National HealthCare Corp. CEO Robert Adams, who has worked for more than four decades at the Murfreesboro-based senior healthcare company, has announced he will retire at the end of this year. Adams, 69, has led NHC since 2004 and before that was president for five years, COO for 10 and a senior vice president for 18. He also has been chairman of the company’s board of directors since the beginning of 2009 and will remain as non-executive chairman.