Fructose stimulates shedding of cytoplasmic droplets from epididymal boar spermatozoa.

The aim of the present study was to establish the presence of an inducer(s) for the shedding of cytoplasmic droplets from boar spermatozoa after ejaculation. Cauda epididymal spermatozoa were incubated with seminal plasma, seminal vesicular fluid (SVF) or chemical agents at 39 degrees C for 30 min. After fixation and staining, percentages of spermatozoa without a droplet were determined. In the samples incubated with seminal plasma, SVF and a filtrate of SVF obtained after passage through an ultrafilter (molecular weight cut-off, 10,000), 43%, 60-69% and 43% of the spermatozoa were without a droplet respectively. The percentage of spermatozoa without a droplet after incubation with D-fructose (1.0 mM), which was one of the energy substrates included in SVF, was 76%. Furthermore, percentages increased to 93% and 90% with the addition of caffeine (2.0 mM) and N6, 2'-O-dibutyryl cyclic adenosine 3',5'-monophosphate (1.0 mM), respectively, but decreased to 48% with the addition of imidazole (2.0 mM). Based on these results, it is suggested that the shedding of cytoplasmic droplets from boar spermatozoa is induced by fructose originating from SVF. It also appears that this event is mediated by increasing the concentration of intracellular cyclic adenosine 3',5'-monophosphate.