SPERM MATURATION IN RHESUS-MONKEY - CHANGES IN ULTRASTRUCTURE, CHROMATIN CONDENSATION, AND ORGANIZATION OF LIPID BILAYER

Background: The changes in ultrastructure, lipid organization, chromat in decondensation, and denaturation of rhesus monkey spermatozoa durin g epididymal maturation were studied. This study would provide backgro und information that would be useful to evaluate adverse effects, if a ny, caused by the use of contraceptive agents. Methods: Adult sexually mature rhesus monkeys were castrated under ketamine anesthesia. The e pididymis was divided into initial segment, caput, corpus, and cauda e pididymides. To study changes in lipid organization of the sperm plasm a membrane during epididymal transit, spermatozoa from different epidi dymal 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, acrid ine orange, and ethidium bromide, respectively, prior to and after exp osure to dithiothreitol (DTT). Results: Testicular spermatozoa (simila r to 40%) showed localization of MC 540 mainly in the midpiece, wherea s remaining sperm did not localize MC 540. Spermatozoa from the initia l segment of the epididymis showed uniform distribution of MC 540 loca lization in the head and midpiece. A pattern of localization of MC 540 similar to mature caudal and ejaculated sperm in which the staining w as restricted to the acrosome and the midpiece first appeared in a sma ll percentage of caput spermatozoa and was completed during transit th rough the corpus epididymidis. Mature spermatozoa from cauda epididymi dis, vas deferens, and ejaculate did not undergo chromatin denaturatio n even after exposure to 10 mM DTT, unlike sperm from testis, initial segment, and caput epididymidis. Spermatozoa exposed to DTT showed chr omatin decondensation; maximum decondensation was seen in testicular s perm and a decrease in the percentage of sperm, showing decondensation , occurred during epididymal transit. Ultrastructural studies showed t hat spermatozoa undergo structural changes during sperm maturation. Co nclusions: The present study shows that rhesus monkey spermatozoa unde rgo 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. (C) 1997 Wiley-Liss, Inc.