Hormonal modulation of atrial natriuretic factor receptors and effects on adrenal glomerulosa cells of female rats

Sex differences in 123I-mIBG scintigraphy imaging techniques in patients with heart failure

BACKGROUND

123I-mIBG-scintigraphy could be a useful stratifying tool for patients with heart failure (HF). The purpose of this retrospective study is to evaluate whether there are differences between men and women with HF in terms of the prediction of cardiac arrhythmic events (AE).

RESEARCH AND METHODS

A total of 306 patients, before implantable-cardioverter-defibrillator (ICD) implantation, were evaluated. They underwent 123I-mIBG-scintigraphy and an evaluation of the results was performed after 85 months of follow-up. Early and late planar and SPECT cardiac images were acquired. Heart-to-mediastinum ratio (HM) for planar images and the sum of the segmental scores (SS) for SPECT were calculated.

RESULTS

In the general population, age, early SS (ESS), late SS (LSS), and ejection fraction (EF) were statistically significant for the prediction of AE at Cox regression, while early and late HM (eHM,lHM) were not significative for the prediction of AE. Population was divided into females and males and univariate analysis was conducted separately for the two cohorts: no significant variables for prediction of AE were found in females. For males, ESS, LSS, EF, and late HM were statistically significant predictors of AE. The overall survival was similar in males and females, but the risk of AE is lower in males than in females.

CONCLUSIONS

123I-mIBG represents a more effective tool for the prediction of AE in male patients than in women.

Sex-related differences in contemporary biomarkers for heart failure: a review

The use of circulating biomarkers for heart failure (HF) is engrained in contemporary cardiovascular practice and provides objective information about various pathophysiological pathways associated with HF syndrome. However, biomarker profiles differ considerably among women and men. For instance, in the general population, markers of cardiac stretch (natriuretic peptides) and fibrosis (galectin‐3) are higher in women, whereas markers of cardiac injury (cardiac troponins) and inflammation (sST2) are higher in men. Such differences may reflect sex‐specific pathogenic processes associated with HF risk, but may also arise as a result of differences in sex hormone profiles and fat distribution. From a clinical perspective, sex‐related differences in biomarker levels may affect the objectivity of biomarkers in HF management because what is considered to be ‘normal’ in one sex may not be so in the other. The objectives of this review are, therefore: (i) to examine the sex‐specific dynamics of clinically relevant HF biomarkers in the general population, as well as in HF patients; (ii) to discuss the overlap between sex‐related and obesity‐related effects, and (iii) to identify knowledge gaps to stimulate research on sex‐related differences in HF.

Ligand-mediated endocytosis and intracellular sequestration of guanylyl cyclase/natriuretic peptide receptors: role of GDAY motif

The guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), also referred to as GC-A, is a single polypeptide molecule having a critical function in blood pressure regulation and cardiovascular homeostasis. GC-A/NPRA, which resides in the plasma membrane, consists of an extracellular ligand-binding domain, a single transmembrane domain, and an intracellular cytoplasmic region containing a protein kinase-like homology domain (KHD) and a guanylyl cyclase (GC) catalytic domain. After binding with atrial and brain natriuretic peptides (ANP and BNP), GC-A/NPRA is internalized and sequestered into intracellular compartments. Therefore, GC-A/NPRA is a dynamic cellular macromolecule that traverses different subcellular compartments through its lifetime. This review describes the roles of short-signal sequences in the internalization, trafficking, and intracellular redistribution of GC-A/NPRA from cell surface to cell interior. Evidence indicates that, after internalization, the ligand-receptor complexes dissociate inside the cell and a population of GC-A/NPRA recycles back to the plasma membrane. Subsequently, the disassociated ligands are degraded in the lysosomes. However, a small percentage of the ligand escapes the lysosomal degradative pathway, and is released intact into culture medium. Using pharmacologic and molecular perturbants, emphasis has been placed on the cellular regulation and processing of ligand-bound GC-A/NPRA in terms of receptor trafficking and down-regulation in intact cells. The discussion is concluded by examining the functions of short-signal sequence motifs in the cellular life-cycle of GC-A/NPRA, including endocytosis, trafficking, metabolic processing, inactivation, and/or down-regulation in model cell systems.

Exogenous oestradiol and progesterone administration does not cause oedema in healthy young women

OBJECTIVE

Oedema is an increase in the extravascular component of extracellular fluid volume (ECFV). Fluid movement across the ECF is controlled by hydrostatic and oncotic pressures, which are influenced by oestradiol and progesterone. Thus we hypothesized that oestradiol decreases, while combined oestradiol + progesterone increases, protein and fluid movement out of the vasculature.

SUBJECTS

Subjects were eight healthy women (22 +/- 2 years).

DESIGN

Oestrogens and progesterone were suppressed with a gonadotropin-releasing hormone antagonist for 16 days; oestradiol (2 x 0.1 mg/day patches) was added for days 5-16 (E(2)) and progesterone (200 mg/day) was added for days 13-16 (E(2)-P(4)).

MEASUREMENTS

We estimated intravascular (plasma) volume (PV), transcapillary albumin escape rate (TER(alb)), and Starling forces (hydrostatic pressures of plasma and interstitium, plasma colloid pressure, capillary filtration coefficient) in the forearm on days 2 (GnRH antagonist), 9 (E(2)) and 16 (E(2)-P(4)).

RESULTS

In E(2), P([E2]) increased from 85 +/- 26 to 984 +/- 136 pmol/ml (P < 0.05), with no change in P([P4]). In E(2)-P(4), P([E2]) increased to 775 +/- 195 pmol/ml and P([P4]) increased from 6.4 +/- 3.2 to 43.8 +/- 16.2 nmol/l, P < 0.05). TER(alb) was lower during E(2) (5.1 +/- 0.9) and E(2)-P(4) (5.0 +/- 1.1) compared to GnRH antagonist (5.8 +/- 0.9%/h, P < 0.05). Plasma volume was unchanged by E(2), and showed a trend (P = 0.07) for an increase during E(2)-P(4) (48.2 +/- 2.9, 49.0 +/- 3.0 and 53.9 +/- 3.5 ml/kg for GnRH antagonist, E(2), E(2)-P(4), respectively). Starling forces were unaffected by hormone treatments. Plasma renin activity and serum aldosterone concentration increased during E(2)-P(4).

CONCLUSIONS

Neither E(2) nor E(2)-P(4) altered TER(alb) sufficiently to impact Starling forces indicating neither E(2) nor P(4) administration at these levels would likely cause oedema.

Regulation of guanylyl cyclase/natriuretic peptide receptor-A gene expression

Natriuretic peptide receptor-A (NPRA) is the biological receptor of the peptide hormones atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). The level and activity of this receptor determines the biological effects of ANP and BNP in different tissues mainly directed towards the maintenance of salt and water homeostasis. The core transcriptional machinery of the TATA-less Npr1 gene, which encodes NPRA, consists of three SP1 binding sites and the inverted CCAAT box. This promoter region of Npr1 gene has been shown to contain several putative binding sites for the known transcription factors, but the functional significance of most of these regulatory sequences is yet to be elucidated. The present review discusses the current knowledge of the functional significance of the promoter region of Npr1 gene and its transcriptional regulation by a number of factors including different hormones, growth factors, changes in extracellular osmolarity, and certain physiological and patho-physiological conditions.

Effects of estrogen and progesterone administration on extracellular fluid

To determine the effect of estrogen and progesterone on plasma volume (PV) and extracellur fluid volume (ECFV), we suppressed endogenous estrogen and progesterone by using the gonadotropin-releasing hormone (GnRH) antagonist ganirelix acetate in seven healthy women (22 ± 1 yr). Subjects were administered GnRH antagonist for 16 days. Beginning on day 5 of GnRH antagonist administration, subjects were administered estrogen (E2) for 11 days, and beginning on day 12 of GnRH antagonist administration, subjects added progesterone (E2-P4) for 4 days. On days 2, 9, and 16 of GnRH antagonist administration, we estimated ECFV (inulin washout), transcapillary escape rate of albumin (TERalb), and PV (Evans blue dye). Plasma E2concentration increased from 17.9 ± 4.5 (GnRH antagonist) to 195.9 ± 60.1 (E2, P < 0.05) to 245.6 ± 62.9 pg/ml (E2-P4, P < 0.05). Compared with GnRH antagonist (1.3 ± 0.5 ng/ml), plasma P4concentration was unchanged during E2(0.9 ± 0.3 ng/ml) and increased to 9.4 ± 3.1 ng/ml during E2-P4( P < 0.05). Both E2(44.1 ± 3.1 ml/kg) and E2-P4(47.7 ± 2.8 ml/kg) increased PV compared with GnRH antagonist (42.8 ± 1.3 ml/kg, P < 0.05). Within-subjects TERalbwas a strong negative predictor of PV (mean r = 0.92 ± 0.03, P < 0.05), and TERalbwas lowest during E2-P4(5.7 ± 0.5, 4.1.0 ± 1.1, and 2.8 ± 0.9%/h, P < 0.05, for GnRH antagonist, E2, and E2-P4, respectively). ECFV was reduced during E2(227 ± 31 ml/kg, P < 0.05) compared with both GnRH antagonist (291 ± 37 ml/kg) and E2-P4(283 ± 19 ml/kg). Thus the percentage of extracellular fluid in the plasma compartment increased to 21.0% ( P < 0.05) during E2compared with GnRH antagonist (16.1%) and E2-P4(17.2%) admistration. Thus E2increased PV via actions on the capillary endothelium to lower TERalband favor intravascular water retention, whereas during E2-P4PV increased via the combined responses of ECFV expansion and lower TERalb.

Estrogen effects on osmotic regulation of AVP and fluid balance

To determine estrogen effects on osmotic regulation of arginine vasopressin (AVP) and body fluids, we suppressed endogenous estrogen and progesterone using the gonadotropin-releasing hormone (GnRH) analog leuprolide acetate (GnRHa). Subjects were assigned to one of two groups: 1) GnRHa alone, then GnRHa + estrogen (E, n = 9, 25 +/- 1 yr); 2) GnRHa alone, then GnRHa + estrogen with progesterone (E/P, n = 6, 26 +/- 3). During GnRHa alone and with hormone treatment, we compared AVP and body fluid regulatory responses to 3% NaCl infusion (HSI, 120 min, 0.1 ml. min(-1). kg body wt(-1)), drinking (30 min, 15 ml/kg body wt), and recovery (60 min of seated rest). Plasma [E(2)] increased from 23.9 to 275.3 pg/ml with hormone treatments. Plasma [P(4)] increased from 0.6 to 5.7 ng/ml during E/P and was unchanged (0.4 to 0.6 ng/ml) during E. Compared with GnRHa alone, E reduced osmotic AVP release threshold (275 +/- 4 to 271 +/- 4 mosmol/kg, P < 0.05), and E/P reduced the AVP increase in response during HSI (6.0 +/- 1.3 to 4.2 +/- 0.6 pg/ml at the end of HSI), but free water clearance was unaffected in either group. Relative to GnRHa, pre-HSI plasma renin activity (PRA) was greater during E (0.8 +/- 0.1 vs. 1.2 +/- 0.2 ng ANG I. ml(-1). h(-1)) but not after HSI or recovery. PRA was greater than GnRHa during E/P at baseline (1.1 +/- 0.2 vs. 2.5 +/- 0.6) and after HSI (0.6 +/- 0.1 vs. 1.1 +/- 1.1) and recovery (0.5 +/- 0.1 vs. 1.3 +/- 0.2 ng ANG I. ml(-1). h(-1)). Baseline fractional excretion of sodium was unaffected by E or E/P but was attenuated by the end of recovery for both E (3.3 +/- 0.6 vs. 2.4 +/- 0.4%) and E/P (2.8 +/- 0.4 vs 1.7 +/- 0.4%, GnRHa alone and with hormone treatment, respectively). Fluid retention increased with both hormone treatments. Renal sensitivity to AVP may be lower during E due to intrarenal effects on water and sodium excretion. E/P increased sodium retention and renin-angiotensin-aldosterone stimulation.

Estrogen and progesterone effects on transcapillary fluid dynamics

The purpose of this study was to determine estrogen (E(2)) and progesterone (P(4)) effects on atrial natriuretic peptide (ANP) control of plasma volume (PV) and transcapillary fluid dynamics. To this end, we suppressed reproductive function in 12 women (age 21-35 yr) using a gonadotropin releasing-hormone (GnRH) analog (leuprolide acetate) for 5 wk. During the 5th week, the women either received 4 days of E(2) administration (17beta-estradiol, transdermal patch, 0.1 mg/day) or 4 days of E(2) with P(4) administration (vaginal gel, 90 mg P(4) twice per day). At the end of the 4th and 5th week of GnRH analog and hormone administration, we determined PV (Evans blue dye) and changes in PV and forearm capillary filtration coefficient (CFC) during a 120-min infusion of ANP (5 ng x kg body wt(-1) x min(-1)). Preinfusion PV was estimated from Evans blue dye measurement taken over the last 30 min of infusion based on changes in hematocrit. E(2) treatment did not affect preinfusion PV relative to GnRH analog alone (45.3 +/- 3.1 vs. 45.4 +/- 3.1 ml/kg). During ANP infusion CFC was greater during E(2) treatment compared with GnRH analog alone (6.5 +/- 1.4 vs. 4.9 +/- 1.4 microl. 100 g(-1) x min(-1) mmHg(-1), P < 0.05). The %PV loss during ANP infusion was similar for E(2) and GnRH analog-alone treatments (-0.8 +/- 0.2 and -1.0 +/- 0.2 ml/kg, respectively), indicating the change in CFC had little systemic effect on ANP-related changes in PV. Estimated baseline PV was reduced by E(2)-P(4) treatment. During ANP infusion CFC was approximately 30% lower during E(2)-P(4) (6.0 +/- 0.5 vs. 4.3 +/- 4.3 microl. 100 g(-1) x min(-1) mm Hg(-1), P < 0.05), and the PV loss during ANP infusion was attenuated (-0.9 +/- 0.2 and -0.2 +/- 0.2 ml/kg for GnRH analog-alone and E(2)-P(4) treatments, respectively). Thus the E(2)-P(4) treatment lowered CFC and reduced PV loss during ANP infusion.

B-type natriuretic peptide receptor expression and activity are hormonally regulated in rat ovarian cells

Natriuretic peptides form a family of structurally related peptides known to regulate salt and water homeostasis and to cause vasodilation. Synthesis of atrial (ANP), brain (BNP), and C-type (CNP) natriuretic peptides occurs mainly in the heart and brain and has been identified recently in the female reproductive tract. The expression of ANP and CNP as well as their cognate guanylyl cyclase receptors (NPR-A and NPR-B, respectively) have been detected in the rat ovary. We have shown previously that the expression of the natriuretic peptides and their receptors in the rat ovary appears to be modulated by the estrous cycle. In the present study we have evaluated the expression of the natriuretic peptide system (peptide and receptor) in ovarian cells (granulosa and thecal-interstitial cells) obtained from immature female rats treated with either diethylstilbestrol (DES), an estrogen analog, or equine CG (eCG), a gonadotropin that possesses both LH and FSH activity. Using a whole cell RRA, we found that CNP binding was increased by 2-fold in granulosa cells taken from animals treated with either DES or eCG. Semiquantitative RT-PCR revealed that granulosa cells from DES- or eCG-treated animals have increased levels of NPR-B messenger RNA (mRNA) transcripts, which was in good agreement with the increased binding. The activity of the receptors was assessed by ligand-dependent stimulation of cGMP release. CNP, but not ANP, stimulated the release of cGMP from granulosa cells obtained from DES-treated, but not from eCG-treated, animals. The relative levels of CNP mRNA in granulosa cells were unaltered by either DES or eCG treatment. In contrast, CNP mRNA levels were increased more than 2-fold, but only in theca-interstitial from the eCG-treated animals. Our results indicate that CNP and NPR-B are expressed in the ovary, and their expression is responsive to hormonal treatments. Furthermore, expression of these components of the natriuretic peptide system appears to be compartmentalized, with CNP being derived from the extrafollicular compartment and acting, through NPR-B, on the granulosa cells.

Physiological variability of fluid-regulation hormones in young women

We tested the physiological reliability of plasma renin activity (PRA) and plasma concentrations of arginine vasopressin (P[AVP]), aldosterone (P[ALD]), and atrial natriuretic peptide (P[ANP]) in the early follicular phase and midluteal phases over the course of two menstrual cycles (n = 9 women, ages 25 +/- 1 yr). The reliability (Cronbach's alpha >/=0.80) of these hormones within a given phase of the cycle was tested 1) at rest, 2) after 2.5 h of dehydrating exercise, and 3) during a rehydration period. The mean hormone concentrations were similar within both the early follicular and midluteal phase tests; and the mean concentrations of P[ALD] and PRA for the three test conditions were significantly greater during the midluteal compared with the early follicular phase. Although Cronbach's alpha for resting and recovery P[ANP] were high (0.80 and 0.87, respectively), the resting and rehydration values for P[AVP], P[ALD], and PRA were variable between trials for the follicular (alpha from 0.49 to 0.55) and the luteal phase (alpha from 0.25 to 0. 66). Physiological reliability was better after dehydration for P[AVP] and PRA but remained low for P[ALD]. Although resting and recovery P[AVP], P[ALD], and PRA were not consistent within a given menstrual phase, the differences in the concentrations of these hormones between the different menstrual phases far exceeded the variability within the phases, indicating that the low within-phase reliability does not prevent the detection of menstrual phase-related differences in these hormonal variables.

Differential effects of rat pregnancy on uterine and lung atrial natriuretic factor receptors

We investigated if the refractoriness to the tocolytic effects of atrial natriuretic factor (ANF) during rat pregnancy is due to a downregulation of one or both guanylyl cyclase (GC)-coupled GC-A and GC-B ANF receptors; lungs were used as controls. Uteri and lungs of virgin, pregnant (days 7, 16, and 21), and day 2 postpartum rats expressed mRNAs for GC-A and GC-B as well as GC-uncoupled ANF-C receptors. GC-B receptor protein was more abundant than GC-A in uteri; the reverse was the case in lungs. Pregnancy decreased uterine mRNAs and proteins for GC-A and GC-B receptors as well as the effects of ANF and C-type natriuretic peptide (CNP) on uterine GC activity; lung ANF receptors and effects of ANF and CNP on lung GC activity were not modulated by pregnancy. It is concluded that pregnancy induces organ-specific modulation of ANF receptors and a downregulation of ANF-GC receptors would minimize interference with uterine motility during pregnancy.

Characteristics of ANP-binding sites in the adrenal capsules of term-pregnant rats

Significant increases of circulatory volume and plasma aldosterone levels are observed in pregnancy. We investigated whether a decrease of atrial natriuretic peptide (ANP) receptors in the adrenal zona glomerulosa (ZG) could explain the marked elevation of plasma aldosterone occurring during pregnancy. 125I-ANP binding was measured in competition experiments using rANP(1-28), ANP(4-23), a truncated analog which has high specificity for the ANP-C receptor, or a combination of both. Western blot experiments were also performed with an investigation into the effect of ANP on aldosterone secretion in adrenal capsule suspensions. 125I-ANP binding on adrenal ZG membranes was displaced by ANP(1-28) with an affinity (Kd) of 313 +/- 39 and 323 +/- 60 pM (NS) for pregnant and non-pregnant rats, respectively. The density of sites (Bmax) decreased slightly but not significantly during pregnancy. Displacement experiments with ANP(4-23) demonstrated a Bmax of 137 and 134 fmol/mg of proteins (NS) for pregnant and non pregnant rats, respectively. Studies were performed to block the ANP-C site. Displacing the remaining 125I-ANP binding with ANP(1-28) led to an affinity constant and receptor density which were not significantly different between the two groups of rats. The results obtained with Western blots showed a single band of 123 kDa with no significant variations in ANP-R1 receptors in the ZG during gestation. The sensitivity of potassium-, ACTH- or angiotensin II-stimulated aldosterone secretion to ANP was not altered by gestation. These data show that the apparent hyperaldosteronism found in normal term-pregnant rats is not the consequence of modifications in the affinity, number and properties of ANP receptor types or in the sensitivity of the aldosterone response to ANP.