The increase in circulating estrogen concentrations that follows injection of Escherischia coli endotoxin (Endo) may be due to increased aromatase activity. We have therefore analysed the effect of the aromatase inhibitor, 4 hydroxyandrostenedione (4OHA) on the steroid hormone response of male rats, particularly the dramatic increase in estrogens and decrease in androgens, induced by Endo.

The concentrations of corticosterone (B), progesterone (P4), 17α hydroxyprogesterone (17αOHP4), androstenedione (Δ4), testosterone (T), estrone (E1) and estradiol (E2) were determined 2 hours after injection of increasing doses of 4OHA with and without Endo.

The increase in serum estrogen concentrations and drop in serum androgen levels in response to Endo were blocked by a single dose of 4OHA. The effect of 4OHA appeared to be dose dependent. Low doses (30 mg/kg and 50 mg/kg) induced significant changes in the estrogen and androgen responses, but the high dose (100 mg/kg) blocked all changes in sex steroids induced by Endo. 4OHA did not alter the Endo-induced changes in other steroids.

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