Plasma atrial peptide concentration during acute changes in cardiac filling pressure induced by a contrast agent

Unravelling the role of epigenetics in reproductive adaptations to early-life environment

Reproductive function adjusts in response to environmental conditions in order to optimize success. In humans, this plasticity includes age of pubertal onset, hormone levels and age at menopause. These reproductive characteristics vary across populations with distinct lifestyles and following specific childhood events, and point to a role for the early-life environment in shaping adult reproductive trajectories. Epigenetic mechanisms respond to external signals, exert long-term effects on gene expression and have been shown in animal and cellular studies to regulate normal reproductive function, strongly implicating their role in these adaptations. Moreover, human cohort data have revealed differential DNA methylation signatures in proxy tissues that are associated with reproductive phenotypic variation, although the cause-effect relationships are difficult to discern, calling for additional complementary approaches to establish functionality. In this Review, we summarize how adult reproductive function can be shaped by childhood events. We discuss why the influence of the childhood environment on adult reproductive function is an important consideration in understanding how reproduction is regulated and necessitates consideration by clinicians treating women with diverse life histories. The resolution of the molecular mechanisms responsible for human reproductive plasticity could also lead to new approaches for intervention by targeting these epigenetic modifications.

B-type natriuretic peptide and N-terminal pro B-type natriuretic peptide are depressed in obesity despite higher left ventricular end diastolic pressures

BACKGROUND

B-type natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) are frequently used in diagnosing and monitoring patients with heart failure. Recent studies have demonstrated that concentrations of these peptides are decreased in obese patients, but whether lower natriuretic peptide concentrations are really due to different hemodynamics is unknown. The relationship between these markers and left ventricular end diastolic pressure (LVEDP) in obesity has not been elucidated.

METHODS

We examined patients undergoing cardiac catheterization who had creatinine of < 2.0, no evidence of myocardial infarction or pulmonary embolism, and no cardiac transplant. Body mass index and LVEDP were determined, and BNP and NT-proBNP obtained at the start of each case. Obesity was defined as body mass index of > or = 30 kg/m2.

RESULTS

Of 203 patients enrolled, 101 were obese. The groups were similar in respect to race, creatinine, cholesterol, and history of dyslipidemia and cardiomyopathy. The obese patients tended to be younger, were more likely to have diabetes and hypertension, and were less likely to have coronary artery disease. The obese patients had higher LVEDP but reduced BNP and NT-pro-BNP. The relationship between the natriuretic peptides and LVEDP was poor, with r values of < 0.1.

CONCLUSIONS

Obese patients have reduced concentrations of BNP and NT-proBNP compared to nonobese patients despite having elevated LVEDP. This suggests that factors other than cardiac status impact on BNP and NT-proBNP concentrations. The poor relationship between natriuretic peptide concentrations and LVEDP also suggests that these concentrations should not be considered surrogates for cardiac filling pressures or volumes.

Stability of B-type natriuretic peptide levels during exercise in patients with congestive heart failure: implications for outpatient monitoring with B-type natriuretic peptide

BACKGROUND

B-natriuretic peptide (BNP), a neurohormone secreted from the cardiac ventricles, reflects left ventricular pressure and correlates to disease severity and prognosis. The fact that BNP levels can now be measured by a rapid assay suggests its potential usefulness in the outpatient clinic. However, if patient activity were to markedly alter BNP levels, its use would be less attractive for monitoring patients in the outpatient clinical setting.

METHODS

A total of 30 patients (10 normal, 10 New York Heart Association [NYHA] class I-II, 10 NYHA class III-IV) exercised with an upright bicycle protocol. Exercise was carried out to 75% of maximum heart rate, and venous blood was sampled before, immediately after, and 1 hour after completion of exercise. Plasma levels of BNP, epinephrine, and norepinephrine were measured.

RESULTS

BNP levels at baseline were 29 +/- 11 pg/mL for normal subjects, 126 +/- 26 pg/mL for NYHA I-II subjects, and 1712 +/- 356 pg/mL for NYHA III-IV subjects. The change in BNP levels with exercise was significantly lower than the change in epinephrine and norepinephrine (P <.001). In normal subjects, BNP increased from 29 pg/mL to 44 pg/mL with peak exercise, still within the range of normal (<100 pg/mL). This is compared with larger increases of norepinephrine (716 pg/mL to 1278 pg/mL) and epinephrine (52 pg/mL to 86 pg/mL) with exercise in normal subjects. There were also only small increases in BNP with exercise in patients with congestive heart failure (NYHA I-II, 30%; NYHA III-IV, 18%). For the same groups, epinephrine levels increased by 218% and 312%, respectively, and norepinephrine levels increased by 232% and 163%, respectively. One hour after completion of exercise, there were only minimal changes in BNP levels from baseline state in normal subjects (+0.9%) and patients with NYHA I-II (3.8%). In patients with NYHA III-IV, there was a 15% increase from baseline 1 hour after exercise.

CONCLUSIONS

BNP levels show only minor changes with vigorous exercise, making it unlikely that a normal patient would be classified as having congestive heart failure based on a BNP level obtained after activity. Prior activity should not influence BNP levels in patients with congestive heart failure. Therefore, when a patient presents to clinic with a marked change in their BNP level, it may reflect a real change in their condition.

Endothelin and atrial natriuretic peptide levels following radiocontrast exposure in humans

Radiocontrast exposure is associated with vasoconstriction of the renal vascular bed and, in certain circumstances, with acute renal failure. This may be influenced by the volume of contrast infused or underlying disease, such as diabetes or renal failure. Changes in circulating vascular regulators, such as endothelin and atrial natriuretic peptide (ANP), may play a role in the development and/or prevention of acute renal failure. Nineteen patients undergoing arteriographic procedures were divided into two groups: large-volume contrast (> or = 150 mL; n = 7) and small-volume contrast (< 150 mL; n = 12). Circulating endothelin levels increased significantly (from 12.3 +/- 1.1 pmol/L to 19.4 +/- 2.2 pmol/L; P < 0.05) following large-volume contrast exposure (group 1) but not following small-volume contrast exposure (group 2) (13.9 +/- 1.7 pmol/L to 12.2 +/- 0.09 pmol/L). ANP levels increased significantly in both groups: 43 +/- 15 pg/mL to 75 +/- 21 pg/mL in group 1 and 33 +/- 16 to 106 +/- 39 pg/mL in group 2. Data from an additional eight patients with underlying diabetes mellitus and/or renal insufficiency also were obtained and were considered separately. Endothelin levels were higher at baseline and increased significantly after contrast (25.7 +/- 5 pmol/L to 55.4 +/- 18 pmol/L) despite the relatively small average volume of contrast infused (112 +/- 15 mL). ANP levels were also highest in these patients (211 +/- 43 pg/mL precontrast and 323 +/- 65 pg/mL postcontrast). No group had a significant change in serum creatinine following contrast exposure. In conclusion, large-volume radiocontrast exposure is associated with an increase in both circulating endothelin and ANP levels. Patients with underlying diabetes or renal insufficiency may have higher baseline levels and a greater tendency to increase endothelin after contrast exposure. While an increase in endothelin may contribute to renal vasoconstriction following radiocontrast exposure, simultaneous increases in ANP may serve to offset this response and protect against changes in renal function.

Plasma brain natriuretic peptide and atrial natriuretic peptide concentrations correlate with left ventricular end-diastolic pressure

The present study was designed to investigate whether brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) plasma concentrations correlate with left ventricular end-diastolic pressure (LVEDP), pulmonary capillary wedge pressure (PCWP), diastolic pulmonary arterial pressure (DPAP), right atrial pressure (RAP), or ejection fraction (EF). Plasma BNP and ANP levels were determined by commercial radioimmunoassays (Peninsula) after Sep Pak C18 extraction in blood samples withdrawn from the pulmonary artery and the left ventricle or from the left ventricle and the femoral vein in 85 patients undergoing diagnostic cardiac catheterization. Linear and nonlinear regression analysis and the paired sample t-test were applied to the data. Pulmonary arterial plasma BNP and ANP levels showed a close nonlinear correlation with LVEDP (BNP: r = 0.94, p < 0.001; ANP: r = 0.81, p < 0.001), a significant linear correlation with PCWP, DPAP, and RAP, and a significant negative correlation with EF. ANP concentrations decreased significantly from the pulmonary artery to the left ventricle and from the left ventricle to the femoral vein (p < 0.001). BNP levels also decreased significantly between the left ventricle and the femoral vein (p < 0.001), but there was no significant difference between pulmonary arterial and left ventricular BNP concentrations. BNP and ANP concentrations correlated significantly between pulmonary arterial and left ventricular blood samples (BNP: r = 0.99, ANP: r = 0.93, p < 0.001) and between left ventricular and peripheral blood samples (BNP: r = 0.99, ANP: r = 0.94, p < 0.001). The present data suggest that peripheral plasma BNP and ANP levels are useful non-invasive indices of cardiac performance.

Atrial natriuretic peptide response to ionic and nonionic contrast left ventriculography

Atrial natriuretic peptide (ANP) levels were measured prior to and at 1 and 5 minutes postcontrast left ventriculography with an ionic contrast agent (diatrizoate), and a nonionic agent (iopamidol) and the results were compared. Since ionic contrast agents have been found to cause an increase in left ventricular end-diastolic pressure (LVEDP) and nonionic agents have been found to have less of an effect on LVEDP, we investigated the response of ANP levels, which have been found to increase secondary to increased LVEDP (atrial pressure), with both agents. A group of 38 patients who were scheduled for left heart catheterization for suspected coronary artery disease was included (19 in each group) and blood samples for ANP levels were drawn from the left ventricles. At the same time, heart rate, LVEDP, and left ventricular systolic pressure (LVSP) were also measured. It was found that the LVEDP increased significantly for both agents at 1 minute postventriculography, but no further change occurred at 5 min. Heart rate increased significantly in the diatrizoate group at 1 minute with a return of heart rate to preventriculography levels at 5 min, while the ANP level and LVSP remained unchanged at 1 minute postventriculography with both agents but increased significantly at 5 min in the diatrizoate group only. This difference in ANP response is not correlated with the LVEDP. The response of ANP may be related to heart rate and/or LVSP.

[Atrial natriuretic factor]

Although ANF research started 30 years ago, the atrial natriuretic factor (ANF) was only discovered recently (1981). The presence of such a factor has been suspected for many years because of histological and physiological arguments. In 1956, Kish found "dense granules" in the atrial walls of guinea pigs. Gauer and Henry could explain some of their experimental results on diuresis and natriuresis only by suggesting the presence of a third hormonal factor, but neither by the renin-angiotensin system, nor the anti-diuretic hormone. Hall et al. were the first to recognize a link between the granules and water and sodium metabolism. But it was De Bold who published the crucial experiment in 1981: injecting right atrial extracts to anaesthetized rats rapidly induced intense and transitory diuresis and natriuresis. ANF was born, and, at the same time, the concept of the heart as an endocrine gland. Indeed, ANF corresponds to the strict definition of a hormone. It has the following properties: natriuresis and diuresis via an increase in glomerular filtration fraction without any major changes in renal plasma flow; direct vasodilation of the large arteries with only few effects on small arterioles and veins. The stimuli for ANF secretion are mechanical and pharmacological, especially drugs currently used by anaesthetists. Atrial distension is the main mechanical stimulus. An increase in atrial transmural pressure is always followed by a release in ANF, but this effect is not constant for increases in intra-luminal pressure. It is the former pressure gradient alone that reflects the volume of the right atrium, the mechanical stimulus for ANF secretion. Tachycardia, or, more precisely, an increase in the atrial contraction rate, also leads to an important release of ANF. Cardiac nerves are not necessary for this, as demonstrated by studies in heart transplant patients. Only few pharmacological agents have been shown to really stimulate ANF secretion. In rats, morphine has a direct secretory effect, whereas ketamine hydrochloride, diethylether and chloral hydrate do so by increasing the release of catecholamines. The effects of alpha, beta adrenergic agonists and calcium agonists remain controversial. ANF, which has diuretic and vasodilator effects, plays a part, together with the renin-angiotensin system and the anti-diuretic hormone, in blood volume control in mammals. However, it has a special role to play, because it is a rapid release hormone: rapid vascular filling leads to an increase in ANF in less than 1 minute, with a parallel increase in diuresis.

Evidence that atriopeptin is not a physiological regulator of sodium excretion

Although much experimental evidence is consistent with the concept that atrial natriuretic factor (atriopeptin) is an important physiological regulator of renal sodium excretion, this hypothesis remains unproven. Indeed, a rapidly expanding collection of experimental data appears to be more compatible with the opposite conclusion, namely that circulating atriopeptin exerts only a trivial effect on renal sodium excretion during normal day-to-day living conditions. In this review, the substantial evidence demonstrating that elevations of plasma atriopeptin from threefold to 13-fold produce only a slowly developing and relatively modest natriuresis is reassessed in light of recently published data indicating that the acute intake of food (the pathway by which essentially all sodium enters the body under normal living conditions) does not increase circulating atriopeptin. These considerations imply that atriopeptin does not contribute to the process that elicits a postprandial natriuresis, a process that presumably is of primary importance in the physiological regulation of sodium balance. In addition, consideration is given to a number of common physiological, experimental, and pathophysiological conditions in which circulating atriopeptin does not correlate with renal sodium excretion. This lack of correlation implies that atriopeptin is not an important regulator of sodium excretion in these situations.

Determinants of atrial natriuretic factor in the adult respiratory distress syndrome

We measured plasma atrial natriuretic factor over the clinical course of 12 patients with the adult respiratory distress syndrome (ARDS). A total of 33 sequential measurements were correlated with 23 hemodynamic, pulmonary, and renal parameters. Atrial natriuretic factor was found to be eight times higher than age-matched healthy control subjects (p = 0.001). Although atrial natriuretic factor correlated well with pulmonary capillary wedge pressure (r = 0.592), there was no significant relationship between right atrial pressure and plasma atrial natriuretic factor (r = 0.258). Atrial natriuretic factor was best related to pulmonary artery systolic pressure (r = 0.751). We conclude that in ARDS, plasma atrial natriuretic factor is markedly elevated and arterial levels are best determined by left atrial pressure and pulmonary hemodynamics, and not by right sided cardiac pressures. The role of increased circulating atrial natriuretic factor in the pathophysiology of ARDS is to be clarified in future studies.