Barry Bonds, Marion Jones, Roger Clemons, Manny Ramirez…the list of athletes that have made the news for taking performance enhancing drugs is long and seems to grow daily. These news stories put hormones such as testosterone in a negative light, but this hormone is essential to human health.
Testosterone is the principal anabolic and sex hormone that plays a wide variety of roles in the body including sexual desire and function, muscular hypertrophy, densification of bones, and hair growth. Although testosterone is largely responsible for those traits and characteristics considered “masculine,” both sexes require it for proper sexual and physical development1. Testosterone also has effects on other systems in the body (Figure 1), including the nervous system.
The previous neuro-endocrine connection blog discussed the interactions between estrogen and serotonin; this time, the relationship between testosterone, prolactin, and dopamine will be discussed.
Dopamine and Testosterone
Dopamine and testosterone have a direct relationship. Dopamine, a neurotransmitter, plays a role in many different functions including cognition, movement, and feelings of pleasure and reward2. The relationship between dopamine and testosterone stems from the interaction both have with prolactin.
Prolactin is a hormone that has many different roles including breast milk production and sexual gratification. The release of prolactin from the pituitary gland is ultimately controlled by pituitary releasing hormone (PRH) produced by the hypothalamus. The increase in prolactin leads to a decrease in testosterone production in the leydig cells of the testes.
The activity of PRH is countered by dopamine, which is also released from the hypothalamus. An up-regulation of dopamine stimulates the release of prolactin inhibitory factor (PIF). PIF inhibits the pituitary from releasing prolactin. Because prolactin inhibits gonadotropin-releasing hormone (GnRH) secretion, the inhibition of prolactin caused by dopamine, increases the secretion of GnRH, therefore increasing the secretion of testosterone 3 (Figure 2).
This is yet another example of the connections between the endocrine and nervous systems. By understanding these relationships, clinicians can more effectively determine the root cause of clinical symptoms and select more effective treatment options for patients.
Guest author: Megan Geitz is a member of the Clinical Support & Education Department at NeuroScience, Inc. and the resident expert in endocrinology and women’s issues.