Rites are performed by vital suppliers (8)
I believe the answer is:
arteries
'vital suppliers' is the definition.
(arteries supply blood)
'rites are performed' is the wordplay.
'performed' indicates an anagram.
'rites'+'are'='ritesare'
'ritesare' is an anagram of 'ARTERIES'.
'by' is the link.
(Other definitions for arteries that I've seen before include "Blood vessels leading from the heart" , "Major thoroughfares for important traffic" , "Vessels that carry blood from the heart to the body" , "Blood vessels - major roads" .)