Annual growth margins excluded insulin supplier (8)
I believe the answer is:
pancreas
'insulin supplier' is the definition.
(organ which releases insulin)
'annual growth margins excluded' is the wordplay.
'annual' becomes 'pa' (abbreviation for 'per annum').
'growth' becomes 'increase' (an increase is a growth or rise).
'margins excluded' indicates the central letters (letters at the margins are removed).
The central letters of 'increase' are 'ncreas'.
'pa'+'ncreas'='PANCREAS'
(Other definitions for pancreas that I've seen before include "Gland secreting digestive enzymes" , "Gland aiding digestion" , "secreting structure" , "Sweetbread" , "It secretes insulin" .)