CAPACITATION OF SPERM: AS A FUNCTION OF THE OVIDUCT

Abstract

Capacitation is defened as a physiological change of sperm in the female reproductive tract which makes it capable of penetrating the ovum. 1st there is the removal or neutralization of the decapacitation factor. 2nd sperm seem to require an acrosome reaction and finally there is a release or activation of lytic sbustances that allow the sperm to pass through the outer investments of the egg. Capacitation is needed in many species including the human. Requirements vary with the species. A precise environment more than a special agent seems to be needed. In rabbits there is need for some special female reproductive tract factor which is sensitive to the hormonal state of the animal. This chapter describes 5 bioassays that measure capacitation of sperm. In Changs original assay sperm are incubated usually in the female reproductive tract of the rabbit (capacitation) and then transferred to the oviduct of another test rabbit which has been given an ovulating injection of luteinizing hormone or human chorionic gonadotropin 12-14 hours previously. Ova are recovered from the test rabbit at 10-30 hours after introducing the sperm. The control test is by placing nonincubated sperm in the contralateral oviduct of the test rabbit. Sperm became capacitated in the uterus in 5-6 hours but required 11 hours in the oviduct. There are several variations of this method. In vitro fertilization is now possible in some species by incubating sperm in blood serum follicular fluid or reproductive tract fluid. After sperm are placed with ova the ova are observed for any sign of fertilization. Any treatment of sperm which will allow them to fertilize ova is considered to have capacitated the sperm. Removal of tetracycline fluorescence from sperm has not been confirmed as effective capacitation. Other tests indicate sperm surface changes during capacitation. Changes in the acrosome have been observed. Ultrastructural studies with the scanning electron microscope have shown changes. A differential staining procedure has been used. Electroanalytical techniques are being developed. Mechanisms involved in the capacitation process involve removal of the decapacitation factor (DF) and activation of acrosomal enzymes. The female tract inactivates antifertility agents DF included bound to the sperm head surface. Activation of acrosomal enqymes is accomplished by removal of inhibitors. The rabbit oviduct behaves differently from the uterus. Estrogen appears to be stimulatory but progestagen may counteract actions of estrogen. If capacitation could be stopped a contraceptive method could be developed. Capacitation does not seem to occur in the pseudopregnant rabbit uterus. The end result of capacitation is to enhance contact between ova and sperm by the release of lytic substances allowing sperm to pass through the cumulus and corona cells around the ova and to penentrate the zona pellucida. The lytic agent permitting penetration of the zona pellucida is a trypsinlike enzyme. Preventing the activation or release of this enzyme is being attempted.