Analysis of reports in the world's literature suggests that average sperm densities for groups of unselected males were relatively constant at about 108 million cells per ml prior to 1950. Subsequent to that time mean sperm densities appear to have declined. Regression analysis indicates the existence of significant negative correlations between mean sperm densities and production of synthetic organic chemicals among other parameters. Phthalate esters are one class of large volume organic chemicals that are known to disturb testicular function in laboratory animals. These compounds are also the most abundant man-made chemicals in the environment. Plots of the concentration of dibutylphthalate in the cellular fraction of ejaculates against either the sperm density or the total number of sperm for the same ejaculates gave two clusters of points. These clusters suggest the existence of two or more populations vis à vis phthalate metabolism; both of which show a negative correlation between phthalate concentration and sperm production.

The cervical mucus penetration tests aid research and determine the clinical importance of positive sperm antibody tests. Limited availability and variability of human cervical mucus have instigated the search for mucus substitutes for these tests. This study compares sperm migration in cervical mucus with that in artificial media including hyaluronate solution, egg white and albumin Tyrode solution. Results were quantified by measuring the migration distance (the maximum distance of capillary migration from a semen reservoir by spermatozoa after 1 h) and the sperm concentration at half the migration distance. The mean of both measures for cervical mucus and hyaluronate solution were equivalent [4.4 +/- 1.1 (SD) versus 4.3 +/- 1.0 cm and 118 +/- 51 versus 111 +/- 44x10(3)/ml], and higher than in egg white and albumin Tyrode solution. Antisperm antibodies impaired sperm penetration in cervical mucus and hyaluronate solution in a similar manner (r = 0.92). These results suggest that hyaluronate solution sufficiently resembles human cervical mucus in terms of penetrability that it may be used as a substitute for mucus in capillary tube tests of sperm function. The higher penetrability of cervical mucus and hyaluronate solution is probably related to a channelling effect due to their polymeric structure.

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