Lipids and their Role in the Metabolism of Semen 129 



Table 18. Changes in the phospholipid content of bull spermatozoa 

 in presence and absence of sugar (Lardy & Phillips, \9A\a) 



(Bull spermatozoa freed from seminal plasma by centrifugation, then 

 diluted with Ringer-phosphate solution to the original volume of semen, 

 and incubated at room temperature.) 



Medium Phospholipid content 



After 10 hr. 



Original incubation 



(mg. P/ml.) (mg. P/ml.) 



Ringer-phosphate 0-38 0-24 



Ringer-phosphate+0-04M-glucose 0-39 0-37 



glycolysable material in the form of fructose, the share of phos- 

 pholipids in sperm metabolism is probably small. But in the epi- 

 didymis, where glycolysable sugar is unavailable, Lardy and Phillips 

 ascribe great importance to the phospholipids as a source of oxida- 

 tive energy. The mechanism of utilization of this reserve is held to 

 involve hydrolytic cleavage of phospholipids foUov^ed by an oxida- 

 tion of the fatty acid portion via the citric acid cycle, and coupled 

 with aerobic phosphorylations. According to Lardy, Hansen and 

 Phillips (1945), the aerobic metabolism of phospholipids in the 

 bovine epididymal spermatozoa is accompanied by an uptake of 

 inorganic phosphate, and the formation of a phosphate ester which 

 is hydrolysed in 7 min. by N-HCl at 100°, and thus resembles 

 adenosine triphosphate. 



The ability to utilize phospholipids as a source of aerobic energy 

 extends to the spermatozoa of lower animals, notably those of the 

 sea-urchin. One of the main differences between mammalian and 

 sea-urchin semen is that the latter contains no glycolysable material 

 in the seminal plasma. The possibility that sea-urchin spermatozoa 

 which have been shed into sea- water, survive at the expense of 

 energy derived from the oxidation of intracellular carbohydrate such 

 as glycogen, also appears remote, in view of the very low content 

 of glycogen-like material in the sperm cells (Stott, 1930; Rothschild 

 and Mann, 1950). On the other hand, according to Rothschild and 

 Cleland (1952), the content of intracellular phospholipids which in 

 fresh sperm of Echinus esculentus is 5-5% of the dry weight or 4-14 

 mg. (0165 mg. P) per 10^*^ sperm cells decreases in the course of 

 aerobic incubation of sperm suspensions in sea-water, at an average 



