Abstract:
Effective use of encapsulated sperm requires careful review of: (a) the conditions under which the procedure can be effectively used; (b) assessment of the effect of storage conditions on sperm survival; (c) description of the environment of the female tract before, during and after capsule deposition; and (d) economic evaluation of impact and costs of the putative technology. Sperm survival depends on successful sustenance over two periods of storage (at subambient temperatures after collection and extension, then at body temperature when placed in the female tract) and one period of action (after release and until fertilization). The bioenergetic requirements of cauda epididymal and ejaculated bull and ram sperm are reviewed in terms of absolute ATP needs and are discussed in terms of storage needs. In addition, sperm inactivation by lipid peroxidation is discussed and suggestions are provided to minimize the process. Two general types of containers are possible. An open porous form allows free passage of nutrients and metabolic products; the entrapped sperm are thus subjected to the changing environment in the female tract. The other form is a sealed capsule that opens to release sperm before ovulation; it provides a sperm storage environment independent of female tract chemistry but introduces problems of nutrient supply and metabolite release. Potential experimental approaches to evaluate each type of system are discussed.