Inhibition of rat liver estrogen 2/4-hydroxylase activity by troleandomycin: comparison with erythromycin and roxithromycin.
Administration of troleandomycin (0.5 mmol.kg-1 p.o. daily for 5 days) decreased by 61% and 36%, respectively, the estradiol and ethinylestradiol 2/4-hydroxylase activities of hepatic microsomes from male Sprague-Dawley rats killed 2 hr after the last dose. This decrease did not appear to be due to the in vivo formation of the inactive cytochrome P-450 p Fe(II)-metabolite complex, since disruption of this complex with potassium ferricyanide did not increase estrogen hydroxylase activities. Troleandomycin administration, however, essentially suppressed cytochrome P-450 UT-A (one of the P-450 forms involved in the hydroxylation of estrogens) and resulted in the appearance of cytochrome P-450 forms whose estradiol hydroxylase activity was inhibitable by troleandomycin in vitro. Similarly, troleandomycin (2 mM) inhibited by 60% estradiol and ethinylestradiol 2/4-hydroxylase activities in microsomes from dexamethasone-treated rats, although it had no inhibitory effect in microsomes from control rats. In contrast, erythromycin and roxithromycin (2 mM) exerted no inhibitory effect, even in microsomes from dexamethasone-treated rats. In vivo, these macrolides (0.5 mmol.kg-1 p.o. daily for 5 days) decreased moderately cytochrome P-450 UT-A levels and estradiol 2/4-hydroxylase activity, and did not modify ethinylestradiol 2/4-hydroxylase activity. We conclude that the administration of troleandomycin, but not that of erythromycin or roxithromycin, decreases ethinylestradiol 2/4-hydroxylase activity in male rat liver microsomes, as a possible consequence of decreased cytochrome P-450 UT-A levels and of the induction of glucocorticoid-responsive P-450 forms whose ethinylestradiol hydroxylase activity is inhibitable by troleandomycin.
Fisher
D
D
Unité de Recherches de Physiopathologie Hépatique (Institut National de la Sauté et de la Recherche Médicale U 24), Hôpital Beaujon, Clichy, France.
Labbe
G
G
Berson
A
A
Tinel
M
M
Loeper
J
J
Larrey
D
D
Pessayre
D
D
D000818:Animals; D019363:Cytochrome P-450 CYP1A1; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004917:Erythromycin / Q000494:pharmacology*; D005292:Ferricyanides / Q000494:pharmacology; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D015575:Roxithromycin / Q000494:pharmacology*; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014217:Troleandomycin / Q000494:pharmacology*
D065607:Cytochrome P-450 Enzyme Inhibitors; D005292:Ferricyanides; C007931:hexacyanoferrate III; D015575:Roxithromycin; D004917:Erythromycin; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D014217:Troleandomycin; D013250:Steroid Hydroxylases; D019363:Cytochrome P-450 CYP1A1; C020120:estrogen 2-hydroxylase