ESTROGEX AND PROGESTERONE 



559 



ill the blood of monkeys as early as the 7th 

 (lay and attain a concentration of 1 fxg. per 

 ml. of serum at ovulation, whereas a maxi- 

 mal concentration of 10 /xg. per ml. is 

 reached at approximately the middle of the 

 luteal phase (Forbes, Hooker and Pfeiffer, 

 1950; Bryans, 1951). Also, some estrogen is 

 present during the luteal phase, probably 

 secreted by the corpus luteum (estrogens 

 can be obtained from luteal tissue) or it 

 may be partially derived from developing 

 follicles. It is unlikely that estrogen is ever 

 entirely absent during a normal menstrual 

 cycle or that the presence of progesterone is 

 completely restricted to the luteal phase. 



The dependence of the reproductive tract 

 on ovarian hormones is strikingly demon- 

 strated by the profound atrophy that fol- 

 lows surgical removal of the ovaries. A pro- 

 gressive decrease in size of the Fallopian 

 tubes, uterus, cervix, and vagina takes place, 

 and usually, the involution of the uterine 

 endometrium involves tissue loss and bleed- 

 ing, commonly referred to as post castra- 

 tional bleeding. Dramatic as these effects 

 may seem, it is equally dramatic to find 

 that these atrophic structures can be re- 

 stored entirely to their original condition by 

 the administration of ovarian hormones. 

 Therefore, it is seen at the beginning that 

 investigations dealing with the physiology 

 of the female reproductive tract of primates 

 in large measure involve a study of the in- 

 dependent and combined actions of estro- 

 gens and progesterone on the activities of 

 the various structures concerned. 



Much can be learned about the action of 

 ovarian hormones by observing the changes 

 they produce in the gross appearance of the 

 atrophied reproductive tract of castrated 

 animals. Daily injections of an estrogen in 

 doses equivalent to 1000 I.U. or more for 

 10 days or a fortnight will restore the uterus, 

 cervix, and vagina to a condition compara- 

 l)le with that found in a normal monkey at 

 the close of the follicular phase of a men- 

 strual cycle (Fig. 9.1A). If a similar cas- 

 trated monkey is given 1 or 2 mg. of pro- 

 gesterone daily for the same length of time, 

 very little if any change in size of the re- 

 productive organs results. However, if first 

 the normal condition is restored by giving 

 estrogen and then is followed by the pro- 

 gesterone treatment, the size of the uterus 



is maintained but that of the cervix and 

 vagina decreases to an extent approaching 

 that in a castrated animal (Fig. 9.1B). Such 

 experiments show that an estrogen promotes 

 growth of the reproductive tract whereas 

 progesterone is comparatively ineffective 

 when given alone. Yet progesterone can 

 maintain the size of the uterus when admin- 

 istered following an estrogen treatment but 

 it does not prevent involution of the cervix 

 and vagina. 



An additional feature of the growth-stim- 

 ulating action of the ovarian hormones is 

 brought out when estrogen and progesterone 

 are administered concurrently. If, after re- 

 pair of the reproductive tract of a castrated 

 animal has been accomplished by a series of 

 injections of estrogen, both estrogen (1000 

 I.U.) and progesterone (1 or 2 mg.) are 

 given daily for 20 days, it will be found that 

 the uterus is larger than when either hor- 

 mone is given alone for a similar length of 

 time, whereas the cervix and vagina have 

 involuted and are approximately the size 

 found in animals given only progesterone. 

 Thus it can be demonstrated that a syner- 

 gistic effect on growth of the uterus occurs 

 when the two hormones are given simultane- 



FiG. 9.1. Reproductive tracts of three adolescent 

 monkeys which were castrated and given estrogen 

 daily for approximately 3 weeks. A shows the con- 

 dition at the conclusion of the estrogen treatment, 

 B the condition following the injection of pro- 

 gesterone for an additional three weeks, and C the 

 effects of continuing the treatment with both es- 

 trogen and progesterone for a like period. 



