The somatostatin receptors have been identified in all secretory types of pituitary cells, and their activation leads to inhibition of hormone secretion. However, the functional expression of somatostatin receptors in gonadotrophs and their roles in control of spontaneous and gonadotropin-releasing hormone (GnRH)-stimulated electrical activity, calcium signaling, and gonadotropin secretion have not been characterized. In the present study, we examined the effect of somatostatin in cultured pituitary gonadotrophs from 4- to 6-day old rats and compared the effect of somatostatin with that of melatonin. Single cell calcium measurements showed that somatostatin inhibited GnRH-stimulated calcium increase in 26% of gonadotrophs. Electrophysiological recording revealed that somatostatin inhibited both calcium mobilization and extracellular Ca2+ entry. In that respect, somatostatin mimicked the action of melatonin. Somatostatin also inhibited GnRH-stimulated gonadotropin release in a static culture by about 25%, and this effect was additive to that of melatonin. These results indicate that somatostatin is able to inhibit hormone secretion at the level of gonadotrophs. These observations are consistent with a hypothesis that neonatal melatonin sensitivity is accompanied by independent somatostatin sensitivity, which is non-selective for individual pituitary hormones.