HYPOOSMOTIC SWELLING OF BOAR SPERMATOZOA COMPARED TO OTHER METHODS FOR ANALYZING THE SPERM MEMBRANE

The aims of this work were to adapt the hypoosmotic swelling test (HOS T) to boar spermatozoa and to compare this method with ether tests whi ch evaluate the integrity of the sperm membrane. The spermatozoa were incubated in 50, 100, 150 or 200 mOsm/L solutions for 5, 30, 60 or 120 min. An easily identifiable swelling and coiling of the tails occurre d when the boar spermatozoa were incubated at 37 degrees C for 30 to 1 20 min in a mixture of fructose and Na-citrate (100-150 mOsm/L). Trans mission electron microscopy showed that the hypoosmotic swelling react ion of the spermatozoa was caused by coiling of the flagellum inside t he plasma membrane. When used as described, HOST was found to be highl y reliable when Known populations of live spermatozoa were tested. We also compared the results obtained with HOST with those obtained using eosin Y and carboxyfluorescein diacetate. The percentage of spermatoz oa unstained with eosin Y and the percentage of spermatozoa which fluo resced with carboxyfluorescein diacetate were similar. However, the hy poosmotic swelling values were significantly below those of the other tests. This may be because either HOST evaluates different aspects of sperm membrane than other sperm membrane tests or the membranes of som e spermatozoa are inactivated by contact with the hypoosmotic solution . In short, our findings suggest that HOST is a sensitive and reproduc ible test to assess the functional integrity of boar sperm membranes a fter incubation under hypoosmotic stress conditions and may be a usefu l tool for detecting subpopulations of subviable spermatozoa when used in conjunction with another type of membrane integrity test. (C) 1997 by Elsevier Science Inc.