BIOLOCiY OF SPERMATOZOA 



721 



voided tliroii^li the vas deferens or he ab- 

 .sorl)ed by the duct iniicosa and i)hago- 

 cyto.scd, as suggested l)y Mason and Sliaver 

 (1952) and Montagna (1955). The possi- 

 bihty of absorption of si)enn and of sperm 

 products by the epithelium poses a signifi- 

 cant problem relating to self -immunization 

 whicli is discussed in a later section. 



F. ACQUISITION BY SPERM OF THE 

 CAPACITY FOR MOTILITY 



By the time spermatozoa are primed for 

 union with the eggs they must be sufficiently 

 activated to undergo independent move- 

 ment, since motility, with rare exceptions, 

 is a prerequisite for fertilization. Sperm ac- 

 tivation is delayed in many species until 

 the gametes are in intimate association. 

 Among l)oth invertebrate and vertebrate 

 animals, instances are known in which 

 sperm are shed in a nonmotile condition 

 and are activated only when passively 

 brought into association with homologous 

 eggs as noted above. Frequently the gam- 

 etes are transferred in large bundles or 

 packets, enclosed in spermatophores, and 

 l)ecome motile only after the casings are 

 rui)tured when in contact with the female 

 I Drew, 1919). Generally, however, the gam- 

 etes are stimulated when shed externally or 

 ejaculated into the female genital tract. 

 This event corresponds to a spectacular mo- 

 ment in the metabolic life of the cell when 

 tlie exergonic processes are shifted into high 

 gear by the abrupt supply of oxygen, sub- 

 strate, or cofactors, in mammals copiously 

 provided by the secretions of the accessory 

 reproductive glands. 



Before ejaculation, and for much of the 

 time during their storage in the ducts, sperm 

 are quite capable of motility but, so far as 

 can be determined, remain, in vivo, in a 

 (|uiescent state (Simeone, 1933). The repro- 

 ductive advantage of this is obvious since, 

 before activation, sperm survival is esti- 

 mated in terms of months; after activity has 

 been acquired, survival is a matter of days 

 or hours (sec Table 13.8). The blocks both 

 to the excessive utilization of energy and to 

 motility, in vivo, are regarded as largely of 

 a pliysical nature — the relative or absolute 

 absence of oxygen which otherwise would 

 encourage aerobic respiration, and the lack 

 of glycolytic substrate, such as glucose or 



fi'uctose, which when present fosters an- 

 aerobic processes (Mann, 1954; Walton, 

 1956). Infrequent reports of transient mo- 

 tility by sperm immediately after removal 

 from the genital tract, thereby implying 

 that the cells are motile in vivo (White, Lar- 

 sen and Wales, 1959), must be confirmed 

 and may be attributable to the admission of 

 oxygen during the sam]>ling procedure. Ear- 

 lier supi^ositions that sperm immobilization 

 within the ducts is due to high CO2 concen- 

 tration or low pH level (Redenz, 1926) 

 have been contraindicated (Bishop and 

 Mathews, 1952a). Other physiologic factors, 

 involving both intrinsic features of the gam- 

 etes and exchange reactions between them 

 and the luminal fluids, may play a role, but 

 if so, their nature and action are unrecog- 

 nized. 



The capacity for motility on a general 

 scale is first attained by sperm during 

 transit through the epididymis (Redenz, 

 1926). Cells removed from the tail of the 

 duct, of the bull for example, immediately 

 become highly active when suspended in 

 physiologic saline and given access to oxy- 

 gen; under anaerobic conditions, glucose, 

 fructose, or mannose initiates vigorous flag- 

 ellation. Sperm removed from the head or 

 the isthmus of the epididymis, on the other 

 hand, rarely become motile and at best 

 show only a slow nonprogressive type of 

 undulation. Other mammals present a simi- 

 lar picture, the precise epidiclymal region 

 where motile capacity is attained varying 

 among species. 



Some degree of flagellation, albeit of a 

 leisurely, low-frequency type, can be ob- 

 served in sperm recovered from the testes 

 of various mammalian species (Tournade, 

 1913; Young, 1929a; Bishop, 1958d). These 

 gametes are incapable of activation to full 

 motility by the addition of oxygen, glyco- 

 lytic substrate, divalent cations (Mg+ + , 

 Ca+ + ), or ATP (Bishop, unpublished 

 data). Austin and Sapsford (1952) have ob- 

 served that the axial filament of the living 

 rat spermatid undergoes mo^-ement even be- 

 fore the flagellum begins to push out from 

 the margin of the roughly sjiherical cell. In 

 lower forms as well, particularly among 

 insects, sperm motility can be seen during 

 the period when the gametes are still at- 

 tached to their nurse cells within the gonad 



