Prolactin lactation

After birth, a rapid drop in progesterone level initially triggers lactation through reversal of inhibitory effects on prolactin (Fig. 44-2). Nipple stimulation then enables lactation to continue once established. During lactation, ineffective removal of milk from the breast, trauma, and skin breaks may lead to problems such as milk stasis, nipple pain, and mastitis.12 Additionally, some women have difficultly initiating lactation due to improper technique and/or activity of inhibitors such as dopamine (Fig. 44-2). 

Yet different elaboration of the same molecule affords a compound (162) that acts as an inhibitor to the pituitary peptide hormone prolactin, the factor responsible for supporting lactation. As such the drug has found use in suppressing lactation and in the treatment of prolactin-dependent breast tumors. 

Prolactin (PRL), produced by the lactotrope cells of the adenohypophysis, is involved with the initiation and maintenance of lactation in females. Its function in males is uncertain. Lactation involves three processes ... 

The dopamine D2 agonists bromocriptine and cabergoline (pp. 114, 188) inhibit prolactin-releasing AH cells (indications suppression of lactation, prolactin-producing tumors). Excessive, but not normal, growth hormone release can also be inhibited (indication acromegaly) (3). 

Stimulates gastric emptying and intestinal transit of barium in cases where delayed emptying interferes with radiological examination of the stomach or small intestine. Unlabeled uses Used to improve lactation. Doses of 30 to 45 mg/day have increased milk secretion, possibly by elevating serum prolactin levels (see Warnings). Also for treatment of postoperative gastric bezoars (10 mg 3 or 4 times daily). 

Long-Evans) breeding- lactation Bd Wt 31.6 F prolactin) chloride... 

As discussed in Section 2.4, there is some evidence that nickel may affect the release of prolactin from the pituitary. In a study limited by decreased water and food intake and increased temperatures, oral exposure of rats resulted in increased pituitary weights in male but not female rats (RTI 1986, 1988a, 1988b). However, decreased prolactin levels were observed in female rats treated with nickel chloride in the drinking water throughout the breeding and lactation of two litters (Smith et al. 1993). 

Human prolactin is similar in structure to human growth hormone, and both are good lactogens. In women, prolactin acts with other hormones on the mammary gland during pregnancy to develop lactation and after birth to maintain it. Hyperprolactinemia causes impotence in men and amenorrhea and infertility in women. Chronically elevated levels of circulating prolactin are associated with suppression of 17-p-estradiol and testosterone production in the ovaries and testes. 

Knockout of the prolactin receptor, rather than knockout of prolactin, is necessary to explore the role of the hormone and its receptor in maternal behavior because several molecules other than prolactin, including growth hormone (GH) and placental lactogens, may stimulate the prolactin receptor. Disruption of the prolactin receptor gene in a mouse model has allowed for assessment of phenotypes associated with partial and complete prolactin receptor deficits (Goffin et ah, 1999). Prolactin receptor knockout mice have severe reproductive deficits. Heterozygous mothers (receptor —/+) were also unable to lactate (Bridges, 1998). 

Estrogens suppress lactation without affecting the prolactin level in plasma. 

The most common undesirable effect of methyldopa is sedation, particularly at the onset of treatment. With long-term therapy, patients may complain of persistent mental lassitude and impaired mental concentration. Nightmares, mental depression, vertigo, and extrapyramidal signs may occur but are relatively infrequent. Lactation, associated with increased prolactin secretion, can occur both in men and in women treated with methyldopa. This toxicity is probably mediated by inhibition of dopaminergic mechanisms in the hypothalamus. 

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