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Inge F. Palm, Eline M. van der Beek, Hans J. M. Swarts, Jan van der Vliet, Victor M. Wiegant, Ruud M. Buijs, Andries Kalsbeek, Control of the Estradiol-Induced Prolactin Surge by the Suprachiasmatic Nucleus, Endocrinology, Volume 142, Issue 6, 1 June 2001, Pages 2296–2302, https://doi.org/10.1210/endo.142.6.8219
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Abstract
In the present study we investigated how the suprachiasmatic nucleus (SCN) controls the E2-induced PRL surge in female rats. First, the role of vasopressin (VP), a SCN transmitter present in medial preoptic area (MPO) projections and rhythmically released by SCN neurons, as a circadian signal for the E2-induced PRL surge was investigated. Using a reverse microdialysis technique, VP was administered in the MPO during the PRL surge, resulting in a suppression of the surge. VP administration before the surge did not affect PRL secretion. Also, administration of a V1a receptor antagonist before the surge was ineffective. Second, lesions of the SCN were made that resulted in constant basal PRL levels, suggesting that with removal of the SCN a stimulatory factor for PRL secretion disappeared. Indeed, the PRL secretory response to blockade of pituitary dopamine receptors was significantly reduced in SCN-lesioned animals. These data suggest that the afternoon decrease of VP release in the MPO by SCN terminals enables the PRL surge to occur, and may thus be a circadian signal for the PRL surge. Simultaneously the SCN is involved in the regulation of the secretory capacity of the pituitary, possibly via specific PRL-releasing factors.