-62 



SPERM, OVA, AND PREGNANCY 



Further study would be desirable to dem- 

 onstrate whether bull semen contains a spe- 

 cific metabolic substance which might ac- 

 count for these effects, or whether, on the 

 other hand, the changes noted are part of 

 a more generally applicable type of cell 

 regulation. For example, both the low rate 

 of endogenous respiration and the Pasteur 

 effect, characteristic of epididymal sperm, 

 indicate an efficient phosphorylating sys- 

 tem; the metabolism of seminal sperm, on 

 the other hand, suggests that uncoupling 

 of respiration and phosphorylation may 

 have occurred {cf. Bomstein and Steberl, 

 1959). The similarity of action of the sperm 

 metabolic regulator and dinitrophenol, a 

 known uncoupling agent, further supports 

 this interpretation (Johnson and Lardy, 

 1950; Lardy, 1953). Lehninger (1955) has 

 stressed the relationship between uncou- 

 pling and the inhibition of the Pasteur effect 

 in other (mitochondrial) metabolic systems. 

 A general type of metabolic regulation 

 such as this, rather than a system unique to 

 one type of cell, might account for some of 

 the apparent discrepancies reported by 

 different investigators in their studies of 

 mammalian gametes (Melrose and Terner, 

 1951). White (1960), for example, working 

 with ram sperm has failed to confirm the 

 work of Lardy and associates; he found no 

 significant difference in oxygen uptake or in 

 fructolysis whether the sperm were from 

 the epididymis or from the ejaculate. At first 

 glance this seems to represent a marked 

 metabolic difference in the sperm of closely 

 related animals; considering, however, the 

 delicate balance of cell regulation at the 

 metabolic level (for general discussion, see 

 Krebs, 1957; Packer and Gatt, 1959) the 

 variation is not necessarily profound. The 

 striking differences shown by Dott (1959) 

 in the epididymal sperm of 5 species of do- 

 mestic mammals may also represent subtle 

 effects of metabolic control rather than 

 overt manifestations of fundamentally dif- 

 ferent systems of cell metabolism. He found 

 that the epididymal sperm of the bull, ram, 

 and rabbit are activated, in vitro, either by 

 oxygen or by fructose under anaerobic con- 

 ditions; boar sperm, however, apparently 

 require oxygen, and stallion sperm require 

 fructose, to initiate motilitv. Once stimu- 



lated, boar sperm glycolyze hexose freely, 

 indicating perhaps that the action of the 

 oxygen is to metabolize an intracellular in- 

 hibitor of some process necessary for motil- 

 ity (Dott, 1959). The response of stallion 

 sperm suggests that the main source of 

 energy is derived from aerobic glycolysis 

 and, further, that endogenous oxidative 

 reserves are scant or that the respiratory 

 processes are inhibited at some critical 

 point. The oxygen uptake of seminal sperm 

 from the stallion is generally low. In cer- 

 tain features this situation in stallion sperm 

 corresponds to the metal)olic behavior of 

 human seminal sperm. 



E. HUMAN SPERM METABOLISM 



Princij^ally through the investigations of 

 MacLeod (1941-1946), the metabolic ac- 

 tivities of sperm in the human ejaculate are 

 generally considered to present a rather 

 unique picture. Human sperm show a high 

 rate of anaerobic glycolysis which is only 

 slightly depressed by oxygen; the rate of 

 oxygen consumption in the presence of 

 glucose is extremely low — according to 

 Terner (1960j, about one tenth that of bull 

 sperm. When hexose is replaced by any one 

 of a number of amino or fatty acids, sperm 

 motility is gradually lost; it is not known, 

 however, to what extent these exogenous 

 substances do or do not penetrate the cell. 

 Of the nonglycolyzable substrates em- 

 ployed, only succinate stimulated oxygen 

 consumption, and this reaction was accom- 

 panied, when glucose was present, by a 40 

 per cent reduction in lactate production 

 (MacLeod, 1946). MacLeod further claimed 

 that oxygen, even at low tensions, is detri- 

 mental to human sperm suspended in Ringer 

 glucose; after several hours at 38°C., aerobic 

 motility is seriously impaired. Motility is 

 also suppressed by glycolytic inhibitors 

 (iodoacetate and fluoride), but is claimed 

 to be unaffected by respiratory poisons 

 (cyanide, azide, and carbon monoxide). 

 These considerations led MacLeod to the 

 conclusion that human sperm rely entirely 

 on the energy of glycolysis for motility and 

 are unable to utilize effectively oxidizable 

 substrate, despite the fact that the cells 

 contain the main components of the cyto- 

 clirome system and tricarboxylic acid cycle. 



