596 



PHY,SI(3L0GY OF GONADS 



however, some alveoli do develop in the 

 mammae of immaturely castrated male rats 

 (Cowie and Folley, 1947d; Cowie, 1949; 

 Ahren and Etienne, 1957) and it has been 

 ])Ostulated that these arise from the en- 

 hanced production by the adrenal cortex of 

 mammogenic steroids (androgens or proges- 

 terone) due to the hormone imbalance 

 brought about by gonadectomy (see Folley, 

 1956 L 



In a recent study, Ahren and Etienne 

 (1957) have shown that the ducts and al- 

 veoli in the mammary gland of the male rat 

 are remarkable in that their epithelial lining 

 is unusually thick, being composed of sev- 

 eral layers of cells. It had been previously 

 noted by van Wagenen and Folley (1939) 

 and Folley, Guthkelch and Zuckerman 

 (1939) that testosterone caused a thickening 

 of the mammary duct epithelium in the 

 monkey and sometimes papillomatous out- 

 growths of epithelium into the lumen of the 

 duct. It would thus seem that, although the 

 hormone of the testis is capable of eliciting 

 alveolar development, these alveoli and 

 ducts differ from those occurring in the fe- 

 male in the nature of their epithelium. It 

 w^as further observed by Ahren and Etienne 

 (1957) that in the castrated male rat the 

 alveoli, which eventually developed, had a 

 simple epithelial lining somewhat similar to 

 that seen in the normal female rat, suggest- 

 ing that, if the adrenals are responsible, the 

 mammogenic steroid is more likely to be 

 progesterone than an androgen. 



A study of considerable clinical interest is 

 that of Pfaltz (1949) on the developmental 

 changes in the mammary gland in the 

 human male. The greatest development 

 reached was at the 20th year; by the 40th 

 year there occurred an atrophy first of the 

 l)arenchyma and later of the connective 

 tissue. In the second half of the fifth decade 

 tliere was renewed growth of the paren- 

 chyma and connective tissues. The hor- 

 monal background of these changes and the 

 possible relationship with prostatic hyjier- 

 trophy are discussed by Pfaltz. (Further 

 details of the microscopic anatomy of the 

 mammary gland of the human male may be 

 found in the studies by Graumann, 1952, 

 1953, and Dabclow, 1957.) 



4- Mammary Development during Preg- 

 nancy 



It has been customary to divide mam- 

 mary changes during pregnancy into two 

 phases, a phase of growth and a secretory 

 phase. In the former there occurs hy- 

 perplasia of the mammary parenchyma 

 whereas, in the latter, the continued increase 

 in gland size is due to cell hypertrophy and 

 the distension of the alveoli with secretion 

 (see Folley, 1952a j . Although it was realized 

 that these two phases merged gradually, re- 

 cent studies have confirmed earh^ reports 

 {e.g., those of Cole, 1933; Jeffers, 1935) that 

 a wave of cell division occurs in the mam- 

 mary gland towards the end of parturition 

 or at the beginning of lactation. Al'tman 

 (1945) described a doubling in number of 

 cells per alveolus, in the mammary gland 

 of the cow at parturition, but the statistical 

 significance of his findings is difficult to 

 assess. More recently, how^ever, Greenbaum 

 and Slater (1957a) found that the DNA 

 content of the rat mammary gland doubled 

 between the end of pregnancy and the 3rd 

 day of lactation, a finding which they in- 

 terpret as resulting in the main from hyper- 

 plasia of the gland cells. Likewise in the 

 mouse mammary gland, Lewin (1957) ob- 

 served between parturition and the 4th day 

 of lactation a great increase both in the 

 DNA content of the mammary gland and 

 in the total cell count. Studies on the factors 

 controlling this wave of cell division are 

 awaited with interest. Also associated with 

 the onset of copious milk secretion is a con- 

 siderable increase in cell volume and coinci- 

 dent ally the mitochondria elongate and may 

 increase in diameter (Howe, Richardson and 

 Birbeck, 1956). Cross, Goodwin and Silver 

 (1958) have followed the histologic changes 

 in the mammary glands of the sow, by 

 means of a biopsy technique, at the end of 

 pregnancy, during parturition, and at wean- 

 ing. At the end of pregnancy there was a 

 ])i'()gr('ssi\-c' distension of the alveoli, tlie 

 existing hyaline eosinoi)hilic secretion within 

 the alveoli was gradually replaced by a ba- 

 sophilic material, and fat globules appeared. 

 At i)arturition the alveoli were contracted 

 and their walls appeared folded (Fig. 10.3). 



