Group B Streptococcus and E. coli LPS‐induced NO‐dependent hyporesponsiveness to noradrenaline in isolated intrapulmonary arteries of neonatal piglets

Abstract

The effects of endotoxin (E. coli lipopolysaccharide, LPS) and heat inactivated group B Streptococcus (GBS) were studied on the contractile responses to noradrenaline (NA) in isolated pulmonary arteries and on the activity of the constitutive and inducible nitric oxide synthase (NOS) in lung fragments of neonatal piglets. Short‐term (≤ 5 h) incubation with LPS (1 μg ml−1) or GBS (3 × 107 colonies forming units ml−1) did not modify the vascular responsiveness to NA (10−8 M‐10−4 m) in isolated intrapulmonary arteries. However, long‐term incubation (20 h) with LPS or GBS produced a significant reduction in the maximal contractile responses and shifted the concentration‐response curve for NA downwards. Endothelium removal or the cyclo‐oxygenase inhibitor meclofenamate (10−5 m) did not affect the GBS‐ and LPS‐induced hyporesponsiveness to NA. The presence of the nitric oxide (NO) precursor, l‐arginine (10−5 m), 30 min prior to the contractility challenge increased the LPS‐ and GBS‐induced pulmonary vascular hyporesponsiveness to NA. In contrast, the addition, prior to the challenge with NA, of the NOS inhibitor NG‐nitro‐l‐arginine methyl ester (l‐NAME, 10−4m) or coincubation with dexamethasone (3 × 10−6m), a potent inhibitor of the induction of NOS, or with the protein synthesis inhibitor cycloheximide (10−5 m) completely restored the reactivity to NA in LPS‐ and GBS‐treated pulmonary arteries. The incubation for 20 h of lung fragments with LPS and GBS produced a significant increase in the Ca2+‐independent (inducible) NOS activity determined by the conversion of radiolabelled l‐arginine to citrulline, but did not modify the constitutive NOS activity. This NOS induction was abolished by coincubation with dexamethasone (3 × 10−6 m). These results demonstrated that prolonged incubation with GBS and LPS causes an induction of NOS activity which results in a reduced vascular responsiveness to NA in pulmonary arteries of neonatal piglets. Thus, induction of NOS seems to be responsible for the delayed pulmonary vascular hyporesponsiveness induced by GBS (a Gram‐positive) and E. coli (a Gram‐negative), the most common causal agents of neonatal sepsis.

Role of nitric oxide in the circulatory failure and organ injury in a rodent model of Gram‐positive shock

“…Moreover, aminoguanidine also reduces the circulatory failure and liver dysfunction caused by endotoxin in the rat , which is secondary to an enhanced formation of NO by iNOS heat-inactivated group B streptococci also resulted in induction of iNOS activity and vascular hyporeactivity to the contractile responses elicited by noradrenaline. This vascular hyporeactivity is prevented by pretreatment of the vessels with dexamethasone or the protein synthesis inhibitor cycloheximide, attenuated by the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), and augmented by the addition of L-arginine to the medium (Villamor et al, 1995). Thus, whole Gram-positive bacteria (Villamor et al, 1995) This study also demonstrates that dexamethasone and aminoguanidine attenuate the fall in Pao2, hence, respiratory dysfunction, caused by co-administration of LTA + PepG suggesting that NO mediates this adverse effect.…”

“…This vascular hyporeactivity is prevented by pretreatment of the vessels with dexamethasone or the protein synthesis inhibitor cycloheximide, attenuated by the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME), and augmented by the addition of L-arginine to the medium (Villamor et al, 1995). Thus, whole Gram-positive bacteria (Villamor et al, 1995) This study also demonstrates that dexamethasone and aminoguanidine attenuate the fall in Pao2, hence, respiratory dysfunction, caused by co-administration of LTA + PepG suggesting that NO mediates this adverse effect. The respiratory dysfunction in septic shock is charaterized by a reduction in pulmonary oxygen uptake resulting in a fall in Pao2 (Deitsch, 1992).…”

Hypoxic pulmonary blood flow redistribution and arterial oxygenation in endotoxin-challenged NOS2-deficient mice

“…The existing evidence is controversial, with reports suggesting that HPV is either increased (11,12) or unchanged (13,14) after acute inhibition of NO formation with L-arginine analogs during sepsis. After an endotoxin challenge, suppression of NOS2 expression with dexamethasone and inhibition of NOS2 activity by administration of L-arginine analogs restore vascular reactivity to vasoconstrictors in both systemic (15) and pulmonary vessels (16). However, the use of L-arginine analogs or dexamethasone to evaluate the role of NOS2 in the endotoxin-induced impairment of HPV is limited by the incomplete specificity of these agents for NOS2.…”

The Role of Endothelin Converting Enzyme Inhibition during Group B Streptococcus–Induced Pulmonary Hypertension in Newborn Piglets

“…This effect may not be significant inasmuch as administration of superoxide dismutase did not attenuate GBS-induced pulmonary hypertension in the lamb (23). Additionally, during sepsis, there may be increased release of nitric oxide systemically (24,25), which can result in increased peroxynitrite levels. Peroxynitrite has been shown to inhibit endothelial nitric oxide synthase (eNOS) activity, although the mechanism is unknown (21).…”

“…The participation of these cytokines in the systemic inflammatory response syndrome and cardiovascular failure has been established and is described to contribute to the observed systemic hypotension (9,15). Second, sepsis induces nitric oxide synthase (iNOS) in the endothelial and vascular smooth muscle cells, enhancing vasodilatation especially during the late phase of sepsis (24,25). Moreover, Markewitz et al (27) demonstrated that ET-1 decreased iNOS mRNA in cytokine-stimulated rat epithelial cells and this effect was reversed by phosphoramidon.…”