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EFFECTS OF ETHINYLOESTRADIOL ON PLASMA LEVELS OF PITUITARY GONADOTROPHINS, TESTICULAR STERIODS AND SEX HORMONE BINDING GLOBULIN IN NORMAL MEN
Author(s) -
LOOK P. F. A.,
FRÖLICH MARIJKE
Publication year - 1981
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1981.tb00192.x
Subject(s) - endocrinology , medicine , sex hormone binding globulin , testosterone (patch) , prolactin , hormone , free fraction , globulin , chemistry , biology , androgen , pharmacokinetics
SUMMARY Daily measurements of plasma FSH, LH, prolactin, testosterone, 17β‐oestradiol and sex hormone binding globulin (SHBG) activity were made in eight healthy, normal men during treatment with oral ethinyloestradiol (EE 2 ) in a dose of 30 μg/day for 5 days following a 5‐day control period. No significant changes in plasma levels of FSH and prolactin during oestrogen treatment occurred. In contrast, plasma concentrations of both LH and testosterone showed a biphasic pattern. Following an initial suppression during the first 3 days of oestrogen treatment both LH and testosterone increased again to baseline values despite continuation of oestrogen administration. The secondary rise of both hormones was associated with (and probably resulted from) a nearly 100% increase in the plasma concentration of SHBG binding activity, and hence reduction of free testosterone index (FTI). Unlike testosterone, plasma 17β‐oestradiol during EE 2 administration did not show a biphasic pattern, but a progressive decline that was positively correlated with the fall in FTI. The rapidity of onset and magnitude of the observed rise in SHBG levels emphasizes the need for measurement of this binding protein (or the free testosterone fraction) in studies on feedback regulation of gonadotrophins employing exogenous EE 2 in human males. The observed increase of SHBG to supraphysiological values suggests that currently employed EE 2 doses in such studies may be less ‘physiologic’ than is often assumed.