Fundamental Cryobiology of Human Spermatozoa and its Relationship to Artificial Insemination Outcomes

 

John K. Critser, Ph.D.

Director, Comparative Medicine Center

Gilbreath-McLorn Professor of Comparative Medicine

University of Missouri-Columbia

Columbia Missouri, 65211

Introduction

 

Empirical methods of cryopreservation developed in the 1950s are still used today for mammalian sperm preservation. In general, survival (as measured by motility) of post-thaw cryopreserved mammalian sperm is usually 50% or less and exhibits wide variability among species and individuals within species. In some mammalian species (e.g., rat), cryosurvival of sperm is so low that frozen-thawed sperm cannot be used for assisted reproduction.

 

Cryopreserved human spermatozoa were first used in the 1950s by Sherman (Sherman, 1964, 1973) and several investigators developed efforts to improve methods of human sperm cryopreservation (Sherman, 1978, 1986). However, even decades later, cryosurvival of human sperm from the general population is still low. The conception rates with frozen-thawed human sperm may be lower than those with non-frozen sperm (Corson et al., 1983; Richardson, 1980). More recent data in this regard are not available because it is not currently possible to conduct experiments addressing this issue since the use of non-frozen, non-quarantined human sperm presents is not possible do to the recognized risk of disease transmission. The low survival of cryopreserved human sperm and the associated lower conception rates are likely due to the fact that procedures for cryopreservation have not been optimized.

 

The process of cryopreservation is comprised of a series of steps in which cells are exposed to non-physiologic conditions. It is possible to divide this series of steps into four major areas: (1) selection of cryoprotective agent (CPA) type and concentration, (2) addition of the CPA, (3) cooling, (4) storage, (5) warming and (6) CPA removal. It is important to recognize that each of these steps is interactive; i.e., the parameters established in one step place constraints upon the other steps. In this context, the decision that is made in step 1 establishes constraints upon all the subsequent steps. Therefore, it is critical to optimize the type and concentration of CPA. However, each of these steps, because they interact with one another, require optimization though knowledge of the underlying fundamental cryobiology of the cell type of interest.

 

The current state of human spermatozoa cryobiology and preservation will be discussed

 

 

 

 

 

References

 

Corson SL, Baxter FR, Baylson MM. (1983). Donor insemination. Obstect. Gynecology Ann. 12: 283.

 

Richardson DW. Factors influencing the fertility of frozen semen. In: Richardson DW, Joyce D, Symonds EM eds. Frozen human semen. Boston: Martinus Nijhoff, 1980: 33-58.

 

Sherman JK. Research on frozen human semen: past, present and future. Fertil Steril 1964; 15: 485-99.

 

Sherman JK. Synopsis of the use of frozen human semen since 1964: state of the art of human semen banking. Fertil Steril 1973; 24: 397-416.

 

Sherman JK. Banks for frozen human semen: current status and prospects. In: The integrity of frozen spermatozoa. Washington DC: National Academy of Science National Research Council, 1978: 78-91.

 

Sherman JK. Current status of clinical cryobanking of human sperm. In: Paulson JD, Negro-Vilar A, Lucena E, Martini L eds. Andrology: male fertility and sterility. New York: Academic Press, 1986: 517-47.