The metabolism of synthetic estrogens in non-users and users of oral contraceptives |
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Authors: | C. Longcope K.I.H. Williams |
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Affiliation: | Worcester Foundation for Experimental Biology 222 Maple Avenue Shrewsbury, Massachusetts 01545 USA |
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Abstract: | Using both pulse injections and constant infusions of 3H-mestranol (3H-ME) (1) and 3H-ethinyl estradiol (3H-EE) we have studied the metabolism of these compounds in non-users and users of oral contraceptives. Following pulse injection of 3H-ME the disappearance of radioactivity could be described as a function which was the sum of two exponentials. Studied by both types of administration there was no difference in the metabolism of 3H-ME in the two groups; the overall mean ± SE metabolic clearance rate (MCR) was 690 ± 45 1/day/m2, the mean ratio of the concentrations of radioactivity as EE following administration of ME (CRBBM, E) was 0. 23 ± 0. 02 and the mean [ρ]BBM, E (fraction of administered ME measured in blood as EE) was 0. 19 (95% confidence limits = 0.15 – 0. 23).Following pulse injection of 3H-EE the disappearance of radioactivity was best described as a function which is the sum of three exponentials. Results from both types of administration revealed no difference in the metabolism of 3H-EE between non-users. The overall mean ± SE MCREE was 630 ± 30 I/day/m2. The MCREE is significantly (0. 02 > P > 0. 01) less than the mean MCR for estradiol reported previously, in both non-users and users of oral contraceptives. The use of oral contraceptives containing estrogens and progestins does not appear to influence the metabolism of the estrogen used. Approximately 20% of mestranol is converted to and appears in the blood as ethinyl estradiol. |
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