(JOO 



PHYSIOLOGY OI-' GONADS 



in which estrogen in physiologic doses causes 

 growth of the ducts and the lobule-alveoL^r 

 system, the classical example being the 

 guinea pig in which functional mammae can 

 be developed after gonadectomy in either 

 sex by estrogen alone. A recent study by 

 Hohn (1957), however, strongly suggests 

 that progesterone from the adrenal cortex 

 participates in the effect. The earlier view, 

 moreover, that complete mammary growth 

 can be evoked in the gonadectomized guinea 

 l)ig by estrogen alone (Turner and Gomez. 

 1934; Nelson, 1937.) does not find support 

 in the recent study of Benson, Cowie, Cox 

 and Goldzveig (1957), who, using both sub- 

 jective and objective methods of assessing 

 the degree of mammary development, found 

 that over a wide dose range of estrone, fur- 

 ther development of the mammary gland 

 was obtained when jirogesterone was also 

 administered; essentially similar conclu- 

 sions have been reached by Smith and Rich- 

 terich (1958). 



Also in this second category are cattle 

 and goats in which, however, the male 

 mammary gland is not equipotential with 

 that of the female. The early studies on 

 these species have been reviewed at length 

 by FoUey and Malpress (1948a) and Fol- 

 ley (1952a, 1956). Briefly it may be said 

 that these studies clearly showed that estro- 

 gen alone induced extensive growth of lob- 

 ule-alveolar tissue of which the functional 

 capacity was considerable although the milk 

 yields in general were less than those ex- 

 pected from similar animals after parturi- 

 tion. The response to estrogen treatment 

 was, moreover, very erratic. It was generally 

 believed that the deficiencies of this treat- 

 ment could be made good if progesterone 

 were also administered, a view supported by 

 the observations of Mixner and Turner 

 (1943) that the mammary gland of goats 

 treated with estrogens, when examined his- 

 tologically, showed the i)resence of cystic 

 alv(>oli, an abnormality which tended to 

 disappear when jirogestcrone was also ad- 

 ministered. 



When progesterone became more readily 

 available, an extensive study of tlie role of 

 estrogen and progesterone in mammary de- 

 velopment in the goat was carried out 

 (Cowie, Folley, ^lalpress and Richai'dson. 



1952; Benson, Cowie, Cox, Flux and Folley, 

 1955). The mammary tissue was examined 

 histologically and the procedure devised by 

 Richardson (see page 594) used to estimate 

 the area and "porosity" of the alveolar epi- 

 thelium. The udders grown in immaturely 

 ovariectomized virgin goats by combined 

 treatment with estrogens and progesterone 

 in various proportions and at different ab- 

 solute dose levels were compared with ud- 

 ders resulting from treatment with estrogen 

 alone. As in the earlier observations of Mix- 

 ner and Turner (1943) , histologic abnormal- 

 ities were noted, the more widespread being 

 a marked deficiency of total epithelial sur- 

 face, associated with the presence of cystic 

 alveoli, in the udders of the estrogen-treated 

 animals. The addition of progesterone pre- 

 vented the appearance of many of these ab- 

 normalities and increased the surface area 

 of the secretory epithelium. JMoreover, when 

 estrogen and progesterone were given in a 

 suitable ratio and absolute level the milk 

 yields obtained were remarkably uniform 

 as between different animals and the glan- 

 dular tissue was virtually free from abnor- 

 malities. 



Studies in the cow have been less exten- 

 sive, but there is evidence that both estrogen 

 and progesterone are necessary for complete 

 normal mammary development (Sykes and 

 Wrenn, 1950, 1951; Reineke, INIeites, Cairy 

 and Huffman, 1952; Flux and Folley, cited 

 by Folley, 1956; Meites, 1960). 



The case for the inclusion of the monkey 

 in the present category has been strength- 

 ened by the excellent monograph of Speert 

 ( 1948) who has had access to more extensive 

 material than many of the earlier workers 

 whose results are reviewed by him (see also 

 Folley, 1952a). The sum total of available 

 evidence now justifies the conclusion that 

 estrogen alone will cause virtually complete 

 growth of the duct and lobule-alveolar sys- 

 tems of the monkey breast. Extensive lobule- 

 alveolar development in the monkey breast 

 in response to estrogen is shown in Figure 

 10.5. The synergistic effect of estrogen and 

 jirogesterone on the monkey breast has not 

 yet been adequately studied, but from avail- 

 able evidence it does not seem to be very 

 dramatic. If it is permissible to argue from 

 pi'iinates to man. it seems jiossible that coidd 



