cant conect to dynamic host-URL

Hi there, ive got a dynamic URL like myname.dyndns.org which links to my
server
where my postgres database runs. The Problem is that the Connection
fails with error:
"Warning: pg_connect(): Unable to connect to PostgreSQL server: unknown
host name: adocom.dyndns.org"

Now, if i ping my dynamic address and use the resulting IP for the
Connection all works fine.
I dont know where my i did something wrong, i use an Java-Applet which
connects also with the dynamic Address and works fine too. :(

Here is my php-Code i use:

// Option-class which holds some information
class Option {
var $host = "myname.dyndns.org"; // Adresse des DBMS-Servers
var $port = "5432"; // Port auf dem
das DBMS laeuft
var $dbname = "Database"; // Name der Datenbank
var $user = "postgres"; // DBMS Benutzer
var $passwd = "secret"; // DBMS Passwort
}

// Connection in index.php
$conn = pg_connect("host=".$OptObj->host." port=".$OptObj->port."
dbname=".$OptObj->dbname." user=".$OptObj->user."
password=".$OptObj->passwd);