Effect of the plasma estrone/17 beta-estradiol ratio on the prolactin and TSH responses to TRH.

This study was undertaken to test whether ratios between plasma concentrations of different estrogens would be more determinant of prolactin (PRL) secretion than plasma concentrations of estrogens per se have been found to be. Oral administration of micronized 17 beta-estradiol in a dose of 2 mg b.i.d. for 1 month to 7 postmenopausal women raised plasma estrone (E1) from a median of 29 to 683 pg/ml and plasma 17 beta-estradiol (E2) from a median of 5.7 to 131 pg/ml. The E1/E2 ratios rose from a median of 4.01 to 4.92 (Pwilcoxon (Pw) greater than 0.025). Basal serum PRL increased from a median of 79.2 to 100 microIU/ml (Pw) greater than 0.025). However, the area under the curve of the PRL response to TRH increased from a median of 2,553 mm2 before to 3,919 mm2 after treatment (Pw less than 0.025). Highly significant correlations existed between the E1/E2 ratios and the PRL responses to TRH both before (rspearman (rs) = 0.964) (Pspearman (Ps) less than 0.005) and after (rs = 1.000) (Ps less than 0.00025) estradiol treatment, whereas no correlations (Ps less than 0.679) existed between plasma concentrations of E1 or E2 per se and either basal serum PRL or PRL response to TRH. The regression curves of best fit between the E1/E2 ratios and the PRL responses to TRH were hyperbolic both before (r = 0.884) and after (r = 0.996) treatment. These results, showing that the E1/E2 ratio rather than the plasma E1 or E2 concentrations per se are correlated to the PRL responses to TRH, imply that the metabolic conversion rate of estrogens modulates PRL secretion.