760 



SPERM, OVA, AND PREGNANCY 



tate production and oxygen consumption. 

 Both turkey and cock sperm also utilize 

 glycolytic and oxidative substrates, al- 

 though at lower rates than those generally 

 found in mammalian spermatozoa (Win- 

 berg, 1939; Pace, Moravec and Mussehl, 

 1952; Bade, Weigers and Nelson, 1956; 

 Lorenz, 1958). 



The range of substrates metabolized by 

 mammalian sperm is extensive and includes 

 carbohydrates, lipids, and amino acids. Of 

 the three readily glycolyzable hexoses — 

 glucose, fructose, and mannose- — glucose is 

 preferentially utilized by sj^erm of the bull, 

 ram, and man (Mann, 1951b; van Tien- 

 hoven, Salisbury, VanDemark and Hansen, 

 1952; Flipse, 1958; Freund and MacLeod, 

 1958). Hexosc degradation is such that one 

 mole of glucose gives rise to two moles of 

 lactate (Flipse and Almquist, 1955; Mac- 

 Leod and Freund, 1958). Lactic acid tends 

 to accumulate, since the rate of glycolysis, 

 in bull sperm for example, exceeds the rate 

 of pyruvate oxidation ( Melrose and Terner, 

 1951). Evidence bearing on the possibility 

 of direct oxidation of glucose by way of the 

 hexose monophosjihate shunt is fragmentary 

 and thus far negative (Wu, McKenzie, Fang 

 and Butts, 1959). Glycolysis can, of course, 

 occur under l)oth aerobic and anaerobic con- 

 ditions. The addition of exogenous hexose 

 to a respiring system of sperm tends to 

 "spare" the respiratory substrate (Lardy 

 and Phillips, 1941; O'Dell, Almquist and 

 Flipse, 1959); this partial inhibition of 

 oxidation by glycolysis is a manifestation 

 of the well known Crabtree effect ( Crabtree, 

 1929; Terner, 1959) and can be interpreted 

 as a form of metabolic regulation. 



Since the initial demonstration (Lardy 

 and Phillips, 1941) that endogenous phos- 

 pholipid seems to constitute the natural 

 respiratory substrate of bull spermatozoa, 

 many oxidizable substances have been 

 shown to increase oxygen uptake or to sup- 

 port sperm motility (Mann, 1954; White, 

 1958). Considerable species variation occurs 

 in the apparent facility with which such 

 substances are oxidized, but some of this 

 variation depends less on utilization than 

 on the extent to which the substances pene- 

 trate specific kinds of sperm. Succinate and 

 malate, for example, can increase the respi- 



ration and motility of washed ram sperm, 

 but are without effect on bull sperm under 

 similar conditions, presumably because of 

 their failure to penetrate the cells (Lardy 

 and Phillips, 1945; Lardy, Winchester and 

 Phillips, 1945). Changes in cell permeability 

 induced by rough handling, severe centrifu- 

 gation, storage, or specific chemical treat- 

 ment, such as exposure to surface-active 

 detergents, can alter the rate and degree of 

 substrate penetration and thereby produce 

 profound changes in respiratory activity 

 (Koefoed-Johnsen and Mann, 1954). 



Among the oxidative substrates which in- 

 crease respiration of mammalian sj)erm 

 may be included the end products of an- 

 aerobic glycolysis — pyruvate and lactate — 

 as well as acetate, butyrate, propionate, 

 citrate, and oxaloacetate (Lardy and Phil- 

 lips, 1944; Mann, 1954). Glycerol is oxi- 

 dized to lactic acid by ram and bull sperma- 

 tozoa (Mann and White, 1957; White, 

 1957), probably by entering the Embden- 

 Meyerhof jjathway as glycerol phosphate at 

 the triose phosphate level. In experiments 

 involving C"-tagged glycerol, it has been 

 claimed that bull sperm can complete the 

 oxidation to C^'*02 under anaerobic condi- 

 tions (O'Dell, Flipse and Almquist, 1956), 

 a point which requires confirmation. The 

 glycerol moiety of the seminal constituent, 

 glycerylphosphorylcholine, apparently is 

 not made available to the sperm for respira- 

 tory activity (Mann and White, 1957). 



In the early work on phospholipid oxi- 

 dation, it was concluded that endogenous 

 reserves are readily utilized and that egg 

 phospholipid can serve as an exogenous 

 source of energy (Lardy and Phillips, 

 1941). This finding is supported by the 

 study of Crawford, Flipse and Almquist 

 (1956) who determined the uptake by bull 

 spermatozoa of P'^--labeled egg phospho- 

 lipid. Bomstein and Steberl (1957), on the 

 other hand, found a negligible decrease in 

 intracellular phospholipid and an inappreci- 

 able utilization of exogenous lecithin during 

 incubation of well washed preparations of 

 bull sperm. Recent re-analysis of the nature 

 of the lipids in ram sperm indicates that 55 

 to 60 per cent is in the form of choline-based 

 acetal phospholipid or plasmalogen (Lo- 

 vern, Olley, Hartree and ]\Iann, 1957). 



