Organs state installed in gutted Gewandhaus (6)
I believe the answer is:
glands
'organs' is the definition.
(gland is a kind of organ)
'state installed in gutted gewandhaus' is the wordplay.
'state' becomes 'land' (synonyms).
'installed in' means one lot of letters goes inside another.
'gutted' suggests removing the centre (to gut something is to remove its insides).
'gewandhaus' with its middle removed is 'gs'.
'land' inserted into 'gs' is 'GLANDS'.
(Other definitions for glands that I've seen before include "Organs that separates substances in the blood" , "Organs that produce secretions" , "Body organs that release secretions" , "Groups of body cells that secrete substances" , "Various body organs that secrete substances" .)