The preovulatory gonadotropin surge in the sheep was recently characterized by a divergent pattern of LH beta and FSH beta mRNAs immediately preceding this event. It is not clear whether this pattern is due to estradiol (E2), inhibin or other effectors. In this study, to determine if E2 may be involved in the divergent beta mRNA patterns seen during the surge, gonadotropin surges were induced in anestrous ewes (An) by E2 (An + E2) and several parameters were then measured. These included the amounts of alpha, LH beta, and FSH beta mRNAs, as assessed by solution hybridization assays, plus pituitary and serum gonadotropin concentrations. The values were compared with those observed in control, An ewes, to assess the effect of E2. The E2 treatment resulted in LH and FSH surges that appeared to be similar to the normal surges seen during the breeding season. Concomitantly, the E2 treatment lowered pituitary concentrations of FSH (P less than 0.05), while LH amounts did not change. Although the effect of E2 on gonadotropin subunit mRNA amounts varied depending upon the individual subunit, the changes that were observed paralleled changes reported during the preovulatory surge of the cycle. Specifically, alpha mRNA amounts increased significantly (P less than 0.001) while FSH beta mRNA amounts fell dramatically (P less than 0.001). Moreover, LH beta mRNA amounts were slightly increased, although not significantly by E2. These results demonstrate that E2 effects changes in the amounts of the gonadotropin subunit mRNAs during an induced gonadotropin surge in An ewes.(ABSTRACT TRUNCATED AT 250 WORDS)