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Hypothalamic and Thyroidal Regulation of Growth Hormone in Tilapia
Melamed, P. M.; Eliahu, N. A.; Levavi-Sivan, Berta et al.
1995In General and Comparative Endocrinology, 97, p. 13-30
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Keywords :
Recombinant Tilapia growth hormone; Radioimmunoassay
Abstract :
[en] A radioimmunoassay (RIA) for recombinant tilapia growth hormone (GH) was established and validated. The ability of various hypothalamic factors to regulate GH secretion in the tilapia hybrid (Oreochromis niloticus x Oreochromis aureus) was studied. Somatostatin1-14 (SRIF1-14; 10-100 micrograms/kg) was found to reduce circulating GH levels in a dose-dependent manner. SRIF1-14 (0.1-1000 nM) inhibited GH release from perifused pituitary fragments (ED50 0.83 nM). Human growth hormone-releasing hormone fragment 1-29 (hGHRH1-29; 100 micrograms/kg) doubled circulating GH levels and modestly stimulated GH secretion in vitro. Carp growth hormone-releasing hormone (cGHRH) stimulated GH secretion in vitro to a similar degree at the same dose (1 microM). Injection of salmon gonadotropin-releasing hormone (sGnRH) superactive analog (10-100 micrograms/kg) increased plasma GH levels sixfold. sGnRH also stimulated GH release in vitro (ED50 142.56 nM). Dopamine (0.1-10 microM) and the D1 DA receptor agonist SKF 38393 increased GH secretion from perifused pituitary fragments dose-relatedly. Thyrotropin-releasing hormone (TRH) had no effect on GH secretion from perifused pituitary fragments, but increased plasma GH levels, as did bovine thyroid stimulating hormone (bTSH). The increased plasma GH in the bTSH-treated fish coincided with a dramatic increase in T4; however, TRH increased GH without changing T4 levels. T3 increased the synthesis of GH by isolated pituitaries (incorporation of [3H]leucine). SRIF1-14 seems to be a most potent hypothalamic regulator of GH secretion in tilapia; sGnRH and DA both increased GH secretion, although sGnRH elicited considerably greater responses at lower doses. Two forms of GHRH increased GH levels, although the unavailability of the homologous peptide prevented an accurate evaluation of its importance in regulating GH secretion. The thyroid axis (TRH, TSH, and T3) stimulates both synthesis and release of GH, although TRH did not appear to have a direct effect on the level of the pituitary.
Disciplines :
Anatomy (cytology, histology, embryology...) & physiology
Author, co-author :
Melamed, P. M.;  Tel Aviv University > Zoology
Eliahu, N. A.;  Tel Aviv University > Zoology
Levavi-Sivan, Berta;  Tel Aviv University > Zoology
Ofir, Michal;  Tel Aviv University > Zoology
Farchi-Pisanty, Odelia;  Tel Aviv University > Zoology
Rentier-Delrue, Françoise ;  Université de Liège - ULiège > Département des sciences de la vie > Biologie et génétique moléculaire - GIGA-R : Coordination scientifique
Smal, Jean;  Eurogentec
Yaron, Zvi;  Tel Aviv University > Zoology
Naor, Zvi;  Tel Aviv University > Biochemistry
Language :
English
Title :
Hypothalamic and Thyroidal Regulation of Growth Hormone in Tilapia
Publication date :
1995
Journal title :
General and Comparative Endocrinology
ISSN :
0016-6480
eISSN :
1095-6840
Publisher :
Elsevier, New York, United States - New York
Volume :
97
Pages :
13-30
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 01 October 2010

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