Evidence for a functional glycogen metabolism in mature mammalian spermatozoa

The glycogen content in fresh raw dog spermatozoa was 0.22 ± 0.03 μmol/mg protein. This matched with the presence of a glycogen-like staining in the head and midpiece. Glycogen levels lowered to 0.05 μmol/mg protein after incubation for 60 min without sugars. Addition of either 10 mM fructose or 10 mM glucose increased glycogen content to 0.70 μmol/mg protein. On the other hand, glycogen synthase activity ratio of fresh dog sperm (0.35 ± 0.07, measured in the absence and the presence of glucose 6-P)increased to 0.55 with 10 mM fructose for 20 min, whereas glucose had a smaller effect. Spermatozoa extracts had also a protein of about 100 Kd, which reacted against a rat liver glycogen synthase antibody. This was located in sperm head and midpiece. Furthermore, glycogen phosphorylase activity ratio measured in presence and absence of AMP (0.25 ± 0.03 in fresh samples) decreased to 0.15 by 10 mM glucose for 20 min, whereas fructose was less potent in this regard. The maximal effect of glucose and fructose were observed from 10-20 mM onwards. This work is the first indication for a functional glycogen metabolism in mammal spermatozoa, which could play an important role in regulating sperm survival in vivo. (C) 2000 Wiley-Liss, Inc.