758 



SPERM. OVA, AND PREGNANCY 



support motility for long periods of time; 

 however, respiratory processes coupled with 

 oxidative phosphorylation are far more ef- 

 ficient and can be assumed to furnish sperm, 

 as other tissues, 8 to 10 times as much 

 ATP for the same amount of initial sub- 

 strate degraded (for general discussion, see 

 Lehninger, 1955; Slater, 1958). Sperm mo- 

 tility is sustained so long as a minimal 

 concentration of intracellular ATP persists ; 

 with the exhaustion of ATP, motility ceases 

 (Engelhardt, 1945; Lardy, Hansen, and 

 Phillips, 1945). In 1945, Lardy and Phillips 

 suggested the presence of ATP in bull sperm 

 and Mann ( 1945) succeeded in isolating 

 from ram sperm the nucleotide, as the bar- 

 ium salt, and characterizing it as ATP. 

 Soon thereafter it was shown to be func- 

 tionally identical with ATP isolated from 

 muscle (Ivanov, Kassavina and Fomenko, 

 1946). ATP has since been extracted from 

 sperm of the sea urchin. Echinus esculentus 

 (Rothschild and Mann, 1950). A consider- 

 able body of evidence has suggested that 

 phosphagen is present in mammalian sperm 

 which might serve as a phosphorus donor 

 for the reconstitution of ATP from adeno- 

 sine diphosphate (ADP) (see Bishop, 1961, 

 for review) ; recently, however. White and 

 Griffiths (1958) re-examined the problem 

 and failed to find any significant amount 

 of creatine phosphate or the enzyme which 

 might take part in transphosphorylation in 

 the sperm of the ram, rabl)it, or bull. 



B. INVERTEBRATE SPERM METABOLISM 



The processes underlying motility and 

 survival of invertebrate spermatozoa are 

 oxygen-dependent and involve the utiliza- 

 tion of endogenous reserves (Rothschild, 

 1951a). In sea urchin sperm, on which such 

 investigations have almost exclusively cen- 

 tered, the oxidative substrate seems to be 

 phospholipid, mainly situated in the mid- 

 piece (Rothschild and Cleland, 1952) . About 

 20 per cent of the intracellular phospho- 

 lipid of the sperm of Echinus esculentus is 

 depleted during incubation over a 7-hour 

 period at 20°C. According to Rothschild, 

 sea-urchin spermatozoa do not utilize glyco- 

 lytic substrates (glucose or fructose), and 

 there is scant evidence of a "sparing" of en- 

 dogenous substrate by exogenous hexose. 



Among certain other forms which, like the 

 sea urchin, reproduce by external fertiliza- 

 tion, the spermatozoa rely principally, if 

 not entirely, on oxidative mechanisms. This 

 is true, for example, of the starfish, Asterias 

 (Barron, 1932) as well as the frog, Rana 

 (Bernstein, 1954). On the other hand, some 

 invertebrate sperm are less restricted in 

 their metabolic capacity. The sperm of the 

 oyster, Saxostrea, for example, normally de- 

 pend on respiratory processes, but if these 

 are inhibited by an oxidative inhibitor such 

 as cyanide, and suitable substrate is present, 

 glycolysis can occur (Humphrey, 1950). 

 Barron (1932) indicated that sperm of vari- 

 ous marine animals differ significantly in 

 their tolerance for anaerobic conditions, as 

 determined by the saf ranin test for oxygen ; 

 sperm of Arbacia, Asterias, and Nereis re- 

 tain their motility and fertilizing capacity 

 when exposed to anaerobiosis for 1, 2, and 

 5 hours, respectively. 



The importance of oxidative phosi)horyla- 

 tion, in contrast to oxygen consumption per 

 se, to sperm motility has been clearly dem- 

 onstrated in the sperm of the clam, Spisula 

 (Gonse, 1959). Dinitrophenol, an uncou- 

 pling agent, inhibits sperm motility while 

 increasing Oo uptake several fold. Amytal, 

 on the other hand, at a concentration which 

 severely depresses respiration, only slightly 

 impairs motility. 



Determinations of respiratory cjuotients 

 (R.Q.) of invertebrate spermatozoa yield 

 values approximating 1.0 (Barron and 

 Goldinger, 1941; Hayashi, 1946; Barron, 

 Seegmiller, Mendes and Narahara, 1948; 

 Spikes, 1949; Humphrey, 1950). Such data 

 suggest carbohydrate rather than lipid 

 or phospholipid as substrate. Rothschild 

 (1951a), however, has emphasized the tech- 

 nical difficulties besetting such determina- 

 tions and the errors which may arise; in 

 his view, loss of bicarbonate from the sea- 

 water diluent gives erroneously high R.Q. 

 values. Yet, in support of the possible utili- 

 zation of glucose or fructose by sea urchin 

 sperm { Arbacia and Psaynmechinus) stands 

 Wicklund's demonstration that exogenous 

 hexose significantly prolongs motility and 

 fertilizing capacity of sperm (in Runnstrom, 

 1949 ) , a point also suggested by the work of 

 Spikes (1949). 



