As the U.S. Senate Finance Committee launched an investigation Tuesday into makers of narcotic painkillers and groups that champion them. Sens. Max Baucus, D-Mont., the finance panel chairman, and Charles Grassley, R-Iowa, sent letters to The American Pain Foundation, three pharmaceutical companies, and five groups that support pain patients, physicians or research. The Federation of State Medical Boards, the trade group for agencies that license doctors, also received a letter, as did The Joint Commission.