Prolactin - Variance in Levels

Variance in Levels

There is a diurnal as well as an ovulatory cycle in prolactin secretion. In many mammals, there is also a seasonal change in prolactin release.

During pregnancy, high circulating concentrations of estrogen increase prolactin levels by 10- to 20-fold. However, at the same time, estrogen, as well as progesterone, inhibit the stimulatory effects of prolactin on milk production. It is the abrupt drop of estrogen and progesterone levels following delivery that allows prolactin — which temporarily remains high — to induce lactation.

After childbirth, prolactin levels fall as the internal stimulus for them is removed. Sucking by the baby on the nipple then promotes further prolactin release, maintaining the ability to lactate. The sucking activates mechanoreceptors in and around the nipple. These signals are carried by nerve fibers through the spinal cord to the hypothalamus, where changes in the electrical activity of neurons that regulate the pituitary gland cause increased prolactin secretion. The suckling stimulus also triggers the release of oxytocin from the posterior pituitary gland, which triggers milk let-down: Prolactin controls milk production (lactogenesis) but not the milk-ejection reflex; the rise in prolactin fills the breast with milk in preparation for the next feed.

In usual circumstances, in the absence of galactorrhea, lactation will cease within one or two weeks of the end of demand breastfeeding.

It has also been found that compared to un-mated males, fathers and expectant fathers have increased prolactin concentrations.

High prolactin levels also tend to suppress the ovulatory cycle by inhibiting the secretion of both follicle-stimulating hormone (FSH) and gonadotropin-releasing hormone (GnRH). High prolactin levels can also contribute to mental health issues.

Prolactin levels peak during REM sleep, and in the early morning. Levels can rise after exercise, meals, sexual intercourse, minor surgical procedures, or following epileptic seizures.

Hypersecretion of prolactin is more common than hyposecretion. Hyperprolactinemia is the most frequent abnormality of the anterior pituitary tumors. Clinical signs include inappropriate lactation, lack of menses, infertility in females, and impotence in males.