Effects of temperature upon capacitation of guinea pig spermatozoa

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Abstract
Spermatogenesis in many mammalian species requires a temperature a few degrees below body core temperature. Upon ascent through the male tract and deposition in the female tract, the temperature of spermatozoa is increased to body core temperature. This report investigates the effects of temperatures above or below normal body core temperature, which is also the usual temperature of in vitro gamete incubations and fertilization, upon sperm acrosome reacting ability and fertility. Epididymal guinea pig spermatozoa were preincubated in a Ca2+-free medium at temperatures of 15°C, 25°C, 37°C, or 44°C for increasing periods of time. At 15°C or 25°C, no or very few spermatozoa acquired the ability to acrosome react upon exposure to Ca2+ even after 18 hr of culture or warming up to 37°C. A known stimulator of acrosome-reacting ability, lysophosphatidylcholine, was ineffective in promoting acrosome-reacting ability in spermatozoa incubated at 15°C or 25°C. At 37°C the percentage of acrosome reaction increased steadily over time, reaching about 65% after 18 hr. At 44°C the time course of acquisition of acrosome-reacting ability was greatly accelerated with a percentage at 2 hr comparable to that achieved at 37°C only after 18 hr of preincubation. This effect of incubation at 44°C could be reversed by cooling the spermatozoa to 37°C before they were exposed to Ca2+. Spermatozoa induced to undergo the acrosome reaction after preincubation at 44°C were fully capable of fertilizing intact guinea pig eggs. These results are discussed in relation to possible temperature-dependent or -sensitive mechanisms that may be components of the capacitation process.