Lipids and calcium uptake of sperm in relation to cold shock and preservation: a review.

The research paper explores the effect of rapid cooling to near freezing point on the sperm of various animals like ram, bull, boar, and stallion. The focus is on potential biological changes in sperm along with suggestions for enhancing sperm lifespan during preservation.

Effect of Cold Shock

• Cold shocking sperm—rapidly cooling them to near freezing point—has a irreversible negative impact on their motility and metabolic activity. This is explicitly observed as disruptions in the acrosome and plasma membrane, parts of a sperm cell.
• For ram sperm, this susceptibility to cold shock is noticed in the proximal corpus region of the epididymis. This happens when the cytoplasmic droplet retracts to the distal part of the sperm midpiece.

Role of Lipids and Cholesterol

• Phospholipids and cholesterol, key components of the sperm membrane, play a significant role in the process of cold shock. Cold shock results in the loss of these lipids from the sperm.
• The vulnerability of sperm to cold shock is associated with a high ratio of unsaturated to saturated fatty acids in phospholipids and low cholesterol content.
• The presence of unsaturated fatty acids makes sperm more susceptible to peroxidation damage, which adversely impacts motility, metabolism, ultrastructural features, and fertility.
• The by-product of fatty acid peroxidation, Hydroxynonenal, has been noted to decrease the motility and oxygen uptake of ram sperm in vitro. It may react with the -SH groups of the axonemal microtubules, a component of sperm structure.

Calcium and Cold Shock

• High concentrations of calcium in external medium may decrease sperm motility and metabolism. The researchers suggest that ‘calcium intoxication’ could be a factor during cold shock.
• Lowering the environmental temperature causes an increase in calcium uptake by sperm. This effect is further aggravated if the rate of cooling is swift.

Protection against Cold Shock

• Phospholipids, especially those present in egg yolk, potentially protect sperm from cold shock damage to some extent. They also prevent an increase in calcium flux into the sperm.
• The paper proposes ways to increase the lifespan of sperm during preservation and microencapsulation. This involves adding agents that stabilize cellular membranes, counteract lipid peroxidation, and reduce calcium uptake.