Health insurer Aetna Inc. has made a deal to buy competitor Humana Inc. in a $37 billion deal the companies say would create the second-largest managed care company. Adding Humana's large business in Medicare Advantage, the federal health care program for seniors, would make Humana the nation's largest Medicare Advantage provider. The purchase price includes a combination of cash and stock worth about $230 per share. Hartford, Conn.-based Aetna says it will retain Humana's Louisville, Kentucky, headquarters as the base for its Medicare, Medicaid and military Tricare businesses. Analysts say the health care overhaul has pushed the insurers to consolidate, and a big deal has been expected for weeks. A bigger insurer can gain more leverage and negotiating power when they hash out rates with care providers.