What is Prolactin?
Prolactin (often abbreviated as PRL) is a mysterious topic among anabolic steroid users in the bodybuilding and athletic communities.
It is often confused with another hormone, progesterone.
Prolactin and progesterone are, in fact, unrelated to each other, except for the fact that both hormones start with the letter P.
Prolactin is a protein hormone, also known as a lactotroph, secreted from the anterior pituitary gland.
While the role of prolactin in vertebrates is to promote and facilitate lactation from the nipples of females after childbirth, its effect on initiating lactation is just one of the many functions prolactin performs in many vertebrates, and it also affects many other functions and processes in other animals.[1]
On the other hand, the hormone progesterone, which is often confused with prolactin, is a steroid hormone that affects the female menstrual cycle, pregnancy (pro-gestational), and embryogenesis in a wide range of species[2].
For now, let’s forget about progesterone and focus solely on prolactin, but progesterone will periodically appear in this article because there are some (mostly antagonistic) connections between progesterone and prolactin.
Prolactin is primarily manufactured and secreted by the anterior pituitary gland, but it is also manufactured to varying degrees in the breasts, lymphocytes, leukocytes, decidua, myometrium, and prostate.[3] [4]
It is a well-known and well-documented fact that prolactin secretion is regulated by the hypothalamus via endocrine neurons that monitor all endocrine activity throughout the body, and that the crucial neurotransmitter dopamine (also known as prolactin-inhibiting hormone) inhibits prolactin secretion by suppressing prolactin through its interaction with D2 receptors on lactotrophs.[5]
Other checks and balances and regulatory mechanisms related to prolactin include progesterone.
Progesterone is actually an inhibitor of prolactin and also acts on breast glandular tissue, the myometrium, and the pituitary gland, but progesterone upregulates prolactin synthesis in the endometrium of females.[6] [7] [8] [9]
As you can see, progesterone acts as both an antagonist and agonist hormone to prolactin.
The relationship between the two is that since both are primarily female sex hormones, they are involved in the female reproductive cycle at different points, often working against each other’s purposes.
The full relationship between the two is not yet completely understood.
The prolactin receptor (PRL receptor) is the receptor site to which prolactin binds to exert its effects, and these receptors are present in various tissues and cell types throughout the body, including all major organs, skeletal muscle, skin, and the central nervous system.[10]
Furthermore, prolactin is known to have a cytokine-like relationship in the regulation and function of the immune system.[11]
Ultimately, prolactin, like any other hormone, plays a very important role in specific bodily functions and should therefore not be completely eliminated or reduced to undetectable levels far below the normal physiological range.
As one would typically expect, both high levels of prolactin (hyperprolactinemia) and very low levels (hypoprolactinemia) can have serious consequences.
Excessively high prolactin levels (hyperprolactinemia) cause several problems for both men and women, with particularly significant issues for men including nipple lactation, loss of libido and sex drive, erectile dysfunction, and the suppression/inhibition of endogenous testosterone production.[12]
Excessively low prolactin levels (hypoprolactinemia) once again lead to an increase in health problems for both women and men, such as metabolic syndrome, anxiety, erectile dysfunction, premature ejaculation, infertility (related to various dysfunctions in sperm production), and hypoandrogenism (a severe decrease in the body’s androgenic activity).[13] [14]
How Important is Prolactin to Anabolic Steroid Users?
Prolactin is not of great direct importance to anabolic steroid users in the same way as estrogen, but there are many anecdotal reports from anabolic steroid users who have reported that their prolactin levels were much higher than normal while using certain drugs.
Many have even provided blood test results as anecdotal evidence to prove it.
However, the trends regarding anabolic steroids and prolactin issues are very diverse, and this is largely due to the fact that, unfortunately, not as much research has been conducted on many anabolic steroids as we would like, so there is no definitive clinical data to draw conclusions from (e.g., the directional relationship of progestins like Trenbolone or Deca (Nandrolone) on PRL levels).
Until the day that direct research on these hypotheses is conducted, we must work with the data that current science has provided us.
In the next article, we will take a closer look at how prolactin relates to male and female physiology and to specific anabolic steroids of particular concern (mainly progestins such as Trenbolone and Nandrolone).
Medical References
[1] Bole-Feysot C, Goffin V, Edery M, Binart N, Kelly PA (June 1998). “Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice”. Endocrine Reviews. 19 (3): 225–68. doi:10.1210/er.19.3.225. PMID 9626554.
[2] “Metabocard for Hydroxyprogesterone”. Human Metabolome Database. Retrieved 31 July 2013.
[3] Ben-Jonathan N, Mershon JL, Allen DL, Steinmetz RW (December 1996). “Extrapituitary prolactin: distribution, regulation, functions, and clinical aspects”. Endocrine Reviews. 17 (6): 639–69. PMID 8969972.
[4] Gerlo S, Davis JR, Mager DL, Kooijman R (October 2006). “Prolactin in man: a tale of two promoters”. BioEssays. 28 (10): 1051–5. doi:10.1002/bies.20468. PMC 1891148. PMID 16998840.
[5] Lehmeyer JE and Macleod RM. 1974. Studies on the mechanism of the dopamine-mediated inhibition of prolactin secretion. Endocrinology. 94(4):1077-85.
[6] Zinger M, McFarland M, Ben-Jonathan N (February 2003). “Prolactin expression and secretion by human breast glandular and adipose tissue explants”. J. Clin. Endocrinol. Metab. 88 (2): 689–96. PMID 12574200.
[7] Assairi L, Delouis C, Gaye P, Houdebine LM, Olliver-Bousquiet M, Denamur R. 1974. Inhibition by progesterone of the lactogenic effect of prolactin in the pseudopregnant rabbit. Biochem. J. 144, 245-252.
[8] Hall TR, Harvey S, Chadwick A. 1984. Progesterone inhibits the release of prolactin and growth hormone from the domestic fowl pituitary in vitro. Br Poult Sci. 25(4):555-9.
[9] CL CHEN and J. MEITES. 1970. Effects of Estrogen and Progesterone on Serum and Pituitary Prolactin Levels in Ovariectomized Rats. Department of Physiology, Michigan State University. Vol. 86, No. 3.
[10] Mancini, T.; Casanueva, FF; Giustina, A (2008). “Hyperprolactinemia and prolactinomas”. Endocrinology and Metabolism Clinics of North America. 37 (1): 67–99, viii. doi:10.1016/j.ecl.2007.10.013. PMID 18226731.
[11] Bole-Feysot C, Goffin V, Edery M, Binart N, Kelly PA (June 1998). “Prolactin (PRL) and its receptor: actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice”. Endocrine Reviews. 19 (3): 225–68. doi:10.1210/er.19.3.225. PMID 9626554.
[12] Melmed S, Kleinberg D 2008 Anterior pituitary. 1n: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia: Saunders Elsevier; 185-261.
[13] Corona G, Mannucci E, Jannini EA, Lotti F, Ricca V, Monami M, Boddi V, Bandini E, Balercia G, Forti G, Maggi M (May 2009). “Hypoprolactinemia: a new clinical syndrome in patients with sexual dysfunction”. J Sex Med. 6 (5): 1457–66. doi:10.1111/j.1743-6109.2008.01206.x. PMID 19210705.
[14] Gonzales GF, Velasquez G, Garcia-Hjarles M (1989). “Hypoprolactinemia in relation to seminal quality and serum testosterone”. Arch Androl. 23 (3): 259–65. doi:10.3109/01485018908986849. PMID 2619414.
