COMPARISON OF THE EFFECTS OF ORAL AND TRANSDERMAL OESTRADIOL ADMINISTRATION ON OESTROGEN METABOLISM, PROTEIN SYNTHESIS, GONADOTROPHIN RELEASE, BONE TURNOVER AND CLIMACTERIC SYMPTOMS IN POSTMENOPAUSAL WOMEN

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Abstract
We compared the effect of administering oestradiol via the transdermal or oral routes in six and eight postmenopausal women respectively. Although both treatments achieved similar plasma levels of oestradiol, oral administration led to much greater increases in plasma levels of oestrone and the sulphates and glucuronides of oestradiol, oestrone and oestriol than transdermal treatment (P < 0.001). Both treatments reduced plasma FSH; from 42 .+-. 10 (SE) IU/l to 30 .+-. 2 IU/l with oral and from 46 .+-. 7 IU/l to 28 .+-. 6 IU/l with transdermal treatment. Urine calcium excretion fell from 0.41 .+-. 0.06 (molar ratio to creatinine) to 0.17 .+-. 0.02 with oral and from 0.25 .+-. 0.06 to 0.13 .+-. 0.02 with transdermal treatment. Patient''s symptoms were improved by both treatments. These changes were related to the plasma oestradiol concentration but not to that of oestrone. Oral, but not transdermal, treatment stimulated hepatic protein synthesis as shown by increased plasma levels of both vitamin D-binding globulin and sex-hormone-binding globulin. We conclude that although both oral and transdermal oestradiol reduce postmenopausal bone loss, gonadotrophin secretion and symptoms, oral treatment also leads to hepatic stimulation and extensive metabolism of oestradiol, both of which may increase side-effects without conferring additional benefit.