Prolactin has a significant role in the physiology of the breast, especially in females. A lack of prolactin secretion or excessive prolactin secretion results in clinically significant, pathologic processes. The level of prolactin hormone is imperative for normal lactational capabilities. Imbalances in prolactin levels can compromise this ability. If the levels are too low, a mother will not be able to produce milk, and if the levels are inappropriately elevated, this can lead to galactorrhea in non-breastfeeding females or males. Furthermore, disruption in the prolactin balance can have significant effects on the menstrual cycle. In females, too much prolactin leads to amenorrhea (absence of menstruation), which results from the prolactin inhibition of GnRH release. In males, however, prolactin level imbalances have different clinical implications. Too much prolactin in males results in headaches and decreased libido. The decreased libido is associated with decreased spermatogenesis as a result of elevated prolactin affecting the hypothalamus-pituitary reproductive axis.[6][7]
Physiology Book By Ak Jain Pdf 14
The pituitary gland sits directly behind the nasal bridge in a protective boney structure called the "sella turcica" and it is connected to the hypothalamus by the infundibular stalk. The hypothalamus is largely responsible for regulating the synthesis and secretion of various hormones within the pituitary gland, including Prolactin. The pituitary gland is structurally divided into anterior and posterior regions. The anterior pituitary is capable of producing and secreting its own hormones, compared to the posterior pituitary gland which acts more as a conduit for presynthesized hormones by the hypothalamus. Prolactin is synthesized by lactotrophs in the anterior pituitary gland. The number of lactotrophs will increase during pregnancy in response to the physiological need to develop breast tissues and to prepare for milk production. It should be noted that the increase in lactotrophs cells is not accompanied by an increase in angiogenesis. This fact is important to understand the pathophysiology behind pituitary infarction and ischemia presented later. Prolactin production is regulated at the gene transcription level. Factors that stimulate production, upregulate prolactin gene transcription while factors that inhibit secretion downregulate prolactin gene transcription.
The pathophysiology of prolactin can include either lack of prolactin production or excessive prolactin production. Prolactin deficiency results in failure to lactate while excessive prolactin results in galactorrhea and infertility. Destruction of the anterior pituitary can cause prolactin deficiency. On the other hand, prolactin excess causes include loss of dopamine inhibition under the influence of antipsychotic drugs or destruction of the hypothalamus/hypothalami-hypophyseal tract. Prolactin-secreting tumors can also cause prolactin excess as is the case with prolactinoma.
Sheehan syndrome is characterized by infarction of the anterior pituitary, which often occurs during delivery but does not manifest until the post-partum period with various endocrinopathies. The pathophysiology of Sheehan syndrome involves a significant blood loss during childbirth, which compromises the blood supply to the enlarged anterior pituitary gland. Prolonged ischemia progresses to ischemic necrosis of the pituitary gland. This damage results in failure to produce the hormones made by the cells within the anterior pituitary gland, such as prolactin-secreting lactotrophs. Symptoms may not manifest until months after the infarction event; thus, a sense of heightened clinical suspicion is necessary when evaluating post-partum mothers with new-onset endocrinopathies or an inability to lactate. The most common presenting symptom of Sheehan syndrome is the failure to lactate (agalactorrhea). Other symptoms are related to the functions of the hormones made by the anterior pituitary such as amenorrhea, decreased sex drive, or symptoms of thyroid insufficiency. Sheehan syndrome represents one of the pathology scenarios where prolactin deficiency is apparent.
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