Ghrelin, an endogenous growth hormone (GH) secretagogue, is shown to increase food intake, which action is similar to that of orexin, also a hypothalamic peptide. Since orexin suppresses pulsatile LH secretion in ovariectomized, (OVX) rats, the present study was undertaken to investigate whether ghrelin also suppresses LH secretion. Effects of intracerebroventricularly injected ghrelin (0.1 nmol/0.3 mul) were examined in OVX rats treated with a small dose of 17 beta -estradiol (E-2). After ghrelin injection, pulsatile LH secretions which were ongoing in these E-2-treated OVX rats were significantly suppressed for about 1 h, whereas GH secretion increased, peaking at 30 min. The main parameter suppressed by ghrelin was the pulse frequency, not the pulse amplitude, suggesting the hypothalamus as the site of ghrelin action. This study provides evidence that ghrelin acts not only in the control of food intake but also in the control of LH secretion.