Prolactin and fructose in human seminal fluid

Two hundred thirty-six semen specimens were obtained in the sterility clinic by masturbation after 3 days of abstinence. In a radioimmunoassay for prolactin (NIH, batch no. 5) the dose-response curve obtained with seminal fluid prolactin was parallel to that obtained with serum prolactin. The average seminal fluid prolactin was 780 microunits/ml (35 ng/ml), three times higher than serum prolactin concentration in men. No relationship was found between seminal prolactin concentration and sperm count (per ml or per ejaculate) or sperm motility. There was a significant and positive correlation between seminal prolactin concentration and fructose concentration. The relationship was of an exponential type. Seminal fructose increased progressively with seminal prolactin; however, for prolactin values above 850 microunits/ml, there was no further increase in seminal fructose. A similar relationship was observed between seminal prolactin concentration and volume of the semen specimens. These data support the concept that prolactin may play a key role in male fertility, perhaps by influencing the composition of the milieu where spermatozoa survive rather than by direct effect on spermatogenesis.