Endogenous Hypothalamic Somatostatins Differentially Regulate Growth Hormone Secretion from Goldfish Pituitary Somatotropes in Vitro

Abstract

Using Southern blot analysis of RT-PCR products, mRNA for three different somatostatin (SS) precursors (PSS-I, -II, and -III), which encode for SS(14), goldfish brain (gb)SS(28), and [Pro(2)]SS(14), respectively, were detected in goldfish hypothalamus. PSS-I and -II mRNA, but not PSS-III mRNA, were also detected in cultured pituitary cells. We subsequently examined the effects of the mature peptides, SS(14), gbSS(28), and [Pro(2)]SS(14), on somatotrope signaling and GH secretion. The gbSS(28) was more potent than either SS(14) or [Pro(2)]SS(14) in reducing basal GH release but was the least effective in reducing basal cellular cAMP. The ability of SS(14), [Pro(2)]SS(14), and gbSS(28) to attenuate GH responses to GnRH were comparable. However, gbSS(28) was less effective than SS(14) and [Pro(2)]SS(14) in diminishing dopamine- and pituitary adenylate cyclase-activating polypeptide-stimulated GH release, as well as GH release resulting from the activation of their underlying signaling cascades. In contrast, the actions of a different 28-amino-acid SS, mammalian SS(28), were more similar to those of SS(14) and [Pro(2)]SS(14). We conclude that, in goldfish, SSs differentially couple to the intracellular cascades regulating GH secretion from pituitary somatotropes. This raises the possibility that such differences may allow for the selective regulation of various aspects of somatotrope function by different SS peptides.

Molecular and expression characterization of two somatostatin genes in the Chinese sturgeon, Acipenser sinensis

“…SS genes displayed different expression levels in the brain of lungfish (Trabucchi et al, 1999), white sturgeon (Trabucchi et al, 2002), goldfish (Yunker et al, 2003), grouper (Ye et al, 2005) and Siberian sturgeon (Adrio et al, 2008). In this study, the two AsSS genes expressed in all subdivisions of brain and pituitary with different expression levels (Fig.…”

“…In white sturgeon, SS2 but not SS1 mRNA was found in the pars intermedia of the pituitary (Trabucchi et al, 2002). Goldfish SS1 and SS3, but not SS2 were detected in cultured pituitary cells (Yunker et al, 2003). Although both AsSS1 and AsSS2 were abundantly expressed in the pituitary of Chinese sturgeon, the paracrine and autocrine effects of AsSSs need to be examined.…”

Rainbow trout somatostatin receptor subtypes SSTR1A, SSTR1B, and SSTR2 differentially activate the extracellular signal-regulated kinase and phosphatidylinositol 3-kinase signaling pathways in transfected cells

“…One possible alternative upstream mechanism is the PLC-protein kinase C (PKC) pathway, which has been shown to be activated in mammalian systems through various SSTRs including SSTR2 (Cervia & Bagnoli 2007). SS signaling through PKC has been demonstrated in goldfish pituitary (Yunker et al 2003).…”

Somatostatin Molecular Variants in the Vitreous Fluid

“…In this regard, it should be noted that the different molecular variants of somatostatin could operate through distinct intracellular mechanisms, thus contributing to the selective regulation of cell function in tissues where more than one isoform is present (37). In fact, somatostatin-14 is the main bioactive molecular form of somatostatin regulating the inhibition of endocrine secretion from the gut, whereas somatostatin-28 rather than somatostatin-14 is the physiological regulator of postprandial insulin secretion (38) and pituitary hormones (39).…”