800

chapter

3 4

Endocrine Metabolism V: Reproductive System

M e stra n o l

(A)

O

II

c=o

M e d ro x y p ro g e s te ro n e a c e ta te

O H

C H 3

I

3

c=o

(B)

R U 4 8 6

(M ifep risto n e)

(C)

F IG U R E 3 4 -9

Structures of steroids used as oral contraceptives. (A) Combination pills containing an estrogen + progestin. (B) The

progestin-only pill. (C) RU-486 or mifepristone, which can be utilized as an abortifacient. [Reproduced with permission

from S. W. Norman and G. Litwack,

H o rm o n es,

2nd ed. San Diego: Academic Press, 1997].

derivatives that have long biological half-lives. The first

three protocols involve estrogen + progestin combina-

tions taken for 3 weeks, followed by no treatment for

1

week.

1. Fixed combined dose of estrogen + progestin daily

(“combination pill”);

2. Biphasic type: fixed dose estrogen + two different

doses of progestin;

3. Triphasic type: fixed dose estrogen + three different

doses of progestin (stepwise increase at

1

-week

intervals); and

4. “Mini” pill, containing a progestin only; taken daily

without interval of withdrawal.