CENTRAL CONTROL OF PITUITARY SECRETION 



IOI9 



with regard to hypothalamic control of the adeno- 

 hypophysis. 



a) Lack of sexual differentiation of anterior pituitary 

 tissue. Gonadotrophic secretion in most female mam- 

 mals occurs cyclically while in the corresponding 

 males a steady level of secretion probably obtains. If 

 ovarian tissue is transplanted into castrate male rats, 

 follicular ripening occurs; but the cycles of ovulation 

 and luteinization have rarely been seen. This is 

 generally taken to indicate a relative lack of secretion 

 of luteinizing hormone by the male pituitary and 

 thought to indicate a sexual differentiation of pituitary 

 tissue. That this conclusion is not true may be seen 

 from the fact that male pituitary tissue grafted under 

 the tuber cinereum of hypophysectomized female rats 

 is capable of maintaining normal estrous cycles and 

 pregnancy in the female hosts (161, 226). Therefore 

 the rhythm of gonadotrophic secretion in the female 

 seems to be dependent neither on the presence of 

 ovaries nor on the presence of a genetically female 

 pituitary gland. It seems likely that anterior pituitary 

 tissue remains pluripotential in its functional ca- 

 pacity and that its pattern of activity in the male or 

 female depends on a stimulus derived from the (male 

 or female) hypothalamus. 



b) Onset of puberty. It has long been known that 

 ovaries obtained from immature donors and trans- 

 planted into ovariectomized adult females show 

 hastened development. In a somewhat similar fashion 

 it has now been shown (161) that pituitary tissue 

 taken from newborn rats and grafted under the tuber 

 cinereurn of adult hypophysectomized females can 

 support adult female reproductive activity long before 

 the donor animals would have reached puberty. Thus 

 the onset of puberty cannot be attributed solely to 

 aging of ovarian or pituitary tissue and is probably 

 dependent on maturation of some neural mechanism, 

 the site of which may be in the hypothalamus. This 

 view is reinforced by those cases of precocious puberty 

 in the human which are associated with small local- 

 ized tumors of the hypothalamus (see 19, 347), and 

 the fact that hypothalamic lesions may hasten the 

 onset of puberty in young rats (84). 



Adrenocorticotrophic Secretion After Pituitary Stalk Section 

 or Transplantation. As first pointed out by Selye (310, 

 311) the release of ACTH from the anterior pituitary 

 is induced by a great variety of stimuli and represents 

 a common response to the adverse changes of the 

 environment which have been grouped under the 

 term 'stressors.' Most studies of pituitary stalk section 

 have been made to see whether the procedure affects 

 the adrenal cortical response to stressful stimuli. In 



^^■■^-i^^m^^mm^, 





.•**• ;^''P 





FIG. 5. Microphotographs of sagittal sections through the 

 hypothalamus, a pituitary graft and base of skull of a rat. X 42 

 Upper: An unstained .section loo /j. thick. Note the vascular 

 connections passing from the primary plexus (P.P.) of the 

 hypophysial portal vessels to the graft (A.L.). India ink in- 

 jected specimen. Lower: An adjacent section through the same 

 specimen as illustrated in upper portion. To show the graft, con- 

 sisting of anterior lobe tissue (.-i.L.). P.P., primary plexus. 

 10 fi thick. Hematoxylin and eosin. [From Harris & Jacob- 

 sohn (161).] 



the hands of earlier workers stalk .section was generally 

 found not to prevent this response. Uotila (333) re- 

 ported that adrenal enlargement consequent to cold 

 exposure was not prevented in the rat by section of the 

 pituitary stalk. Similarly this procedure failed to pre- 

 vent the adrenal hypertrophy elicited by cold in the 

 rat (17) and dog (197), the cold-induced adrenal 

 cholesterol depletion in the guinea pig (324), and 

 the adrenal ascorbic acid response to injection of 

 histamine (53) or surgical trauma (108) in the rat. 

 However, it has since been shown that regeneration 

 of the hypophysial portal vessels may occur across 

 the site of pituitary stalk section. Among later workers 

 who have taken this factor into account may be 

 mentioned the following. Hume (184) placed a 

 polythene sheet between the cut ends of the stalk in 

 the dog and observed, nevertheless, a normal eosino- 



