A comparison of heat-induced hyperactivation in patients' sperm after colloid or pentoxifylline wash methods

Thermotaxis of mammalian sperm

Sperm are guided through the female reproductive tract. A temperature difference of about 2 °C exists between the storage site and fertilization site of the mammalian oviduct, leading to the hypothesis that sperm can sense and swim towards the oocyte along a rising temperature gradient, known as thermotaxis. Research over the past two decades has reported that sperm feature a sophisticated thermal detection system to detect and track ambient temperature gradients. More recently, thermotaxis is expected to be added to the microfluidic isolation method based on sperm tactic responses for sperm selection. In this paper, mammalian sperm thermotaxis is discussed, explaining the underlying behavioral mechanisms and molecular basis, according to the latest research. Finally, this paper explores the possible application of sperm thermotaxis in assisted reproductive technologies.

Thermotaxis of human sperm cells in extraordinarily shallow temperature gradients over a wide range

On the basis of the finding that capacitated (ready to fertilize) rabbit and human spermatozoa swim towards warmer temperatures by directing their movement along a temperature gradient, sperm thermotaxis has been proposed to be one of the processes guiding these spermatozoa to the fertilization site. Although the molecular mechanism underlying sperm thermotaxis is gradually being revealed, basic questions related to this process are still open. Here, employing human spermatozoa, we addressed the questions of how wide the temperature range of thermotaxis is, whether this range includes an optimal temperature or whether spermatozoa generally prefer swimming towards warmer temperatures, whether or not they can sense and respond to descending temperature gradients, and what the minimal temperature gradient is to which they can thermotactically respond. We found that human spermatozoa can respond thermotactically within a wide temperature range (at least 29–41°C), that within this range they preferentially accumulate in warmer temperatures rather than at a single specific, preferred temperature, that they can respond to both ascending and descending temperature gradients, and that they can sense and thermotactically respond to temperature gradients as low as <0.014°C/mm. This temperature gradient is astonishingly low because it means that as a spermatozoon swims through its entire body length (46 µm) it can sense and respond to a temperature difference of <0.0006°C. The significance of this surprisingly high temperature sensitivity is discussed.

Effect of heat-induced hypermotility on pregnancy rate in intrauterine insemination for male factor infertility associated with asthenospermia: a prospective, randomized, controlled study

OBJECTIVE

To assess the effect of mild heat for the enhancement of sperm fertilizing capacity in intrauterine insemination for male factor infertility associated with asthenospermia.

MATERIAL AND METHOD

Prospective, controlled, clinical study. Male factor infertility associated with asthenozoospermia was the criteria for inclusion. Ninety-seven couples were randomized to the study group while 100 couples were randomized to serve as the control group. Semen samples from the study group were processed with Percoll gradient and were left for incubation at 40 degrees C for 2 h. Semen samples from the control group were processed with Percoll gradient method and were incubated at 37 degrees C. Main outcome measure was the pregnancy rate.

RESULTS

The mean concentration of total motile sperm (TMS) in the study group was 11.20 +/- 4.22 x 10(6) (range 7-18) after wash with Percoll while was increased to 62.41 +/- 12.49 x 10(6) (range 44-71) after heat treatment. The mean concentration of TMS in the control group was 13.90 +/- 5.66 x 10(6) (range 8-19) after wash with Percoll while was increased to 17.73 +/- 3.67 x 10(6) (range 14-22) after incubation at 37 degrees C. The difference in TMS concentrations between the study and the control group after incubation at different temperatures was statistically significant (p < 0.005). There were 24 pregnancies in the study group, providing a pregnancy rate of 24.7%. In the control group eight pregnancies were achieved (8%) (p = 0.001).

CONCLUSION

Mild heat was found remarkably effective in asthenozoospermic males for increasing the concentration of inseminated total motile sperm and the pregnancy rate correspondingly.