Fructose and Fructofysis 153 



however, the situation differs in that the rate of fructose utiliza- 

 tion becomes smaller, and moreover, lactic acid undergoes further 

 oxidation, thus providing an additional source of metabolic energy. 

 It remains for further study to ascertain what type of carbohydrate 

 metabolism predominates in spermatozoa during their existence in 

 either the male or female genital tract. However, so far as in vitro 

 studies are concerned, they show that lactic acid can be efficiently 

 oxidized by spermatozoa even when the partial pressure of oxygen 

 has been reduced to a level as low as that which normally prevails 

 in animal tissues (Mann, 1951Z)); suitably diluted suspensions of ram 

 spermatozoa show in presence of 1 % O2 a respiratory rate as high 

 as in air, and lactate is capable of maintaining the oxygen uptake 

 equally well in 1% as in 20%, oxygen. 



Pasteur effect and the ^metabolic regulator'' 



It was said earher that the spermatozoa obtained directly from 

 the epididymis in some ways behave like suspensions of washed 

 ejaculated sperm; as a matter of fact, however, these two types of 

 sperm cells possess distinct characteristics (Henle and Zittle, 1942; 

 Lardy, Hansen and Phillips, 1945). Washed epididymal bovine 

 spermatozoa have a lower endogenous respiration than those in 

 ejaculated bull semen. But if sugar is added or if the spermatozoa 

 are removed from the epididymis after a period of storage in the 

 refrigerator, then their oxygen uptake is distinctly higher. More- 

 over, on addition of sugar, epididymal spermatozoa produce lactic 

 acid much more rapidly under anaerobic than aerobic conditions, 

 whereas in ejaculated sperm the rate of glycolysis is not much 

 higher in the presence than in the absence of oxygen. To account 

 for these differences, the Wisconsin workers determined the rate of 

 anaerobic and aerobic glycolysis as well as of oxygen uptake, in 

 epididymal spermatozoa to which glucose was added, and calcu- 

 lated the 'Meyerhof oxidation quotient' which measures the Pasteur 

 effect, that is the extent to which glycolysis is inhibited by oxygen. 

 The average value for the Meyerhof quotient calculated from twelve 

 experiments on bull epididymal sperm was 9-6, as against 5 recorded 

 for ejaculated sperm (Lardy, 1952). This difference, according to 

 Lardy, Ghosh and Plant (1949), is due to the presence in bull sper- 

 matozoa of a 'metabolic regulator' which occurs in the epididymal 



