Burnett, John C.

Recent studies have found endothelin-1 (ET), a potent vasoconstrictor of endothelial cell origin, is increased in congestive heart failure (CHF) in plasma and correlates with increased atrial pressures. Additionally, it has been shown that, despite increased circulating ET concentrations in CHF, a decreased responsiveness to exogenous ET infusion exists in an experimental model of CHF induced by rapid pacing. The present study was designed to determine whether plasma ET would be increased in a model of low cardiac output congestive failure without elevated atrial pressures produced by thoracic inferior vena caval constriction (TIVCC). In addition, we sought to determine whether this model of low cardiac output would show a full vasoconstrictive response to exogenous ET infusion and whether atrial natriuretic factor (ANF) infused acutely to achieve pathophysiological concentrations would modulate the systemic and renal hemodynamic responses to exogenous ET. Dogs were studied in the anesthetized state at 8-9 days after the TIVCC or sham operation. Baseline ET levels were significantly increased in the TIVCC dogs (n = 14) compared with sham operated dogs (n = 6; 41.4 +/- 7.1 vs. 17.9 +/- 1.5 pg/ml, respectively; P less than 0.05). With exogenous ET infusion (5 ng.kg-1.min-1), an intact systemic and renal vasoconstrictor response in the TIVCC dogs was observed. ANF prevented the systemic vascular and arterial pressure responses to ET. However, the potent renal vasoconstricting action of ET was not prevented by ANF. These studies suggest that ET may play an important role in maintaining blood pressure in the setting of low cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)

Experiments were designed to determine whether chronic increases in arterial blood flow alter production of or response to nitric oxide and endothelin. Canine femoral arteries proximal to an arteriovenous fistula- and from the contralateral sham-operated blood vessels were removed, cut into rings, and suspended for measurement of isometric force in organ chambers. The remainder of the artery was homogenized for measurement of endothelin content by radioimmunoassay. NG-monomethyl-L-arginine (10(-4) M) caused concentration-dependent increases in tension only in fistula-operated arteries. Endothelium-dependent relaxations to acetylcholine and BHT-920 were greater in fistula- compared with sham-operated arteries. These differences were reduced by the arginine analogue. Pertussis toxin (100 ng/ml) inhibited relaxations to acetylcholine only in fistula-operated arteries and to BHT-920 only in sham-operated arteries. Contractions to endothelin-1 were greater in fistula- compared with sham-operated arteries. These results suggest that chronic increases in blood flow enhance the tonic and receptor-stimulated production of nitric oxide and its release by receptors coupled to pertussis toxin-sensitive guanine nucleotide regulatory proteins. Furthermore, chronic increases in blood flow may either inhibit the production of endothelin or promote its depletion from endothelial cells while simultaneously increasing the sensitivity of the smooth muscle to its contractile effects.

Experiments were designed to compare the sensitivity of venous and arterial smooth muscle to endothelin and to determine whether contractions to the peptide could be inhibited by endothelium-derived relaxing factor and nitric oxide. Rings of canine left anterior descending coronary, femoral, and mesenteric arteries and femoral and saphenous veins with and without endothelium were suspended for measurement of isometric force. In the presence of indomethacin, phentolamine, and propranolol, endothelin initiated concentration-dependent increases in tension in all rings. The veins were more sensitive to the peptide than were the arteries. Endothelin depolarized the smooth muscle of the saphenous veins and mesenteric arteries; the threshold concentration for depolarization was approximately 100 times lower in the veins (10(-10) M) than in the arteries (10(-8) M). Removal of the endothelium enhanced the sensitivity only of venous smooth muscle to endothelin. However, stimulation of the endothelium in the arteries with either acetylcholine or the calcium ionophore A23187 rapidly inhibited the maximal tension developed to the peptide. Nitric oxide inhibited contractions to endothelin in arteries and veins without endothelium; the inhibition was greater in the arteries than in the veins. These results indicate that venous smooth muscle is more sensitive than arterial smooth muscle to endothelin. In both blood vessels, endothelium-derived relaxing factor(s) can inhibit contractions to the peptide.

Studies were performed in two groups of anesthetized dogs (n = 5 per group) to determine the cardiovascular and renal actions of synthetic C-type natriuretic peptide (CNP). Systemic infusion of CNP (group 1; 10 and 50 ng.kg-1.min-1 iv) resulted in marked cardiovascular hemodynamic effects characterized by a decrease in mean arterial pressure, cardiac output, and atrial pressures in association with a decrease in sodium excretion. Bolus administration of CNP (group 2; 5 micrograms/kg iv) to minimize cardiovascular hemodynamic changes resulted in only a transient decrease in arterial pressure. Sodium excretion decreased despite a return of arterial pressure to baseline. These biological responses were associated with increases in plasma guanosine 3',5'-cyclic monophosphate (cGMP) in both groups but with no change in urinary cGMP. With both systemic infusion or bolus administration of CNP, significant increases in plasma aldosterone were observed in association with increases in distal nephron sodium reabsorption. This study demonstrates that CNP exhibits profound systemic hemodynamic actions and is indirectly, or perhaps directly, antinatriuretic.

The aim of the present study was to investigate the influence of inhibitors of endothelium-dependent relaxing factor on the release of atrial natriuretic factor from isolated rat atria. Electrical stimulation of the tissue produced a frequency-dependent increase in secretion of atriopeptide from basal levels. Saponin (0.3 mg/ml for 45 min) augmented the basal release of the peptide. Methylene blue (10(-5)M), oxyhemoglobin (10(-6)M), or hydroquinone (10(-5)M), agents that inhibit the effects of endothelium-derived relaxing factor by different mechanisms, caused an increase in the basal secretion of atrial natriuretic factor. Blockade of cyclooxygenase with indomethacin (10(-5)M) did not alter the release of atriopeptide, suggesting that it is not controlled by endogenous prostaglandins. These results would be explained if the inhibitors tested were to interfere with a factor released continuously from either endocardial cells or endothelial cells of the atrial blood vessels and having the same nature as endothelium-derived relaxing factor. Such release may exert a tonic negative modulatory influence on the secretion of atrial natriuretic factor.

Cenderitide is a novel designer natriuretic peptide (NP) composed of C‐type natriuretic peptide (CNP) fused to the C‐terminus of Dendroaspis natriuretic peptide (DNP). Cenderitide was engineered to coactivate the two NP receptors, particulate guanylyl cyclase (pGC)‐A and ‐B. The rationale for its design was to achieve the renal‐enhancing and antifibrotic properties of dual receptor activation, but without clinically significant hypotension. Here we report the first clinical trial on the safety, tolerability, and cyclic guanosine monophosphate (cGMP) activating properties of Cenderitide in subjects with stable heart failure (HF). Four‐hour infusion of Cenderitide was safe, well‐tolerated, and significantly increased plasma cGMP levels and urinary cGMP excretion without adverse effects with no change in blood pressure. Thus, Cenderitide has a favorable safety profile and expected pharmacological effects in stable human HF. Our results support further investigations of Cenderitide in HF as a potential future cGMP‐enhancing therapeutic strategy.

The natriuretic peptides (NPs) B-type NP (BNP) and urodilatin (URO) exert renal protective properties via the particulate guanylyl cyclase A receptor (pGC-A). As a potential renal-enhancing strategy, we engineered a novel designer peptide that we call CRRL269. CRRL269 was investigated in human cell lines and in normal canines to define potential cardiorenal enhancing actions. The mechanism of its cardiorenal selective properties was also investigated. In vitro NP receptor activity was quantified with guanosine 3′,5′-cyclic monophosphate generation. In vivo effects were determined in normal canine acute infusion studies. We observed that CRRL269 demonstrated enhanced pGC-A activity in renal compared with nonrenal cell lines. CRRL269 exerted enhanced resistance to neprilysin compared with URO. Importantly, CRRL269 exhibited significant and greater increases in urinary sodium excretion and diuresis, with less blood pressure reduction, than BNP or URO in normal canines. CRRL269 retained potent renin-angiotensin-aldosterone system (RAAS) suppressing properties shared by URO and BNP. Also, CRRL269 exerted less arterial relaxation and higher cAMP cardiomyocytes generation than BNP. CRRL269 possessed superior renal and pGC-A activating properties compared with BNP or URO in vitro. CRRL269 exerted enhanced renal actions while suppressing RAAS in vivo and with less hypotension compared with URO or BNP. Together, our study suggests that CRRL269 is a promising innovative renal-enhancing drug, with favorable protective actions targeting cardiorenal disease states through the pGC-A receptor.

The release of Ca2+ from intracellular stores is a fundamental element of signaling pathways involved in regulation of vascular tone, proliferation, apoptosis, and gene expression. Studies of sea urchin eggs have led to the identification of three functionally distinct Ca2+ signaling pathways triggered by IP3, cADPR, and NAADP. The coexistence and functional relevance of these distinct intracellular Ca2+ release systems has only been described in a few mammalian cell types. The purpose of this study was to determine whether the IP3, cADPR, and NAADP Ca2+ release systems coexist in smooth muscle cells (SMC) and to determine the specificity of these intracellular Ca2+ release pathways. Microsomes were prepared from rat aortic SMC (VSMC) and were loaded with 45Ca2+. cADPR, NAADP, and IP3 induced Ca2+ release from VSMC microsomes in a dose-dependent fashion. Heparin blocked only IP3-mediated Ca2+ release, whereas the ryanodine channel inhibitors 8-Br-cADPR and ruthenium red blocked only cADPR-induced Ca2+ release. Nifedipine, an L-type Ca2+ channel blocker, inhibited NAADP elicited Ca2+ release, but had no effect on IP3- or cADPR-mediated Ca2+ release. An increase in pH from 7.2 to 8.2 inhibited cADPR-mediated Ca2+ release, but had no effect on IP3- or NAADP-induced Ca2+ release. By RT-PCR, VSMC expressed ryanodine receptor types 1, 2, and 3. Ca2+-dependent binding of [3H]-ryanodine to VSMC microsomes was enhanced by the ryanodine receptor agonists 4-chloro-methyl-phenol (CMP) and caffeine, but was inhibited by ruthenium red and cADPR. We conclude that VSMC possess at least three functionally distinct pathways that promote intracellular Ca2+ release. IP3-, cADPR-, and NAADP-induced intracellular Ca2+ release may play a critical role in the maladaptive responses of VSMC to environmental stimuli that are characteristically associated with hypertension and/or atherogenesis.

Breast cancer radiotherapy increases the risk of heart failure with preserved ejection fraction (HFpEF). Cardiomyocytes are highly radioresistant, but radiation specifically affects coronary microvascular endothelial cells, with subsequent microvascular inflammation and rarefaction. The effects of radiation on left ventricular (LV) diastolic function are poorly characterized. We hypothesized that cardiac radiation exposure may result in diastolic dysfunction without reduced EF. Global cardiac expression of the sodium-iodide symporter (NIS) was induced by cardiotropic gene (adeno-associated virus serotype 9) delivery to 5-wk-old rats. SPECT/CT (125I) measurement of cardiac iodine uptake allowed calculation of the 131I doses needed to deliver 10- or 20-Gy cardiac radiation at 10 wk of age. Radiated (Rad; 10 or 20 Gy) and control rats were studied at 30 wk of age. Body weight, blood pressure, and heart rate were similar in control and Rad rats. Compared with control rats, Rad rats had impaired exercise capacity, increased LV diastolic stiffness, impaired LV relaxation, and elevated filling pressures but similar LV volume, EF, end-systolic elastance, preload recruitable stroke work, and peak +dP/d t. Pathology revealed reduced microvascular density, mild concentric cardiomyocyte hypertrophy, and increased LV fibrosis in Rad rats compared with control rats. In the Rad myocardium, oxidative stress was increased and in vivo PKG activity was decreased. Experimental cardiac radiation exposure resulted in diastolic dysfunction without reduced EF. These data provide insight into the association between cardiac radiation exposure and HFpEF risk and lend further support for the importance of inflammation-related coronary microvascular compromise in HFpEF. NEW & NOTEWORTHY Cardiac radiation exposure during radiotherapy increases the risk of heart failure with preserved ejection fraction. In a novel rodent model, cardiac radiation exposure resulted in coronary microvascular rarefaction, oxidative stress, impaired PKG signaling, myocardial fibrosis, mild cardiomyocyte hypertrophy, left ventricular diastolic dysfunction, and elevated left ventricular filling pressures despite preserved ejection fraction.