Abstract
One male rat pituitary placed in a chamber was perifused with cyclic somatostatin (GIF) for 30 min. Either 160nM or 1.6μM GIF caused a decrease in the release of GH. The release of TSH was also decreased by 160nM GIF, and paradoxically increased by 1.6μM GIF. Increasing the dose of GIF to 16μM resulted in an abrupt rise in the release of both GH and TSH during the perfusion; then the level of GH decreased to the nadir level followed by an elevation above the base line, while that of TSH promptly fell back toward the base line. The release of PRL was not clearly affected by 16μM GIF.[Tyr8]-GIF did not have such stimulatory activities. These results indicate that GIF not only inhibits the release of GH and TSH, but also stimulates that of GH and TSH in this system, depending on its dose.
