Growth hormone (GH)-releasing heptapeptide, but not GH-releasing hormone, inhibits thyrotropin-stimulated thyroid hormone secretion and cAMP formation in cultured human thyroid follicles.
Synthetic heptapeptide growth hormone-releasing peptide-1 (GHRP-1) potently stimulates GH release in many species, including humans. We investigated the direct in vitro effect of this peptide, compared to growth hormone-releasing hormone (GHRH), on cultured human thyroid follicles. The results indicate that whereas GHRP-1 (6-600 micrograms/l) or GHRH (6-600 micrograms/l) alone had no effect on basal triiodothyronine (T3) secretion or cAMP formation, the heptapeptide (6-600 micrograms/l), but not GHRH (6-1200 micrograms/l), dose-dependently inhibited thyrotropin (TSH)-stimulated T3 secretion and cAMP formation. Moreover, GHRP-1 also dose-dependently inhibited forskolin-stimulated T3 secretion. It would seem, therefore, that the GHRP-1-induced inhibitory effect on thyroid function is located downstream of cAMP formation, without necessarily excluding an additional inhibitory action at a pre-cAMP site. These results additionally demonstrate differences in the mode of action of GHRP-1 and GHRH.
Kraiem
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Endocrine Research Unit, Carmel Medical Center, Haifa, Israel.
Bowers
C Y
CY
Sobel
E
E
Laron
Z
Z
D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D006801:Humans; D009842:Oligopeptides / Q000494:pharmacology*; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D013963:Thyroid Hormones / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology; D013974:Thyroxine / Q000378:metabolism; D014284:Triiodothyronine / Q000378:metabolism
D009842:Oligopeptides; D013963:Thyroid Hormones; D014284:Triiodothyronine; C079956:alanyl-histidyl-(2-naphthyl)alanyl-tryptophyl-phenylalanyl-lysinamide; D005576:Colforsin; D013972:Thyrotropin; D013007:Growth Hormone-Releasing Hormone; D000242:Cyclic AMP; D013974:Thyroxine