In vitro studies on TSH secretion and adenylate cyclase activity in a human TSH-secreting pituitary adenoma. Effects of somatostatin and dopamine

A. Spada, M. Bassetti, E. Martino, G. Giannattasio, P. Beck-Peccoz, A. Sartorio, L. Vallar, L. Baschieri, A. Pinchera, G. Faglia

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We have studied the in vitro TSH secretion and the adenylate cyclase (AC) activity of a human pituitary adenoma surgically removed from a hyperthyroid patient showing high serum TSH levels. The tumor appeared almost homogeneously constituted by cells positive for an anti-TSH-beta antiserum and showing the ultrastructural characteristics of the adenomatous thyrotrophs. Adenoma fragments released in vitro a large amount of TSH (148.4 μU/mg prot/30 min), alpha-subunit(35.5 ng/mg prot/30 min) and TSH-beta (10.1 ng/mg prot/30 min). The effects of somatostatin (GHRIH) and dopamine (DA) on the hormone release have been tested in vitro. Both agents markedly inhibited the release of intact TSH and TSH-beta whereas the release of alpha-subunit was less affected. The two agents were effective at concentrations higher than 10−8M. The ability of GHRIH and DA in modulating the AC activity was investigated in membrane fraction preparations. GHRIH inhibited AC at concentrations higher than 10 −7M. The maximal inhibition was 32% at 10−5 M. Conversely, DA slightly stimulated AC activity. This effects was not mimicked by the dopaminergic ergot CH 29–717, which was completely ineffective on the enzyme. These results suggest that: 1) in this TSH-secreting pituitary adenoma a normal secretory response to the inhibiting agents (GHRIH and DA) is present; 2) different mechanisms of transduction of the GHRIH and DA signals (cAMP dependent and cAMP independent) could be operating in this tumor.

Original languageEnglish
Pages (from-to)193-198
Number of pages6
JournalJournal of Endocrinological Investigation
Issue number3
Publication statusPublished - 1985



  • adenylate cyclase
  • dopamine
  • pituitary adenomas
  • somatostatin
  • TSH

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

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