Introduction  – What is Prolactin?

Prolactin (often abbreviated as PRL) is a mysterious subject among the anabolic steroid using bodybuilding and athletic community. It is often confused with another hormone, Progesterone. The two hormones Prolactin and Progesterone have virtually nothing to do with one another except for the fact that both of these hormones start with the letter P. Prolactin is a protein hormone, also known as Lactotrope, which is secreted by the anterior pituitary gland. Prolactin’s role in vertebrates involves promoting and facilitating mammary growth lactation from the nipples in females following childbirth, but the influence of Prolactin on the initiation of lactation is but only one of many functions that Prolactin serves in many vertebrates, and also influences many other functions and processes in other animals[1]. On the other hand, the hormone Progesterone, which Prolactin is commonly and frequently confused with, is a steroid hormone which serves to affect the female menstrual cycle, pregnancy (the promotion of gestation), and embryogenesis in a vast range of species[2]. For now, we will forget about Progesterone and focus almost exclusively on Prolactin, though Progesterone will periodically come up throughout this article as well, as there are some (mostly antagonizing) links between the two.

Although Prolactin is primarily manufactured and secreted by the anterior pituitary gland, it is also manufactured in varying degrees in the breasts, lymphocytes, leukocytes, decidua, myometrium, and the prostate gland[3] [4]. PRL secretion is regulated by the hypothalamus via the endocrine neurons that monitor all endocrine activity in the body as a whole, and it is a well-known and well-documented fact that dopamine (also known as Prolactin Inhibitory Hormone), an important neurotransmitter, is inhibitive of Prolactin via its interaction with D2 receptors of the lactotrophs, resulting in inhibition of Prolactin secretion[5]. Other checks-and-balances and control mechanisms involving Prolactin include Progesterone. Progesterone is actually an inhibitor of Prolactin, and does so at the site of breast glandular tissue, the myometrium, and at the pituitary gland as well, but Progesterone does up-regulate Prolactin synthesis in the endometrium in females[6] [7] [8] [9]. As we can see, Progesterone serves as both an antagonistic and agonistic hormone to Prolactin. The relation between the two is such that as both hormones are primarily female sex hormones, they are involved in female fertility cycles at different points that tend to counteract the purposes of one another. The total relationship between the two is still not completely understood.

The Prolactin receptor (PRL receptor) is the receptor site at which prolactin binds with in order to exert its effects, and this receptor is diverse in many tissues and cell types within the body, including all of the major organs, skeletal muscle, skin, and the central nervous system[10]. Prolactin is also known to have a cytokine-like relationship in immune system regulation and function[11]. At the end of the day, Prolactin, like many hormones, is of high valued importance for certain functions in the body and should never be completely eliminated or reduced to undetectable levels far below normal physiological ranges.

As would normally be expected, there are severe implications with both elevated levels (hyperprolactinaemia) as well as very low levels (hypoprolactinaemia). Excessively elevated levels of Prolactin (hyperprolactinaemia) bring with it a whole host of concerns for both males and females alike, some of particular importance for men include lactation from the nipples, the loss of sex drive and libido, as well as erectile dysfunction and the suppression/inhibition of endogenous Testosterone production[12]. Excessively reduced levels of Prolactin (hypoprolactinaemia) are once again associated with a plethora of health concerns in females and males alike, including metabolic syndrome, anxiety, erectile dysfunction, premature ejaculation, infertility (relating to disruptions in various functions of sperm production), and hypoandrogenism (a severe reduction in androgenic activity in the body)[13] [14].

What Importance is Prolactin to the Anabolic Steroid User?

Although Prolactin does not have as much of a direct importance to the anabolic steroid user as something like Estrogen does, there are a plethora of anecdotal reports of anabolic steroid using individuals who have used particular compounds and reported much higher than normal Prolactin levels. Many individuals have even provided their blood test results as anecdotal evidence to attest to this. However, there has been wild variation in the trends concerning the Prolactin issue with anabolic steroids, and much of this is due to the fact that there unfortunately does not exist as much research on many anabolic steroids as we would like, and so there is no solid clinical data from which we can draw conclusions (e.g. the direction relation of a Progestin such as Trenbolone or Deca-Durabolin (Nandrolone) on PRL levels). Until the day that studies on such hypotheses are directly conducted, we will have to work with the data that science has currently provided us.

Throughout the remaining sections of this article, we will explore Prolactin in greater depth/detail and how it relates to the physiology of men, women, and possibly certain anabolic steroids of particular concern (primarily 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”. Endocr. Rev. 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”. Endocr. Rev. 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 prolactin and growth hormone release from fowl pituitary glands in vitro. Br Poult Sci. 25(4):555-9.

[9] C. L. 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. Volume 86 Issue 3.

[10] Mancini, T.; Casanueva, FF; Giustina, A (2008). “Hyperprolactinemia and Prolactinomas”. Endocrinology & 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”. Endocr. Rev. 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. Willams 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 as related to seminal quality and serum testosterone”. Arch Androl. 23 (3): 259–65. doi:10.3109/01485018908986849. PMID 2619414.