Ontogeny of Endocrine Correlation 



593 



processes can continue for a while in the 

 denervated adrenal of the adult. On the 

 other hand, the rate of formation and release 

 of adrenaline into the blood in the adult are 

 partly regulated by the nervous system. The 

 approximate time of release including quan- 

 tity present in the blood stream of the em- 

 bryo or fetus covild be readily determined, 

 since bio-assay methods sensitive to concen- 

 trations of adrenaline of 1 in 500,000, or 

 less, are available. 



Once adrenaline is liberated into the blood 

 stream, which seems likely to occur toward 

 the end of embryonic life, the question arises 

 as to its interrelations with other substances 

 within the embryo. (See p. 609.) It is well 

 known that, as a hormone, adrenaline has a 

 highly selective action on effectors innervated 

 by the sympathetic nervous system. Of partic- 

 ular interest here, however, is that on the 

 basis of recent investigations (see Long, '49, 

 for evidence and theoretical considerations) 

 it plays a role in the endocrine activity of the 

 adrenal cortex. The administration of adrena- 

 line as well as its liberation following stimu- 

 lation of the sympathetic nei-vous system 

 causes an increase in adrenal cortical activity. 

 Although adrenaline acts as a potent stimulus 

 to adrenal cortical activity, its mechanism of 

 action is unknown. According to the theory 

 of Long its action is indirect, involving the 

 correlation and interplay of anterior pitui- 

 tary, adrenal cortex, and medulla. The par- 

 ticular merit of this theory is that it combines 

 in one comprehensive picture a variety of 

 factors or conditions, such as activity of the 

 sympathetic nervous system (adrenaline re- 

 lease), adrenocorticotrophic hormone, and 

 stress, all of which are known to call forth 

 secretion by the cortex. Their interaction 

 constitutes an adaptive mechanism enabling 

 the organism to adjvist itself to stresses which 

 may arise within or without it. It is con- 

 ceivable, therefore, that such an interplay of 

 anterior pitviitary-adrenal functions as they 

 become established in the embryo creates an 

 internal milieu essential for maintaining a 

 normal state of balance, and in preparing 

 the organism for exigencies appertaining to 

 birth and early postnatal life. 



ANTERIOR PITUITARY-GONAD 

 RELATIONS 



The gonad is the third component of the 

 endocrine system with which the anterior 

 pituitary becomes interrelated during the 

 course of ontogeny. The concept of anterior 

 pituitary-gonad relations is based almost 



entirely on extensive researches on immature 

 and adult vertebrates. Experimental proce- 

 dures designed to determine the effects of 

 removal of one gland upon the other and/or 

 in combination with implantation of either 

 gland or the administration of their active 

 principles as well as the effects of anterior 

 lobe implants on sexually immature animals 

 have yielded evidence which clearly estab- 

 lished for many species that specific gonado- 

 trophic secretions of the anterior lobe are 

 essential to the maintenance of structure and 

 function of the gonads, which in turn by 

 secreting sex hormones affect receptor sex 

 structures such as the gonoducts and acces- 

 sory glands. Moreover, sex hormones re- 

 leased by the gonads have a reciprocal effect 

 on the anterior pituitary, regulating release 

 of gonadotrophic hormones. (For supporting 

 evidence and citations see Engle, '39; Fevold, 

 '39; Moore and Price, '32; Smith, '39.) 



The main problem for consideration here 

 is the sequence of events in the establishment 

 of functional relations between anterior pi- 

 tuitary and gonad. Particular attention will 

 be given to such specific problems as (a) 

 the time and degree to which the entire 

 course of gonad development is dependent 

 upon gonadotrophic secretions, and (b) 

 whether the onset of production of sex hor- 

 mones and their effects on receptor sex struc- 

 tures precedes or coincides with beginning 

 anterior lobe activity. 



ONSET OF SEX-HORMONE ACTIVITY 

 OF THE GONAD 



As a basis of approach to the over-all 

 problem of the development of functional 

 interaction between the gonad and the an- 

 terior pituitary, the time course in the dif- 

 ferentiation of functional activity of the 

 gonad will be examined first. At what period 

 are sex hormones initially produced? When 

 are they released into the blood circvilation 

 in quantities sufficient to act on such ter- 

 minal receptors as the seminal vesicle, gono- 

 duct, and phallus, sex structures which react 

 selectively to sex hormones? These questions 

 can be best answered by a consideration of 

 the following several lines of evidence (also 

 refer to Table 27). 



1. As is known from the work of Lillie 

 ('17), the vascular connections of the fetal 

 membranes of twin embryos in cattle usually 

 become sviitable for the intermingling of the 

 blood of the co-twins either prior to or at 

 about the time that structural sex differ- 

 entiation of the gonad sets in (25-mm. 



