Effects of Short-Term Exposure to Catecholestrogens on Serum Concentrations of Gonadotrophins and Metabolism of Catecholestrogens in Ovariectomized Rats

Summary

Equimolar amounts (36.8 nmol) of estradiol and the two Catecholestrogens (CE's) 4-hydroxyestradiol (4-OHE₂) and 2-hydroxyestradiol (2-OHE₂) were injected subcutaneously to ovariectomized adult rats. Serum levels of both LH and FSH were determined at short-term intervals. Moreover, serum levels of the administered steroids and their main free and conjugated metabolites were monitored.

Serum levels of the injected steroids reached peak values at different time points: estradiol between 60 and 240 min, CE's between 30 and 60 min. Peak height also differed significantly: with estradiol highest (1500 pg/ml), followed by 4-OHE₂ (540 pg/ml) and then 2-OHE₂ (135 pg/ml) (ratio 11:4:1). This mirrored the different MCR's of the steroids: CE's, especially 2-OHE₂, were rapidly and extensively methylated and/or - to a lesser degree - conjugated. Estradiol remained mainly unchanged. LH-serum levels in steroid treated animals showed - irrespective of the steroid used - a uniform reaction pattern: they were significantly depressed 60 to 240 min after injection and - with the exception of estradiol treated rats - reached pretreatment levels again 480 min after injection. Ultra-short (15 min) effects were not observed. FSH serum levels in CE treated animals were not significantly altered, only E₂ application led to a significant but small decrease in FSH levels 240 and 480 min after its injection.

In conclusion, neither the effect of 4-OHE₂ nor that of 2-OHE₂ corresponded to the different MCR's or the MCR-corrected affinities for the classical estrogen receptor. A non-genomic mechanism may be responsible for this impaired effect of CE's.

Key-Words:

Catecholestrogens - 4-Hydroxyestrogens - 2-Hydroxyestrogens - Short-Term Effect on Gonadotrophins - Metabolism In Vivo - Rats