STEROID SEX HORMONES 



653 



ments in which it was found that the in- 

 crease in enzyme activity is inhibited by 

 ethionine and this inhibition is reversed 

 by methionine. The amino acid analogue 

 ethionine is known to inhibit protein syn- 

 thesis and this inhibition of protein syn- 

 thesis is overcome by methionine. 



The injection of estrogen into the im- 

 mature or castrate rodent produces a strik- 

 ing uptake of water by the uterus followed 

 by a marked increase in its dry weight 

 (Astwood, 1938). Holden (1939) postu- 

 lated that the imbibition of water results 

 from vasodilatation and from changes in the 

 permeability of the blood vessels of the 

 uterus. There is clear evidence (Mueller, 

 1957) that the subsequent increase in dry 

 weight is due to an increased rate of syn- 

 thesis of proteins and nucleic acids. The 

 sex hormones and other steroids could be 

 pictured as reacting with the protein or 

 lipoprotein membrane around the cell or 

 around some subcellular structure like a 

 surface-wetting agent and in this way in- 

 ducing a change in the permeability of the 

 membrane. This might then increase the 

 rate of entry of substances and thus alter 

 the rate of metabolism within the cell. 

 This theory could hardly account for the 

 many notable specific relationships between 

 steroid structure and biologic activity. 

 Spaziani and Szego (1958) postulated that 

 estrogens induce the release of histamine in 

 the uterus and the histamine then alters the 

 permeability of the blood vessels and pro- 

 duces the imbibition of water secondarily. 



The uterus of the ovariectomized rat is 

 remarkably responsive to estrogens and 

 has been widely used as a test system. 

 After ovariectomy, the content of ribo- 

 nucleic acid of the uterus decreases to a 

 low level and then is rapidly restored after 

 injection of estradiol (Telfer, 1953). A 

 single injection of 5 to 10 yu,g. of estradiol 

 brings about (1) the hyperemia and water 

 imbibition described previously; (2) an 

 increased rate of over-all metabolism as 

 reflected in increased utilization of oxygen 

 (David, 1931; Khayyal and Scott, 1931; 

 Kerly, 1937; MacLeod and Reynolds, 1938; 

 Walaas, Walaas and Loken, 1952a; Roberts 

 and Szego, 1953a) ; (3) an increased rate 

 of glycolysis (Kerly, 1937; Carroll, 1942; 

 Stuermer and Stein, 1952; Walaas, Walaas 



and Loken, 1952b; Roberts and Szego, 

 1953a) ; (4) an increased rate of utilization 

 of phosphorus (Grauer, Strickler, Wolken 

 and Cutuly, 1950; Walaas and Walaas, 

 1950) ; and (5) tissue hypertrophy as re- 

 flected in increased dry weight (Astwood, 

 1938), increased content of ribonucleic acid 

 and protein (Astwood, 1938; Telfer, 1953; 

 Mueller, 1957), and finally, after about 

 72 hours, an increased content of desoxy- 

 ribonucleic acid (Mueller, 1957). 



An important series of experiments by 

 Mueller and his colleagues revealed that 

 estrogens injected in vivo affect the metab- 

 olism of the uterus which can be detected 

 by subsequent incubation of the uterus in 

 vitro with labeled substrate molecules. 

 Mueller (1953) first showed that pre- 

 treatment with estradiol increases the rate 

 of incorporation of glycine-2-C^'* into uter- 

 ine protein. He then found that estrogen 

 stimulation increases that rate of incorpo- 

 ration into protein of all other amino acids 

 tested: alanine, serine, lysine, and trypto- 

 phan. The peak of stimulation occurred 

 about 20 hours after the injection of estra- 

 diol. In further studies (Mueller and Her- 

 ranen, 1956) it was found that estrogen 

 increases the rate of incorporation of gly- 

 cine-2-C^^ and formate-2-C^'* into protein, 

 lipid, and the purine bases, adenine and 

 guanine, of nucleic acids. A stimulation of 

 cholesterol synthesis in the mouse uterus 

 20 hours after administration of estradiol 

 was shown by Emmelot and Bos (1954). 



In more detailed studies of the effects of 

 estrogens on the metabolism of "one-carbon 

 units" Herranen and Mueller (1956) found 

 that the incorporation of serine-3-C^'* into 

 adenine and guanine was stimulated by 

 pretreatment with estradiol. The incorpora- 

 tion was greatly decreased when unlabeled 

 formate was added to the reaction mixture 

 to trap the one-carbon intermediate. In 

 contrast, the incorporation of C^^02 into 

 uridine and thymine by the surviving uter- 

 ine segment was not increased by pretreat- 

 ment with estradiol in vivo (Mueller, 

 1957). 



To delineate further the site of estrogen 

 effect on one-carbon metabohsm, Herranen 

 and Mueller (1957) studied the effect of 

 estrogen pretreatment on serine aldolase, 

 the enzyme which catalyzes the equilibrium 



