The nucleotide sequence of the
cDNA encoding a sperm
protein (rSMP-B) was determined in a previous study. Two
peptide segments corresponding to the extracellular domain of the deduced sperm
polypeptide were synthesized as multiple
antigen peptide (MAP) and designated as rSMP-229 and
rSMP-230. Polyclonal
antibodies were raised against the two MAPs. Sera obtained from rabbits immunized with
rSMP-230 interacted with human and rabbit sperm
membrane proteins with estimated molecular sizes of 72 and 20.1 kD, respectively. Adult female and male rats were immunized with the MAPs and their fertilities determined. Immunization of female rats with rSMP-229 and
rSMP-230 induced
infertility in 25% and 83% of the treated animals, respectively. All male rats immunized with rSMP-229 remained fertile; whereas animals immunized with
rSMP-230 did not mate with normal cycling female rats. Three impotent male rats were found to regain their mating potency 45 days after the last booster injection. These findings demonstrated that immunization with
rSMP-230 induced a reversible impotency in male rats. Serum
testosterone and LH levels were reduced in rSMP-230-immunized male rats and were elevated in rSMP-229-immunized animals. Histopathological examination of sections of testes from male rats immunized with
rSMP-230 showed impairment of spermatogenesis and sloughing of germ cells into the lumen of the seminiferous tubules. The testes of male rats immunized with rSMP-229 showed normal morphology and active spermatogenesis with scattered foci of nodular
hyperplasia of Leydig cells in the interstitial areas. In conclusion, immunization with synthetic
peptide segments corresponding to different domains of a deduced sperm
protein induced
infertility in a significant number of female rats and transient impotency in male rats.