Hypoxic coronary vasodilatation and cGMP overproduction are blocked by a nitric oxide synthase inhibitor, but not by a guanylyl cyclase ANF receptor antagonist

Increased release of nitric oxide in ischemic hearts after exercise in patients with effort angina

OBJECTIVES

The aim of this study was to determine whether the release of nitric oxide (NO) from the ischemic heart increases during exercise in patients with effort angina.

BACKGROUND

Myocardial ischemia increases NO production in the canine heart, but no such increase has been demonstrated in the ischemic human heart.

METHODS

Fifteen patients with effort angina underwent supine ergometer exercise tests. All patients had severe proximal stenosis (>90%) in the left anterior descending coronary artery. The control group consisted of 17 subjects without coronary artery disease or systemic hemodynamic abnormalities.

RESULTS

Neither the lactate extraction ratio (LER) nor the difference in NO concentration between coronary venous and arterial blood (deltaVA[NO]) was affected by exercise in the control subjects. In patients with effort angina, neither variable differed from that in the control group at rest; however, exercise markedly decreased LER and significantly increased deltaVA(NO) (from 4.7 +/- 0.3 to 16.5 +/- 1.6 micromol/liter, p < 0.001) in the patient group. The extent of decrease in LER was significantly correlated with the extent of increase in deltaVA(NO) in the patients with effort angina (r2 = -0.837, p < 0.001).

CONCLUSIONS

Provocation of myocardial ischemia by exercise stress increases NO production in the hearts of patients with effort angina.

Role of guanylyl cyclase receptors for CNP in salt secretion by shark rectal gland

The role of C-type natriuretic peptide (CNP) and its guanylyl cyclase-linked receptors in mediating salt secretion by the rectal gland of the spiny dogfish shark (Squalus acanthias) was investigated using HS-142-1, a competitive inhibitor of the binding of natriuretic peptides to their guanylyl cyclase receptors. CNP binds to receptors and activates guanylyl cyclase in rectal gland membranes in a way that is inhibited by HS-142-1. Guanylyl cyclase activation in rectal gland membranes is far more sensitive to CNP than to atrial natriuretic peptide, whereas the reverse is true for membranes derived from mammalian (rabbit) renal collecting duct cells. HS-142-1 inhibited the stimulatory effect of CNP on ouabain-inhibitable oxygen consumption by rectal gland tubules. In explanted rectal glands continuously perfused with blood from intact donor sharks, HS-142-1 inhibited the increase in salt secretion normally provoked by infusing isotonic saline solutions into the donor animal. These results strongly support the view that CNP released into the systemic circulation in response to volume expansion mediates the secretion of chloride by the rectal gland via receptors linked to guanylyl cyclase.

Neutral endopeptidase 24.11 in neutrophils modulates protective effects of natriuretic peptides against neutrophils-induced endothelial cytotoxity

This study was performed to determine effects of atrial and brain natriuretic peptides (ANP, BNP) on neutrophils-induced endothelial injury which is known to play a role in the pathophysiology of ischemia/reperfusion myocardial injury and to examine whether the effects of ANP and BNP on neutrophils are modulated by neutral endopeptidase 24.11 (NEP) in neutrophils themselves. The incubation of human neutrophils with ANP and BNP inhibited the neutrophils-induced detachment of cultured human endothelial cells (HEC). The inhibitory effect of ANP and BNP was associated with the suppressions of the neutrophils adhesiveness to HEC, CD18 expression on the neutrophils and elastase release from the neutrophils. Coincubation with UK73967 or phosphoramidon, inhibitors of NEP, potentiated all of the effects of ANP and BNP on the neutrophil functions, and the NEP inhibitors protected degradation of ANP and BNP by the neutrophils. NEP enzymatic activity in the particulate fractions and immunoreactive NEP expression were found to increase in the neutrophils from patients with early phase of acute myocardial infarction (AMI) by 5.2- and by 4.2-fold of the neutrophils from patients with late phase of AMI, respectively. In an in vivo canine model of myocardial ischemia/reperfusion, the intravenous administration of UK73967 suppressed the neutrophil adherence to endothelium and the neutrophil accumulation in the ischemic/reperfused myocardium. The results indicate that ANP and BNP, which are known to increase in AMI, modulate the neutrophil functions and exert protective effects against the neutrophils-induced endothelial cytotoxity. But the effects are suppressed due to their degradation by the neutrophil own NEP. Thus, neutrophil NEP, which also increases in AMI, may play a role in the pathophysiology of neutrophils-mediated ischemia/reperfusion endothelial and myocardial injury.