Interferometric dry mass and microspectrophotometric arginine determinations on bull sperm nuclei with normal and abnormal DNA content

Rheotaxis of spermatozoa

1. The response of human and bull spermatozoa to vertical velocity gradients has been examined, the fluid flow being in horizontal planes. 2. Dead human and bull spermatozoa point downstream (negative rheotaxis) in the top half of a parabolic velocity gradient and upstream (positive rheotaxis) in the bottom half. Although spermatozoa point preferentially in one or other direction, parallel to the stream ­ lines, in linear velocity gradients, this cannot be described as positive or negative rheotaxis because the direction in which the spermatozoa point is determined by the direction of shear. 3. The response of dead human and bull spermatozoa to velocity gradients is due to the head of the spermatozoon having a higher specific gravity than the tail, which causes the spermatozoon to sink head first in a medium of lower specific gravity than that of the spermatozoon. 4. Live human and bull spermatozoa exhibit positive rheotaxis, i.e. they swim up stream, in both halves of a parabolic velocity gradient. 5. The behaviour of previously flow-orientated spermatozoa in a just-reversed velocity gradient has been photographed and analysed. Though the mechanism whereby dead spermatozoa re-orientate in such conditions is understood, live spermatozoa, which also re-orientate in these conditions, may do so by a different and, at present, unknown mechanism.

The spermatozoan genome and fertility

The strategy for effective reproduction by eliminating genetically unbalanced gametes during spermatogenesis and transport varies in degree of success within as well as among species, but in no animal has it been reported to be completely effective. In the human subject, for example, it is estimated that one in every 50 ejaculated spermatozoa is genetically abnormal. The causal basis of these anomalies is poorly understood. Meiotic accidents, environmental mutagens, and gamete senescence in utero are all implicated. However, many of these abnormal cells are fertile. This fact plus the weight of the evidence reviewed suggest that fertility differences among males which cannot be ascribed to measurable differences in semen characteristics reflect, in large part, the increased opportunity of nuclear defective gametes in the semen of some males to effect fertilization. The elimination of embryos arising from eggs fertilized by genetically defective spermatozoa through spontaneous abortions, although biologically costly, must be viewed as the final check for the elimination of genetic detritus of the species.

Energy conversion in bull sperm flagella

With the use of a specially developed incubation chamber the rates of motility, respiration, and fructolysis were measured simultaneously on semen samples. By inhibiting the respiration with antimycin A, and/or the fructolysis with 2-deoxyglucose, the rates of each of the two ATP-producing pathways could be reduced independently. In this way the ratio of the amount of free energy produced by respiration and by fructolysis could be varied at will from 1 to 0. In uninhibited preparations approximately 75% of the free energy derives from respiration, and 25% from fructolysis. By the use of the absolute rates of respiration, fructolysis, and motility, the efficiency of the conversion of free energy into hydrodynamic work was calculated. After correction for the decay of the preparation during the experiment, this conversion efficiency was found to be 30-45% lower for free energy from respiration than for free energy from fructolysis. The difference in distribution of the enzymes for fructolysis and respiration over the flagellum was ruled out as the cause of the efficiency difference. The respiration could be 70% inhibited by oligomycin. It is concluded that approximately one-third of the free energy from respiration is used for maintenance of the mitochondria.