Atrial-specific granule number and plasma atrial natriuretic peptide in rats: effects of beta-adrenoceptor blockade and sodium intake

Comparison of ANP and BNP Granular Density in Atria of Rats After Physiological and Pathological Hypertrophy

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones located in atria granules. Both peptides respond to cardiac pressure and volume dynamics and accordingly serve as translation biomarkers for the clinical treatment of heart failure. Serum ANP and BNP play central secretary roles in blood pressure and cardiac output regulation and have proven utility as differential biomarkers of cardiovascular proficiency and drug-induced maladaptation, yet both peptides are impervious to exercise-induced hypertrophy. We employed immunoelectron microscopy to examine the effects of 28 days of chronic swim exercise or administration of a PPARγ agonist on atrial granules and their stored natriuretic peptides in Sprague Dawley rats. Chronic swimming and drug treatment both resulted in a 15% increase in heart weight compared with controls, with no treatment effects on perinuclear granule area in the left atria (LAs). Drug treatment resulted in larger size granules with greater BNP density in the right atria. Comparing swimming and PPARγ agonist treatment effects on ANP:BNP granule density ratios between atrial chambers revealed a shift toward a greater proportion of ANP than BNP in LAs of swim-trained rats. These data suggest a distinction in the population of ANP and BNP after chronic swim or PPARγ that makes it a novel metric for the differentiation of pathological and physiological hypertrophy.

Atrial natriuretic peptide (ANP)-granules in the guinea pig atrial and auricular cardiocytes: an immunocytochemical and ultrastructural morphometric comparative study

The atrial natriuretic peptide (ANP) is a peptide hormone that is mainly produced in the cardiac atria, where it is stored within granules. It is known that the four regions of the atrial-auricular complex (two atria and two auricles) produce and store ANP in the granules. However, no report has been presented comparing the presence of ANP, and the number and diameter of atrial granules in the atria and auricles. ANP immunoreactivity was detected in cardiocytes from the four regions of the atrial-auricular complex. No differences were observed among the regions. The number of granules was greatest in the right atrium followed by the left atrium and left auricle and right auricle, in this order. The diameter of granules in the cardiocytes was significantly largest in the right atrium and reduced via the left auricle to the left atrium and right auricle. Both the number and diameter of the granules are larger in the right atrium in comparison with the other regions of the atrial-auricular complex, which leads to the supposition that this region is the one that most synthesizes and stores the ANP.

Is there a link between salt-intake and atrial natriuretic peptide system during hypertension induced by nitric oxide blockade?

Long-term nitric oxide (NO) blockade is known to induce a severe and progressive hypertension. The influence of the salt-intake on atrial natriuretic peptide (ANP) system in this hypertension model is unknown. The aim of this study was to evaluate ANP plasma levels, content and mRNA in atria of male Wistar rats chronically treated with oral Nomega-nitro-L-arginine methyl ester (L-NAME) after 4 weeks of high-salt diet. The high-salt diet induced an increase (P < 0.05) in ANP plasma levels in normotensive rats and no significant changes in hypertensive animals. We observed a significant increase in the ANP content in the left and right atria of hypertensive rats (P < 0.001) when compared to normotensive ones. However, no significant changes were observed during high-salt diet in normotensive and hypertensive animals. Northern blot analysis revealed that ANP gene expression is higher in the right and left atria of hypertensive rats when compared to normotensive rats. However, we found no significant changes in ANP mRNA of rats treated with high-salt diet in normotensive and hypertensive rats when compared to low-salt diet. The present observations indicate no interaction between salt-intake and activation of the ANP system during chronic nitric oxide synthase (NOS) inhibition.

Potential mechanisms for functional changes in taste receptor cells following sodium deficiency in mammals

Sodium is an essential nutrient for life, and its level in the body is tightly regulated. When sodium deficient, some mammals alter their behavior towards salt by avidly consuming it, even at concentrations animals typically choose to avoid. This change in acceptance is accompanied by a reduction in the response of the gustatory chorda tympani nerve to sodium solutions. More specifically, the response rate of the sodium-specialist units to NaCl stimulation is reduced following sodium deficiency or adrenalectomy. The initial transduction of the chemical signal is mediated, in part, by Na+ influx through epithelial Na+ channels in the apical membrane of taste cells that synapse with the specialist neurons. Circulating hormones like angiotensin II and adrenocorticotropin hormone, which are released in response to sodium deficiency and adrenalectomy, could regulate the activity of Na+ channels through G-protein linked second-messenger systems. These putative pathways are of interest because they have been described in mammalian taste receptor cells. The present review will summarize evidence linking some hormones of fluid homeostasis with the apparent attenuation of input from sodium-specialist neurons.

Distribution of immunoreactive atrial and brain natriuretic peptides in the heart of the chicken, quail, snake and frog

The distribution of atrial natriuretic peptide (ANP)- and brain natriuretic peptide (BNP)-granules was examined immunohistochemically and ultrastructurally in the hearts of the chicken, Japanese quail, Japanese rat snake and bull-frog. Moreover, natriuretic peptide (NP)-granules in the cardiocytes were analyzed by ultrastructural morphometry. Immunohistochemically, ANP-immunoreactivity (IR) was not detected in any cardiocytes, but BNP-IR was detectable in most atrial and ventricular cardiocytes of both chicken and quail. In the snake, ANP-IR was seen in most atrial and ventricular cardiocytes, which showed traces and negative in BNP-IR, respectively. Both ANP- and BNP-IR were detected in the atrial and ventricular cardiocytes in the frog. Ultrastructurally, most of NP-granules were found in the perinuclear region in the chicken, quail and snake atrium, but the frog atrial cardiocytes had granules generally dispersing widely in the cell. By ultrastructural morphometry, the number of granules in the atrial cardiocyte was greatest in the frog, followed by the snake, and chicken or quail, in this order. The diameter of granules in the atrial cardiocyte was largest in the snake and reduced via the frog to the chicken or quail. In the ventricular cardiocytes of all species, the number and size of granules were significantly less than that in the atrial ones. These results indicated that the hearts of the chicken and quail contain only BNP, and that there are two different natriuretic peptides, ANP and BNP, in the snake and frog hearts.

Morphometric analysis of atrial natriuretic peptide-containing granules in atriocytes of rats with experimental congestive heart failure

The morphometric characteristics of atrial natriuretic peptide-containing granules were studied in atrial myoendocrine cells of rats with aorto-caval fistula, an experimental model of congestive heart failure. A total of 6680 granules of control and aorto-caval rats were analyzed by a computerized image analysis system that evaluated the number and sectioned surface area of granules and their subcellular location. Compared with control animals, rats with congestive heart failure displayed a slight increase in the number of peripheral granules, adjacent to the sarcolemma, but not centrally located in the Golgi areas. The mean sectioned surface area of granules in rats with congestive heart failure was about 50% of that in controls, both in the right and left atria. Rats with aorto-caval fistula had a higher percent of small granules and lower percent of large granules compared with controls. The data demonstrate different morphometric characteristics in atrial natriuretic peptide-containing granules in atriocytes in rats with experimental congestive heart failure; this may reflect the enhanced synthesis and release of atrial natriuretic peptide in heart failure.

Short term effects of acute inhibition of the angiotensin-converting enzyme on the renin-angiotensin system and plasma atrial natriuretic peptide in healthy dogs fed a low-sodium diet versus a normal-sodium diet

The purpose of the present study was to quantify some of the short term responses of the renin-angiotensin system (RAS) to a recommended dosage of the angiotensin-converting enzyme inhibitor enalapril in clinically healthy dogs fed a normal-sodium and a low-sodium diet. A single dose of enalapril (0.5 mg/kg PO) was given to eight clinically healthy male Beagle dogs after a period where the dogs were fed a normal-sodium diet and low-sodium diet, respectively. Serum angiotensin-converting enzyme activity (ACE), plasma renin activity (PRA), plasma aldosterone concentration (PAC), and plasma atrial natriuretic peptide (ANP) concentration were measured during the following twenty-four hour period. The data indicate that enalapril induced a potent blockade of the renin-angiotensin system (RAS) for at least twenty-four hour. Specifically, enalapril during low-sodium diet elicited an exaggerated increase in PRA and a diminished decrease in ACE and ANP when compared to the results of the drug during normal-sodium diet. Long term controlled studies of enalapril in dogs with congestive heart failure (CHF) are warranted in order to determine the duration of action and optimal dose of enalapril.

Selective alpha-1 adrenoceptor blockade and renal sodium handling in humans

In animal studies, acute interruption of the activity of renal alpha-1 adrenoceptors by renal denervation results in an increase in sodium and water excretion. Chronic selective blockade of alpha-1 adrenoceptors by prazosin in clinical practice has been associated with sodium retention, however. Previous studies in the authors' laboratory using chronic alpha-1 blockade in the rat have demonstrated a decreased ability to excrete a saline load. Therefore, the authors determined the effect of chronic selective alpha-1 adrenoceptor blockade with prazosin in eight healthy volunteers. Volunteers underwent a water load to establish a water diuresis, followed by a modest saline load using intravenous saline (0.9% NaCl). This experimental protocol was repeated after four weeks of prazosin therapy (5 mg twice daily). Prazosin failed to alter body weight (73.6 +/- 4.2 versus 74.5 +/- 4.1 kg, expressed as mean +/- standard error), mean blood pressure (86.7 +/- 2.7 versus 84.7 +/- 2.3 mm Hg), creatinine clearance (127.0 +/- 8.5 versus 133.4 +/- 12.0 mL/min), renal blood flow as measured by para-aminohippurate clearance (1202 +/- 88 versus 1175 +/- 69 mL/min) and the 24-hour sodium excretion (115 +/- 11 versus 128 +/- 19 mmol). In the presence of the experimentally induced saline load, chronic prazosin treatment was associated with a decreased free water clearance (e.g., hour 3, 7.8 +/- .7 versus 6.3 +/- 2.0 mL/min; P < or = .05) and fractional excretion of sodium (e.g., hour 3, 1.48 +/- .10 versus 1.15 +/- .13; P < or = .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic factor in cats subjected to acute myocardial ischaemia

Eighteen anaesthetized open chest cats were subjected to 10, 30, or 50 min occlusion of the left anterior descending coronary artery (LAD). Heart rate, left ventricular end-diastolic (LVEDP) and systolic pressure (LVSP), and dp/dt were continuously recorded during the experiments. Prior to LAD-occlusion, and just before termination of the experiments, blood samples were collected from the left femoral artery for measurements of atrial natriuretic factor (ANF), catecholamines, electrolytes, urea, and creatinine. Simultaneously, biopsies were collected from the right auricular wall. The tissue was embedded in Lowicryl K4M, and ultrathin sections were incubated with anti-ANF antibodies and secondary antibodies conjugated to gold particles. The density of ANF-containing atrial-specific granules labelled with gold particles was morphometrically calculated. LVEDP increased significantly in all three time groups, and when pooling the pre- and postocclusion values, there was an increase from 5.1 +/- 0.4 to 10.3 +/- 1.2 mmHg (p < 0.05). The noradrenaline level increased from 0.93 +/- 0.18 to 2.34 +/- 0.75 nmol l-1 (p < 0.05) after LAD-occlusion. Similarly, the mean plasma level of ANF in the 18 cats increased from 57.6 +/- 11.9 to 98.9 +/- 22.6 pmol l-1 (p < 0.05). Atrial granular density appeared to decline after 10 min of occlusion (from 0.141 +/- 0.017 to 0.127 +/- 0.022 granules-1 microns 2 sarcoplasm), and after 30 min there was a significant decrease (0.080 +/- 0.012 granules/microns 2, p < 0.05). However, after 50 min occlusion the granular density was almost restored (0.133 +/- 0.017 granules/microns 2). Plasma ANF showed a positive linear correlation to LVEDP and to the noradrenaline level.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term captopril in young and old patients with mild hypertension

The decrease in renal blood flow (RBF) observed in patients with hypertension can be increased with converting enzyme inhibition (CEI). It is unknown whether the decrease in RBF observed with age can also be increased with CEI. This study compared the short- and long-term effects of captopril monotherapy in young (less than 50 years) and old (greater than 65 years) hypertensive patients. Captopril effectively decreased blood pressure in both groups (diastolic blood pressure less than 90 mm Hg), with the young patients requiring a lower dose (.7 mg/kg) than the elderly patients (1.2 mg/kg). Creatinine and para-aminohippurate clearances were maintained in both groups, with a decrease in renal vascular resistance being observed in the younger patients. Serum aldosterone levels fell significantly after each dose of captopril at all phases of the study, with no change observed in plasma renin levels. Atrial natriuretic peptide (ANP) level was increased in the elderly patients receiving placebo (48.8 +/- 8 pg/mL) when compared with the young subjects (24 +/- 3.8 pg/mL). Captopril did not alter ANP levels in either group.