You can reverse directions and go from the upper bound to the lower one:
SQL> SQL> begin-- w w w. j a v a 2s. co m 2 for main_c in reverse 1..3 3 loop 4 DBMS_OUTPUT.put_line(main_c); 5 end loop; 6 end; 7 / 3 2 1 PL/SQL procedure successfully completed. SQL>