LDH-C4 in human seminal plasma and its relationship to testicular function. I. Methodological aspects.

LDH-C4 is a lactate dehydrogenase isoenzyme specific for spermatocytes, spermatids and spermatozoa. Its presence in seminal plasma therefore stems from its release by one or more of these cell types. LDH-C4 has been analyzed quantitatively in semen samples from men under different experimental conditions. Incubation of semen at 37 degrees C for up to 6 h did not alter LDH-C4 activity in seminal plasma. When volunteers donated several semen samples with different time intervals (4 h to 7 days) between the ejaculations, the LDH-C4 activity showed only moderate variations when expressed per 100 million spermatozoa. The relatively constant relationship between LDH-C4 activity and the number of sperm in the ejaculate, and the observation that there was no leakage of LDH-C4 from the ejaculated sperm, indicate that this enzyme originates from the testis. It could, therefore, be a chemical marker reflecting the degree of germ cell degeneration in the seminiferous epithelium in relation to the number of spermatozoa formed during the same time period. In contrast to the small intra-individual variation for LDH-C4 activity per 100 million sperm (mean cv = 36.6%, N = 5), there was a large inter-individual variation. In 79 men with a barren union the mean LDH-C4 activity was 28.9 nanokatal/100 million sperm (95% confidence limits 0 to 114).