Cryoprotective agent and temperature effects on human sperm membrane permeabilities: convergence of theoretical and empirical approaches for optimal cryopreservation methods

Previous reports have left unresolved discrepancies between human sperm cry opreservation methods developed using theoretical optimization approaches a nd those developed empirically, This study was designed to investigate poss ible 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 degrees C, then returne d to isosmotic media while changes in cell volume were monitored, Activatio n energies (E-a) of the hydraulic conductivity (L-p) in the presence of cry oprotective agents (CPA) (L-p(CPA)) were 22.2 (DMSO), 11.9 (glycerol), 15.8 (PG), and 7.8 (EG) kcal/mol, The E-a values of the membrane permeability t o CPA (PCPA) were 12.1 DMSO), 10.4 (glycerol), 8.6 (PG) and 8.0 (EG) kcal/m ol, These data indicated that even at low temperatures, EG permeates fastes t, The high L-p(CPA) in the presence of EG and low associated E-a would all ow spermatozoa to remain closer to equilibrium with the extracellular solut ion during slow cooling in the presence of ice. Collectively, these data su ggest that the increase of the E-a of L-p in the presence of CPA at low tem perature is the likely reason for the observed discrepancy between theoreti cal predictions of spermatozoa freezing response and empirical data.