Investigations carried out on the protozoan Paramecium tetraurelia and the cyanobacteria Synechococcus lividus, which were shielded against background radiation or exposed to very low doses of gamma radiation, demonstrated that radiation can stimulate the proliferation of these two single-cell organisms. Radiation hormesis depends on internal factors (age of starting cells) and external factors (lighting conditions). The stimulatory effect occurred only in a limited range of doses and disappeared for dose rates higher than 50 mGy/y.

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Oxygen radical generation is known to be detrimental to sperm function, especially motility, through the lipid peroxidation of the membranes. Generation of reactive oxygen species can be induced by leukocyte contamination, sperm centrifugation and the presence of abnormal spermatozoa with excess residual cytoplasm. This study aims to evaluate the effect on sperm motility of incubation in an antioxidant-containing solution, during liquefaction and centrifugation. Thirty semen samples were each divided into two equal parts: one mixed with Tyrode's solution, the other with a salt solution containing antioxidants (Sperm-Fit; Ellios Bio-Media, Paris, France). All the procedures were identical in the two groups. The ratio of leukocytes to spermatozoa was significantly correlated with the motility after liquefaction and after a 24 h incubation in routine in-vitro fertilization (IVF) medium and with the number of motile spermatozoa recovered after Percoll preparation. Moreover, when this ratio was > or = 0.2, all motility parameters were lowered. Incubation with Sperm-Fit allowed a higher percentage of motility after Percoll preparation when the ratio was > or = 0.2 (48 +/- 5% versus 41 +/- 6% for Sperm-Fit and Tyrode's solution respectively; P < 0.05) and a greater number of motile spermatozoa recovered after Percoll preparation, whatever the ratio (3.2 +/- 1.0 x 10(6) versus 2.4 +/- 0.7 x 10(6) for Sperm-Fit and Tyrode's solution respectively when ratio > or = 0.2; 18.1 +/- 3.4 x 10(6) versus 14.4 +/- 2.9 x 10(6) for Sperm-Fit and Tyrode's solution respectively when ratio < 0.2; P < 0.05). These results show that incubation with antioxidants during liquefaction and centrifugation increases recovery of motile spermatozoa.

To determine whether the characteristics of Percoll-selected spermatozoa are more predictive of in-vitro fertilization (IVF) results than are those of native semen, 118 semen samples from patients undergoing an IVF attempt were studied. Motility, using computer-assisted sperm analysis, and morphology were recorded before and after sperm selection on a Percoll gradient. Percoll selection increased the percentage of morphologically normal spermatozoa (58.2 +/- 19.9% versus 47.9 +/- 17.9%; p < 0.0001). This increase concerned almost all abnormalities and especially abnormalities of the midpiece (cytoplasmic droplets and bent tails). However, morphology of spermatozoa in the Percoll fraction had the same predictive value for IVF as did that for whole semen. Concerning motility, all parameters, except linearity, were improved by Percoll preparation, and their predictive value for IVF results was significantly higher in the Percoll fraction than in native semen. Therefore, it is concluded that, even if sperm characteristics are improved dramatically after Percoll selection, only motility analysis then gave more practical information than did analysis of sperm characteristics in native semen. This suggests that impairment of spermiogenesis, which presumably induces sperm abnormalities, is more important than are the actual characteristics of the spermatozoa.