Effect of chilling on the motility and acrosomal integrity of rat sperm in the presence of various extenders.

Studies were conducted to determine the effect of chilling on rat sperm and optimal components (extenders) to avoid chilling-induced injury. In the first experiment, the effects of chilling (at 4, 10, or 22 degrees C) on the motility and acrosomal integrity of epididymal sperm from 2 strains of rats (Sprague-Dawley and Fischer 344, F344) were compared. In the second experiment, the motility of epididymal Sprague-Dawley rat sperm after exposure to extenders (HEPES-buffered Tyrode lactate, skim milk, lactose monohydrate, Tris-citrate, and TEST) and cooling and warming was determined. We tested the effects of supplementing base extender solutions with 20% lactose-egg yolk (LEY) alone or in combination with a commercial SDS-based paste (0.5%, v/v) in preventing chilling injury. The motility after each treatment was determined after both cooling and warming. In the third experiment, the motility of Sprague-Dawley rat sperm were compared after supplementing the base extenders with either 0.4 M permeating cryoprotective agent (CPA; glycerol, ethylene glycol, propylene glycol, or DMSO) or 0.1 M nonpermeating CPA (raffinose and sucrose) after cooling and warming. The results showed that chilling significantly reduced the motility-but not acrosomal integrity-of Sprague-Dawley and F344 sperm. Neither motility nor acrosomal integrity differed between Sprague-Dawley and F344 strains. The addition of LEY into each extender significantly prevented motility loss after chilling. These results will be useful during the preparation of optimal extenders and development of successful cryopreservation protocol for rat sperm.