What Can We Learn from Rodents about Prolactin in Humans?

Abstract

Prolactin (PRL) is a 23-kDa protein hormone that binds to a single-span membrane receptor, a member of the cytokine receptor superfamily, and exerts its action via several interacting signaling pathways. PRL is a multifunctional hormone that affects multiple reproductive and metabolic functions and is also involved in tumorigenicity. In addition to being a classical pituitary hormone, PRL in humans is produced by many tissues throughout the body where it acts as a cytokine. The objective of this review is to compare and contrast multiple aspects of PRL, from structure to regulation, and from physiology to pathology in rats, mice, and humans. At each juncture, questions are raised whether, or to what extent, data from rodents are relevant to PRL homeostasis in humans. Most current knowledge on PRL has been obtained from studies with rats and, more recently, from the use of transgenic mice. Although this information is indispensable for understanding PRL in human health and disease, there is sufficient disparity in the control of the production, distribution, and physiological functions of PRL among these species to warrant careful and judicial extrapolation to humans.

Prolactin secretion patterns: basic mechanisms and clinical implications for reproduction

“…Furthermore, in comparison to the normally low circulating levels of PRL (5-25 ng/ml; Kacsoh 2000), elevated levels have been reported in the late follicular phase and during the luteal phase of the normal menstrual cycle (L'Hermite & Robyn 1972, Brumstead & Riddick 1992, which might -at least partly -be due to an increase in estradiol. However, currently available data on the effect of estradiol in the regulation of PRL secretion in humans are controversial (Ben-Jonathan et al 2008). In contrast to rodents, the normal daily PRL secretory profile of humans displays a distinct circadian pattern characterized by a rise during nocturnal sleep and a rapid fall after awakening (Kawagoe et al 1988).…”

“…As critical parameters of the PRL secretion controlling system in humans are missing, this impedes the design of a detailed mathematical model. Nevertheless, the rat still serves as an indispensable source of information on the neuroendocrine regulation of PRL secretion (Ben-Jonathan et al 2008), and thus the rat model is a very valid guide for a future human model.…”

“…There is some evidence that a PRL surge occurs during ovulation coincident with the secretory peak of LH as in rodents (Vekemans et al 1977, Suganuma et al 1988, although the extent seems to be much weaker in women than in rats (Ben-Jonathan et al 2008). Furthermore, in comparison to the normally low circulating levels of PRL (5-25 ng/ml; Kacsoh 2000), elevated levels have been reported in the late follicular phase and during the luteal phase of the normal menstrual cycle (L'Hermite & Robyn 1972, Brumstead & Riddick 1992, which might -at least partly -be due to an increase in estradiol.…”

“…Prolactin (PRL) is an exceptional hormone with important implications for reproduction and sexual behavior (Ben-Jonathan et al 2008). More than 300 biological functions, for example immune functions, osmoregulation, reproduction, and behavior, have been described so far, and its pleiotropic features are unique (Freeman et al 2000, Grattan & Kokay 2008.…”

La prolactine et son fragment 16 kDa dans les tissus de mammifères

“…la forme 16K [10]. Dans le tissu adipeux humain, pré-adipocytes et adipocytes différenciés expriment des récepteurs, fixent la PRL et sont aussi des sites de synthèse et de sécrétion de PRL endogène [11]. Le placenta et les structures annexes de l'utérus de plusieurs espèces [12], la prostate [13], les chondrocytes [14], plusieurs types de cellules du système immunitaire [15], des cellules du myocarde [16], les glandes lacrymales [17], la rétine [18], fixent la PRL et la produisent.…”