Atrial natriuretic polypeptide in bovine adrenal medulla

Current topics in pheochromocytoma

Pheochromocytoma is the tumor that produces catecholamines and originates from chromaffin cells, which are differentiated from sympathoadrenal progenitor cells of neural crest under the influence of glucocorticoids. Genetic abnormalities of familial pheochromocytomas have elucidated oncogenic genetic bases of the tumor, including gene abnormalities of the RET proto-oncogene in multiple endocrine neoplasia type 2, VHL gene in von Hippel Lindau's disease or the NF1 gene in neurofibromatosis. Co-localization of various substances with catecholamines in the tumor, including neuropeptide Y, opioid peptides or adrenomedulOFF peptide elevating cAMP production, is recognized. The significance of these substances in modulating clinical features of pheochromocytomas is not fully understood.

Increased plasma atrial natriuretic factor in catecholamine-producing tumor patients

The aim of this study was to evaluate plasma levels of ANF in patients with catecholamine-secreting tumors with and without hypertension and to relate ANF secretion to levels of plasma and urinary catecholamines and blood pressure. Twenty-one pheochromocytoma (15 with sustained, 6 with paroxysmal hypertension), 6 neuroblastoma (1 hypertensive) patients and 28 aged-matched controls were studied in basal conditions. Plasma and urinary norepinephrine (NE),epinephrine (E), dopamine (DA) and DOPA were determined by HPLC-ED and plasma ANF by RIA. Both neuroblastoma and pheochromocytoma patients had significantly higher plasma ANF levels than controls. Neuroblastomas showed higher ANF concentration than pheochromocytomas. No differences were found in plasma ANF between hypertensive and normotensive patients. Pheochromocytomas with ANF levels within the normal range had plasma and urinary NE and urinary DA and DOPA levels significantly higher than patients with high ANF. Plasma ANF levels were unrelated to systolic or diastolic blood pressure or heart rate. A negative correlation between plasma ANF and urinary DA was found only in the patients groups. In conclusion, plasma ANF was increased in pheochromocytoma and neuroblastoma patients. Our data suggest that the excessive catecholamine secretion is not responsible for the increased ANF secretion in these patients. The significance of the relationships among plasma ANF and urinary and plasma catecholamines requires further investigation.

Atrial natriuretic factor: does it have a role in psychiatry?

Atrial natriuretic factor (ANF) is the first of a group of atrial natriuretic peptides (ANPs) discovered since 1981. This group of peptides is thought to have an important role in sodium homeostasis and regulation of fluid volume. Although the role of ANF in cardiovascular and renal disorders is under investigation, the specific signaling involvement that ANF may have in the central nervous system is still unexplored. To date, ANF has not as yet been associated with a given functional area in the brain, nor has it been shown to be linked to any particular psychopathology. Neuropharmacology research of these peptides and their drug manipulation is needed to advance our knowledge of the possible role of ANF in psychiatry beyond the current level of speculation.

A comparative study of the effect of atrial natriuretic peptide (ANP) on the secretory activity of rat adrenal cortex and angiotensin-II-responsive adrenocortical autotransplants

Rat adrenocortical autotransplants regenerated from capsular-tissue fragments implanted in the musculus gracilis displayed an in-vitro basal gluco- and mineralocorticoid secretion qualitatively similar to that of adrenal quarters from control rats. Moreover, like adrenal quarters, they responded to angiotensin-II (Ang-II, 10(-8) M) by raising their yield of 18-hydroxylated steroids (18-hydroxy-11-deoxycorticosterone, 18-hydroxycorticosterone and aldosterone). ANP (10(-8) M), one of the main negative modulators of the zona-glomerulosa (ZG) mineralocorticoid secretion, totally blocked the ANG-II stimulating effect on adrenal quarters, but not that on adrenocortical autotransplants. Autoradiography showed that, in contrast with ZG cells of control rats, ZG-like cells of transplants did not significantly bind 125I-ANP. The hypothesis is discussed that ZG-like cells of regenerated adrenocortical nodules lack specific receptors for ANP.

Atrial natriuretic peptide kinetic studies in patients with cardiac dysfunction

Three studies were performed: (1) a controlled investigation of alpha-human atrial natriuretic peptide (alpha-hANP) total body production and metabolic clearance rates using a bolus infusion technique (controls, patients 1 to 6); (2) a study of alpha-hANP kinetics in cardiac dysfunction patients using a constant infusion method (patients 7 to 14); and (3) a right heart catheterization study to determine the amount of alpha-hANP released into the circulation at the level of the right heart, estimated by the step-up in alpha-hANP concentration between the superior and inferior vena cava and the pulmonary artery, in the patients with left ventricular dysfunction. Baseline venous plasma alpha-hANP was 27.3 +/- 16.5 pg/ml in the controls (mean +/- SD; N = 6), 141.6 +/- 138.0 pg/ml in patients 1 to 6 (P less than 0.05 compared to controls), and 167.5 +/- 145.7 pg/ml in patients 7 to 14. Total body alpha-hANP production rate was markedly elevated in patients 1 to 6 compared to controls (0.45 +/- 0.36 vs. 0.11 +/- 0.06 micrograms/min, P less than 0.05) and was similar to that determined by the continuous infusion technique in patients 7 to 14 (0.62 +/- 0.44 micrograms/min, P = 0.49 compared to patients 1 to 6). alpha-hANP release into the right heart (0.17 +/- 0.11 micrograms/min), however, was significantly lower than total body production rate in the cardiac dysfunction patients, indicating that total body alpha-hANP secretion occurs from sites in addition to drainage into the right heart via the coronary sinus and anterior cardiac veins. Right atrial pressure correlated with the alpha-hANP released into the right heart.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Atrial and brain natriuretic peptide in adrenal steroidogenesis

We elucidated the role of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in human and bovine adrenocortical steroidogenesis. The urinary volume, sodium excretion and cyclic GMP (cGMP) excretion and plasma cGMP were markedly increased by the synthetic alpha-human ANP (alpha-hANP) infusion in healthy volunteers. Plasma arginine vasopressin (AVP) and aldosterone levels were significantly suppressed. Both ANP and BNP inhibited aldosterone, 19-OH-androstenedione, cortisol and DHEA secretion dose-dependently and increased the accumulation of intracellular cGMP in cultured human and bovine adrenal cells. alpha-hANP significantly suppressed P450scc-mRNA in cultured bovine adrenal cells stimulated by ACTH. Autoradiography and affinity labeling of [125I]hANP, and Scatchard plot demonstrated a specific ANP receptor in bovine and human adrenal glands. Purified ANP receptor from bovine adrenal glands identified two distinct types of ANP receptors, one is biologically active, the other is silent. A specific BNP receptor was also identified on the human and bovine adrenocortical cell membranes. The binding sites were displaced by unlabelled ANP as well as BNP. BNP showed an effect possibly via a receptor which may be shared with ANP. The mean basal plasma alpha-hANP level was 25 +/- 5 pg/ml in young men. We confirmed the presence of ANP and BNP in bovine and porcine adrenal medulla. Plasma or medullary ANP or BNP may directly modulate the adrenocortical steroidogenesis. We demonstrated that the lack of inhibitory effect of alpha-hANP on cultured aldosterone-producing adenoma (APA) cells was due to the decrease of ANP-specific receptor, which caused the loss of suppression of aldosterone and an increase in intracellular cGMP.

A novel 1745-dalton pyroglutamyl peptide derived from chromogranin B is in the bovine adrenomedullary chromaffin vesicle

1. Following the recent demonstration of a glutaminyl cyclase activity localized in adrenomedullary chromaffin vesicles, an assay was developed to isolate and characterize posttranslationally modified peptides from this tissue which contain pyroglutamate. This assay consisted of spectrometric identification of peptides before and after enzymatic removal of pyroglutamyl residues. 2. Using this procedure, a pyroglutamyl peptide (BAM-1745) was isolated and sequenced and was shown to be a significant component of adrenomedullary secretory vesicles. 3. A computer search through the Swiss-Prot protein sequence database revealed a 93% identity of BAM-1745 and a fragment of human chromogranin B (Gln580-Tyr593).

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.

Atrial natriuretic peptide in peripheral organs other than the heart

The heart atria represent the major site of synthesis of atrial natriuretic peptide (ANP) in mammals including man, and its function as a regulator of water and salt homeostasis has been repeatedly suggested. However, more recently ANP has been located in organs not intimately related to cardiovascular physiology, e.g. the adrenals, lungs, and gut, as well as tissues belonging to the lymphatic, reproductive or endocrine systems. Thus, ANP might serve many more physiological roles than originally thought, but the functional significance of ANP in these non-cardiac tissues is presently poorly understood.

Atrial natriuretic factor is a new neuromodulatory peptide

In this commentary, we will briefly discuss the potential regulatory role of atrial natriuretic factor in peripheral autonomic nervous system function. The focus will be on atrial natriuretic factor's involvement in cardiovascular homeostasis through its peripheral effect on sympathetic nervous activity, which may complement its humoral role. [Kuchel et al. (1987) Life Sci. 40, 1545-1551; Lang et al. (1985) Nature 314, 264-266]. We will attempt to support the hypothesis of its neuromodulatory action on efferent autonomic outflow. Specifically, the role of atrial natriuretic factor in the regulation of the synthesis and release of neurotransmitters and in synaptic transmission at the level of the sympathetic ganglia will be outlined. Its potential usefulness in neurobiological studies will also be indicated.

Sympathoadrenal inhibition by atrial natriuretic peptide is not attenuated during development of congestive heart failure in dogs

The feedback control of neuroendocrine activity by cardiopulmonary blood volume is disturbed in congestive heart failure. By analyzing plasma catecholamine kinetics, we tested in 11 chronically instrumented conscious dogs whether attenuations in the sympathoadrenal inhibition induced by atrial natriuretic peptide (ANP) contributed to this disturbance. Low-output failure was brought about by continuous ventricular pacing at 265 beats/min for 2 weeks. This resulted in a decline in aortic flow by 37 +/- 5% (SEM), an increase in peripheral vascular resistance by 48 +/- 4%, a 13 +/- 3-fold elevation in plasma ANP, a 9 +/- 3-fold elevation in plasma renin activity, and an augmentation of the norepinephrine-release rate into plasma by 132 +/- 17%. During ANP infusion, the epinephrine-release rate declined by 26 +/- 5% per 10-fold elevation in plasma ANP before pacing and by 31 +/- 7% (not significantly different) after 2 weeks of pacing. Before pacing, ANP attenuated plasma renin activity and caused hypotension without a rise in norepinephrine-release rate. After 2 weeks of pacing, ANP lowered norepinephrine release (by 16 +/- 6%) without affecting blood pressure or plasma renin activity, and vascular nonresponsiveness to ANP was verified under autonomic blockade. These data indicate that, during the development of heart failure, an inhibitory action of ANP on norepinephrine release is unmasked by an ANP-specific vascular desensitization, whereas the inhibition of epinephrine release is observed throughout. It is concluded that ANP-induced sympathoadrenal inhibition is not attenuated and, therefore, does not contribute to the disturbed regulation observed early in the development of failure.

Effect of atrial natriuretic factor (ANF) on nicotinic acetylcholine receptor channels in bovine chromaffin cells

Bovine chromaffin cells have binding sites for rat atrial natriuretic factor (ANF), as demonstrated autoradiographically by using the 125I-labelled peptide. Patch-clamp recording revealed that ANF reduces acetylcholine (ACh)-induced membrane currents in chromaffin cells at physiological membrane potentials. The effect was dose-dependent with the IC50 value being 5.2 microM ANF and the Hill coefficient close to 1. The channel block was absent at positive membrane potentials, indicating a non-competitive interaction of ANF with the open ACh receptor channel. Fragments of ANF had a much less pronounced action, which is possible due to their structure and molecular charge being different to ANF. The block of nicotinic ACh receptor channels may enable ANF to control the secretion of catecholamines from adrenal chromaffin cells.