Effect of ghrelin and thyrotropin-releasing hormone on prolactin secretion in normal women.

It is known that ghrelin stimulates the secretion of prolactin in women. The aim of this study was to examine the effect of exogenous thyrotropin-releasing hormone (TRH) on ghrelin-induced prolactin release. Ten healthy normally cycling women were studied in four menstrual cycles. The women were injected intravenously in late follicular phase (follicle size 16-17 mm) with a single dose of normal saline (cycle 1), ghrelin (1 microg/kg) (cycle 2), thyrotropin-releasing hormone (200 microg) (cycle 3), and ghrelin plus thyrotropin-releasing hormone (cycle 4). Blood samples in relation to saline or drugs injection (time 0) were taken at -15, 0, 15, 30, 45, 60, 75, 90, and 120 min. The prolactin and growth hormone responses were assessed. After ghrelin administration (cycles 2 and 4), plasma ghrelin, serum prolactin, and growth hormone levels increased rapidly, peaking at 15-30 min (p<0.001). The injection of thyrotropin-releasing hormone (cycle 3) stimulated prolactin secretion markedly (p<0.001), but reduced growth hormone levels significantly (p<0.05). Ghrelin induced a smaller prolactin increase than thyrotropin-releasing hormone (p<0.05). The combination of ghrelin and thyrotropin-releasing hormone induced a similar increase in prolactin levels as with thyrotropin-releasing hormone alone. No changes in growth hormone and prolactin levels were seen after saline injection. These results demonstrate that the stimulating effect of ghrelin on prolactin secretion is not additive with that of thyrotropin-releasing hormone.