SUBJECTING HORSE SPERMATOZOA TO HYPOOSMOTIC INCUBATION - EFFECTS OF OUABAIN

Although hypoosmotic tests are widely used to assess spermatozoal qual ity in different species, they have not been used extensively in the s tallion. Moreover, the role of the Na+/K+, ouabain sensitive-ATP-ase i n the response of equine sperm to hypoosmotic shock is not well unders tood. This study tests two hypotheses: 1) that equine spermatozoa will respond to a hypoosmotic medium by swelling of the tail, and 2) that addition of ouabain will increase the percentage of swollen sperm tail s. Ejaculates from 3 stallions were collected with an artificial vagin a and diluted in Kenney's medium (Time=0). Aliquots were randomly sele cted to be incubated in an isoosmotic (297 mOsm) or different hypoosmo tic media that were composed of citrate or of citrate with fructose. T he osmolarity of the hypoosmotic media with citrate ranged from 18 to 96 mOsm, and the medium composed of citrate plus fructose (HOS medium) was of 153 mOsm. Moreover, aliquots of spermatozoa pretreated with ou abain were added to the isoosmotic medium and also to the HOS and the 96 mOsm citrate medium (ORT medium). Incubation of equine sperm in the hypoosmotic media resulted in a time- and osmolarity-dependent swelli ng of the sperm tail, reaching maximum values after incubation for 20- 30 min in both the HOS and ORT media. Ouabain induced a dose-dependent effect on swollen tails and viability in fresh semen and also affecte d some parameters related to motility. Ouabain also increased the swel ling response in a hypoosmotic medium although viability decreased. Th e percentage of swollen tails after incubation in ORT and HOS media sh owed significant correlations to viability, altered acrosomes and tota l motility, but not to other parameters of horse semen analysis. Our r esults suggest that hypoosmotic tests could be used to improve standar d horse semen analysis. Additionally, Na+/K+-ATP-ase activity could be related to the response against hypoosmotic shock of horse spermatozo a. (C) 1997 by Elsevier Science Inc.