Scrotal heat stress induces altered sperm chromatin structure associated with a decrease in protamine disulfide bonding in the stallion

A variety of testicular insults can induce changes in the structure of sper matozoal chromatin, resulting in spermatozoal DNA that is more susceptible to acid-induced denaturation. The degree of change in the DNA can be measur ed using the sperm chromatin structure assay (SCSA), The SCSA measures the relative amounts of single- and double-stranded DNA after staining with the metachromatic dye, acridine orange. Here we used a stallion model (n = 4) to study the effects of scrotal heat stress on spermatozoal DNA, This model was created by insulating stallion t estes for 48 h and collecting sperm daily thereafter for 60 days, Changes i n the SCSA were then correlated with protamine disulfide content and protam ine types and levels. Results of the SCSA indicated that the susceptibility of spermatozoal DNA t o denaturation was dependent on the spermatogenic cell stage that the ejacu lated sperm was in at the time of the heat stress. Spermatozoa with altered DNA had a decrease in the extent of disulfide bonding that was associated with an increase in the susceptibility of DNA to denaturation. However, the re were no detectable changes in either the protamine type or level, Thus, in this model, decreased disulfide bonding is associated with an increased susceptibility of spermatozoal DNA to denaturation in the absence of protam ine changes.