LDH‐C4 in human seminal plasma and its relationship to testicular function

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Abstract
Lactate dehydrogenase (EC 1.1.1.27) isoenzyme LDH-C4 (LDH-X) has been analyzed quantitatively in semen from men with different fertility status, such as men with pregnant wives, men with primary or secondary infertility, volunteers, men taking salazopyrine and men exposed to very hot baths. LDH-C4 activity per ml or per ejaculate was not related to the fertility status of the men. The situation was different when the LDH-C4 sperm ratio was used as a variable. The median (p50) LDH-C4 activity in semen was (in nanokat/108 spermatozoa) 9.4 for samples from men (N = 34) whose wives were in early pregnancy, 24.7 for men (N = 102) with primary infertility and 28.8 for men (N = 18) taking sulphasalazine. The differences in median values between the former group and the latter two groups were highly significant (P < 0.001). In addition, semen samples from 3 infertile men who took daily hot baths as a habit, had a significantly higher LDH-C4/sperm ratio than samples collected during periods when they did not take hot baths. Semen samples were subdivided according to the number of spermatozoa in the ejaculate after correction for days of abstinence and the size of the testes. These was an inverse correlation between the LDH-C4/sperm ratio and the adjusted sperm count (million per day and per ml testes). Men with an adjusted sperm count of 0.5 or less has a median (p50) LDH-C4 activity of 38 nanokat/103 spermatozoa compared to 14.5 in samples from men with an adjusted sperm count of more than 1.0 (P < 0.001). The LDH-C4/sperm ratio in seminal plasma may therefore serve as an indicator of the function of the seminiferous epithelium, and its assessment may provide a new means for the study of spermatogenesis and male reproduction.