Signal transduction mechanisms mediating secretion in goldfish gonadotropes and somatotropes

Abstract

The intracellular signal transduction mechanisms mediating maturational gonadotropin and somatotropin secretion in goldfish are reviewed. Several major signaling mechanisms, including changes in intracellular [Ca2+], arachidonic acid cascades, protein kinase C, cyclic AMP/protein kinase A, calmodulin, nitric oxide, and Na+/H+ antiport, are functional in both cell types. However, their relative importance in mediating basal secretion and neuroendocrine-factor-regulated hormone release differs according to cell type. Similarly, agonist- and cell-type-specificity are also present in the transduction pathways leading to neuroendocrine factor-modulated maturational gonadotropin and somatotropin release. Specificity is present not only in the actions of different regulators within the same cell type and with the same ligand in the two cell types, but this also exists between isoforms of the same neuroendocrine factor within a single cell type. Other evidence suggests that function-selectivity of signaling may also result from differential modulation of Ca2+ fluxes from different sources. The interaction of different second messenger systems provide the basis by which regulation of maturational gonadotropin and somatotropin release by multiple neuroendocrine factors can be integrated at the target cell level.

Octylphenol and UV-B radiation alter larval development and hypothalamic gene expression in the leopard frog (Rana pipiens).

“…It is clear from our data that UV-B increases cytochrome C gene expression in the metamorph hypothalamus, which could be reasonably expected to affect cytochrome C activity, perhaps affecting cellular metabolism and OP action. Moreover, interactions between signal transduction pathways are known to occur in neuroendocrine systems (60,61) and during embryonic development of the brain and spinal cord (62,63). Although we do not yet know which signaling pathways are involved in the UV-B and OP responses, we hypothesize that there may be an interaction in several downstream signaling mechanisms that could account for our observations.…”

Function-specific calcium stores selectively regulate growth hormone secretion, storage, and mRNA level

“…sGnRH, cGnRH-II, dopamine, and pituitary adenylate cyclaseactivating polypeptide are all known to require VGCC activation to sustain long-term (2 h) evoked GH release (9). Recent preliminary experiments have shown that sGnRH and cGnRH-II stimulated GH mRNA accumulation in vitro and in vivo over the same time period when it was inhibited by KCl (28).…”

“…However, Ca 2ϩ -dependent signaling cascades differ considerably between these cell types (9,(23)(24)(25)(26). It is likely that the actions of Tg may be cell type specific.…”

Inducción hormonal de la espermiación y criopreservación de esperma en anguila europea (Anguilla anguilla).

“…Las GnRHs, producidas en neuronas presentes en diferentes áreas del cerebro, acceden a la hipófisis de los teleósteos a través de las citadas conexiones neuronales directas. Su interacción con receptores específicos, situados en la membrana de las células gonadotropas y acoplados a diversos sistemas de segundos mensajeros, estimula la síntesis y secreción de las gonadotrofinas (Hazum y Conn, 1988;Chang et al, 2000).…”

“…Las GnRHs, producidas en neuronas presentes en diferentes áreas del cerebro, acceden a la hipófisis de los teleósteos a través de las citadas conexiones neuronales directas. Su interacción con receptores específicos, situados en la membrana de las células gonadotropas y acoplados a diversos sistemas de segundos mensajeros, estimula la síntesis y secreción de las gonadotrofinas (Hazum y Conn, 1988;Chang et al, 2000).No obstante, la actividad hipofisaria no sólo está regulada por las GnRHs, sino que existen otros factores cerebrales que estimulan o inhiben esta actividad (Peter et al, 1991;Kah et al, 1993;Trudeau, 1997;Yaron et al, 2003). Se ha descrito la existencia de un factor inhibidor de la liberación de gonadotrofinas, que se ha identificado como la dopamina, y de otras moléculas que intervienen en esta regulación, como ciertos neuropéptidos (péptidos opioides, neuropéptido Y, galanina, colecistoquinina, polipéptido activador de la adenil ciclasa de pituitaria o PACAP), monoaminas (noradrenalina, serotonina) y aminoácidos neurotransmisores (ácido γ-aminobutírico o GABA, taurina, ácido glutámico, ácido aspártico, alanina).…”