56 The Biochemistry of Semen 



Sperm inhibitors and spermicidal substances 



So far, detailed studies on the mechanism which underlies the 

 action of sperm inhibitors, have been relatively limited in scope and 

 concerned largely with chemical compounds which affect respiration 

 and glycolysis, among them cyanide, azide, dinitrophenol, and 

 fluoride, or which combine with sulphydryl groups, e.g. iodoacetate, 

 iodoacetamide, <?-iodosobenzoate, and /7-chloromercuribenzoate. 

 Even these studies, however, have clearly indicated the existence of 

 remarkable species differences in sperm behaviour. Thus for instance, 

 iodoacetate which is one of the strongest inhibitors of sperm activity 

 in higher animals, has a pronounced stimulating action on the 

 oxygen uptake of sea-urchin spermatozoa; this peculiar effect of 

 iodoacetate is shared by other sulphydryl-binding compounds, as 

 well as by malonate and nitrogen mustard (Barron and Goldinger, 

 \9A\b', Barron, Nelson and Ardao, 1948; Barron, Seegmiller, 

 Mendes and Narahara, 1948). It is interesting and important to 

 note that widely divergent results may be attained with a given 

 substance according to a particular set of experimental conditions: 

 rabbit spermatozoa, washed and resuspended in a sugar-free isotonic 

 medium, are immobilized completely by 00001m 2 : 3 : 5-triphenyl- 

 tetrazolium chloride, but a 200 times higher concentration of this 

 substance is ineffective towards sperm suspended in a glucose-con- 

 taining medium (Bishop and Mathews, 1952). It is equally salutary 

 to bear in mind that a substance which does not increase the initial 

 rate of sperm activity, may nevertheless be utilized by the sperma- 

 tozoa as an essential nutrient. For instance, most of the sugars 

 and fatty acids which are oxidized by spermatozoa, do not act by 

 increasing the initial rate of respiration but by maintaining it. 



Surprisingly enough, many substances endowed with pronounced 

 pharmocological action in the whole animal, such as the alkaloids, 

 appear to exert little or no effect upon spermatozoa in vitro. Sperm 

 cells are also remarkably resistant to ethanol. Ivanov (1913) observed 

 excellent motility in dog sperm to which he added 2-5% ethanol, 

 and he managed to obtain live and normal offspring from an animal 

 inseminated with semen mixed with 10% ethanol. It may be men- 

 tioned here that ethanol is one of the substances which are definitely 

 known to pass into semen after ingestion by the animal (Farrell, 



