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Hypothalamic Control of Prolactin Secretion

المؤلف:  Norman, A. W., & Henry, H. L.

المصدر:  Hormones

الجزء والصفحة:  3rd edition , p66

2026-06-25

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In mammals the primary hypothalamic control of prolactin secretion is predominantly through the inhibitory action of dopamine, secreted by neurons in the dorsomedial area of the arcuate nucleus and the inferior ventromedial nucleus of the hypothalamus. Prolactin is the only pituitary hormone regulated in this fashion—that is, showing unrestrained secretion in the absence of hypothalamic input. Figure 1 depicts the signaling leading to the restraint of prolactin secretion by dopamine. The most immediate (within seconds) response to dopamine is increased potassium conductance and inactivation of voltage sensitive Ca2+ channels. The resulting diminished intracellular Ca2+ leads to reduced exocytosis of secretory vesicles containing prolactin. Within a few minutes, inhibition of adenyl cyclase reduces intracellular Ca2+ leading to decreased prolactin gene expression. Sustained expo sure to dopamine input leads to decreased lactotroph proliferation.

Fig1. Hypothalamic control of prolactin secretion. The inhibitory effect of the dopamine receptor, D2R, the predominant influence on prolactin secretion by the lactotroph, results from inhibition of cyclic AMP production, which decreases PRL gene expression. The inwardly rectifying potassium channel is also inhibited by D2R activation, reducing intracellular Ca2+ and exocytosis of secretory vesicles containing prolactin. The receptors and signaling pathways for two known hypothalamic stimulators of PRL secretion, thyrotropin releasing hormone (TRH) and vasoactive intestinal peptide (VIP), are also shown, as is the stimulation of PRL gene expression by the activated estrogen receptor (ER). AC, adenylyl cyclase; PLC, phospholipase C.

Figure 31 also shows the receptors for two other hypothalamic peptides, thyrotropin-releasing hormone (TRH) and vasoactive intestinal peptide (VIP), which have been shown to be capable of stimulating prolactin secretion. These effects are exerted through the signaling pathways shown and result in increased expression of the prolactin gene. The physiological role of these stimulatory peptides in humans remains somewhat unclear, however, and by far the most powerful positive influence on prolactin secretion is the neuronal one exerted by suckling as discussed in section V.B following and in Chapter 14.