i6o 



PHYSIOLOGICAL TRIGGERS 



of certain steroid hormones with specific proteins (cf. 24, 26, 36). A portion of 

 the studies from our own laboratories will be presented, with the rationale that 

 such combinations have potentially great significance in elucidation of transport 

 and triggering mechanisms in vivo. 



The observations from these laboratories that the liver was essential for 

 estrogenic activity (cf. 36), coupled with the well-established role of this organ 

 in the elaboration of certain of the plasma proteins, suggested that hepatic 

 tissue may be the site of formation or com.bination of the estroprotein complex 

 present in the circulating plasma of several species. Accordingly, in vitro studies 

 were undertaken of the capacity of the liver and other tissues to influence the 

 formation of this complex. A portion of these studies has been presented in 

 detail elsewhere (33, 34). They were made possible by the availability of estrone 



Fig. 5. Incorporation of C'^ 

 into serum proteins after incuba- 

 tion of estrone-i6-C'^ with dif- 

 ferent tissues. The ether-soluble 

 fraction of the serum proteins 

 following strong acid hydrolysis is 

 shown. Incubations were carried 

 out for 2 hours. Height of the bars 

 for serum control, normal and 

 regenerating liver samples repre- 

 sents an average of 3-5 samples; 

 values for the other tissues are the 

 result of single determinations. 

 (Reprinted from ref. s:^ by per- 

 mission of the editor and pub- 

 lishers.) 



and estradiol labeled at the i6-position with C'^ The use of these materials 

 allowed experiments to be designed in which a few micrograms of the steroid, 

 approaching physiological orders of magnitude, could be incubated with rat 

 tissues in an homologous serum medium. The distribution of the estrogen or 

 its metabolic products in various fractions of the incubation mixture could 

 later be determined by radioactivity measurements. Figure 5 demonstrates 

 that of the tissues studied, only surviving liver influenced the incorporation of 

 radioactivity derived from estrone-i6-C'^ into the proteins of the serum me- 

 dium. The extent of the binding was correlated with the functional state of the 

 tissue and with time of incubation. These, and related observ^ations reported 

 elsewhere, suggest that the binding of estrogen or its metabolic products to 

 the cerum jiroteins is catalyzed by a specific enzyme system found in liver, but 

 not in spleen, uterus or kidney. This /// vilro model system may be rcpresenta- 



