Is calcium or cyclic AMP involved in the inhibitory effect on pituitary hormone secretion of the tripeptide aldehyde proteinase inhibitors?

G. B. Makara, T. Szentendrei, Gy Rappay

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The mechanism by which tripeptide aldehyde proteinase inhibitors decrease prolactin (PRL) and growth hormone (GH) secretion was studied. Agents known to modify the intracellular levels of cyclic adenosine monophosphate (cAMP) or cytosolic free calcium were used in monolayer cultures of the rat anterior pituitary gland. The phosphodiesterase inhibitor isobutyl-methylxanthine (IBMX), 8-bromo-cAMP and forskolin all stimulated PRL release. Boc-D-Phe-Pro-arginal (Boc-DPPA) at 1 mmol/1 concentration was a potent inhibitor of basal PRL release and significantly decreased the effect of 8-Br-cAMP, forskolin or IBMX (0.5 mmol/1). Forskolin (1 μmol/1) stimulated ACTH, PRL and GH release and all these effects were decreased by 100 μmol/1 of Boc-D-Phe-Phe-lysinal (Boc-DPPL), Neither tripeptide aldehyde affected the forskolin-induced rise in intracellular cAMP. Growth hormone releasing factor (hpGRF, 1 nmol/1) stimulated both GH release and intracellular cAMP generation; Boc-DPPL (100 μmol/1) significantly decreased stimulated GH release without affecting cAMP accumulation. Increasing medium K+ to 10 times normal level stimulated PRL release presumably by enhancing Ca2+ entry into the cells and 1 mmol/1 Boc-DPPA decreased high potassium-stimulated PRL release. The ionophore A-23187 stimulated PRL release at 10 jumol/1 but not at 1 μmol/1. At 1 jumol/1 A-23187 prevented the Boc-DPPA-induced inhibition of PRL release. These findings suggest that the tripeptide aldehyde proteinase inhibitors inhibit PRL and GH release at a site beyond cAMP formation.

Original languageEnglish
Pages (from-to)63-69
Number of pages7
JournalMolecular and Cellular Endocrinology
Issue number1-2
Publication statusPublished - Jul 1987



  • Calcium ionophore
  • Forskolin
  • Growth hormone
  • Growth hormone releasing factor
  • High potassium
  • Prolactin

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology

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