CAPACITATION IN VITRO OF RABBIT SPERM WITH MULE EOSINOPHILS

Capacitation of rabbit sperm in vitro has been reported1, but never when mixed with live heterologous granulocytes; neither has it been accomplished with incubation for only several hours. A hypothetical explanation as to the nature of capacitation, which enables sperm to penetrate and utimately fertilize ova, has been published elsewhere2. A recently perfected technique is available for indirect measurement of capacitation3. This fluorometric procedure requires the labelling of sperm with tetracycline HCl (T-HCl) (ref. 4), and its removal correlates with conditions in which sperm are known to capacitate. Repeated attempts to remove T-HCl from sperm in vitro failed5 until such sperm were mixed with mule leucocytes. Further experimentation revealed mule neutrophils which phagocytosed rabbit sperm whereas eosinophils removed T-HCl but left sperm intact and alive. Removal of T-HCl from sperm in vitro in itself does not prove that these sperm are capacitated. Proof lies in the ability of these sperm to fertilize rabbit ova. Rabbit sperm can be placed experimentally in the oviduct several hours after ovulation and, unless these sperm are capacitated, the ova fail to cleave3. The work described here provides experimental evidence of partial capacitation in vitro. © 1969 Nature Publishing Group.