HYPOPHYSEAL MORPHOLOGY 



205 



erally. Cell cords composed mainly of preg- 

 nancy cells occur and isolated cords of this 

 nature may be conspicuous in certain re- 

 gions. The chromophobes of the vascular 

 zone of the anterior lobe near its attach- 

 ment to the stalk ("zona tuberalis") are not 

 affected by pregnancy changes. The preg- 

 nancy cells are, therefore, not derived from 

 chromophobes in general but from chromo- 

 phobic cells having a specific distribution. 



There are two important differences be- 

 tween human pregnancy cells and the 

 carminophil cells of the rabbit, cat, and 

 monkey. First, the human pregnancy cell 

 granules are orangeophil rather than car- 

 minophil. The distinctive color difference 

 between a-cells and pregnancy cells is, 

 therefore, in the human hypophysis the 

 reverse of that seen in the other species. 

 Second, the distribution is different from 

 that seen in the monkey where carminophil 

 cells are especially concentrated in the zona 

 tuberalis. Despite these differences, the 

 pregnancy cells appear to be functionally 

 analogous to the carminophil cells and are 

 presumably the source of prolactin secre- 

 tion. 



H. LACTATION 



The characteristic feature of the pars 

 anterior at and shortly after parturition 

 is the increased amount of acidophil gran- 

 ulation present. Kirkraan (1937) found in 

 the guinea pig that the acidophils increase 

 in numbers towards the end of pregnancy 

 and attain a maximum soon after parturi- 

 tion. Wolfe and Cleveland (1933b) reported 

 a similar increase in granulation of acido- 

 phils in the rat hypophysis towards the end 

 of pregnancy. Everett and Baker (1945) 

 found that after parturition in the rat, 

 the acidophil cells increased by almost 100 

 per cent in the first three days of the 

 lactation period. This increase in the num- 

 ber of acidophil cells visualized was ac- 

 complished without an increased number 

 of mitoses or any increase in the size of 

 the gland and was, therefore, due to the 

 regranulation of acidophil cells which had 

 been degranulated during pregnancy. Hunt 

 (1949), however, found that mitoses were 

 present in some but not all rat hypophyses 

 after parturition. Even allowing for this 



latter observation it seems that the in- 

 creased number of acidophil cells at the time 

 of parturition can be accounted for by the 

 accumulation of secretory granules in the 

 cells of the acidophil class. Purves and 

 Griesbach (unpublished) have found that 

 this increase in granulation occurs in the 

 acidophil cells which are remote from the 

 blood vessels and connective tissue septa 

 and which are considered to be related to 

 prolactin secretion. It has already been 

 noted that in the cat a granulation of 

 carminophil cells occurs which is at its 

 maximum at the time of parturition (Daw- 

 son, 1946) , these cells also being considered 

 the specific secretors of prolactin. In ac- 

 cordance with this view, Hurst and Turner 

 (1942) reported that in the rat, rabbit, 

 mouse, guinea pig, and cat the prolactin 

 content of the hypophysis was at its highest 

 level during the first few days after parturi- 

 tion. 



In connection with the question whether 

 there is a separate lactogenic factor secreted 

 during lactation, different from the luteo- 

 trophic and mammogenic factor secreted 

 during pregnancy as Turner (1939) pos- 

 tulated, cytologic observations indicate an 

 activity in a single specific cell type as- 

 sociated with both mammary growth during 

 pregnancy and lactogenesis after parturi- 

 tion. There is, during early lactation, a 

 phase of secretory activity in these special- 

 ized acidophil cells which is at its maximum 

 about the 16th day of lactation in the cat 

 (Dawson, 1946). Thereafter the reaction 

 wanes in a manner which suggests that a 

 continuation of lactation is not dependent 

 on the continued secretion of this factor. 

 It is, therefore, probable that the continua- 

 tion of an established lactation in those 

 animals in which lactation is of consider- 

 able duration is not dependent on the con- 

 tinued secretion of prolactin. In conform- 

 ity with this view, prolactin has been 

 found to stimulate metabolic changes in 

 slices of mammary gland tissue from rats on 

 days 1 to 4 of lactation (Folley, 1952). On 

 the other hand, purified prolactin prepa- 

 rations have not shown any galactopoietic 

 effect in the cow during the declining phase 

 of lactation (Folley and Young, 1938). 



