On the role of glucose in capacitation and acrosomal reaction of guinea pig sperm

In order to determine whether metabolizable sugars delayed capacitation of guinea pig spermatozoa, these cells were pre‐incubated in Tyrode's pyruvate lactate glucose medium (T‐PLG) or Tyrode's glucose solution (T‐G). They were then transferred to minimal culture medium containing pyruvate and lactate (MCM‐PL) and the occurrence of acrosomal reactions (AR) was determined by light microscopic observations of wet mount aliquots. The percentage of acrosomal reactions was quantitated in fixed samples and occurrence of a true AR was confirmed by electron microscopy. Activated acrosome‐reacted spermatozoa were observed within 5 min when cells were transferred to MCM‐PL solution, after preincubating them for 60–120 min either in T‐PLG or T‐G media. By 15 min in MCM‐PL the percentage of acrosome‐reacted spermatozoa reached values similar to those obtained in cells pre‐incubated from the beginning in MCM‐PL medium (P > 0.05 in both) but significantly different from T‐PLG and T‐G controls (P < 0.0005 in both). The acrosomal reaction was external calcium dependent and independent of the Tyrode's media pH ranging from 7.2 to 8.0. The results obtained suggested that capacitation occurred in T‐PLG and that it was not delayed by glucose; the results also suggested that capacitation could occur within a short time with glucose as the only exogenous substrate, but that the acrosome reaction could have been arrested by a glucose metabolite. Data are presented which suggest that intracellular levels of glucose‐6‐phosphate (as 2‐deoxyglucose‐6‐phosphate)could play a key role in the expression of the acrosome reaction in sperm already able to perform it. A new hypothesis is suggested for the development of the fertilizing potential of guinea pig sperm when in the female genital tract.