Veterinary Andrology and Reproductive Techniques

Hypo osmotic swelling test

HYPO OSMOTIC SWELLING TEST (HOST)

Introduction and Principle of the test

• The integrity of plasma membrane is a pre-requisite for maintaining fertility.
• The spermatozoa undergo important events in the female reproductive tract like capacitation and acrosome reaction to attain fertilizing ability.
• For these events to take place the spermatozoa must maintain the functional integrity of cell membrane.
• Further the process of fertilization involves complex biochemical and physiological events that are not measured by the gross physical indicators used in routine semen evaluation.
• Hence there is a need for a test that is inexpensive, technically simple and reasonably accurate that could be used as an adjunct to the standard semen evaluation methods.
• Fluid transport occurs in an intact cell membrane under hypo osmotic conditions until equilibration is reached between inside and outside the cell.

When the sperms placed in hypo osmotic media, to create equilibration inside of sperm and outside media the water will move from media to inside the sperm cell.

• Due to influx of fluid there will be bulging or bending of the tail fibre occurs.

The influx of water into the sperm causes bulging of sperm head and bending of sperm tail. This is known as "swollen sperm" and "tail curling".

• This phenomenon is known as or the sperm with curled tail is known as Spermatozoa with chemically and physically intact membrane will show tail curling under hypo osmotic conditions whereas spermatozoa with an inactive membrane will not.

Live sperms will react for hypo osmotic media and dead sperms will not react.

• During cryopreservation, spermatozoa are subjected to stress that can alter membrane integrity and hypo osmotic swelling test (HOST) is found to be useful as a measure of cryosurvival of spermatozoa.
• Various media are used to provide hypo osmotic conditions to spermatozoa to test the functional integrity of cell membrane.
• Distilled water can be used as hypo osmotic medium in HOST.
• The results of the studies on HOST and fertility of frozen semen in bulls indicate that with higher HOS spermatozoa give higher fertility rate.
• HOS also has positive correlation with freezability of semen.

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