Increased circulating concentration of the N-terminus of the atrial natriuretic factor prohormone in persons with pheochromocytomas

Natriuretic peptides: Another tool for the management of cancer?

The connection between heart failure (HF) and cancer through multiple pathways such as inflammation, oxidative stress, and neurohormonal activation, among others, is well established. As a consequence, increases in plasma levels of several biomarkers have been described in both disorders. The most consistent information is related to natriuretic peptides (NPs). Although they are known to be produced in the ventricles as a response to myocardial distension, and thus can be useful for the diagnosis and prognosis of HF, and also for the management of chemotherapy-induced myocardial damage, they are also produced by tumour cells. In this regard, increased plasma levels of NPs have been described in patients with multiple malignancies in the absence of volume overload. Natriuretic peptide levels have been shown to correlate directly with the extension of tumours and with poorer outcomes. Moreover, some data indicate that they may help in the detection of subclinical tumours. Given that these peptides have been described to have anti-proliferative and anti-angiogenic effects, a plausible hypothesis is that they may be produced by tumours as a negative feed-back mechanism to avoid tumour progression. This would lead to increased levels of NPs in plasma that could be potentially useful for early detection of malignancies as well as for a prognostic assessment. Nevertheless, since the sample size of many studies published so far is limited, more data are needed to provide consistent data in order to confirm or rule out this hypothesis.

Cardiac and kidney hormones cure up to 86% of human small-cell lung cancers in mice

BACKGROUND

Four cardiac hormones synthesized by the same gene, i.e. atrial natriuretic peptide, vessel dilator, long acting natriuretic peptide and kaliuretic peptide, and the kidney hormone urodilatin have anticancer effects in vitro.

MATERIALS AND METHODS

These cardiac hormones and urodilatin were infused subcutaneously for 28 days with weekly fresh hormones since they lose biological effects at body temperature for more than a week at 0.3 nm kg(-1) body weight in athymic mice bearing human small-cell lung carcinomas.

RESULTS

Long acting natriuretic peptide, vessel dilator, kaliuretic peptide, atrial natriuretic peptide and urodilatin eliminated 86%, 71%, 57%, 43% (P < 0.001 for the cardiac hormones) and 25% (P < 0.05; urodilatin) of the human small-cell lung carcinomas. The treated small-cell lung carcinomas that were not cured grew rapidly, similar to the untreated controls, whose volume was 7 fold larger in 1 week, 18-fold increased in 2 weeks, 39-fold increased in 3 weeks, 63-fold increased in 1 month and 97-fold increased in volume in 6 weeks. One vessel dilator treated small-cell lung carcinoma animal developed a large tumour (8428 mm3 volume) on treatment and this tumour was eliminated with utilizing atrial natriuretic peptide and then long acting natriuretic peptide sequentially.

CONCLUSIONS

Four cardiac hormones eliminate up to 86% of human small-cell lung carcinomas in athymic mice. Urodilatin can also eliminate small-cell lung carcinomas but at a lower cure rate of 25%. Unresponsive lesions can be eliminated by utilizing different hormones synthesized by the atrial natriuretic peptide gene in a sequential manner.

Four cardiac hormones cause cell death of melanoma cells and inhibit their DNA synthesis

BACKGROUND

There will be an estimated 59,940 new cases of melanoma and 8,110 deaths from melanoma in the United States in 2007. There has been no improvement in survival with melanomas in the last 22 years, with current treatment indicating that new treatment(s) of melanoma are drastically needed. Four cardiac hormones ie, atrial natriuretic peptide, vessel dilator, long-acting natriuretic peptide, and kaliuretic peptide, have significant anticancer effects in adenocarcinomas.

METHODS

Dose-response curves evaluated the effects of these cardiovascular hormones on cell death and DNA synthesis in several melanoma cell lines in culture for 96 hours. Receptors to mediate these peptide hormones effects were examined in the melanoma cells with Western blots. Their intracellular mediator-analog 8-bromo-cyclic GMP was used to determine if it could mimic their effects on decreasing melanoma cell number and DNA synthesis.

RESULTS

The four cardiac hormones caused cell death in up to 71% (P < 0.001) of the melanoma cells within 24 hours. Cardiac hormone receptors (NPR-A, -B, -C) were present on the melanoma cells, and each of the peptide hormones decreased DNA synthesis within the melanoma cells up to 73% (P < 0.001) at their 1-microM concentrations. 8-Bromo-cyclic GMP mimicked their effects, decreasing the number of melanoma cells up to 67% and their DNA synthesis by 58% (both at P < 0.01).

CONCLUSIONS

These results indicate that 4 cardiac hormones have potent beneficial effects by increasing cell death in up to 71% of melanoma cells within 24 hours mediated in part by a 73% decrease in their DNA synthesis.

Vasoactive peptides in cardiovascular (patho)physiology

Numerous vasoactive agents play an important physiological role in regulating vascular tone, reactivity and structure. In pathological conditions, alterations in the regulation of vasoactive peptides result in endothelial dysfunction, vascular remodeling and vascular inflammation, which are important processes underlying vascular damage in cardiovascular disease. Among the many vasoactive agents implicated in vascular (patho)biology, angiotensin II (Ang II), endothelin (ET), serotonin and natriuretic peptides appear to be particularly important because of their many pleiotropic actions and because they have been identified as potential therapeutic targets in cardiovascular disease. Ang II, ET-1, serotonin and natriuretic peptides mediate effects via specific receptors, which belong to the group of G-protein-coupled receptors. ET, serotonin and Ang II are primarily vasoconstrictors with growth-promoting actions, whereas natriuretic peptides, specifically atrial, brain and C-type natriuretic peptides, are vasodilators with natriuretic effects. Inhibition of vasoconstrictor actions with drugs that block peptide receptors, compounds that inhibit enzymes that generate vasoactive peptides or agents that increase levels of natriuretic peptides are potentially valuable therapeutic tools in the management of cardiovascular diseases. This review focuses on ET, natriuretic peptides and serotonin. The properties and distribution of these vasoactive agents and their receptors, mechanisms of action and implications in cardiovascular (patho)physiology will be discussed.

Urodilatin and four cardiac hormones decrease human renal carcinoma cell numbers

BACKGROUND

Mortality from renal-cell cancer remains a significant problem with an estimated 12,600 deaths in the United States in 2005 even with current treatment(s) of surgery, chemotherapy, radiation and immunotherapy. Four cardiac natriuretic peptides, that is, atrial natriuretic peptide, vessel dilator, long-acting natriuretic peptide and kaliuretic peptide have significant anti-cancer effects in breast, pancreatic, prostate and colon adenocarcinomas.

MATERIALS AND METHODS

These four peptide hormones plus brain natriuretic peptide (BNP), C-natriuretic peptide (CNP) and urodilatin, a peptide hormone formed in the kidney by a different post-translational processing of the atrial natriuretic peptide prohormone, were evaluated for their anti-cancer effects in renal carcinomas.

RESULTS

Dose-response curves revealed a significant (P < 0.0001) decrease in human renal carcinoma cells with each 10-fold increase in concentration from 1 microm to 100 microm of five of these peptide hormones. There was an 81%, 74%, 66%, 70% and 70% elimination within 24 h in renal carcinoma cells secondary to vessel dilator, kaliuretic peptide, urodilatin, atrial natriuretic peptide and long-acting natriuretic peptide, respectively (P < 0.0001 for each), whereas BNP had no effect and CNP decreased renal cancer cell number by 10% (P = 0.04) at their 100 microm concentrations. Three days after treatment with these peptide hormones, the cancer cells began to proliferate again. The four cardiac hormones and urodilatin decreased DNA synthesis from 65-84% (P < 0.00001), whereas BNP and CNP decreased DNA synthesis 3% and 12% (both non-significant). Western blots revealed for the first time natriuretic peptide receptors (NPR)-A, -B and -C were present in the renal cancer cells.

CONCLUSIONS

These results indicate that urodilatin and the four cardiac hormones have potent anti-cancer effects by eliminating up to 81% of renal carcinoma cells within 24 h of treatment.

Long-acting natriuretic peptide, vessel dilator, and kaliuretic peptide enhance urinary excretion rate of albumin, total protein, and beta(2)-microglobulin in patients with congestive heart failure

BACKGROUND

Albumin excretion is increased in persons with congestive heart failure (CHF), but the mechanism of this increase is unknown. Atrial natriuretic peptide (ANP) does not correlate with this albumin excretion, but the other 3 cardiac hormones derived from the ANP prohormone have never been investigated as to whether they can enhance albumin and/or protein excretion in persons with CHF.

METHODS AND RESULTS

Long-acting natriuretic peptide (LANP), vessel dilator, and kaliuretic peptide (100 ng/kg body weight/min) given intravenously for 60 minutes to NYHA Class III CHF patients (n = 24) increased the albumin excretion rate 2- to 7-fold (P <.001) and total protein excretion rate 2- to 5-fold (P <.001). These peptide hormones similarly enhanced beta(2)-microglobulin, a specific marker of proximal tubular reabsorption, excretion rate 25- to 40-fold (P <.0005) at the end of their respective infusions. Three hours after stopping their respective infusions, the beta(2)-microglobulin excretion rate was still 11- to 33-fold (P <.0005) increased.

CONCLUSIONS

LANP, vessel dilator, and kaliuretic peptide each enhance albumin and total protein excretion in persons with CHF. Part of the mechanism of this enhanced protein excretion is the inhibition of proximal tubular reabsorption of protein as shown by the beta(2)-microglobulin data.

N-terminal fragments of the proatrial natriuretic peptide in patients before and after hemodialysis treatment

BACKGROUND

Fragments derived from the prohormone of alpha-human atrial natriuretic peptide (alpha-ANP) in patients with cardiac failure are more closely related to the disease state than intact alpha-ANP.

METHODS

Specific immunoassays have been developed to detect proANP 1-30, proANP 31-67, and proANP 1-98. Plasma concentrations of these fragments were determined in 122 hemodialysis patients with and without cardiac dysfunction, with and without hypertension, as well as with and without dialysis-associated hypotensive episodes either before or after a regularly scheduled hemodialysis session. The effects of different dialyzer membranes were also evaluated. The results of these assays along with other markers of volume regulation such as alpha-ANP and cyclic 3',5' guanosine monophosphate (cGMP) were compared with those of healthy controls.

RESULTS

Predialytic and postdialytic plasma concentrations of the proANP fragments were markedly higher in uremic patients than in controls (98-fold for proANP 1-98, 56-fold for proANP 31-67, and 35-fold for proANP 1-30). All proANP fragments, alpha-ANP, and cGMP decreased during hemodialysis. A strong linear correlation was found between predialytic and postdialytic plasma levels. There was no correlation, however, with the amount of fluid removed during hemodialysis. Patients with altered left ventricular hemodynamics displayed significantly higher plasma concentrations of all proANP fragments and alpha-ANP, but not cGMP, than patients with normal cardiac function. Hemodialysis patients with moderate or severe hypertension had higher concentrations of proANP fragments, alpha-ANP, and cGMP than patients with normal blood pressure or patients with only mild hypertension. There was no significant difference in circulating levels of proANP peptides, alpha-ANP, and cGMP between patients with and without frequent dialysis-associated hypotensive episodes. Cellulose-triacetate dialyzers reduced plasma levels of proANP 1-30, proANP 31-67, and proANP 1-98 significantly more than polysulfone dialyzers, but alpha-ANP and cGMP levels were not different.

CONCLUSIONS

Circulating alpha-ANP and proANP fragments are influenced by a variety of factors such as end-stage renal disease, hemodialysis treatment, dialyzer membrane material, cardiac dysfunction, and hypertension. Therefore, these are not useful markers to accurately estimate volume status in hemodialysis patients.

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.

Elevated atrial natriuretic peptides and early renal failure in type 2 diabetic Goto-Kakizaki rats

The present investigation was designed to determine if atrial natriuretic peptides (ANPs) are increased in a spontaneous model of non-obese type 2 diabetes, the Goto-Kakizaki (GK) rat. Four peptide hormones originating from the ANP prohormone were increased twofold (P < .05) to sixfold (P < .01) in the circulation of GK rats compared with nondiabetic Wistar rats from which the GK colony was originally derived. Thus, ANP, long-acting natriuretic peptide (LANP), vessel dilator, and kaliuretic peptide were (mean +/- SE) 497 +/- 78, 1,285 +/- 105, 457 +/- 45, and 385 +/- 87 pg/mL in GK rats, versus 78 +/- 23, 542 +/- 77, 137 +/- 26, and 134 +/- 33 pg/mL, respectively, in Wistar rats. In evaluating the cause of the increased ANPs, the blood volume of GK rats (16.2 +/- 0.4 mL) was significantly (P < .01) increased compared with Wistar rats (9.5 +/- 0.3 mL). The ventricles of GK rats were not dilated when examined by transthoracic echocardiography, but the venous system was markedly distended. GK rats had a 48% to 79% decrease in renal function (ie, increased serum creatinine and blood urea nitrogen [BUN]) compared with Wistar rats. These results indicate that circulating ANPs are increased in the GK spontaneously diabetic rat secondary to (1) increased blood volume, which leads to increased synthesis and release of ANPs, and (2) renal failure, which results in a delayed metabolic processing of these peptides. The early combined increases of the four atrial peptides collectively may contribute to the hyperfiltration that occurs in early diabetes mellitus.

Environmental upregulation of the atrial natriuretic peptide gene in the living fossil, Limulus polyphemus

Northern blot analysis revealed that atrial natriuretic peptide (ANP) gene expression occurs in heart, hematocytes and gills of the invertebrate Limulus polyphemus, the horseshoe crab. In low salinity and on land ANP prohormone messenger RNA in Limulus' heart was 32-fold less compared to that in a vertebrate heart (i.e., rat, Rattus norvegicus). ANP gene expression doubled (P < 0.05) in Limulus' heart and gills with change from land and low salinity to medium salinity and osmolality. ANP gene expression was 10-fold higher in Limulus' gills in seawater (i.e., high salinity). The products of this ANP gene expression (i.e., ANP, long acting natriuretic peptide, vessel dilator and kaliuretic peptide) were released and increased in the circulation, i.e., hemolymph, of Limulus proportional to the increase in salinity and osmolality (P = <0.01). These results suggest that modification of ANP gene expression enables animals to adapt to freshwater, seawater, and land.

Atrial natriuretic peptides increase calcitonin gene-related peptide within human circulation

Long-acting natriuretic peptide (LANP), vessel dilator, and atrial natriuretic factor (ANF) (each infused at 100 ng/kg body weight [BW].min for 60 minutes) increased the circulating concentration of calcitonin gene-related peptide (CGRP) threefold to fourfold in 30 healthy humans. Within 30 minutes of stopping ANF infusion, the CGRP circulating concentration had returned to preinfusion levels, whereas its increase secondary to the other atrial peptides was still significant 2 to 3 hours after cessation of their infusions. There was a 50% decreased excretion (P < .001) of CGRP into the urine secondary to LANP and vessel dilator, which correlated with the increase of CGRP in the circulation. The ANF-induced 50% decreased CGRP excretion occurred after the circulating concentration of CGRP had returned to preinfusion levels. Kaliuretic peptide did not affect CGRP circulating concentration or excretion into urine. These data suggest that LANP and vessel dilator inhibit the metabolic breakdown of CGRP as part of their mechanism of increasing CGRP in plasma, whereas the ANF effect of increasing CGRP in plasma appears to be secondary to stimulating the release of CGRP.

Pheochromocytoma in dogs and cats

Pheochromocytomas are endocrine tumors arising from chromaffin cells (pheochromocytes) of the adrenal glands in dogs and cats. The clinical symptomatology produced results from the direct presence and space-occupying nature of the tumor, or the secondary presence of excessive amounts of excreted catecholamines. Diagnosis and management of pheochromocytomas remain great challenges for veterinary clinicians. The diagnosis is based on the results of supporting routine lab evaluation, blood-pressure determinations, selected biochemical and pharmacologic tests, and a number of imaging techniques. Surgical extirpation continues to be the only definitive treatment for the pheochromocytoma. Medical therapy is used to stabilize the metabolic and cardiovascular states of the patient in a preoperative and surgical setting as well as to manage chronic long-term effects of excess catecholamines in patients with inoperable or metastatic disease.

Atrial natriuretic peptide increases adrenomedullin in the circulation of healthy humans

Adrenomedullin (ADM) is a new 52 amino acid peptide originally isolated from extracts of human pheochromocytoma. ADM's biologic properties are nearly identical to those of atrial natriuretic peptides. Thus, the 4 peptide hormones originating from amino acids 1-30 [long acting natriuretic peptide], 31-67 [vessel dilator], 79-98 [kaliuretic peptide] and 99-126 [atrial natriuretic factor; ANF] of the 126 amino acid ANF prohormone as well as ADM have blood pressure lowering and diuretic properties. The present investigation was designed to determine if one or more of these 4 atrial natriuretic peptides increase adrenomedullin within the circulation of healthy humans. Infusion of 100 ng/kg body weight/minute for 60 minutes of the respective atrial peptides resulted in a 4-fold (P < 0.001) increase in the circulating concentration of adrenomedullin secondary to the ANF infusion but no increase in adrenomedullin with the long acting natriuretic peptide, vessel dilator, or kaliuretic peptide infusions. The four-fold increase of adrenomedullin in the circulation persisted throughout the infusion of ANF, but returned to pre-infusion levels within 30 minutes of stopping the ANF infusion. Infusion of 10 pg/kg body weight/minute for 60 minutes of ANF resulted in a 2 1/2-fold increase (P < 0.05) in the circulating concentration of adrenomedullin. There was a significant (P < 0.01) diuresis and blood pressure lowering effect with each of the atrial natriuretic peptides in the present investigation. This investigation suggests that 1) atrial natriuretic factor increases the release of adrenomedullin and 2) that the diuretic and blood pressure lowering effects previously attributed to atrial natriuretic factor may be partially due to adrenomedullin since both increased during the ANF infusion and both have similar biologic effects. As opposed to atrial natriuretic factor, adrenomedullin was not increased by long acting natriuretic peptide, vessel dilator, or kaliuretic peptide suggesting that their biologic effects do not involve adrenomedullin.

Atrial natriuretic peptides and cyclic guanosine monophosphate metabolism

Atrial natriuretic factor (ANF), consisting of amino acids 99-126 of the 126 amino acid ANF prohormone, increases cyclic guanosine monophosphate (GMP) (thought to be the mediator of its physiologic effects) in plasma and urine of human subjects. Long-acting natriuretic peptide, vessel dilator, and kaliuretic peptide, consisting of amino acid 1-30, 31-67, and 79-98, respectively, of this same prohormone have natriuretic, diuretic, kaliuretic, and blood pressure lowering properties in humans. These three new peptide hormones increase cyclic GMP in vitro but were never investigated to determine whether they also cause extrusion of cyclic GMP from cells, resulting in an increase of cyclic GMP in plasma and/or urine. Infusion of each of these peptide hormones at their 100 ng/kg body weight/min concentrations for 60 minutes into healthy humans resulted in a sevenfold increase in cyclic GMP in plasma and urine secondary to ANF, but no significant increase secondary to the other atrial peptide hormones. Based on the current data, ANF has a unique effect on the metabolism of cyclic GMP, causing it to be extruded from the cell, whereas the other three atrial peptides represent the more classical metabolism of cyclic GMP via cyclic GMP phophodiesterases.

Blood pressure and atrial natriuretic peptides correlate throughout the day

Vessel dilator consisting of amino acids (a.a.) 31-67 and atrial natriuretic factor (ANF) composed of a.a. 99-126 of the 126 a.a. ANF prohormone circulate in humans and have potent vasodilatory properties. To determine whether these atrial natriuretic peptides are directly related to blood pressure in healthy normotensive humans, we recently had the unique opportunity to examine the circadian rhythms of vessel dilator, ANF, and blood pressure in seven individuals in 1988 and again in 1993. The changes in mean arterial pressure and systolic and diastolic blood pressure in these individuals during this 5-year hiatus allows comparison in the same individual, if circulating concentrations of atrial natriuretic peptides directly correlate with naturally occurring changes in blood pressure. In both 1988 and in 1993 vessel dilator and ANF each had significant (p < 0.001) circadian rhythms with their peak concentrations at 4:00 AM being nearly twice their concentrations at 4:00 PM. Mean arterial pressure, systolic blood pressure, and diastolic blood pressure also had significant circadian rhythms with peaks and troughs that were exactly opposite to those of ANF and vessel dilator. A significant inverse correlation between 24-hour averages of mean arterial blood pressure and 24-hour averages of vessel dilator (p = 0.05) and ANF (p = 0.02) was also found. These data suggest that vessel dilator and ANF are important for the maintenance of blood pressure within the normotensive range.

Temporal (circadian) and functional relationship between atrial natriuretic peptides and blood pressure

Long-acting natriuretic peptide, vessel dilator, and atrial natriuretic factor consisting of amino acids (a.a.) 1 to 30, 31 to 67, and 99 to 126 of the 126-a.a. atrial natriuretic factor (ANF) prohormone, respectively, circulate in humans and have potent vasodilatory properties. To determine if these atrial natriuretic peptides are directly related to blood pressure in clinically healthy normotensive humans, we obtained 24-h profiles of vessel dilator, long-acting natriuretic peptide, ANF, and blood pressure in 10 men in 1988 and 11 men in 1993 (seven men were studied twice) to compare circulating concentrations of atrial natriuretic peptides with naturally occurring changes in blood pressure. Overall, vessel dilator, long-acting natriuretic peptide, and ANF each had significant (p<0.001) circadian rhythms, with peak concentrations late during sleep (at 04:00 h) being nearly twice their concentrations in the afternoon and evening. This high-amplitude circadian change allowed for the refinement of normal limits for ANF peptides by computing 3-hourly tolerance intervals (chronodesms) against which to compare time-specified single samples for normality. Systolic, diastolic, and mean arterial blood pressure also had significant circadian rhythms (p<0.001) with peaks and troughs that were exactly opposite those of the ANF peptides. In addition to this inverse temporal relationship, there was a significant inverse correlation between absolute values for blood pressure and each ANF peptide (p<0.001), implying a functional relationship. These data suggest that in addition to other well-established neurochemical factors, the ANF peptides (vessel dilator, long-acting natriuretic peptide, and ANF) are important for the maintenance of blood pressure and modulation of its circadian rhythm.

Atrial natriuretic hormones originating from the N-terminus of the atrial natriuretic factor prohormone

1. Four peptide hormones consisting of amino acids 1-30 (Long Acting Sodium Stimulator), 31-67 (Vessel Dilator), 79-98 (Kaliuretic Stimulator) and 99-126 (atrial Natriuretic Factor [ANF]) originate from the same 126 amino acid ANF prohormone. 2. Each of these four peptide hormones circulates as a distinct peptide with vessel dilator and long acting sodium stimulator circulating at 10- to 24-fold higher concentrations than ANF while kaliuretic stimulator circulates at a three-fold higher concentration than ANF. 3. Each of these peptide hormones is released with an increase in central volume causing stretch of the atrium of the heart and with rapid heart beats greater than 125 beats/min. 4. Each of these peptide hormones lowers blood pressure, causes a diuresis and enhances sodium and/or potassium excretion. 5. In disease states which retain sodium and water such as congestive heart failure (CHF), each of these atrial peptides increases in the circulation proportionately to the severity of sodium retention, but of the radioimmunoassays to each of these hormones only the vessel dilator radioimmunoassay differentiates between mild (class I) CHF and healthy individuals.

Pheochromocytoma. Update on diagnosis, localization, and management

Pheochromocytoma, although rare, is associated with a high degree of morbidity and mortality if not recognized. A high degree of suspicion in patients with new-onset hypertension; hypertension with sudden worsening or development of diabetes mellitus; or a family history of MEN, neuroectodermal tumors, or simple pheochromocytoma should prompt biochemical confirmation with either 24-hour urine catecholamines (norepinephrine and epinephrine) or total MET (NMET plus MET). Following confirmation of the diagnosis, radiologic studies with CT and (if needed) MIBG are employed to localize the tumor. Surgical removal is the only definitive therapy. Medical management with alpha-blocking agents, to control symptoms and prevent a hypertensive crisis, is generally advocated for 2 weeks preoperatively and intraoperatively. Occasionally, beta-blockers, employed only after adequate alpha-blockade, are necessary to control tachycardia and tachyarrhythmias. High-dose MIBG and combination chemotherapy have been used adjunctively to treat malignant pheochromocytoma, although neither modality provides lasting satisfactory results. Normal urine assays performed 2 weeks postoperatively ensure the complete removal of all tumor. Additionally, lifelong follow-up (yearly initially) is necessary to detect any signs of benign recurrence or malignancy because these have been reported to occur as long as 41 years after the initial surgical resection. Biochemical evidence of excess catecholamine production usually precedes the clinical manifestations of catecholamine excess when these tumors recur.

Production of immunoreactive atrial natriuretic polypeptide in neuroendocrine tumors

BACKGROUND

Peptide hormone synthesis in neuroendocrine tumors is a well-recognized phenomenon. However, production in neuroendocrine tumors of atrial natriuretic polypeptide (ANP), a newly discovered peptide hormone from the heart, has not been studied extensively.

METHODS

The presence of immunoreactive human ANP (IR-hANP) in neuroendocrine tumors was determined using a specific human ANP radioimmunoassay. Neuroendocrine tumors examined included 9 small cell carcinomas of the uterus, 28 small cell carcinomas of the lung, 20 carcinoid tumors, 54 pancreatic endocrine tumors, 17 neuroblastic tumors, 14 pheochromocytomas, and 14 medullary carcinomas of the thyroid. Twenty atrial tissues also were examined as the control. Molecular size of IR-hANP in the extracts of atrial and tumor tissues was determined by gel chromatography.

RESULTS

IR-hANP was detected in the extracts of small cell carcinoma of the uterus, small cell carcinoma of the lung, and carcinoid tumor, with concentrations ranging from 3.1 to 210 ng/g wet weight tissue. No IR-hANP was detected in the extracts of pancreatic endocrine tumor, neuroblastic tumor, pheochromocytoma, and medullary carcinoma of the thyroid. The frequency of production of IR-hANP in neuroendocrine tumors was highest in small cell carcinoma of the uterus (44%), followed by small cell carcinoma of the lung (18%) and carcinoid tumor (15%). IR-hANP present in the extracts of small cell carcinomas of the uterus had molecular size heterogeneity, with three fragments in addition to alpha-, beta- and gamma-human ANP.

CONCLUSIONS

These results indicate that IR-hANP is produced by neuroendocrine tumors and that the molecular size of IR-hANP in tumor tissues is different from that in atrial tissues.

Normalization of circulating atrial natriuretic peptides in cardiac transplant recipients

To assess whether heart transplantation (Htx) alters the marked elevation of circulating atrial natriuretic peptides usually found in patients with congestive heart failure (CHF), 14 subjects (nine with compensated and five with decompensated CHF), each with an ejection fraction < or = 28%, were evaluated. Immediately before and hourly for the first 12 hours after Htx, then daily for 21 days and every 1 to 4 weeks for 6 months, the circulating concentrations of the N-terminus (pro atrial natriuretic factor [ANF] 1-98), midportion of the N-terminus (pro ANF 31-67), and C-terminus (that is, ANF) of the 126 amino acid prohormone were measured. Increased (p < 0.001) levels of these peptides were found in superior vena cava, right atrial, and peripheral venous samples 1 hour after Htx in all subjects except one. The atrial natriuretic peptide levels correlated only with right atrial pressure (p < 0.01) in the first 24 hours. Circulating concentrations of these peptides returned to those of healthy adults between 5 and 12 days after Htx in 11 out of 14 Htx recipients. Thus successful Htx can restore the elevated circulating concentrations of atrial natriuretic peptides to those of healthy adults.

Molecular forms of circulating atrial natriuretic peptides in human plasma and their metabolites

High performance gel permeation chromatography (HP-GPC) followed by four radioimmunoassays (RIAs) devised to amino acids (a.a.) 1-30, 31-67, 79-98, and 99-126 of the 126 a.a. atrial natriuretic factor (ANF) prohormone revealed that the proANF(1-30) assay immunoreactivity in plasma is 50% proANF(1-30) and 50% proANF(1-98). The HP-GPC evaluation of plasma followed by proANF(31-67) and ANF [i.e., proANF(99-126)] assays revealed that proANF(31-67) and ANF circulate as distinct peptides. the HP-GPC plasma examination followed by proANF(79-98) assay immunologically recognized three peaks in plasma consistent with proANF(1-98), -(68-98), and -(79-98). Similar HP-GPC evaluation of urine followed by these RIAs indicated that the proANF(1-30), -(79-98), and ANF assays only recognize 500 mol.wt. or less peptides, and the proANF(31-67) RIA recognizes a nearly intact proANF(31-67) with only two to three amino acids removed during processing of this peptide.

Atrial natriuretic peptides are present throughout the plant kingdom and enhance solute flow in plants

The present investigation was designed to 1) determine if atrial natriuretic-like peptides are present throughout the plant kingdom and 2) to determine if these peptides increase the flow of solute and/or water upward to leaves and flowers of plants. The 126-amino acid prohormone of atrial natriuretic factor (proANF)-(1-30), proANF-(31-67), and atrial natriuretic factor (ANF)-like peptides were present in the roots, stems, leaves, and flower petals of the more highly developed plants (Tracheophyta), with their highest concentrations being: Florida beauty > buddhist pine > Boston fern > rose = geranium = resurrection plant or club moss > Moses-in-the-cradle > Florida coontie. These peptides were also present in Bryophata (plants without vascular tissue or roots) and even in Euglena, flagellated chlorophyll-containing plants without leaves, stems, or roots. proANF-(1-30), proANF-(31-67), and proANF-(79-98) but not ANF (each at < 5.9 pg/ml) significantly increased (P < 0.001) the flow of colored water up stems, coloring their flowers 15-35 min earlier than the other one-half of the same flowers without exogenous peptide addition. These same peptides increased the rate of transpiration (i.e., loss of water from the leaves) and the absorption of solutions. High-performance gel permeation chromatography revealed that proANF-(1-30), proANF-(31-67), and ANF extracted from plants are very similar to their pure synthetic human sequences, with elution profiles and molecular weights of the plant extracts duplicating those of the pure synthetic peptides.

Atrial natriuretic factor prohormone peptides are present in a variety of tissues

Utilizing two sensitive and specific radioimmunoassays which immunologically recognize 1) the 98 amino acid (a.a.) N-terminus and 2) the 28 a.a. C-terminus (i.e., a.a. 99-126) of the 126 a.a. atrial natriuretic (ANF) prohormone, various tissues including aorta, kidney, small intestine, colon, liver, spleen, lung, and testis were investigated to determine if the ANF prohormone was present in any of these tissues in addition to its previously demonstrated presence in heart and brain. Aorta with 62.3 +/- 3 ng of the N-terminus/g of tissue and 51.6 +/- 1.8 ng of the C-terminus of the ANF prohormone/g of tissue had the highest concentration of the ANF prohormone of the previously undescribed ANF prohormone-containing tissues. The next highest concentration of the ANF prohormone was in the intestine, followed by lung and spleen. Pancreas, liver and kidney had similar levels of immunologically recognized ANF prohormone (approximately 1/50 of the aorta), while the testis and cerebrum had low levels. These results suggest that a much larger variety of tissues synthesize and/or store the ANF prohormone than is presently thought.

Weight reduction decreases the circulating concentration of the N-terminus of the ANF prohormone

The N-terminus of the atrial natriuretic factor (ANF) prohormone (ie, proANF 1-98) contains two vasodilatory peptides consisting of amino acids (aa): aa 1-30 (ie, proANF 1-30) and aa 31-67 (ie, proANF 31-67) of the 126 aa prohormone. The relationship of this N-terminus to the renin-aldosterone axis and blood pressure reduction was investigated in 18 obese subjects (5 hypertensive and 13 normotensive) placed on a 12-week, low sodium (40 mmol), weight reducing diet. The N-terminus of the ANF prohormone and proANF 31-67, which circulates as a distinct entity after being proteolytically cleaved from the N-terminus, were significantly (p less than 0.001) higher (767 +/- 1.01 and 816 +/- 135 fmol/ml) in the obese hypertensive group compared with the obese normotensive group (377 +/- 24 and 356 +/- 17 fmol/ml, respectively) prior to beginning the weight reduction program. There was a dramatic fall in the N-terminus and in proANF 31-67 after 1 week of weight reduction in both obese groups, which correlated with the decrease in mean arterial pressure during the first week and throughout the 12 weeks of weight reduction (r = .54, p less than 0.001 and r = .59, p less than 0.001, respectively). ProANF 1-98 had a significant (p less than 0.01) inverse correlation with plasma renin in both obese groups. ProANF 31-67, likewise, had an inverse correlation with plasma renin in the hypertensive (p less than 0.002), as well as the normotensive (p less than 0.03) subjects. ProANF 31-67 did not significantly correlate with aldosterone in either group.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise increases the circulating concentration of the N-terminus of the atrial natriuretic factor prohormone in normal individuals

Recently two peptides consisting of amino acids (aa) 1 to 30 and 31 to 67 of the N-terminus of the 126 aa prohormone of atrial natriuretic factor (proANF), as well as atrial natriuretic factor (ANF, aa 99 to 126; C-terminus), were found to have vasodilatory and natriuretic properties. These peptides, as well as ANF, circulate in humans as part of the N-terminus of the prohormone. To determine the effect of graded exercise on the circulating concentrations of the N-terminus and C-terminus of the ANF prohormone in normal persons, 12 healthy individuals (mean age 45 +/- 2 years) were evaluated before, for 2 hours after, and during bicycle exercise at a work loads of 25, 50, 75, 100, 125, 150, and 175 W. Both the N- and C-terminus of the ANF prohormone were released simultaneously with graded exercise in direct proportion to the intensity of the work load, measured objectively via maximal oxygen consumption (VO2max), respiratory quotient, and heart rate. Both the N-terminus and C-terminus of the ANF prohormone had strong positive correlations (p less than 0.001) with blood pressure, heart rate, VO2max, and respiratory quotient. Following exercise, the C-terminus returned to preexercise levels within 30 minutes, while the N-terminus remained significantly elevated at 30 and 60 minutes postexercise, reflecting the longer half-life of the N-terminus in the circulation.

Aprotinin blocks the binding of pro atrial natriuretic peptides 1 to 30, 31 to 67, and 99 to 126 to human placental membranes

Two peptides with natriuretic and diuretic properties consisting of amino acids 1 to 30 and 31 to 67 of the 98 amino acid N-terminal end of the prohormone of atrial natriuretic factor, which normally circulates in humans, were investigated to determine if they have specific binding sites of placental membranes. Competitive binding experiments revealed that atrial natriuretic peptides 1 to 30, 31 to 67, and 99 to 126 (i.e., C-terminus) each had specific and separate binding sites. The dissociation constants for atrial natriuretic peptides 1 to 30, 31 to 67, and 99 to 126 binding to human placental membranes were similar at 4.3 +/- 0.6 nmol/L, 3.1 +/- 0.4 nmol/L, and 2.9 +/- 0.5 nmol/L, respectively. Each peptide bound to the placental membranes between 10(-8) and 10(-11) mol/L but could bind to the other peptides' receptors only at supraphysiologic concentrations of 10(-6) and 10(-7) mol/L. The protease inhibitor aprotinin (50 micrograms/ml) blocked the binding of the atrial natriuretic peptides 1 to 30, 31 to 67, and 99 to 126 to their respective receptors. These results suggest that atrial natriuretic peptides 1 to 30 and 31 to 67 do not work through the atrial natriuretic factor receptor but rather have their own separate and distinct receptors on placental membranes and that the protease inhibitor aprotinin antagonizes their respective binding to placental membranes, suggesting that integral membrane proteases may be modulators of atrial natriuretic peptides receptor function.

Atrial natriuretic peptide hormonal system in plants

To determine if atrial natriuretic peptides are present in plants as well as animals, where they are important for water and sodium metabolism, the leaves and stems of the Florida Beauty (Dracena godseffiana) were examined. The N-terminus consisting of amino acids (a.a.) 1-98 (i.e., pro ANF 1-98), the mid portion of the N-terminus (a.a. 31-67; pro ANF 31-67), and C-terminus (a.a. 99-126; ANF) of the 126 a.a. atrial natriuretic factor (ANF) prohormone were all present in the leaves and stems of this plant. The concentrations of pro ANF 1-98, pro ANF 31-67 and ANF-like peptides of 120 +/- 20, 123 +/- 21, and 129 +/- 20 ng/g of plant tissue in leaves and 109 +/- 20, 96 +/- 21, and 124 +/- 18 ng/g of tissue, respectively, in the stems were lower (P less than 0.05) than their concentrations in rat (Rattus norvegicus) heart atria of 196 +/- 40, 192 +/- 28, and 189 +/- 15 ng/g of tissue respectively, but higher (P less than 0.001) than their respective concentrations of 4.3 +/- 1.4, 4.1 +/- 1.2, and 3.9 +/- 1 ng/g of rat heart ventricular tissue. We conclude that the atrial natriuretic peptide-like hormonal system is present in the plant kingdom as well as in the animal kingdom.

The N-terminal and C-terminal portions of the atrial natriuretic factor prohormone increase during preeclampsia

The influence of preeclampsia on the circulating concentrations of the 28-amino-acid carboxy terminus (C-terminus) (i.e., atrial natriuretic factor) and the amino terminus (N-terminus) of the 126-amino-acid atrial natriuretic factor prohormone (pro ANF) was studied in the third trimester with the use of three specific radioimmunoassays that recognize: (1) atrial natriuretic factor (i.e., amino acids 99 to 126), (2) the whole 98-amino-acid N-terminus, and (3) amino acids 31 to 67 from the midportion of the N-terminus of the prohormone. The C-terminus was significantly increased (p less than 0.001) in the third trimester in women with preeclampsia, the mean +/- SEM of 15 subjects was 150 +/- 7 pg/ml versus 89 +/- 7 pg/ml in the third trimester in 12 women during normal pregnancies and 65 +/- 2 pg/ml in 19 healthy nonpregnant women. The whole 98-amino-acid N-terminus, likewise, was significantly increased (p less than 0.001) in women with preeclampsia to 4706 +/- 629 pg/ml versus 2160 +/- 79 pg/ml in women in the third trimester of normal pregnancies and versus the circulating concentration of 1847 +/- 127 pg/ml in healthy nonpregnant women. ProANF 31 to 67 mean circulating concentration in preeclampsia was 4638 +/- 725 pg/ml, which was also significantly (p less than 0.001) increased compared with its mean circulating concentration in the third trimester of normal pregnancy of 1758 +/- 83 pg/ml or that in healthy nonpregnant women (1400 +/- 105 pg/ml). The circulating concentrations of both the N-terminus and C-terminus of the atrial natriuretic factor prohormone decreased within 24 hours after delivery in contrast to a normal pregnancy in which they both increase post partum. These results indicate a marked difference in the metabolism of both the N-terminus and the C-terminus of the atrial natriuretic factor prohormone in women with preeclampsia versus that in women with normal pregnancies or that in healthy nonpregnant women.

The N-terminus, C-terminus, and vessel dilator of the ANF prohormone are present in the urine and increase with ventricular fibrillation

The N-terminus consisting of amino acids (a.a.) 1-98 (i.e., proANF 1-98), C-terminus (i.e., ANF; a.a. 99-126) and midportion of N-terminus consisting of a.a. 31-67 (proANF 31-67; Vessel Dilator) of the 126 a.a. ANF prohormone were present in the urine in 5-to-8-fold increased concentrations versus their plasma concentrations in 6 dogs under basal conditions. With acute coronary occlusion the right atrial plasma concentrations of these peptides increased two-to-three-fold, while in the urine only proANF 31-67 increased (3.5-fold). Ventricular fibrillation caused a 4-to-10-fold increased secretion into the right atrial chamber with a simultaneous 3-to-4.7-fold increase in the urine of proANF 1-98, proANF 31-67, and ANF. This investigation demonstrates that proANF 1-98, proANF 31-67 and ANF are normally present in urine and increase in the urine with cardiac stimuli that cause their release from the heart.