Copeptin Immunoreactivity and Calcium Mobilisation in Hypothalamic Neurones of the Rat

Abstract

Copeptin is cleaved from the C-terminus of vasopressin (VP) prohormone. Immunohistochemical studies have revealed intense copeptin-immunoreactivity (irCOPT) in neurones of the rat hypothalamic nuclei, including paraventricular, supraoptic, suprachiasmatic, periventricular, and accessory secretory. Varicose cell processes emanated from irCOPT neurones, some of which projected caudally and traversed the internal layer of the median eminence, and terminated in the posterior pituitary. Double-labelling hypothalamic sections with copeptin antiserum and VP or oxytocin antiserum revealed an extensive overlapping of irCOPT and irVP neurones. The biological activity of human synthetic nonglycosylated copeptin or VP was evaluated in vivo and in vitro. Copeptin (1, 10, and 20 nmol/kg) injected i.v. caused no significant changes in the mean arterial pressure (MAP) and heart rate of urethane-anaesthetised rats. VP (0.1 nmol/kg) increased MAP, which was accompanied by a small decrease of the heart rate. The ratiometric fluorescence method was employed to assess changes in intracellular Ca2+ concentrations [Ca2+](i) which served as an index of the biological activity of peptides. VP (1 microM) markedly increased [Ca2+](i) of rat hypothalamic neurones or vascular smooth muscle cells, whereas copeptin (100 nm to 1 microM) caused a low amplitude, sustained increase of [Ca2+](i) in a population of hypothalamic neurones, but not in any of the vascular smooth muscle cells tested. The results obtained demonstrate that copeptin is expressed in VP neurones and that the peptide in the concentrations tested, although causing little or no detectable changes of blood pressure and heart rate in anaesthetised rats nor changes in [Ca2+](i) of cultured aortic smooth muscle cells, increases [Ca2+](i) in a small population (< 2%) of hypothalamic neurones tested, indicating that copeptin is biologically active in mammalian neurones.

Alteration of serum and cardiac tissue adropin, copeptin, irisin and TRPM2 expressions in DOX treated male rats

“…Serum copeptin levels were higher than serum adropin and irisin levels in rats after DOX treatment, which indicates that DOX caused changes in serum copeptin, adropin, TRPM2 and irisin synthesis. High levels of copeptin in serum may be due to other copeptin sources; it is synthezied in neurons of the rat hypothalamic nuclei including the paraventricular, supraoptic, suprachiasmatic, periventricular and accessory secretory nuclei (Gao et al 2008). DOX induced heart failure causes hypothalamic excitation in rats, which suggests that it may contribute to the release of copeptin into the circulation from this region of the brain.…”

“…Copeptin immunoreactivity also is present in the neurons of hypothalamic nuclei including paraventricular, supraoptic, suprachiasmatic, periventricular, and accessory secretory areas. Its synthesis is stimulated by variations in blood volume or osmotic pressure; thus it can regulate osmotic and cardiovascular homeostasis (Gao et al 2008). Elevated copeptin concentrations have been described in cases of acute myocardial infarction (AMI).…”

Variation of pro‐vasopressin processing in parvocellular and magnocellular neurons in the paraventricular nucleus of the hypothalamus: Evidence from the vasopressin‐related glycopeptide copeptin

“…For example, copeptin is required for correct folding of the AVP precursor, and its absence may lead to an inefficient monomer folding that contributes to the pathogenesis of human hypothalamic diabetes insipidus (Barat, Simpson, & Breslow, 2004). Roles of copeptin in modulating cellular functions have also been explored, and it has been reported that copeptin causes a low amplitude, slow increase of [Ca 2+ ] i in a population of cultured rat hypothalamic neurons (Gao et al, 2008). Copeptin (both copeptin 1-39 [full length] and the C-terminal fragment 22-39) also potentiate the amplitude of excitatory postsynaptic potentials evoked in neurons of the rat lateral septum (van den Hooff, Seger, Burbach, & Urban, 1990), indicating that the C-terminal component of copeptin may modulate neuronal activity in the brain.…”