658 



PHYSIOLOGY OF GONADS 



kidney. The growth of any tissue involves 

 the utilization of energy, derived in large 

 part from the oxidation of substrates, for 

 the synthesis of new chemical bonds and for 

 the reduction of substances involved in the 

 synthesis of compounds such as fatty acids, 

 cholesterol, purines, and pyrimidines. 



The physiologic responses to estrogen 

 action, such as water imbibition and protein 

 and nucleic acid synthesis, are processes not 

 directly dependent on the activity of trans- 

 hydrogenase. However, all of these processes 

 are endergonic, and one way of increasing 

 their rate would be to increase the supply of 

 biologically available energy by speeding 

 up the Krebs tricarboxylic acid cycle and 

 the flow of electrons through the electron 

 transmitter system. Much of the oxidation 

 of substrates by the cell produces TPNH, 

 whereas the major fraction of the biologi- 

 cally useful energy of the cell comes from the 

 oxidation of DPNH in the electron trans- 

 mitter system of the cytochromes. Hormonal 

 control of the rat of transfer of hydrogens 

 from TPN to DPN could, at least in theory, 

 influence the over-all rate of metabolism in 

 the cell and secondarily influence the 

 amount of energy available for synthetic 

 processes. Direct evidence of this was shown 

 in our early experiments in which the oxy- 

 gen consumption of tissue slices of target 

 organs was increased by the addition of 

 estradiol (Hagerman and Villee, 1952; Vil- 

 lee and Hagerman, 1953). 



This theory assumes that the supply of 

 energy is rate-limiting for synthetic proc- 

 esses in these target tissues and that the 

 activation of the estrogen-sensitive enzyme 

 does produce a significant increase in the 

 supply of energy. The addition of estradiol 

 in vitro produces a significant increase in 

 the total amount of isocitric acid dehy- 

 drogenated by the placenta (Villee, Loring 

 and Sarner, 1958) . Slices of endometrium to 

 which no estradiol was added in vitro 

 utilized oxygen and metabolized substrates 

 to carbon dioxide at rates which paralleled 

 the levels of estradiol in the blood and urine 

 of the patient from whom the endometrium 

 was obtained (Hagerman and Villee, 

 esses in these target tissues and that the 

 1953b). Estradiol increases the rate of syn- 

 thesis of ATP by liomogenates of human 



placenta (Villee, Joel, Loring and Spencer, 

 1960). 



The reductive steps in the biosynthesis of 

 steroids, fatty acids, purines, serine, and 

 other substances generally require TPNH 

 rather than DPNH as hydrogen donor. The 

 cell ordinarily contains most of its TPN 

 in the reduced state and most its DPN in 

 the oxidized state (Glock and McLean, 

 1955). If the amount of TPN+ is rate- 

 limiting, a transhydrogenase, by oxidizing 

 TPN and reducing DPN, would permit 

 further oxidation of substrates such as iso- 

 citric acid and glucose 6-phosphate, which 

 require TPN+ as hydrogen acceptor and 

 which are key reactions in the Krebs tri- 

 carboxylic acid cycle and the hexose mono- 

 phosphate shunt, respectively. Furthermore, 

 the experiments of Kaplan, Schwartz, Freeh 

 and Ciotti (1956) indicate that less bio- 

 logically useful energy, as ATP, is obtained 

 when TPNH is oxidized by TPNH cyto- 

 chrome c reductase than when DPNH is 

 oxidized by DPNH cytochrome c reductase. 

 Thus, a transhydrogenase, by transferring 

 hydrogens from TPNH to DPN before 

 oxidation in the cytochrome system, could 

 increase the energy yield from a given 

 amount of TPNH produced by isocitrate or 

 glucose 6-phosphate oxidation. The in- 

 creased amount of biologically useful energy 

 could be used for growth, for protein and 

 nucleic acid synthesis, for the imbibition of 

 water, and for the other physiologic effects 

 of estrogens. 



Estrogen stimulation of the transhy- 

 drogenation reaction would tend to decrease 

 rather than increase the amount of TPNH 

 in the cell. Thus the estrogen-induced stimu- 

 lation of the synthesis of steroids, fatty 

 acids, proteins, and purines in the uterus 

 can be explained more reasonably as due to 

 an increased supply of energy rather than 

 to an increased supply of TPNH. 



The theory that estrogens stimulate trans- 

 hydrogenation by acting as coenzymes 

 which are rapidly and reversibly oxidized 

 and reduced does not explain the pro- 

 nounced estrogenic activity in vivo of stil- 

 bestrol, 17a-ethinyl estradiol, or bfsdehy- 

 drodoisynolic acid, for these substances do 

 not contain groups that could be readily 

 oxidized or reduced. The exact mechanism 



