48 The Biochemistry of Semen 



A lowered rate of fructolysis has been observed in certain cases 

 of human subfertiHty (Davis and McCune, 1950; Birnberg, Sherber 

 and Kurzrok, 1952). However, in human semen with its physio- 

 logically low sperm density but high fructose content, it is actually 

 more convenient to assess the rate of fructose utilization by measur- 

 ing the formation of lactic acid (chemically or manometrically) 

 rather than the disappearance of sugar. In any case, if one were to 

 measure fructolysis in human semen by the disappearance of sugar, 

 it would be essential to use a photometric method specific for 

 fructose, and not base the results merely upon the changes in 'reduc- 

 ing value', because human semen contains a fair amount of reducing 

 substances other than carbohydrate, which represent a substantial 

 proportion of the total 'reducing value' towards reagents such as 

 cupric hydroxide, ferricyanide etc. Moreover, the content of these 

 reducing substances often increases during the incubation of semen, 

 thus rendering unreliable, not to say senseless, determinations of 

 fructose based upon reduction measurements. 



Methylene-blue reduction test 



A method often used in the evaluation of semen quality is the 

 'methylene-blue reduction test' which is the outcome of dehydro- 

 genase activity of the semen and depends on the determination of 

 the time which it takes a semen sample to decolorize a certain 

 amount of methylene blue, under standard conditions of incuba- 

 tion in vitro (S^rensen, 1942; Beck and Salisbury, 1943; VanDemark, 

 Mercier and Salisbury, 1945; Boenner, 1947). In S0rensen's original 

 method the incubation was carried out in a Thunberg tube, but in 

 Russia (Milovanov and Sokolovskaya, 1947) and in France (Brochart, 

 1948Z)), the test was later performed by introducing a drop of semen 

 mixed with methylene blue into a capillary tube and by observing 

 the decolorization in the central portion of the column; in good- 

 quality bull semen, with high density and motility, decolorization 

 usually takes place within less than 10 min. at 20°; if it extends 

 beyond 30 min., it signifies poor semen quality. However, though 

 useful, the test is of limited scope, not least because as long ago as 

 1941, Lardy and Phillips showed that the reduction of methylene 

 blue by sperm suspensions may be markedly delayed by a variety 

 of substances including glucose, lactate and citrate. 



