The use of HOS test to evaluate membrane functionality of boar sperm capacitated in vitro

The functional and structural integrity of sperm membrane are crucial for the viability of spermatozoa. The commonly used staining test (eosin + nigrosin) for assessing sperm membrane measures only its structural integrity. The hypoosmotic swelling test (HOS) originally developed for human sperm (Jeyendran et al. 1984) has been also applied to several species of domestic animals (bull, pig, horse, dog). The test enables to evaluate the functional status of the sperm membrane. The principle of HOS is based on water transport across the sperm tail membrane under hypoosmotic conditions. It has previously been used to assess the semen quality (Revell and Mrode 1994), to analyse fertilizing capacity (Rota et al. 2000; Perez-Llano et al. 2001) and also to detect viable, immotile cells for ICSI (Intra-cytoplasmic sperm injection) in human (Zeyneloglu et al. 2000). There are two procedures commonly used for sperm capacitation in the pig-sperm washing and incubation before insemination (Nagai 1994). Capacitation involves several changes like removing molecules coating the sperm head membrane, changes in membrane fluidity and intracellular ion concentration (Green and Watson 2001). Thus the membrane integrity as well as functionality may be affected as shown by Harrison (1996). The aim of the present study was to analyse changes in sperm membrane integrity after in vitro capacitation by use of the HOS test.