Occurrence of headless sperms in adolescent rat urine

Increased incidence of headless sperms (HS) was spontaneously observed in the urine of adolescent naïve male SPF/VAF Crl:CD(SD) rats. To clarify the factors contributing to this event, the HS incidence in urine and the epididymis was periodically examined in conjunction with measurements of testis and epididymis weights, motility and morphology of sperms and testosterone, transferrin or follicle-stimulating hormone (FSH) concentrations in serum and/or the testis. The urinary HS incidence was 61%, 69%, 44%, 30%, 14%, 9% and 7% in 100 sperms counted at ages 8, 9, 10, 11, 12, 13 and 14 weeks, respectively; namely, HS peaked at 9 weeks, gradually decreased from 10 weeks and became almost a plateau from 12 weeks onwards. The epididymal HS incidence, which was lower than that in urine, peaked at 8 weeks, decreased from 10 weeks and became almost zero from 12 weeks. By scanning electron microscopy of HS in the epididymis, a narrow gap between the sperm head and neck was clearly seen along with the posterior ring. Concentrations of testicular testosterone and transferrin, a marker for Sertoli cell maturation, reached mature animal levels at 12 weeks. In contrast, no change in serum FSH concentration was seen throughout the study period. These results demonstrate that a marked increase in urinary HS incidence in naïve rats at ages 8-11 weeks would be a physiological phenomenon seen in connection with the process of Sertoli cell maturation.