Feedback regulation of growth hormone synthesis and secretion in fish and the emerging concept of intrapituitary feedback loop

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Vol. 144; no. 3; pp. 284 - 305
• Main Authors: Wong, Anderson O.L., Zhou, Hong, Jiang, Yonghua, Ko, Wendy K.W.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2006
• Subjects: Animals; Autocrine/paracrine interactions; Feedback control; Feedback, Physiological; Fish; Fishes - metabolism; Gene expression; Gene Expression Regulation; Gonadotrophs; Gonadotropins - metabolism; Growth hormone; Growth Hormone - biosynthesis; Growth Hormone - metabolism; Luteinizing hormone; Luteinizing Hormone - metabolism; Mammals - metabolism; Pisces; Pituitary; Pituitary Gland - metabolism; Signal transduction; Somatotrophs; Gonadotrophs; Signal transduction; Pituitary; Luteinizing hormone; Autocrine/paracrine interactions; Fish; Feedback control; Somatotrophs; Growth hormone; Gene expression
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/j.cbpa.2005.11.021

Growth hormone (GH) is known to play a key role in the regulation of body growth and metabolism. Similar to mammals, GH secretion in fish is under the control of hypothalamic factors. Besides, signals generated within the pituitary and/or from peripheral tissues/organs can also exert a feedback control on GH release by effects acting on both the hypothalamus and/or anterior pituitary. Among these feedback signals, the functional role of IGF is well conserved from fish to mammals. In contrast, the effects of steroids and thyroid hormones are more variable and appear to be species-specific. Recently, a novel intrapituitary feedback loop regulating GH release and GH gene expression has been identified in fish. This feedback loop has three functional components: (i) LH induction of GH release from somatotrophs, (ii) amplification of GH secretion by GH autoregulation in somatotrophs, and (iii) GH feedback inhibition of LH release from neighboring gonadotrophs. In this article, the mechanisms for feedback control of GH synthesis and secretion are reviewed and functional implications of this local feedback loop are discussed. This intrapituitary feedback loop may represent a new facet of pituitary research with potential applications in aquaculture and clinical studies.