH statement

** Stock has fallen 13.4% in the past 12 months

(Reporting by Padmanabhan Ananthan)

((Padmanabhan.Ananthan@thomsonreuters.com;))