The high frequency of a variety of disorders observed in Baltic seals have
been correlated with elevated concentrations of organochlorines. For this s
tudy, we determined hepatic CYP1A activities and apoprotein levels in ringe
d seals (Phoca hispida) exposed to high levels of organochlorides in the Ba
ltic Sea and in corresponding seals from a relatively unpolluted area (Sval
bard Region). Activities of ethoxyresorufin deethylase (EROD) and pentoxyre
sorufin depentylase (PROD) in seal liver microsomes were increased about 3-
fold in the Baltic sample, the EROD activity reaching similar levels to tho
se found in 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced rats (about 1,2 nmo
l/mg protein per min). No sex-related differences in EROD or PROD activitie
s were observed in either population. Hepatic CYP1A levels in ringed seals
were further characterised by inhibition and Western blot analysis. a-Napht
hoflavone and furafylline were used as chemical inhibitors, having highly s
pecific inhibiting effects on CYP1A1 and CYP1A2, respectively, in rat and h
uman liver. cc-Naphthoflavone inhibited potently both EROD and PROD activit
ies, while inhibition by furafylline was weaker. A monoclonal antibody spec
ific to CYP1A in the rat (MAb 1-7-1), used in the immunoblots, revealed a s
ubstantially increased amount of CYP1A protein in the Baltic seals. CYP2B-r
elated proteins were not detected in any seal sample using MAb 2-66-3, whic
h is specific for rat CYP2B. Thus, both inhibition and Western blotting exp
eriments indicate that CYP1A is mainly responsible for the marked increase
in microsomal EROD and PROD activities in the livers of Baltic ringed seals
. Since the properties of all CYP enzymes vary between species, further stu
dies are needed to verify whether CYP1A1 or CYP1A2 mediates the observed ER
OD induction in the ringed seal. (C) 1998 Elsevier Science B.V. All rights
reserved.