SECURITIES

Luther Medical Products Inc., Costa Mesa, announced that MedChem Products Inc. of Woburn, Mass, another leading maker of catheter systems, has offered to acquire it for an estimated $11 million in cash or stock. . . . Southwest Airlines, fulfilling its pledge to combat United Airlines’ planned Shuttle in California, said it will add 15 flights in California starting Nov. 15. . . . Woodland Hills-based Health Systems International Inc. said it plans to expand to the East Coast by acquiring M.D. Enterprises of Connecticut Inc., a physician-owned health maintenance organization, for $101 million in stock. . . . In a consolidation in the life insurance industry, Torchmark Corp. of Birmingham, Ala., is buying Waco, Tex.-based American Income Holding Inc. for $563.5 million, the companies announced.