Sperm maturation in rhesus monkey: changes in ultrastructure, chromatin condensation, and organization of lipid bilayer.

BACKGROUND

The changes in ultrastructure, lipid organization, chromatin decondensation, and denaturation of rhesus monkey spermatozoa during epididymal maturation were studied. This study would provide background information that would be useful to evaluate adverse effects, if any, caused by the use of contraceptive agents.

METHODS

Adult sexually mature rhesus monkeys were castrated under ketamine anesthesia. The epididymis was divided into initial segment, caput, corpus, and cauda epididymides. To study changes in lipid organization of the sperm plasma membrane during epididymal transit, spermatozoa from different epididymal segments and ejaculated spermatozoa were exposed to merocyanine 540 (MC 540). The changes in chromatin denaturation and decondensation were assessed by using the nucleic acid-specific fluorochromes, acridine orange, and ethidium bromide, respectively, prior to and after exposure to dithiothreitol (DTT).

RESULTS

Testicular spermatozoa (approximately 40%) showed localization of MC 540 mainly in the midpiece, whereas remaining sperm did not localize MC 540. Spermatozoa from the initial segment of the epididymis showed uniform distribution of MC 540 localization in the head and midpiece. A pattern of localization of MC 540 similar to mature caudal and ejaculated sperm in which the staining was restricted to the acrosome and the midpiece first appeared in a small percentage of caput spermatozoa and was completed during transit through the corpus epididymidis. Mature spermatozoa from cauda epididymidis, vas deferens, and ejaculate did not undergo chromatin denaturation even after exposure to 10 mM DTT, unlike sperm from testis, initial segment, and caput epididymidis. Spermatozoa exposed to DTT showed chromatin decondensation; maximum decondensation was seen in testicular sperm and a decrease in the percentage of sperm, showing decondensation, occurred during epididymal transit. Ultrastructural studies showed that spermatozoa undergo structural changes during sperm maturation.

CONCLUSIONS

The present study shows that rhesus monkey spermatozoa undergo reorganization of the plasma membrane lipids and stabilization of disulfide linkages during epididymal transit. The results would be of use in evaluating the action of potential male contraceptive drugs on epididymal spermatozoa.