Carbachol-induced cosecretion of immunoreactive atrial natriuretic peptides with catecholamines from cultured bovine adrenal medullary cells

Catecholamines, cardiac natriuretic peptides and chromogranin A: evolution and physiopathology of a 'whip-brake' system of the endocrine heart

In the past 50 years, extensive evidence has shown the ability of vertebrate cardiac non-neuronal cells to synthesize and release catecholamines (CA). This formed the mindset behind the search for the intrinsic endocrine heart properties, culminating in 1981 with the discovery of the natriuretic peptides (NP). CA and NP, co-existing in the endocrine secretion granules and acting as major cardiovascular regulators in health and disease, have become of great biomedical relevance for their potent diagnostic and therapeutic use. The concept of the endocrine heart was later enriched by the identification of a growing number of cardiac hormonal substances involved in organ modulation under normal and stress-induced conditions. Recently, chromogranin A (CgA), a major constituent of the secretory granules, and its derived cardio-suppressive and antiadrenergic peptides, vasostatin-1 and catestatin, were shown as new players in this framework, functioning as cardiac counter-regulators in 'zero steady-state error' homeostasis, particularly under intense excitatory stimuli, e.g. CA-induced myocardial stress. Here, we present evidence for the hypothesis that is gaining support, particularly among human cardiologists. The actions of CA, NP and CgA, we argue, may be viewed as a hallmark of the cardiac capacity to organize 'whip-brake' connection-integration processes in spatio-temporal networks. The involvement of the nitric oxide synthase (NOS)/nitric oxide (NO) system in this configuration is discussed. The use of fish and amphibian paradigms will illustrate the ways that incipient endocrine-humoral agents have evolved as components of cardiac molecular loops and important intermediates during evolutionary transitions, or in a distinct phylogenetic lineage, or under stress challenges. This may help to grasp the old evolutionary roots of these intracardiac endocrine/paracrine networks and how they have evolved from relatively less complicated designs. The latter can also be used as an intellectual tool to disentangle the experimental complexity of the mammalian and human endocrine hearts, suggesting future investigational avenues.

The interplay between chromogranin A-derived peptides and cardiac natriuretic peptides in cardioprotection against catecholamine-evoked stress

Chromogranin A (CgA) is the major soluble protein co-stored and co-released with catecholamines (CAs) from secretory vesicles in the adrenal medulla chromaffin cells. Present in the diffuse neuroendocrine system, it has also been detected in rat and human cardiac secretory granules where it co-stores with natriuretic peptide hormones (NPs). Mounting evidence shows that CgA is a marker of cardiovascular dysfunctions (essential hypertension, hypertrophic and dilatative cardiomyopathy, heart failure) and precursor of the cardioactive peptides vasostatin-1 (VS-1) and catestatin (Cts). This review focuses on recent knowledge regarding the myocardial, coronary and anti-adrenergic actions of VS-1. In particular, the negative inotropism, lusitropism and coronary dilation effects of rat CgA1-64 (rCgA) and human recombinant STACgA1-78 (hrSTACgA1-78) are summarized with attention on their counteracting isoproterenol- and endothelin-1-induced positive inotropism, as well as ET-1-dependent coronary constriction. The interactions between vasostatins (VSs), NPs and CA receptors are proposed as a paradigm of the heart capacity to organize complex connection-integration processes for maintaining homeostasis under intense cardio-excitatory stimuli (myocardial stress).

Receptors for natriuretic peptides in adrenal chromaffin cells

Atrial, brain, and C-type natriuretic peptides of the atrial natriuretic peptide family are present in adrenal chromaffin cells, and are secreted with catecholamines by exocytosis. These peptides modulate the physiological functions of the cells such as synthesis and secretion of catecholamines in an autocrine manner interacting with natriuretic peptide receptors.

Atrial natriuretic factor modifies the biosynthesis and turnover of norepinephrine in the rat adrenal medulla

In the present work we investigate atrial natriuretic factor (ANF) effects on the endogenous content, utilization and turn over of norepinephrine (NE), on tyrosine hydroxilase (TH) activity, on cAMP and cGMP levels, and on phosphatidylinositol hydrolysis in rat adrenal medulla in order to assess the possible mechanisms underlying ANF effects on NE metabolism. Results showed that ANF (5 microg/kg) increased NE endogenous content (44%) and diminished the amine utilization. On the other hand, the atrial factor (10 nM) inhibited both spontaneous and evoked, by 100 mM KCl TH, activity (48% and 59%, respectively). When second messenger systems were studied results showed that 10 nM ANF increased cGMP levels in adrenal medulla (51%), while it modified neither cAMP levels nor phosphatidylinositol hydrolysis. These results suggest that ANF may play an important role in the modulation of the sympathoadrenergic system function, behaving as a putative neuromodulator.

Receptors for atrial natriuretic peptide in adrenal chromaffin cells

Receptors for atrial natriuretic peptide (ANP) in isolated bovine adrenal chromaffin cells were characterized. 125 I-ANP specifically bound to the cells with a Kd of 103 pM and a Bmax of 5.6 fmol/10(6) cells (16.5 fmol/mg of cell protein). C-ANF, a highly selective ligand for ANP-C receptors of natriuretic peptides, did not compete for 125 I-ANP binding at concentrations up to 10nM. Chemical cross-linking of 125I-ANP to the cells showed a single molecular size of the 120 kDa binding site on SDS gel electrophoresis under reducing conditions. CNP, a specific peptide for the ANP-B receptor, was much less potent than ANP in inhibiting 125 I-ANP binding and in displacing 125 I-ANP from the 120 kDa band. These results suggest that ANP specifically binds to the ANP-A receptor of 120 kDa and that there is no ANP-C receptor in bovine adrenal chromaffin cells.

Effects of atrial natriuretic factor on norepinephrine release evoked by angiotensins II and III in the rat adrenal medulla

Atrial natriuretic factor (ANF) effects on neuronal norepinephrine (NE) release evoked by angiotensin II (ANG II) or angiotensin III (ANG III) were studied in the rat adrenal medulla. ANF 10 nM diminished the increase of NE release induced by ANG II (1 microM), ANG III (1 microM) or 100 mM KCl. When 10 nM ANF was added to the medium containing KCl plus ANG II or KCl plus ANG III, the reduction of 3H-NE output by ANF was greater than when the atrial factor was added to the medium containing only ANG II or ANG III. Since both ANG II and ANG III have a physiological role on catecholamine metabolism, these peptides could modulate the adrenal medulla functions. ANG II and ANG III enhance NE release and decrease NE uptake in the rat adrenal medulla. Present results show that ANF is a physiological antagonist of both ANG II and ANG III, in the process of NE secretion. The interaction between ANF and the renin-angiotensin system could contribute to the regulation of the adrenal medulla catecholamines pathway and sympathetic activity.

Ca(2+)-dependent cosecretion of adrenomedullin and catecholamines mediated by nicotinic receptors in bovine cultured adrenal medullary cells

Bovine cultured adrenal medullary cells (4 x 10(6)) contained 4266.5 +/- 370.0 fmol of immunoreactive adrenomedullin and 373.4 +/- 32.6 nmol of catecholamines. Nicotinic (but not muscarinic) receptors mediated the Ca(2+)-dependent co-secretion of adrenomedullin and catecholamines, with the molar ratio of adrenomedullin/catecholamines secreted into the medium being equal to the ratio stored in the cells. The concentration-response curve of carbachol for adrenomedullin secretion (EC50 42 microM) was similar to that for catecholamine secretion (EC50 63 microM). Reverse phase HPLC analysis showed that immunoreactive adrenomedullins in the cells and secreted into the medium were both eluted exclusively at the position almost identical to synthetic human adrenomedullin[1-52]NH2.

Quantitation of epinephrine and norepinephrine secretion from individual adrenal medullary cells by microcolumn high-performance liquid chromatography

The cellular response of individual adrenal medullary cells to a prolonged stimulation with carbamylcholine (carbachol) was studied using microcolumn high-performance liquid chromatography (MHPLC) with electrochemical detection. Chromaffin cells will not release all of their catecholamine stores when continuously exposed to a secretagogue. The process of desensitization prevents the continued release of catecholamines after a certain percentage of chemical stores have been depleted. The percentage of a cell's chemical stores released upon stimulation was determined, and whether there is a difference in release between the cell types was examined. A single cell was exposed to a stimulation solution for 5.0 min at 25 degrees C. Approximately 80% of the solution was removed and analyzed on a microcolumn reversed-phase chromatography column. A lysing solution was immediately added to the miniaturized vial which still contained the cell, and this solution was also analyzed chromatographically. The first run was used to determine the amount of catecholamine the cell released upon stimulation. The second run determined the amount of catecholamine that remained in the cell. From these values the percentage of catecholamine released was calculated. Twenty-seven individual cells were studied by this method, and 22 could be classified as norepinephrine or epinephrine dominant. There was no statistical difference in the amount of catecholamine the norepinephrine dominant cells released (14 +/- 5%, n = 11) as compared to the epinephrine dominant cells (12 +/- 4%, n = 11).

Modulation of the rat adrenal medulla norepinephrine secretion in a sodium-free medium by atrial natriuretic factor

The effects of atrial natriuretic factor (ANF) on [3H]norepinephrine ([3H]NE) release evoked by a sodium-free medium (SFM) were studied. Experiments were performed in rat adrenal medulla slices incubated in vitro. Results showed that [3H]NE release evoked by the omission of Na+ was decreased by 10 nM ANF. In addition, when the Ca2+ was omitted from the SFM, NE output was partially diminished. Nevertheless, if ANF was added to SFM/Ca(2+)-free medium (CFM), NE secretion showed no modifications compared with SFM/CFM. Present results raise the hypothesis that two mechanisms could be involved in NE output evoked by a SFM in the rat adrenal medulla: one independent of and the other dependent on the extracellular calcium. Moreover, ANF only diminished NE secretion evoked by SFM dependent on extracellular calcium and did not modify calcium-independent NE release.

Ultracytochemical localization of particulate guanylate cyclase in rat adrenal gland exposed to stimulation by porcine brain natriuretic peptide

We studied the cytochemical localization of particulate guanylate cyclase (GC) in rat adrenal gland after stimulation with porcine brain natriuretic peptide (pBNP) by electron microscopy. In the adrenal cortex, GC activity, as demonstrated by the presence of reaction product, was prevalently localized to the zona glomerulosa and zona fasciculata, while the zona reticularis showed little GC reaction product. In the adrenal medulla, GC reaction product was present only in adrenalin-containing cells. All GC positivity was associated with intracellular membranes. No GC reaction product was detected in specimens incubated in media devoid of pBNP. In parallel samples incubated in the presence of rat atrial natriuretic factor (rANF), the distribution of rANF-stimulated GC activity was similar to that of pBNP-stimulated GC activity.

Post-translational processing and secretory pathway of human atriopeptin in rat pheochromocytoma cells

Atriopeptin (AP) is expressed in several tissues with each tissue capable of specific differences in processing of the prohormone (pro-AP) to mature low molecular forms of the peptide. Since pro-AP has low biological activity, processing into mature AP is a critical activation event. This observation prompted us to study whether granule storage or regulated secretion of AP is essential for cleavage of mature peptide. We examined the processing of AP in adrenal medulla derived cells, using the rat pheochromocytoma cell line (PC12 cell) stably transfected with a genomic human AP DNA in the presence and absence of nerve growth factor (NGF), and also examined the mechanism of AP secretion and compared the results with those obtained using transfected chinese hamster ovary cells (CHO cells). The amount of prohormone was 5-10 fold higher than that of low molecular form of AP in the transfected PC12 cells. This ratio was essentially unchanged in differentiated PC12 cells after NGF treatment of the cells. Potassium depolarization of the transfected PC12 cells caused a 5-fold increase in AP release into the medium primarily as the intact prohormone. On the other hand, transfected CHO cells only exhibited constitutive AP release which is non-response to depolarization. These results suggest that the AP prohormone is sorted into secretory granules as the prohormone in PC12 cells and undergoes regulated release in response to depolarization indicating granule storage or release is not the critical determinant of AP prohormone cleavage.

Stimulatory effects of brain natriuretic peptide on cyclic GMP accumulation and tyrosine hydroxylase activity in cultured bovine adrenal medullary cells

We studied the effect of brain natriuretic peptide (BNP) on the accumulation of cyclic GMP and the phosphorylation and activity of tyrosine hydroxylase, compared with that of atrial natriuretic peptide (ANP), in cultured bovine adrenal medullary cells. 1. BNP as well as ANP increased cellular cyclic GMP accumulation in a concentration-dependent manner (10-1000 nmol/l). BNP (1 mumol/l) and ANP (1 mumol/l) produced a 60-fold and 30-fold increase in cyclic GMP accumulation, respectively. 2. The stimulatory effects of BNP and ANP on cyclic GMP accumulation were observed even when Ca2+ or Na+ was removed from the incubation medium. 3. 12-O-Tetradecanoylphorbol 13-acetate (TPA), an activator of protein kinase C, inhibited the stimulatory effect of BNP on cyclic GMP accumulation in a concentration-dependent manner (1-100 nmol/l). Furthermore, the BNP-induced accumulation of cyclic GMP was attenuated by forskolin (1 mumol/l), an activator of adenylate cyclase. 4. BNP (1 mumol/l) and ANP (1 mumol/l) caused a significant increase in phosphorylation and activity of tyrosine hydroxylase in the cells. 5. In digitonin-permeabilized cells, cyclic GMP (1-100 mumol/l) activated tyrosine hydroxylase in the presence of ATP and Mg2+. These results suggest that BNP stimulates the accumulation of cyclic GMP in a manner similar to that of ANP. The increased accumulation of cyclic GMP by these peptides may be negatively modulated by protein kinase C and cyclic AMP and may cause the phosphorylation and activation of tyrosine hydroxylase in cultured bovine adrenal medullary cells.

The effect of splanchnic nerve stimulation on the uptake of atrial natriuretic peptide by the adrenal gland in conscious calves

A technique has been developed with which it has been possible to quantify the output of a wide variety of agonists including catecholamines, glucocorticoids, mineralocorticoids, enkephalins and various peptides, from the adrenal gland in the conscious unrestrained calf; also to investigate responses to electrical stimulation of the peripheral end of the splanchnic nerve below any behavioural threshold. In the present study this methodology has been employed to investigate the extent to which stimulation of the splanchnic sympathetic innervation affects adrenal handling of atrial natriuretic peptide as this peptide has been identified within the adrenal medulla in this species. Stimulation of the splanchnic nerve at frequencies which raised the concentration of atrial natriuretic peptide like-immunoreactivity (ANP) by 25% led to an abrupt increase in the uptake of the peptide by the right adrenal gland by about 250%. During nerve stimulation more than 20% of the ANP that was estimated to be presented to the gland was taken up, by comparison with less than 13% of the amount presented which was taken up before and after stimulation. These results suggest that stimulation of the splanchnic nerve may specifically enhance the uptake of ANP by the adrenal gland and represent the first report of such a mechanism in respect of any biologically active peptide so far as we are aware.