triggers using row values

I'm trying to create a trigger which will pass a value from the row
into the procedure to execute. All the documentation I can find shows
only constant arguments being passed. For example,
CREATE TRIGGER if_dist_exists
BEFORE INSERT OR UPDATE ON films FOR EACH ROW
EXECUTE PROCEDURE check_primary_key ('did', 'distributors', 'did');

That doesn't seem very useful. Here's what I'm trying:
netbill=> create trigger set_stale_1
netbill-> after insert or update or delete on dns_a for each row
netbill-> execute procedure set_zone_stale(zid);
ERROR: CreateTrigger: function set_zone_stale() does not exist

I have a function defined as set_zone_stale(int). How can I call
it using the zid field from the changed record?