Fructose and Fructolysis 137 



can be seen from Tables 4 and 5, which include values for fructose 

 in several species. But, when comparisons are made between a species 

 with fructose-rich semen (bull) and one notoriously poor in seminal 

 fructose (boar), it must not be forgotten that the volume of a single 

 boar ejaculate is almost a hundred times that of a bull, so that in 

 effect, a single ejaculate of either species contains about the same 

 absolute amount of fructose. There are species, however, in which 

 fructose is altogether absent from semen or present only in traces, 

 and it is through the study of these animals that we may hope to 

 gain insight into the problem of alternative sugars in semen. Cock 

 semen for example, has no fructose or a negligible amount only, but 

 it contains a certain amount (20-100 mg./lOO ml.) of anthrone- 

 reactive material of which a variable fraction disappears on 

 oxidation with glucose oxidase and must therefore, be identical 

 with glucose (Mann and Hancock, 1952). Rabbit semen, unlike 

 that of bull, ram and man, contains occasionally an appreciable 

 admixture of glucose in addition to fructose (Mann and Parsons, 

 1950). 



Site of formation 



The reason for the conspicuous species differences in the concen- 

 tration of fructose as well as the individual fluctuations (Table 4 

 and 5), is the fact that fructose is a product not of the testes, but 

 of the male accessory organs of reproduction, principally the seminal 

 vesicles (Mann, \9A6b). Naturally, the highly variable anatomical 

 characteristics of these glands such as their size, actual storage 

 capacity, and secretory ability, are important factors which deter- 

 mine the final output of fructose in the ejaculate (Fig. 4). All these 

 considerations are pertinent to studies of human semen because of 

 the exceptionally large individual variations in the secretory func- 

 tion of the seminal vesicles and their rather small storage capacity 

 which explains why the collection of consecutive ejaculates within 

 a few days, usually yields samples with a conspicuously low level 

 of fructose. It appears that a time interval of about two days is 

 required to replenish the store of fructose in the vesicular secretion of 

 man. Unlike in certain other mammals, the human seminal vesicle 

 and vas deferens open into the urethra through a common channel 

 known as the ejaculatory duct. Consequently, any obstruction at the 



