Effect of ghrelin and metoclopramide on prolactin secretion in normal women

Abstract

Administration of ghrelin to women stimulates the secretion of PRL but the mechanism is not known. The aim of the study was to investigate the effect of the dopamine receptor blocker, metoclopramide, on ghrelin-induced PRL release. Ten healthy normally cycling women were studied in the midluteal phase of 4 menstrual cycles. A single dose of normal saline (cycle 1), ghrelin (1 μg/kg) (cycle 2), metoclopramide (20 mg) (cycle 3), and ghrelin plus metoclopramide (cycle 4) was given to the women iv. Blood samples in relation to the iv injection (time 0) were taken at -15, 0, 15, 30, 45, 60, 75, 90, and 120 min. The response of PRL and GH was assessed. Following ghrelin administration (cycles 2 and 4), plasma ghrelin and serum PRL and GH levels increased rapidly, peaking at 30 min (p<0.001). PRL was also increased after the injection of metoclopramide (p<0.001, cycle 3), but the increase was much greater than after the administration of ghrelin. The combination of ghrelin and metoclopramide stimulated PRL secretion to the same extent with metoclopramide alone. No changes in GH and PRL levels were seen after saline injection. These results demonstrate that the stimulating effect of ghrelin on PRL secretion is not additive with that of metoclopramide, although a dose range study might provide further information.