WASHINGTON NAT'L <WNT> BUYS UNITED PRESIDENTIAL Washington National Corp's Washington National Insurance Co said it bought the remaining 15 pct of United Presidential Corp's <UPCO> outstanding shares at 19 dlrs a share cash. The acquisition of the shares is part of a plan of exchange approved by United Presidential shareholders at a special meeting March 6. The purchase of the remaining United Presidential stake follows Washington National's buying 85 pct of United Presidential in a 19 dlrs a share tender offer which terminated December 12.