Influence of the cholesterol content of mammalian spermatozoa on susceptibility to cold-shock

Abstract

The cholesterol content of spermatozoa with highly unsaturated phospholipids, i.e., ram and bull, which are very susceptible to cold-shock was compared with that of rabbit and human spermatozoa which have more saturated phospholipids and a greater resistance to cold-shock. The level of cholesterol in the seminal plasma was also estimated. Cholesterol was present in ram and bull spermatozoa in comparable amounts (280–346 μg) and at approximately half the level (in micrograms per 10 9 spermatozoa) in rabbit and human spermatozoa (545–556 μg). The molar ratio of cholesterol: phospholipid in rabbit and human spermatozoa was 0.88 and 0.99, respectively, which is similar to the ratio of these lipids in erythrocytes and higher than the ratio of 0.38 and 0.45 for ram and bull spermatozoa, respectively. This ratio is of some importance in determining the nature and degree of packing in the spermatozoan membrane; higher levels of cholesterol result in a more cohesive, rigid, and impermeable structure. A definite relationship is apparent between the ratio of cholesterol: phospholipid, the ratio of polyunsaturated: saturated phospholipid-bound fatty acids, and the susceptibility of the spermatozoa to cold-shock.