Somatostatin-25 (0.1 pM-1 nM) significantly inhibits secretion of growth hormone in the in vitro system, and is 3-14 times more effective than the tetradecapeptide. Somatostatin-25 (0.1 nM-1pM) also inhibits secretion of growth hormone induced by the addition of prostaglandin 2 (PGE2). However, Somatostatin-25 shows no effect on the secretion of prolactin.