Variety of GH and TSH responses to somatostatin in perifused rat pituitaries in vitro.

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Abstract
One male rat pituitary placed in a chamber was perifused with cyclic somatostatin (GIF) for 30 min. Either 160 nM or 1.6 .mu.M GIF decreased the release of GH [growth hormone]. The release of TSH [thyrotropin] was also decreased by 160 nM GIF, and paradoxically increased by 1.6 .mu.M GIF. Increasing the dose of GIF to 16 .mu.M 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 [prolactin] was not clearly affected by 16 .mu.M GIF. [Tyr8]-GIF did not have such stimulatory activities. GIF probably not only inhibits the release of GH and TSH, but probably also stimulates that of GH and TSH in this system, depending on its dose.