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INTERACTION OF CLONIDINE AND GHRH ON GH SECRETION IN VIVO AND IN VITRO
Author(s) -
ALBAROTH JULIA,
LOSA MARCO,
SPIESS YURIKO,
SCHOPOHL JOCHEN,
MÜLLER O. ALBRECHT,
WERDER KLAUS
Publication year - 1989
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1111/j.1365-2265.1989.tb01419.x
Subject(s) - clonidine , endocrinology , medicine , in vivo , bolus (digestion) , growth hormone–releasing hormone , chemistry , hormone , biology , growth hormone , microbiology and biotechnology
SUMMARY To investigate the mechanism by which clonidine stimulates GH‐secretion in vivo and in vitro , we studied its interaction with GHRH. In vivo: eight or six normal male subjects were submitted to five protocols: (1) 150 μg clonidine orally followed by 50 μg GHRH 1–44 i.v. 2 h later, (2) 50 μg GHRH 1–44 i.v. followed by 150 μg clonidine orally 2 h later, (3) 150 μg clonidine orally followed by GHRH i.v. 30 min later, (4) 300 μg clonidine orally followed by 50 μg GHRH i.v. 3 h later and (5) 50 μg GHRH i.v. followed by 300 μg clonidine orally 90 min later. In vitro: Rat anterior pituitary cells were coincubated with clonidine (10 ‐11 , 10 ‐9 , 10 ‐7 and 10 ‐5 m) and GHRH (0.005, 0.05, 10 nM) for 4h. Results: 150 μg clonidine alone does not stimulate GH‐secretion. Furthermore, the GH‐increase was not significantly different when GHRH bolus was given before, after or together with clonidine. When 300 μg clonidine was given before GHRH GH‐levels were significantly higher (max 28.6 ± 8.0 mU/1) at 90 min, compared to when clonidine was given after GHRH (max 7.8 ± 3.6 mU/1). The GHRH bolus after clonidine led to a significantly lower GH‐increase (max 31.6 μg 17.0 mU/1) compared to the GHRH‐induced GH‐increase (max 47.2 μg 13.0 mU/1) before clonidine. In vitro , clonidine had no stimulatory effect on GHRH‐stimulated GH secretion. These findings are compatible with clonidine leading to stimulation of GH by inducing endogenous GHRH release.