Actions of L-363,586, a cyclic hexapeptide analogue of somatostatin, on GH secretion by human somatotrophinoma cells in vitro.

L-363,586 is a cyclic, hexapeptide analogue of somatostatin-14 with potent inhibitory actions on rat growth hormone (GH) release in vitro. The studies reported here investigate the direct effects of L-363,586 on basal and growth hormone-releasing factor (GRF)-stimulated GH secretion from 3 human somatotrophinomas in dispersed cell culture. 1nM and 10nM L-363,586 inhibited both basal and GRF-stimulated GH release from cells of all 3 somatotrophinomas during a 2h treatment period, whilst 100nM L-363,586 had a prolonged inhibitory action on basal GH secretion from cells of 2 of the tumours throughout treatment and recovery periods. Rebound release of GH was observed with cells of 1 tumour following treatment with L-363,586 plus GRF. The actions of L-363,586 were similar to those of somatostatin-14. These data suggest that L-363,586 may have a role in the treatment of acromegaly.