For humans and other animals, development of a male organ was thought to be driven by “male hormones” (androgens) produced by the testes of the male fetus as it grows in the uterus. Some of the masculinising hormones that drive penis development may come from other sources in the developing fetus. These include the liver, the adrenals (small glands found on the kidneys) and placenta.
Male develops from an embryonic structure called the genital tubercle or GT. The GT is present in both males and females, and develops into either a clitoris or penis, depending on its exposure to hormones secreted by the developing gonads (ovaries or testes).
In males, the developing testes produce testosterone. This circulates in the developing fetus and causes masculinisation of target tissues and induces penis development from the GT.
It is the local conversion of testosterone to DHT within the tissue that is important for penis development and other changes. There are several ways in which the fetus can make DHT. The most simple is via conversion from testicular testosterone (the so-called “canonical” pathway). However, DHT can also be produced via other steroid hormone pathways active in many tissues, which is explored further in this new paper.
Understanding the pathways that control penis development is important. Disorders affecting penis development are among the most common birth defects seen in humans, with hypospadias (a disorder affecting development of the urethra) currently affecting around 1 in every 115 live males born in Australia, and rates are on the rise.
In fact, the incidence of hypospadias has doubled over the past 40 years. Such a rapid increase in incidence has been attributed to environmental factors, with endocrine disrupting chemicals (EDCs) being proposed as a major cause. EDCs are man-made chemicals used in many industries – for example, in the production of plastics, cosmetics, flame retardants and pesticides. They can interfere with hormone and metabolic systems in our bodies.
Of the 1,484 EDCs currently identified, a large number are known to negatively affect male reproductive development.
Many studies have identified how EDCs negatively affect organs, such as the liver and adrenals, leading to diseases and disorders which damage the health of these organs and disturb male development.