IN-VITRO MODULATION OF 17-BETA-ESTRADIOL-INDUCED VITELLOGENIN SYNTHESIS - EFFECTS OF CYTOCHROME P4501A1 INDUCING COMPOUNDS ON RAINBOW-TROUT(ONCORHYNCHUS-MYKISS) LIVER-CELLS

Cytochrome P4501A1 (CYP1A1) induction, particularly in liver, is a use ful marker of exposure of fish to polycyclic- and halogenated-aromatic hydrocarbons. However, the relationship between toxicity and CYP1A1 i nduction in fish is uncertain. Some compounds that induce CYP1A1 are a ntiestrogenic in mammalian bioassay, and this effect is linked to aryl hydrocarbon (Ah) receptor and/or increased catabolism of 17-beta-estr adiol. Liver of fish synthesizes estrogen-inducible egg yolk precursor protein vitellogenin (Vg) which is critical for oocyte maturation and ovarian development. To determine if CYP1A1-associated endocrine modu lation could occur in fish liver, primary cultures of rainbow trout li ver cells were co-administered 17-beta-estradiol and CYP1A1 inducing c ompounds or mixtures. Protein synthesis and enzyme activity of cells w ere optimal when cultured in a modified HEPES buffered Medium 199 at 1 5 degrees C. Vg and albumin (Alb), estimated by ELISA measurement of c oncentration in the media 48 h after treatment, formed the basis for t he test. Equivalent viability (mitochondrial dehydrogenase activity) a nd secretory functional capacity (Alb synthesis) were estimated and co rrelated with other results. In descending order, 2,3,4,7,8-pentachlor odibenzofuran (10(-12) to 10(-8) M) > 2,3,7,8-tetrachlorodibenzo-p-dio xin (TCDD) congruent to 2,3,7,8-tetrachlorodibenzofuran (10(-12) to 10 (-8) M) > beta-naphthoflavone (10(-7) to 10(-6) M) inhibited Vg synthe sis in 17-beta-estradiol treated liver cells. Potency of inhibition di rectly related to strength as an inducer of CYP1A1 protein. At 10(-8) M, PCB congeners 77, 126, 156 did not inhibit Vg synthesis and induced no to moderate levels of CYP1A1 protein or EROD activity. At 10(-8) M , congener 114, a weak EROD inducer, potentiated Vg synthesis relative to cells treated with 17-beta-estradiol alone. The results of this st udy increase our understanding of the consequences of hepatic CYP1A1 i nduction, forewarn of reproductive impairment of sexually maturing fis hes exposed to CYP1A1 inducing compounds and argue for further, more d etailed in vivo investigation.