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This Article Full Text Full Text (PDF) All Versions of this Article: 70/5/1299    most recent biolreprod.103.022806v2 biolreprod.103.022806v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gregory, S. J. Articles by Tortonese, D. J. Search for Related Content PubMed PubMed Citation Articles by Gregory, S. J. Articles by Tortonese, D. J. Agricola Articles by Gregory, S. J. Articles by Tortonese, D. J.

Effects of Prolactin on the Luteinizing Hormone Response to Gonadotropin- Releasing Hormone in Primary Pituitary Cell Cultures During the Ovine Annual Reproductive Cycle

Department of Anatomy,² University of Bristol, Bristol BS2 8EJ, England, United Kingdom Medical Research Council Human Reproductive Sciences Unit,³ Edinburgh EH16 4SB, Scotland, United Kingdom

In the sheep pituitary, the localization of prolactin (PRL) receptors in gonadotrophs and the existence of gonadotroph-lactotroph associations have provided morphological evidence for possible direct effects of PRL on gonadotropin secretion. Here, we investigated whether PRL can readily modify the LH response to GnRH throughout the ovine annual reproductive cycle. Cell populations were obtained from sheep pituitaries during the breeding season (BS) and the nonbreeding season (NBS), plated to monolayer cultures for 7 days, and assigned to receive one of the following treatments: 1) nil (control), 2) acute (90- min) bromocriptine (ABr), 3) chronic (7-day) bromocriptine (CBr), 4) ABr and PRL, 5) CBr and PRL, 6) PRL alone, or 7) thyrotropin-releasing hormone. Cells were treated as described above, with the aim of decreasing or increasing the concentrations of PRL in the culture, and simultaneously treated with GnRH for 90 min. The LH concentrations in the medium were then determined by RIA. GnRH stimulated LH in a dose-dependent manner during both stages of the annual reproductive cycle. During the NBS, single treatments did not significantly affect the LH response to GnRH. However, when PRL was combined with bromocriptine, either acutely or chronically, GnRH failed to stimulate LH release at all doses tested (P < 0.01). In contrast, during the BS, the LH response to GnRH was not affected by any of the experimental treatments. These results reveal no apparent effects of PRL alone, but an interaction between PRL and dopamine in the regulation of LH secretion within the pituitary gland, and a seasonal modulation of this mechanism.

¹ Correspondence: Domingo J. Tortonese, Department of Anatomy, University of Bristol, Southwell Street, Bristol BS2 8EJ, England, United Kingdom. FAX: 44 117 925 4794; d.tortonese{at}bristol.ac.uk

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