[TRANSACT]Can't Switch From Master To Another Database

Hello,

I encounter a problem with a small portion of sqlcode. I try to go on
database using "use dbname" but i always stay in master. I execute
script with the sa user.

declare @dbnamesysname
declare @ret_codeint

DECLARE db_cursor CURSOR FOR
select
name
from
master..sysdatabases
where
name not in ('master', 'model', 'tempdb', 'pubs', 'Northwind')

-- Open cursor
OPEN db_cursor
FETCH NEXT FROM db_cursor INTO @dbname

WHILE @@FETCH_STATUS = 0
BEGIN
execute ('use ' + @dbname)
execute ('select db_name()')

Thank's for help,
Pierrot.