The peak moment of fertilization – the penetration of the sperm into the ovum – can be prevented with a substance present in aloe that does not cause side effects, which is sometimes the case with hormonal contraceptive treatments. This compound limits the motility of the male gametes, which are thus left without sufficient vigor to enter the female reproductive cell.
The substance, which is also found in the Maytenus ilicifolia shrub, native to South America, and in dandelions, can serve as emergency contraception taken before or after sexual intercourse, or permanent if administered through a patch on the skin or a vaginal ring. According to the authors of the finding, human sperm take five to six hours to mature in the female reproductive system, which gives time to administer this chemical compound that blocks their mobility.
Molecular barriers
Biologist Polina Lishko, director of the research, calls these plant substances “molecular condoms.” As he explains on the website of his university, “they block fertilization even when applied in very low doses, ten times lower than the levels of levonorgestrel present in morning-after pills. It seems a better option to use a compound of plant origin, non-toxic and without hormones “.
The male sex cells navigate towards the ovum thanks to the rhythmic and regular movements of their tail. When they are reaching their goal, that rhythm increases and the movements of their tail become asymmetrical to allow them to pierce the protective layer of the egg, penetrate it and fertilize it. Researchers have discovered that this process is triggered by the influence of progesterone, which opens the calcium channels that give way to the egg and stimulates the sperm. They also found that another hormone – pregnenolone – plays the same role.
Guided by indigenous peoples
Once this mechanism was understood, the scientists looked for substances that closed the calcium channel and decreased the mobility of the sperm. To do this, they reviewed the natural contraceptives used by indigenous peoples from various parts of the world.
They identified two compounds – lupeol and pristimerin – that fulfilled these functions. They are found in plants such as aloe, dandelion, Maytenus ilicifolia –used as a natural contraceptive in Paraguay–, Tripterygium wilfordii vine – exploited by traditional Chinese medicine to prevent pregnancy – and mango.
Lishko and his colleagues are working with researchers in Oregon to test the contraceptive effectiveness of these substances in in vitro fertilization in primates – so far it has only been studied with human sperm – and they are looking for a cheap source of these compounds, since they are at such low concentrations in wild plants that harvesting them is not profitable.
