Effect of Ejaculation Frequency on the Water Volume of Rabbit Spermatozoa as Determined by Electron Spin Resonance Spectroscopy

An electron spin resonance (ESR) technique using 2H-Tempone to measure the water-accessible volume of rabbit spermatozia was evaluated. We determined that the ESR signal from 2H-Tempone in buffer decayed after being combined with spermatozoa and that the rate of decay was variable among sperm samples. To reduce variation in sperm volume determinations, a method was developed that accounts for the decay during the period of observation. ESR of 2H-Tempone also was used to measure the water-accessible volume of sperm from rabbits ejaculated once daily for 4 days following a 1–2-week sexual rest. Under this regimen, the average water volume determined by ESR declined from 15 μm3 on the first day of ejaculation to 6.3 μm3 on the fourth successive day of ejaculation. However, no corresponding decrease was observed in dimensions of sperm in photomicrographs. We concluded that the nature of the interaction of sperm and 2H-Tempone was affected by the ejaculation frequency of the animal providing the sample, resulting in a decreased ESR signal but not a real decrease in sperm volume. Although the biological significance of these observations is not yet understood, we suggest that the ejaculation regimen of an animal should be considered when determining sperm water volume using ESR.