nameservers in arpa-zone

[ap__@]

Hello,
I want to add some additional nameservers to domain x.y.z.in-addr.arpa. (IN NS )
(to plesk not overwrite)

how to do it?

 

[ap__@]

explanation

sample:
===
>cat /var/named/run-root/var/zzz.yyy.xx.in-addr.arpa
; *** This file is automatically generated by Plesk ***
$TTL 86400

@ IN SOA hosting.isp.com. root.isp.com. (
1226391305 ; Serial
10800 ; Refresh
3600 ; Retry
604800 ; Expire
10800 ) ; Minimum

IN NS hosting.isp.com.
134 IN PTR hosting.isp.ru.
1 IN PTR host1.isp.ru.

=end sample

how to add string
IN NS ns2.isp.com.
?