Glycoprotein secretions of the epididymis in the rabbit and hamster: localization on epididymal spermatozoa and the effect of specific antibodies on fertilization in vivo.

To assess the functional significance of glycoprotein secretions of the rabbit and hamster epididymis during sperm maturation and fertilization, antibodies have been raised against acidic protein fractions isolated from epididymal fluid. Specific antiserum was elicited against each of three rabbit glycoproteins designated R1, R2, and R3 with isoelectric points of pI 3.45, 4.15, and 4.65 respectively, and against one hamster glycoprotein (Hl), pI 3.40. Epididymal glycoproteins on the surface of washed spermatozoa from various regions of the epididymis were localized by the fluorescent antibody technique and by sperm agglutination with antiserum. They were first detected on restricted regions of spermatozoa from the distal caput and corpus epididymidis and each antigen had a characteristic binding pattern. The effect of specific antibodies on fertilization in vivo was tested in rabbits by preincubating cauda epididymal spermatozoa with heat-treated antiserum or univalent immunoglobulin fragments before their deposition into oviducts of does induced to ovulate. In all cases, fertilization rates were significantly reduced (P less than or equal to 0.05) compared with controls, the most effective antiserum being against glycoprotein antigen R1 found only on the anterior acrosome of spermatozoa. Heat-treated antiserum against H1 glycoprotein placed in the bursal cavity of ovulating females significantly inhibited fertilization in the hamster (P less than or equal to 0.005). These results are discussed in relation to the modification to the sperm plasmalemma during maturation.