Effects of melatonin and prolactin in reproduction: review of literature

Abstract

Conflict of interest: noneThe pineal gland is responsible for producing a hormone called melatonin (MEL), and is accepted as the gland that regulates reproduction in mammals. Prolactin (PRL) also exhibits reproductive activity in animals in response to photoperiod. It is known that the concentrations of PRL are high in the summer and reduced during winter, the opposite of what is seen with melatonin in these seasons. In placental mammals, both prolactin and melatonin affect implantation, which is considered a critical point of pregnancy, since a successful pregnancy requires the development of a synchronous interaction between the endometrium and blastocyst for placental development. It is also known that PRL levels during pregnancy are essential for the maintenance of pregnancy, because this hormone induces the corpus luteum to produce progesterone, in addition to stimulating blastocyst implantation to maintain pregnancy and form the placenta. However, melatonin levels in plasma have also been shown to increase during pregnancy, peaking at the end of this period, which suggests that this hormone plays an important role in the maintenance of pregnancy. Thus, it is clear that treatment with prolactin or melatonin interferes with the processes responsible for the development and maintenance of pregnancy.Keywords: pineal gland, pregnancy, progesterone, estrogens. pineal glandThe pineal gland develops from the roof of the diencephalon, behind the third ventricle, measuring approximately 8x4mm in adults, and weighing approximately 0.1 to 0.18g. It originates from an evagination from the roof of the diencephalon, acquires a cone-like shape, and is located in the epithalamic region between the posterior and habenular commissures. A small ependymal recess from the third ventricle extends a short rod, which allows the connection of the pineal body to the roof of the diencephalon. It is almost completely surrounded by the pia mater. 1The pineal gland has a strong blood supply, and is the second organ (behind the kidney) with the highest blood flow in relation to tissue mass. The numerous capillaries within the parenchymal cells allow intense metabolic activity. The endothelium of the pineal is fenestrated. The blood supply is greater during the night, probably related to increased indole metabolism during these hours, that is, increased production of the hormone melatonin which is an indolamine. Removal of the superior cervical ganglion concomitantly decreases the metabolic activity of the gland and 2/3 of its normal blood flow. Most of this blood supply is provided by branches originating from the posterior choroidal arteries. 2The pineal differs from almost all of the brain by the absence of a blood-brain barrier, but resembles other periventricular glands, such as the median eminence, subfornical organ (SFO) and subcomissural organ (SCO), being derived from the ependymal cells in the roof of the third ventricle. Histologically, its parenchyma consists of two types of cells: pinealocytes and neuroglia. The pinealocytes ...

Effect of Melatonin Implants during the Non-Breeding Season on the Onset of Ovarian Activity and the Plasma Prolactin in Dromedary Camel

“…It is well established that this hormone stimulates mammary gland development and regulation of lactation. In human and rodents, prolactin also intervenes in the control of ovarian steroidogenesis, formation of corpus luteum, and modulation of the effects of gonadotropins ( 65 ). The observed low concentrations of prolactin over 2 months coincide with high ovarian activity and estradiol synthesis in the MT group and with a low gonadal activity in the control group.…”

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“…As also noted above, exposure to artificial light can potentially suppress melatonin, production. Suppressed melatonin production has been linked to reproductive functions of the gonadal pituitary axis and prolactin secretion111 ) . This suggests that disturbance of melatonin levels may lead to modulation of the individual’s reproductive physiology and subsequent susceptibility to neoplastic growth.…”

Melatonin and Mesenchymal Stem Cells as a Key for Functional Integrity for Liver Cancer Treatment

“…Melatonin (MLT), N-acetyl-5-methoxytryptamine, is a natural substance that has been recognized in all major living species including plants, animals, bacteria, other unicellular microorganisms and human being [44,93]. This natural substance is normally secreted during the dark phase of the daily light-dark cycle [94]. Given its lipophilic nature, MLT is mainly produced by the pineal gland, then released into the circulation and gains access to various fluids, tissues and cellular compartments [95,96].…”