The Epididymis, Sperm Maturation and Fertilisation

The epididymis has great significance in the reproductive biology of the male and it is gaining recognition as an organ worthy of study in its own right - where the secretory and absorptive activities of one tissue (the epithelium) profoundly modify the function of another (the spermatozoon). Apart from cases of epididymal agenesis or physical blockage, however, it is not yet known to what extent mal functions of the epididymis contribute to "unexplained" male infer tility, but its importance as a target for antifertility agents in the male is now widely appreciated. This monograph evolved from two lectures on epididymal func tion given at the National Research Institute for Family Planning, Beijing and the Sichuan Provincial Family Planning Research Insti tute, Chengdu, China in 1983. In order to stress for this audience the central importance of the epididymis in fertilisation, and so highlight its potential for attack by antifertility agents, the talks attempted to put the epididymis in reproductive perspective by stressing the func tional development of the sperm cells during their sojourn in the epididymis, rather than merely listing the changes observed in them.

The epididymis has great significance in the reproductive biology of the male and it is gaining recognition as an organ worthy of study in its own right - where the secretory and absorptive activities of one tissue (the epithelium) profoundly modify the function of another (the spermatozoon).

I. Maturation of Spermatozoa in the Epididymis.- 1. Acquisition in the Epididymis of Sperm Fertilising Ability.- 2. Involvement of the Epididymis in the Development of Sperm Fertilising Ability.- 3. The Nature of the Androgen-Dependent Epididymal Secretions Involved.- 4. Response of Immature Spermatozoa to Epididymal Secretions.- 5. Scope of this Review.- 6. Summary.- 7. References.- II. Fertilisation.- A. Sperm Motility.- 1. The Need for Flagellar Activity of Sperm for Them to Reach the Egg.- 2. The Ability of Immature Spermatozoa to Reach the Site of Fertilisation.- 3. Development in the Epididymis of Sperm Motility In-Vitro.- 4. The Nature of the Reduced Motility of Immature Spermatozoa.- 5. Involvement of the Epididymis in the Maturation of Motility.- 6. Induction of Motility in Immature Spermatozoa In-Vitro.- 7. Relationship of Induced Forward Motility to Fertilising Ability.- 8. Summary.- 9. References.- B. Capacitation.- 1. Detection of Capacitation.- 2. Changes in the Sperm Surface During Capacitation.- 3. Mechanisms of Capacitation.- 4. Consequences for Membrane Fluidity.- 5. Action of Decapacitation Factors.- 6. Maintenance of Motility.- 7. Requirements of Capacitation.- 8. Development in the Epididymis of the Ability of Spermatozoa to be Capacitated.- 9. Involvement of the Epididymis in Permitting Capacitation.- 10. Summary.- 11. References.- C. Consequences of Capacitation. I. Sperm-Egg Binding.- 1. Sperm-Egg Binding.- 2. Relationship to Capacitation.- 3. Relationship to the Acrosome Reaction.- 4. Mechanisms of Binding.- 5. Development in the Epididymis of the Ability of Sperm to Bind to Eggs.- 6. Involvement of the Epididymis in the Development of the Sperm Surface.- 7. Summary.- 8. References.- D. Consequences of Capacitation. II. The Acrosome Reaction.- 1. The Acrosome Reaction.- 2. Mechanism of the Acrosome Reaction.- 3. Requirements for the Acrosome Reaction.- 4. Stimulus to the Acrosome Reaction.- 5. Relationship to Capacitation.- 6. Relationship to Hyperactivated Motility.- 7. Relationship to Fertilisation.- 8. Site of the Acrosome Reaction.- 9. Consequences of the Acrosome Reaction.- 10. Development in the Epididymis of the Ability of Spermatozoa to Undergo the Acrosome Reaction.- 11. Involvement of the Epididymis in Permitting the Acrosome Reaction.- 12. Summary.- 13. References.- E. Consequences of Capacitation. III. Hyperactivation.- 1. Hyperactivation.- 2. Requirements of Hyperactivated Motility.- 3. Mechanisms of Hyperactivated Motility.- 4. Stimulus to Hyperactivated Motility.- 5. Relationship to Capacitation.- 6. Relationship to the Acrosome Reaction.- 7. Relationship to Fertilisation.- 8. Site of Hyperactivated Motility.- 9. Consequences of Hyperactivated Motility.- 10. Development in the Epididymis of the Ability of Sperm to Display Hyperactivated Motility.- 11. Involvement of the Epididymis in Permitting Hyperactivation.- 12. Summary.- 13. References.- F. Sperm-Egg Fusion.- 1. Binding to the Vitellus.- 2. Fusion with the Vitellus.- 3. Relationship to Capacitation.- 4. Relationship to the Acrosome Reaction.- 5. Relationship to Sperm Motility.- 6. Regions of the Sperm Head Involved in Fusion.- 7. Basis of Fusion.- 8. Development in the Epididymis of the Ability of Sperm to Fuse with Eggs.- 9. Involvement of the Epididymis in Permitting Sperm-Egg Fusion.- 10. Summary.- 11. References.- G. Post-Fusion Events.- 1. Activation of the Eggs.- 2. Decondensation of Sperm Chromatin.- 3. Formation of the Male Pronucleus.- 4. Chromosome Condensation.- 5. Development in the Epididymis of the Ability of Sperm to Interact with the Vitellus.- 6. Involvement of the Epididymis in Permitting Post-Fusion Events.- 7. Summary.- 8. References.- III. Function of the Epididymis and Its Secretory Products.- A. Epididymal Structure and Function.- 1. Introduction.- 2. Epididymal Structure.- 3. Blood Supply.- 4. Lymphatics.- 5. Methods of Study.- 6. Epithelial Cells.- 7. Testicular Control of Epididymal Function.- 8. Permea