Biological Effects of Various Doses of Vaginally Administered Conjugated Equine Estrogens in Postmenopausal Women*

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Abstract
To determine whether vaginal administration of conjugated equine estrogens (VCE) could provide physiological replacement while avoiding effects on hepatic function, as occurs with oral administration, a study was conducted in which 20 postmenopausal women were evaluated before and after the vaginal administration of CE. The dosages studied were 0.3, 0.625,1.25, and 2.5 mg/day for 4 weeks. Twenty premenopausal women were also studied, and their values were presumed to reflect normal physiological function. The findings in the postmenopausal women were compared with previously reported results obtained in a similar group of subjects given oral CE (OCE). Vaginal cytology returned to premenopausal values with 0.3 mg VCE. This response was similar to that exerted with 1.25 mg OCE. Stepwise increases in circulating estrone and estradiol occurred with increasing dosages. The 2.5-mg dosage of VCE raised estrone levels to values similar to those in premenopausal women in the late follicular phase, and estradiol concentrations were similar to early follicular phase concentrations. Limited or no responses of the systemic markers of estrogen action occurred with all doses of VCE. Small decreases in LH and FSH levels occurred, but no dosage significantly reduced the level of either gonadotropin. Although the urinary calcium to creatinine ratio was significantly reduced by the two largest dosages of VCE, the effect of the 2.5-mg dosage was less than that observed with 0.625 mg OCE, the lowest dosage that protects against osteoporosis. Hepatic protein synthesis was significantly increased only by the higher dosages tested. No dosage had a significant effect on circulating levels of triglycerides or total or fractionated cholesterol levels. These data suggest that the vaginal administration of CE exerts mainly a local effect, with limited or no measurable changes in systemic markers of the action of estrogen.