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Content available remote Cortistatin and pituitary hormone secretion in rat
Cortistatin (CST), a novel neuropeptide, shows high structural homology and functional resemblance with somatostatin. CST binds with high affinity to all somatostatin receptors, and contrary to somatostatin, is also able to bind with MrgX2 and GH secretagogue receptor of ghrelin (GHS-R1) receptors. The aim of the present investigation was to evaluate in vivo the effect of peripheral administration of cortistatin on pituitary hormone release in comparison with somatostatin (SS) treatment. Adult male rats used in the experiment, were given peripheral injection of cortistatin, somatostatin or vehicle. Blood was withdrawn 60 and 120 minutes thereafter. We found short lasting significant decrease of GH concentration as a result of administration of CST and SS when compared with saline injected controls. Prolactin levels were increased 60 min after cortistatin but not to somatostatin injection. There was no effect of CST on both LH and FSH concentration; however, SS administration influenced gonadotropin secretion. We conclude that cortistatin play a regulatory role in pituitary secretion. Moreover, some differences have been found when compared cortistatin to somatostatin. Thus, when analyzing the mechanism of cortistatin activity it is worth to consider the effect of binding with receptors of somatostatin, specific receptor for CST (MrgX2) and GHS-R.
The effect of γ-aminobutyric acid-receptor agonists, GABA and muscimol on the pituitary-adrenocortical activity, measured indirectly through corticosterone secretion, and the receptors involved were investigated in conscious rats. GABA given ip induced a dual effect, in lower dose (10mg/kg) it significantly decreased the resting serum corticosterone levels while in higher doses (100-500mg/kg) it considerably raised that level. Muscimol (0.5mg/kg ip) also increased the corticosterone concentration. Both GABA and muscimol given intracerebroventricularly (icv) induced a significant, dose-related increase in serum corticosterone levels. Bicuculline, a GABAA-receptor antagonist, totally abolished the corticosterone response to GABA but did not influence the response to muscimol. Pretreatment with atropine did not affect the corticosterone response to GABA but significantly diminished the response to muscimol. These results suggest that GABA moderately inhibits the pituitary-adrenal axis at the pituitary level but significantly stimulates it at the hypothalamic level. The stimulatory effect of GABA, but not muscimol, is mediated by hypothalamic GABA A-receptors, and in the effect of muscimol hypothalamic cholinergic, muscarinic receptors are involved to a significant extent.
This review briefly summarizes recent findings on lactotrophs in the pituitary gland and extrapituitary tissues as a no homologous group cell types of different embryonic origin, morphology and biological function. They display a remarkable adaptation to altered physiological condition. Their functions are derived from structural polymorphism, local synthesis, divergent intracellular signaling pathways and target genes. Most of them are heterogenous with respect to basal hormone release, electrical activity and responsiveness to stimulatory/inhibitory factors, depending upon gender and physiological state of animal. The circulating prolactin (PRL) produced by many types of lactotrophs can act in edocrine/paracrine/autocrine manner, respectively as a hormone, growth factor, neurotransmitter or immunoregulator. At the cellular level PRL exerts mitogenic, morphogenic and secretory activity. Numerous factors of the central and peripheral origin are involved in the mechanism regulating PRL secretion, causing an increase or decrease of the hormone concentration in the circulation. The certain feedback mechanism keep the pituitary lactotrophs to be not overactive
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