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Metabolic Clearance Rates and Metabolism of Mestranol and Ethynylestradiol in Normal Young Women¹

Departments of Medicine and Biochemistry, Queen's University and Kingston General Hospital Kingston, Ontario, Canada

Using the constant infusion technique, the metabolic clearance rates for mestranol and ethynylestradiol were measured in normal young women. The mean ± 1 SD for mestranol was 1741 mean ± 393 L/24 hr and for ethynylestradiol was 1345 mean ± 221 L/24 hr. The mean conversion ratios for mestranol to ethynylestradiol (X^EE₂/X^M) was 0.236 and to ethynylestradiol sulfate (X^EE₂^s/X^M) was 3.369; that for ethynylestradiol to the sulfate (X^EE₂^s/X^M) was 6.476. The mean transfer constant for mestranol to ethynylestradiol ([]BB^MEE₂) was 0.182. The principal circulating form of both the synthetic estrogens appears to be ethynylestradiol sulfate.

¹ Supported in part by grants from Ortho Research Foundation (No. 1708A) and the Medical Research Council of Canada (MA-1852, MA-2338).

Received July 31, 1972.