The concentration of pepsinogen C in human semen and the physiological activation of zymogen in the vagina

The relationship between male infertility and the pepsinogen C content in semen has been investigated. The activation of the seminal pepsinogen C in the vagina has been studied under physiological conditions. Samples of semen from 48 vasectomized males and from 46 males of infertile couples were analyzed for pepsinogen C by radioimmunoassay. No correlation was found between the level of pepsinogen C and seminal characteristics, including sperm concentration, motility, and morphologic features. The mean concentration of pepsinogen C was 42.2 micrograms/ml; the first, second, and third quartile were 18.4, 29.6, and 57.6 micrograms/ml, respectively. No significant difference in the level of pepsinogen C was observed between semen of normal quality, semen of reduced quality, and semen with aspermia. Activation of pepsinogen C occurred within 3 h when semen was incubated at pH below 5.0 at 37 degrees C. Intravaginal activation was investigated in six experiments in which semen from two males was instilled in three females. In four experiments with two couples, post-coital activation was investigated. Pepsin C activity in vaginal fluid was detected an average of 3 h (range 2-5 h) and 5 h (4-7 h) after instillation or ejaculation, respectively. Vaginal pH had then been below 4.5 for approximately 1 h. Pepsin C activity was present in the vagina for more than 24 h thereafter. It is most likely that seminal pepsin C is without influence on the fertilizing spermatozoon. However, pepsin C may exert a local effect in the vagina by degrading seminal proteins, thus preventing an immunogenic response in females.