Plasma ACTH Levels In Rats Research Articles

Relaxin-3 stimulates the neuro-endocrine stress axis via corticotrophin-releasing hormone

Relaxin-3 is a member of the insulin superfamily. It is expressed in the nucleus incertus of the brainstem, which has projections to the hypothalamus. Relaxin-3 binds with high affinity to RXFP1 and RXFP3. RXFP3 is expressed within the hypothalamic paraventricular nucleus (PVN), an area central to the stress response. The physiological function of relaxin-3 is unknown but previous work suggests a role in appetite control, stimulation of the hypothalamic-pituitary-gonadal axis and stress. Central administration of relaxin-3 induces c-fos expression in the PVN and increases plasma ACTH levels in rats. The aim of this study was to investigate the effect of central administration of human relaxin-3 (H3) on the hypothalamic-pituitary-adrenal (HPA) axis in male rodents in vivo and in vitro. Intracerebroventricular (i.c.v) administration of H3 (5 nmol) significantly increased plasma corticosterone at 30 min following injection compared with vehicle. Intra-PVN administration of H3 (1.8-1620 pmol) significantly increased plasma ACTH at 1620 pmol H3 and corticosterone at 180-1620 pmol H3 at 30 min following injection compared with vehicle. The stress hormone prolactin was also significantly raised at 15 min post-injection compared with vehicle. Treatment of hypothalamic explants with H3 (10-1000 nM) stimulated the release of corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP), but H3 had no effect on the release of ACTH from in vitro pituitary fragments. These results suggest that relaxin-3 may regulate the HPA axis, via hypothalamic CRH and AVP neurons. Relaxin-3 may act as a central signal linking nutritional status, reproductive function and stress.

207. Development of non-peptide antagonist ligands acting for CRF 1 receptors

Evidence has been accumulated suggesting that CRF mediates the endocrine, autonomic, behavioral and immune responses to stressful stimuli. Immunohistochemical and anatomical data supported the notion that this peptide fulfills all of the characteristics of a bona fide neurotransmitter. CRF exerts its actions through interaction with multiple CRF receptor binding sites. The cloning of these multiple receptors for CRF as well as the recent discovery of non-peptide receptor antagonists for CRF receptors have begun a new era of study for this neurotransmitter. The receptors for CRF fall into two distinct classes encoded by two different genes and have been termed the CRF1 and CRF2 receptors belonging to the superfamily of the class B G-protein coupled receptors. Heterologous expression of the human receptors in mammalian cell lines has made possible the identification of non-peptide, high affinity, and selective receptor antagonists. These compounds which can functionally inhibit the actions of CRF on the in vitro stimulation of cAMP or ACTH release from cultured rat anterior pituitary cells. In addition, they attenuate CRF or stress-induced elevations in plasma ACTH levels in rats demonstrating that pituitary CRF1 receptors can be blocked. When administered systemically, these compounds cross the blood-brain-barrier and interact directly with central CRF1 receptors in brain regions rich with this subtype as evidenced by ex vivo receptor autoradiography. While the discovery of specific or selective CRF2 receptor antagonists has not yet been forthcoming, a great deal of evidence is emerging that suggests that CRF1 receptor antagonists will prove useful in the discovery and development of potential orally active therapeutics for various neuropsychiatric disorders.

Recent Advances with the CRF1 Receptor: Design of Small Molecule Inhibitors, Receptor Subtypes and Clinical Indications

Corticotropin-releasing factor (CRF) has been widely implicated as playing a major role in modulating the endocrine, autonomic, behavioral and immune responses to stress. The recent cloning of multiple receptors for CRF as well as the discovery of non-peptide receptor antagonists for CRF receptors have begun a new era of CRF study. Presently, there are five distinct targets for CRF with unique cDNA sequences, pharmacology and localization. These fall into three distinct classes, encoded by three different genes and have been termed the CRF1 and CRF2 receptors (belonging to the superfamily of G-protein coupled receptors) and the CRF-binding protein. The CRF2 receptor exists as three splice variants of the same gene and have been designated CRF2a CRF2b and CRF2g. The pharmacology and localization of all of these proteins in brain has been well established. The CRF1 receptor subtype is localized primarily to cortical and cerebellar regions while the CRF2a receptor is localized to subcortical regions including the lateral septum, and paraventricular and ventromedial nuclei of the hypothalamus. The CRF2b receptor is primarily localized to heart, skeletal muscle and in the brain, to cerebral arterioles and choroid plexus. The CRF2g receptor has most recently been identified in human amygdala. Expression of these receptors in mammalian cell lines has made possible the identification of non-peptide, high affinity, selective receptor antagonists. While the natural mammalian ligands oCRF and r/hCRF have high affinity for the CRF1 receptor subtype, they have lower affinity for the CRF2 receptor family making them ineffective labels for CRF2 receptors. [125I]Sauvagine has been characterized as a high affinity ligand for both the CRF1 and the CRF2 receptor subtypes and has been used in both radioligand binding and receptor autoradiographic studies as a tool to aid in the discovery of selective small molecule receptor antagonists. A number of non-peptide CRF1 receptor antagonists that can specifically and selectively block the CRF1 receptor subtype have recently been identified. Compounds such as CP 154,526 (12), NBI 27914 (129) and Antalarmin (154) inhibit CRF-stimulation of cAMP or CRF-stimulated ACTH release from cultured rat anterior pituitary cells. Furthermore, when administered peripherally, these compounds compete for ex vivo [125I]sauvagine binding to CRF1 receptors in brain sections demonstrating their ability to cross the blood-brain-barrier. In in vivo studies, peripheral administration of these compounds attenuate stress-induced elevations in plasma ACTH levels in rats demonstrating that CRF1 receptors can be blocked in the periphery. Furthermore, peripherally administered CRF1 receptor antagonists have also been demonstrated to inhibit CRF-induced seizure activity. These data clearly demonstrate that non-peptide CRF1 receptor antagonists, when administered systemically, can specifically block central CRF1 receptors and provide tools that can be used to determine the role of CRF1 receptors in various neuropsychiatric and neurodegenerative disorders. In addition, these molecules will prove useful in the discovery and development of potential orally active therapeutics for these disorders.

The neurosteroid tetrahydroprogesterone attenuates the endocrine response to stress and exerts glucocorticoid-like effects on vasopressin gene transcription in the rat hypothalamus

The neurosteroid tetrahydroprogesterone (5 alpha-pregnan-3 alpha-ol-20-one, allopregnanolone, THP), has been previously shown to counteract the anxiogenic effects of corticotropin-releasing hormone (CRH) and to interfere with noradrenergic and corticosteroid-mediated regulation of CRH release and gene transcription. Those observations indicated that, besides its sedative and analgesic activity, THP may also affect the neuroendocrine response to stress in a mode resembling that of corticosteroids. To examine this possibility, we compared the ability of THP, its precursor progesterone (P4), and the glucocorticoids dexamethasone (DEX) and corticosterone (CORT) to influence the pituitary-adrenal response to acute emotional stress and the adrenalectomy-induced increase in the gene transcription of the stress-related peptide arginine vasopressin (AVP) and of corticosteroid receptors (MR and GR) in the brain. Pretreatment of rats with a single dose of THP or P4 (50 micrograms/kg) significantly attenuated the elevation of plasma adrenocorticotropin (ACTH) and serum corticosterone after emotional stress; both steroids were, however, less potent than a similar dose of DEX. Administration of 1 mg of THP, CORT, or P4 to adrenalectomized (ADX) rats attenuated the increase in AVP mRNA levels in the ventromedial subdivision of the hypothalamic paraventricular nucleus (PVN), as compared with vehicle-treated ADX rats. However, whereas CORT and P4 influenced the ADX-induced increase in the transcription of both types of corticosteroid receptors in the hippocampus, these were unaffected by THP. In contrast to the glucocorticoids, THP and P4 failed to decrease plasma ACTH levels in rats deprived of endogenous steroids. These results demonstrate that the neurosteroid THP and its precursor P4 resemble glucocorticoids in their suppression of the pituitary-adrenal response to emotional stress; however, THP influences the transcription of glucocorticoid-responsive genes in brain structures involved in the regulation of the hypothalamo-pituitary-adrenal system in a fashion that is quite distinct from that obtained with glucocorticoids.