198 



HYPOPHYSIS AND GONADOTROPHIC HORMONES 



Finerty and Binhammer (1952» and 

 Finerty, Hess and Binhammer (1952) stud- 

 ied the early responses of the hypophysis to 

 the acute stress of severe burns in the rat. 

 No changes were observed in the differential 

 cell counts nor in the degree of specific gran- 

 ulation of the cells stained by the azan 

 method. There was, however, an increase 

 in the number of acidophil cells per field in 

 sections stained by the acid hematein 

 method of Rennels (1951). Timmer and 

 Finerty (1956) supplied the explanation of 

 this discrepancy. The results of azan stain- 

 ing were expressed by differential cell 

 counts and did not show any change. The 

 results of the acid hematein staining were 

 expressed as cells per field, and the increase 

 in this number was the result of a shrinkage 

 in the gland which occurred after scalding. 

 Thus, although there were no more acid 

 hematein stained cells in the hypophysis, 

 they were closer together after scalding. 



Knigge (1955) found, in thyroidecto- 

 mized animals in which acidophil granules 

 were absent, that there was no acid hema- 

 tein staining before or after scalding. 



D. THE SIXTH CELL TYPE 



The pars anterior of the rat is particu- 

 larly reactive to changes in the rate of hor- 

 mone secretion, and the absence of any 

 striking change in the stainable cells after 

 adrenal ablation suggests that corticotrophin 

 may be secreted by chromophobes in this 

 species, or that corticotrophin is secreted 

 by a different mechanism from that respon- 

 sible for the secretion of other anterior lobe 

 hormones. The discovery by Farquhar 

 (1957) of a sixth cell type in the pars an- 

 terior of the rat may provide an explanation 

 of these peculiarities. These cells, which 

 can be clearly seen only by electron micros- 

 copy, are very different from any of the 

 other five types. The cytoplasm is rela- 

 tively empty and contains few formed ele- 

 ments (mitochondria, endoplasmic reticu- 

 lum). Secretory granules are absent. 



A distinctive feature of this additional 

 cell type is its location throughout tiie an- 

 terior lobe in groups around follicles or 

 ductules which contain colloid of low den- 

 sity. Some follicles are large and undoubt- 

 edly are analogous to colloid cysts, but 

 small follicles which jn-obably eould not 



be distinguished by light microscopy are 

 much more numerous. The cells lining the 

 follicles have angular contours, and the 

 nucleus is eccentrically located. The 

 amount of colloid seems to vary with the 

 amount of corticotrophin in the gland, being 

 increased after cortisone injection and de- 

 creased after partial adrenalectomy. No 

 marked response of the cells to the stimula- 

 tion of partial adrenalectomy was observed. 

 The identification of this sixth cell type as 

 a corticotroph can only be regarded as ten- 

 tative. Farquhar suggested that corticotro- 

 phin may be stored in the form of colloid 

 and released by some mechanism similar to 

 that by which thyroid hormone is mobilized 

 from the colloid of the thyroid follicles. 

 This would explain the difficulties in relat- 

 ing corticotrophin secretion or storage to 

 changes in the granulated cells observed by 

 the light microscope. 



My own observations show that this cell 

 often has an extremely irregular shape with 

 long and tenuous cytoplasmic projections 

 extending between adjacent granulated cells 

 or deeply indenting their cytoplasm. The 

 cross section of the enclosed space is often 

 elongated, suggesting that this cavity often 

 takes the form of a cleft rather than a fol- 

 licle or tubular ductule. 



X. The Pars Intermedia and Intermedin 

 Secretion 



Intermedin is an adenohypophyseal hor- 

 mone, distinct from the other adenohypo- 

 physeal hormones. This is evident from the 

 fact that it is formed in a different site. In 

 addition to causing dispersion of pigment in 

 mclanophores, intermedin acting over a 

 long time also stimulates the formation or 

 deposition of melanin. Intermedin is se- 

 creted by a specific cell type in the adeno- 

 hyjiophysis. The recognition of this specific 

 tyjie is simple in most vertebrates because 

 the cells are concentrated into a zone, the 

 pars intermedia. 



Evidence of the specific hormone content 

 of the pars intermedia was first obtained by 

 Smith and Smith (1923b) in tests of the 

 different regions of the beef hypophysis, 

 and has been confirmed by Lewis, Lee and 

 Astwood (1937), and r.iroiid and :\Iartinet 

 (1948). 



Intermedin seems to be located in a small 



