Increased concentrations of atrial and plasma atrial natriuretic peptide in castrated male rats

Endocrine functions of the heart: from bench to bedside

Heart has a recognized endocrine function as it produces several biologically active substances with hormonal properties. Among these hormones, the natriuretic peptide (NP) system has been extensively characterized and represents a prominent expression of the endocrine function of the heart. Over the years, knowledge about the mechanisms governing their synthesis, secretion, processing, and receptors interaction of NPs has been intensively investigated. Their main physiological endocrine and paracrine effects on cardiovascular and renal systems are mostly mediated through guanylate cyclase-A coupled receptors. The potential role of NPs in the pathophysiology of heart failure and particularly their counterbalancing action opposing the overactivation of renin-angiotensin-aldosterone and sympathetic nervous systems has been described. In addition, NPs are used today as key biomarkers in cardiovascular diseases with both diagnostic and prognostic significance. On these premises, multiple therapeutic strategies based on the biological properties of NPs have been attempted to develop new cardiovascular therapies. Apart from the introduction of the class of angiotensin receptor/neprilysin inhibitors in the current management of heart failure, novel promising molecules, including M-atrial natriuretic peptide (a novel atrial NP-based compound), have been tested for the treatment of human hypertension. The development of new drugs is currently underway, and we are probably only at the dawn of novel NPs-based therapeutic strategies. The present article also provides an updated overview of the regulation of NPs synthesis and secretion by microRNAs and epigenetics as well as interactions of cardiac hormones with other endocrine systems.

Effect of Testosterone on Natriuretic Peptide Levels

BACKGROUND

Circulating natriuretic peptide (NP) levels are markedly lower in healthy men than women. A relative NP deficiency in men could contribute to their higher risk of hypertension and cardiovascular disease. Epidemiological studies suggest testosterone may contribute to sex-specific NP differences.

OBJECTIVES

This study aimed to determine the effect of testosterone administration on NP levels using a randomized, placebo-controlled design.

METHODS

One hundred and fifty-one healthy men (20 to 50 years of age) received goserelin acetate to suppress endogenous production of gonadal steroids, and anastrazole to suppress conversion of testosterone to estradiol. Subjects were randomized to placebo gel or 4 different doses of testosterone (1%) gel for 12 weeks. Serum N-terminal-pro-B-type natriuretic peptide (NT-proBNP) and total testosterone levels were measured at baseline and follow-up.

RESULTS

Men who did not receive testosterone replacement (placebo gel group) after suppression of endogenous gonadal steroid production experienced a profound decrease in serum testosterone (median 540 to 36 ng/dl; p < 0.0001). This was accompanied by an increase in median NT-proBNP (+8 pg/ml; p = 0.02). Each 1-g increase in testosterone dose was associated with a 4.3% lower NT-proBNP at follow-up (95% confidence interval: -7.9% to -0.45%; p = 0.029). An individual whose serum testosterone decreased by 500 ng/dl had a 26% higher predicted follow-up NT-proBNP than someone whose serum testosterone remained constant.

CONCLUSIONS

Suppression of testosterone production in men led to increases in circulating NT-proBNP, which were attenuated by testosterone replacement. Inhibition of NP production by testosterone may partly explain the lower NP levels in men. (Dose-Response of Gonadal Steroids and Bone Turnover in Men; NCT00114114).

Effect of testosterone treatment on cardiac biomarkers in a randomized controlled trial of men with type 2 diabetes

OBJECTIVE

To assess the effect of testosterone treatment on cardiac biomarkers in men with type 2 diabetes (T2D).

DESIGN

Randomized double-blind, parallel, placebo-controlled trial.

PATIENTS

Men aged 35-70 years with T2D and a total testosterone level ≤12·0 nmol/l (346 ng/dl) at high risk of cardiovascular events, median 10-year United Kingdom Prospective Diabetes Study (UKPDS) coronary heart disease (CHD) risk 21% (IQR 16%, 27%). Eighty-eight participants were randomly assigned to 40 weeks of intramuscular testosterone undecanoate (n = 45) or matching placebo (n = 43).

MAIN OUTCOME MEASURES

N-terminal pro B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin T (hs-cTnT).

RESULT

Testosterone treatment reduced NT-proBNP (mean adjusted difference (MAD) in change over 40 weeks across the testosterone and placebo groups, -17·9 ng/l [95% CI -32·4, -3·5], P = 0·047), but did not change hs-cTnT (MAD, 0·41 ng/l (95% CI -0·56, 1·39), P = 0·62). Six men, three in each group experienced an adverse cardiac event, displaying already higher baseline NT-proBNP (P < 0·01) and hs-cTnT levels (P = 0·01). At baseline, 10-year UKPDS CHD risk was associated positively with NT-proBNP (τ = 0·21, P = 0·004) and hs-cTnT (τ = 0·23, P = 0·003) and inversely with testosterone (total testosterone τ = -0·18, P = 0·02, calculated free testosterone τ = -0·19, P = 0·01), but there was no significant association between testosterone and cardiac biomarkers (P > 0·05).

CONCLUSIONS

In this trial of men with T2D and high cardiovascular risk, testosterone treatment reduced NT-proBNP and did not change hs-cTnT. Further studies should determine whether men with increased cardiac biomarkers prior to testosterone therapy are at higher risk of testosterone treatment-associated adverse cardiac events.

Circulating C-type natriuretic peptide and its relationship to cardiovascular disease in the general population

C-type natriuretic peptide (CNP) is an endothelium-derived peptide that is released as a protective mechanism in response cardiovascular injury or disease. However, no studies have investigated circulating CNP, identifying clinical factors that may influence CNP and its relationship to cardiovascular disease in the general population. We studied 1841 randomly selected subjects from Olmsted County, MN (mean age, 63±11 years; 48% men). Plasma CNP was measured by a well-established radioimmunoassay and echocardiography, clinical characterization, and detailed medical record review were performed. We report that CNP circulates at various concentrations (median, 13 pg/mL), was unaffected by sex, was weakly associated by age, and that highest quartile of CNP identified a high-risk phenotype. Subjects with CNP in the highest quartile were associated with increased risk of myocardial infarction (multivariable-adjusted hazard ratio, 1.51; 95% confidence interval, 1.09-2.09; P=0.01) but not heart failure, cerebrovascular accidents, or death during a follow-up of 12 years. Addition of the highest quartile of CNP to clinical variables led to a modest increase in the integrated discrimination improvement for risk of myocardial infarction. In a large community-based cohort, elevated circulating CNP identified a high-risk phenotype that included cardiovascular comorbidities and left ventricular dysfunction, and provided evidence that highest concentrations of CNP potentially has prognostic value in predicting future risk of myocardial infarction. Together, these data from the general population highlight the potential value of CNP and support the need for additional studies to evaluate whether mechanisms regulating CNP could improve outcomes.

NH2-terminal probrain natriuretic peptide is associated with diabetes complications in the EURODIAB Prospective Complications Study: the role of tumor necrosis factor-α

OBJECTIVE

Circulating levels of NH(2)-terminal probrain natriuretic peptide (NT-proBNP), a marker of acute heart failure, are associated with increased risk of cardiovascular disease (CVD) in the general population. However, there is little information on the potential role of NT-proBNP as a biomarker of vascular complications in type 1 diabetic patients. We investigated whether serum NT-proBNP levels were associated with micro- and macrovascular disease in type 1 diabetic subjects.

RESEARCH DESIGN AND METHODS

A cross-sectional nested case-control study from the EURODIAB Prospective Complications Study of 507 type 1 diabetic patients was performed. Case subjects (n = 345) were defined as those with one or more complications of diabetes; control subjects (n = 162) were those with no evidence of any complication. We measured NT-proBNP levels by a two-site sandwich electrochemiluminescence immunoassay and investigated their associations with complications.

RESULTS

Mean NT-proBNP levels were significantly higher in case than in control subjects. In logistic regression analyses, NT-proBNP values >26.46 pg/mL were independently associated with a 2.56-fold increased risk of all complications. Odds ratios of CVD (3.95 [95% CI 1.26-12.35]), nephropathy (4.38 [1.30-14.76]), and distal symmetrical polyneuropathy (4.32 [1.41-13.23]) were significantly increased in patients with NT-proBNP values in the highest quartile (>84.71 pg/mL), independently of renal function and known risk factors. These associations were no longer significant after inclusion of TNF-α into the model.

CONCLUSIONS

In this large cohort of type 1 diabetic subjects, we found an association between NT-proBNP and diabetic micro- and macrovascular complications. Our results suggest that the inflammatory cytokine TNF-α may be involved in this association.

Effects of transdermal testosterone on natriuretic peptide levels in women: a randomized placebo-controlled pilot study

OBJECTIVE

To investigate whether testosterone administration alters natriuretic peptide levels in women.

DESIGN

Three-month, double-blind, randomized, placebo-controlled study.

SETTING

Clinical research center.

PATIENT(S)

Fifty-one women with hypoandrogenemia due to hypopituitarism.

INTERVENTION(S)

Transdermal testosterone (300 μg daily) or placebo patch.

MAIN OUTCOME MEASURE(S)

N-Terminal pro-B-type natriuretic peptide (NT-proBNP) levels.

RESULT(S)

NT-proBNP levels decreased in the transdermal testosterone group compared with placebo over three months. The difference between groups remained significant after controlling for baseline age, systolic blood pressure, body mass index, and homeostasis model assessment of insulin resistance. Change in NT-proBNP over 3 months was inversely associated with change in free testosterone levels.

CONCLUSION(S)

Testosterone administration to women results in decreased natriuretic peptide levels, suggesting that testosterone may be an inverse regulator of the natriuretic peptide system.

CLINICAL TRIALS REGISTRATION NUMBER

NCT00027430.

Influence of sex and hormone status on circulating natriuretic peptides

OBJECTIVES

The aim of this study was to assess the relationship between sex hormones and natriuretic peptide levels in community-based adults.

BACKGROUND

Women have higher circulating natriuretic peptide concentrations than men, but the mechanisms for these sex-related differences and the impact of hormone therapy are unclear. Experimental studies suggest that androgens may suppress natriuretic peptide secretion.

METHODS

We measured N-terminal pro-B-type natriuretic peptide (NT-proBNP), total testosterone, and sex hormone-binding globulin plasma levels in 4,056 men and women (mean age 40 ± 9 years) from the Framingham Heart Study Third-Generation cohort. Sex/hormone status was grouped as: 1) men; 2) post-menopausal women not receiving hormone replacement therapy; 3) pre-menopausal women not receiving hormonal contraceptives; 4) post-menopausal women receiving hormone replacement therapy; and 5) pre-menopausal women receiving hormonal contraceptives.

RESULTS

Circulating NT-proBNP levels were associated with sex/hormone status (overall p < 0.0001). Men had lower NT-proBNP levels than women of all menopause or hormone groups, and women receiving hormonal contraceptives had higher NT-proBNP levels than women who were not receiving hormone therapy (all p < 0.0001). These relationships remained significant after adjusting for age, body mass index, and cardiovascular risk factors. Across sex/hormone status groups, free testosterone (FT) levels decreased and sex hormone-binding globulin levels increased in tandem with increasing NT-proBNP levels. In sex-specific analyses, NT-proBNP levels decreased across increasing quartiles of FT in men (p for trend <0.01) and women (p for trend <0.0001). Adjustment for FT markedly attenuated the association between sex/hormone status and NT-proBNP concentrations.

CONCLUSIONS

These findings suggest that lower levels of circulating androgens and the potentiating effect of exogenous female hormone therapy contribute to the higher circulating NT-proBNP concentrations in women.

Thirty years of the heart as an endocrine organ: physiological role and clinical utility of cardiac natriuretic hormones

Thirty years ago, De Bold et al. ( 20 ) reported that atrial extracts contain some biologically active peptides, which promote a rapid and massive diuresis and natriuresis when injected in rats. It is now clear that the heart also exerts an endocrine function and in this way plays a key role in the regulation of cardiovascular and renal systems. The aim of this review is to discuss some recent insights and still-debated findings regarding the cardiac natriuretic hormones (CNHs) produced and secreted by cardiomyocytes (i.e., atrial natriuretic peptide and B-type natriuretic peptide). The functional status of the CNH system depends not only on the production/secretion of CNHs by cardiomyocytes but also on both the peripheral activation of circulating inactive precursor of natriuretic hormones and the transduction of the hormone signal by specific receptors. In this review, we will discuss the data supporting the hypothesis that the production and secretion of CNHs is the result of a complex integration among mechanical, chemical, hemodynamic, humoral, ischemic, and inflammatory inputs. The cross talk among endocrine function, adipose tissue, and sex steroid hormones will be discussed more in detail, considering the clinically relevant relationships linking together cardiovascular risk, sex, and body fat development and distribution. Finally, we will review the pathophysiological role and the clinical relevance of both peripheral maturation of the precursor of B-type natriuretic peptides and hormone signal transduction .

Involvement of cholecystokinin receptor in the inhibition of gastrointestinal motility by oxytocin in ovariectomized rats

The effects of oxytocin on gastric emptying, gastrointestinal transit, and plasma levels of cholecystokinin (CCK) were studied in ovariectomized rats. Gastrointestinal motility was assessed in rats 15 min after intragastric instillation of a test meal containing charcoal and Na2 51CrO4. Gastric emptying was determined by measuring the amount of radiolabeled chromium contained in the small intestine as a percentage of the initial amount received. Gastrointestinal transit was evaluated by calculating the geometric center of distribution of the radiolabeled marker. Blood samples were collected for CCK radioimmunoassay. After administration of oxytocin (0.2-0.8 mg/kg), gastric emptying and gastrointestinal transit were inhibited, whereas plasma concentration of CCK was increased in a dose-dependent manner. Atosiban, an oxytocin receptor antagonist, effectively attenuated the oxytocin-induced inhibition of gastric emptying and gastrointestinal transit. However, administration of atosiban alone had no effect on gastric emptying and gastrointestinal transit. The selective CCK1 receptor antagonists, devazepide and lorglumide, effectively attenuated the oxytocin-induced inhibition of gastric emptying and gastrointestinal transit. L-365, 260, a selective CCK2 receptor antagonist, did not alter the oxytocin-induced inhibition of gastric emptying and gastrointestinal transit. These results suggest that oxytocin inhibits gastric emptying and gastrointestinal transit in ovariectomized rats via a mechanism involving the stimulation of CCK release and CCK1 receptor activation.

Sex dimorphism in cardiac pathophysiology: experimental findings, hormonal mechanisms, and molecular mechanisms

The higher cardiovascular risk in men and post-menopausal women implies a protective action of estrogen. A large number of experimental studies have provided strong support to this concept. However, the recent clinical trials with negative outcomes regarding hormone replacement therapy call for "post hoc" reassessment of existing information, models, and research strategies as well as a summary of recent findings. Sex steroid hormones, in particular estrogen, regulate numerous processes that are related to the development and progression of cardiovascular disease through a variety of signaling pathways. Use of genetically modified models has resulted in interesting information on diverse actions mediated by steroid receptors. By focusing on experimental findings, we have reviewed hormonal, cellular, and signaling mechanisms responsible for sex dimorphism and actions of hormone replacement therapy and addressed current limitations and future directions of experimental research.

Effects of evodiamine on gastrointestinal motility in male rats

The effects of evodiamine on gastric emptying, gastrointestinal transit, and plasma levels of cholecystokinin (CCK) were studied in male rats. Evodiamine, isolated from the dry unripened fruit of Evodia rutaecarpa Bentham (a Chinese medicine named Wu-chu-yu), has been recommended for abdominal pain, acid regurgitation, nausea, diarrhea, and dysmenorrhea. Gastrointestinal motility was assessed in rats 15 min after intragastric instillation of a test meal containing charcoal and Na(2)51CrO(4). Gastric emptying was determined by measuring the amount of radiolabeled chromium contained in the small intestine as a percentage of the initial amount received. Gastrointestinal transit was evaluated by calculating the geometric center of distribution of the radiolabeled marker. Blood samples were collected for CCK radioimmunoassay (RIA). After administration of evodiamine (0.67-6.00 mg/kg), both gastric emptying and gastrointestinal transit were inhibited, whereas the plasma concentration of CCK was increased in a dose-dependent manner. The selective CCK(1) receptor antagonists, devazepide and lorglumide, effectively attenuated the evodiamine-induced inhibition of gastric emptying and gastrointestinal transit. L-365,260 (3R-(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3-yl)-N'-(3-methylphenyl)-urea), a selective CCK(2) receptor antagonist, did not alter the evodiamine-induced inhibition of gastric emptying and gastrointestinal transit. These results suggest that evodiamine inhibits both gastric emptying and gastrointestinal transit in male rats via a mechanism involving CCK release and CCK(1) receptor activation.

Pathophysiological and clinical relevance of circulating levels of cardiac natriuretic hormones: are they merely markers of cardiac disease?

Several specific and sensitive markers for myocardial injury as well as diagnostic tests for the assessment and stratification of cardiovascular risk have been recently introduced in clinical laboratories. However, until a few years ago, there were no laboratory tests for diagnosis, stratification and follow-up of patients with heart failure. The assay for cardiac natriuretic hormones (CNH) fills this gap. Heart failure is not only the most frequent "final common pathway" in cardiovascular disease, but is also the most common primary hospital discharge diagnosis, as well as the most common cause of death in patients over 50 years of age in Western countries; therefore, CNH assay may be destined to assume a growing relevance in clinical cardiology. However, to consider CNH assay only as a general and functional indicator of cardiac structural disease, without recalling that atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are powerful hormones, may lead to underestimation of the physiological role they play in healthy subjects as well as in patients with heart failure. Indeed, the circulating levels of CNH should be always interpreted taking into account not only hemodynamic factors and myocardial performance, but also their relationship with the counter-regulatory neuroendocrine system (including renin-angiotensin-aldosterone system, sympathetic system, endothelins, cytokines and vasopressin), as well as other hormones (such as sex steroid hormones, thyroid hormones and glucocorticoids).

The circulating levels of cardiac natriuretic hormones in healthy adults: effects of age and sex

In order to study the relationships between sex hormones, aging, and circulating levels of cardiac natriuretic peptides and to define reference values for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) assays, we measured the plasma levels of cardiac natriuretic peptides in a large group of healthy adults divided according to age and sex. We studied 216 healthy subjects of both sexes (109 men and 107 women) with age ranging from 20 to 77 years (mean 43.2+/-14.8 years). All subjects were non-obese and had normal arterial blood pressure; they were free from acute diseases, including asymptomatic heart disease. Highly sensitive and specific IRMA methods were used to measure plasma ANP and BNP. The mean ANP value in healthy adult subjects of both sexes was 17.8+/-10.9 pg/ml with no significant difference between men (16.7+/-10.0 pg/ml) and women (18.8+/-11.7 pg/ml). The mean BNP value in healthy adult subjects of both sexes was 9.9+/-9.0 pg/ml with a significant difference (p<0.0001) between men (7.7+/-7.1 pg/ml) and women (12.2+/-10.2 pg/ml). There was a weak linear relationship between age and either ANP (r=0.350, p<0.0001) or BNP (r=0.254, p=0.0002) values. When the circulating levels of cardiac natriuretic hormones, and age and sex were analyzed by multiple stepwise regression analysis, both age and sex significantly and independently contributed to the regression. Our study indicates independent positive effects of aging and female sex hormones on ANP and BNP levels in healthy adult subjects. These effects should be taken into account in the calculation of appropriate reference values for cardiac natriuretic hormones.

Regulation of natriuretic peptide secretion by the heart

Secreted by the heart, more specifically by atrial cardiomyocytes under normal conditions but also by ventricular myocytes during cardiac hypertrophy, natriuretic peptides are now considered important hormones in the control of blood pressure and salt and water excretion. Studies on natriuretic peptide secretagogues and their mechanisms of action have been complicated by hemodynamic changes and contractions to which the atria are constantly subjected. It now appears that atrial stretch through mechano-sensitive ion channels, adrenergic stimulation via alpha 1A-adrenergic receptors, and endothelin via its ETA receptor subtype are major triggering agents of natriuretic peptide release. With several other stimuli, such as angiotensin II and beta-adrenergic agents, modulation of natriuretic peptide release appears to be linked to local generation of prostaglandins. In all cases, intracellular calcium homeostasis, controlled by several ion channels, is considered a key element in the regulation of natriuretic peptide secretion.

Inhibition of gastric emptying and intestinal transit by amphetamine through a mechanism involving an increased secretion of CCK in male rats

1. The effect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats. 2. Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not affected by the chronic administration of amphetamine. 3. Plasma CCK levels were increased dose-dependently by amphetamine. 4. Proglumide, a CCK receptor antagonist, prevented amphetamine-induced inhibition of gastric emptying and the decrease in GI transit in male rats. 5. The selective CCK(A) receptor antagonist, lorglumide, dose-dependently attenuated the amphetamine-induced inhibition of gastric emptying in male rats. In contrast, the selective CCK(B) receptor antagonist, PD 135,158, did not reverse the effect of amphetamine on gastric emptying. 6. Both lorglumide and PD 135,158 reversed the inhibitory effect of amphetamine on GI transit in male rats. 7. These results suggest that amphetamine-induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.

Effects of long-term administration of octreotide on sodium retention and atrial natriuretic peptide in carbon tetrachloride-induced cirrhotic rats

BACKGROUND/AIMS

To realize the roles of peripheral vasodilatation and atrial natriuretic peptide in the formation of cirrhotic ascites, the effects of long-term administration of octreotide on carbon tetrachloride-induced cirrhotic rats were evaluated.

METHODS

Urine sodium excretion, hemodynamics, plasma atrial natriuretic peptide levels, renin activities and aldosterone concentrations were compared between cirrhotic and control rats (protocol 1); and between octreotide- (65 micrograms/kg, twice daily for 10 days, subcutaneously) and placebo-treated (5% dextrose) cirrhotic rats (protocol 2). In an in vitro experiment, right atrial tissue of cirrhotic rats was incubated with different concentrations of octreotide to evaluate the release of atrial natriuretic peptide (protocol 3).

RESULTS

Cirrhotic rats had significantly lower urine sodium excretion and systemic vascular resistance, and significantly higher plasma atrial natriuretic peptide levels, renin activities and aldosterone concentrations than control rats. Compared with placebo-treated cirrhotic rats, octreotide caused increased urine sodium excretion (-10 +/- 4% vs. 13 +/- 8% from baseline values, p < 0.05) and systemic vascular resistance (2.6 +/- 0.1 vs. 3.3 +/- 0.3 mmHg.min.100 g.ml-1, p < 0.05); and decreased plasma atrial natriuretic peptide levels (166.7 +/- 24.8 vs. 234.0 +/- 19.2 pg/ ml, p < 0.05), renin activities (2.45 +/- 0.49 vs. 4.36 +/- 0.53 ng.ml-1.h-1, p < 0.01) and aldosterone concentrations (290.2 +/- 40.0 vs. 483.3 +/- 82.6 pg/ml, p < 0.05). In the in vitro experiment, right atrial release of atrial natriuretic peptide of cirrhotic rats was not significantly changed when incubated with different concentrations of octreotide.

CONCLUSIONS

Octreotide ameliorates renal sodium retention and suppresses plasma levels of atrial natriuretic peptide of ascitic cirrhotic rats with a novel mechanism via, at least partly, the modification of peripheral vascular resistance.

Alterations with age of the T3-stimulated release of atrial natriuretic peptide and its effect on water and sodium metabolism in rats

The influence of age on urinary excretion of sodium and water and in vitro release of atrial natriuretic peptide (ANP) were studied in rats. Older rats had increased daily water intake and urine output. They also had increased plasma ANP, decreased right atrial contents of ANP and increased ANP release in response to 10 nM T3. The ageing process may have altered the regulatory mechanisms of water metabolism and secretion of ANP.

The influence of reproductive hormones on ANF release by rat atria

The effects of subcutaneous (sc) administration of estradiol (50 micrograms/100 microliters/day x 10 day) or testosterone (15 mg/100 microliters twice a week x 2 weeks) on ANF release were examined in isolated perfused rat atria. The concentration of ANF in the perfusate was measured by radioimmunoassay, under basal conditions (atrial wall unstressed), and during atrial distention (intraluminal pressure raised to 4, 6, and 10 cm water). In both male and female control (vehicle-injected) groups, increased atrial pressure resulting in distention of the atrium caused a significant increase in ANF release. Estradiol increased basal secretion of ANF but did not influence stretch-induced stimulation of ANF secretion. By contrast, although testosterone did not affect basal secretion, it completely abolished the stretch-induced increase in ANF secretion. Neither estradiol nor testosterone affected atrial compliance.