J.A. Gilmore1,2, J. Liu1, E.J. Woods1,2, A.T. Peter2 and J.K. Critser1,2
1 Cryobiology Research Institute, The Herman B Wells Center for Pediatric Research, Riley Hospital for Children, 1044 West Walnut Street, Indianapolis, IN 46202 and 2 Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907, USA
Previous reports have left unresolved discrepancies between human sperm cryopreservation methods developed using theoretical optimization approaches and those developed empirically. This study was designed to investigate possible reasons for the discrepancies. Human spermatozoa were exposed to 1 mol/l glycerol, 1 mol/l dimethyl sulphoxide (DMSO), 1 mol/l propylene glycol (PG) or 2 mol/l ethylene glycol (EG) at 22, 11 and 0°C, then returned to isosmotic media while changes in cell volume were monitored. Activation energies (Ea) of the hydraulic conductivity (Lp) in the presence of cryoprotective agents (CPA) (LpCPA) were 22.2 (DMSO), 11.9 (glycerol), 15.8 (PG), and 7.8 (EG) kcal/mol. The Ea values of the membrane permeability to CPA (PCPA) were 12.1 (DMSO), 10.4 (glycerol), 8.6 (PG) and 8.0 (EG) kcal/mol. These data indicated that even at low temperatures, EG permeates fastest. The high LpCPA in the presence of EG and low associated Ea would allow spermatozoa to remain closer to equilibrium with the extracellular solution during slow cooling in the presence of ice. Collectively, these data suggest that the increase of the Ea of Lp in the presence of CPA at low temperature is the likely reason for the observed discrepancy between theoretical predictions of spermatozoa freezing response and empirical data.
Key words: cryobiology/membrane/permeability/spermatozoa/temperature
Source: Human Reproduction, Vol. 15, No. 2, 335-343, February 2000.