N. P. Wiklund

Endogenous nitric oxide is present in the exhaled air of rabbits, guinea pigs and humans

The presence of nitric oxide (NO) in the exhaled air of humans and of anaesthetized rabbits and guinea pigs was demonstrated by chemiluminescence, diazotization and mass spectrometry. This NO is endogenously produced in the lung by an NO synthase, since its generation in guinea pigs and rabbits was inhibited by N omega-nitro-L-arginine methyl ester and NG-monomethyl-L-arginine, inhibitors of this enzyme. The effect of the inhibitors was reversed by the precursor of NO synthesis, L-arginine. Since NO is produced by normal vascular endothelium for the physiological regulation of blood flow and pressure and also by activated macrophages to contribute to non-specific immunity, our experiments suggest that NO may play both vascular regulatory and host defence roles in pulmonary physiology and pathophysiology.

Release of nitric oxide evoked by nerve stimulation in guinea-pig intestine.

Non-adrenergic non-cholinergic nerves provide the main inhibitory autonomic supply to intestinal smooth muscle and other organ systems. Nitric oxide is likely to act as a neurotransmitter in these nerves and a nitric oxide synthase has been demonstrated in autonomic neurons. However, there are as yet no biochemical measurements of nerve-induced release of nitric oxide or its breakdown products nitrite and nitrate. We have examined the possibility that nitric oxide is released by stimulation of autonomic nerves in the guinea-pig intestine by studying the release of nitric oxide, nitrite and nitrate. The biological activity of a vascular relaxing factor released by the activation of these nerves was compared with that of nitric oxide using a bioassay system as previously described. Nitrite and nitrate release were measured by high-performance liquid chromatography using UV absorbance. The relaxation of the bioassay tissues to nerve stimulation was indistinguishable from the relaxation induced by nitric oxide. Both relaxations were equally unstable and inhibited to a similar degree by haemoglobin and enhanced by superoxide dismutase. Furthermore, the release of the relaxing factor was attenuated by treatment with the nitric oxide synthase inhibitor N omega-nitro-L-arginine. Concomitant with the release of the relaxing factor, which was frequency dependent, there was a frequency-dependent release of nitrite and nitrate in amounts sufficient to explain the vascular relaxations observed during nerve stimulation. The release of nitrite and nitrate was also inhibited by treatment with the nitric oxide synthase inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

VISUALISATION OF NITRIC OXIDE RELEASED BY NERVE STIMULATION

We have visualised nitric oxide (NO) released from the electrically stimulated myenteric plexus and hypogastric nerve. NO was visualised by a reaction with luminol and hydrogen peroxide to generate photons which were counted using a microscope coupled to a photon counting camera. Electrical stimulation of the tissues induced an increase in photon counts which was frequency‐dependent and prevented by inhibition of the NO synthase or by tetrodotoxin. The light emitted during nerve stimulation was not only observed at the nerve terminals but also at the axon and soma. Our results indicate that NO released from the whole nerve cell may affect target cells surrounding all parts of the nitrergic neuron. Thus, NO functions as a unique mechanism of synaptic and non‐synaptic communication in the nervous system. J. Neurosci. Res. 47:224–232, 1997.

Adenosine enhancement of adrenergic neuroeffector transmission in guinea-pig pulmonary artery.

1 Adenosine and its derivatives N6‐[(R)−1‐methyl‐2‐phenylethyl]adenosine (R‐PIA) or 5′‐N‐ethylcarboxamideadenosine (NECA) enhanced nerve‐induced contractile responses and augmented the basal smooth muscle tone in transmurally stimulated isolated strips of the guinea‐pig pulmonary artery. 2 Adenosine, R‐PIA and NECA enhanced contractile responses induced by noradrenaline, whereas N6‐[(S)−1‐methyl‐2‐phenylethyl]‐adenosine (S‐PIA) was virtually inactive. 3 Adenosine, R‐PIA and NECA inhibited the nerve stimulation evoked release of [3H]‐noradrenaline. However, the total release of [3H]‐noradrenaline during the periods of NECA application was increased. 4 The nucleoside effects were blocked by the adenosine receptor antagonist 8‐p‐sulphophenyltheophylline. 5 8‐p‐Sulphophenyltheophylline inhibited nerve‐induced contractions and lowered basal muscle tone in preparations not having received any exogenous purines. 6 It is suggested that the observed stimulatory effects on muscle tone and on contractile responses to transmural nerve stimulation are mainly due to action at postjunctional stimulatory A1 adenosine receptors. In addition, actions at prejunctional inhibitory A1 and stimulatory A2 adenosine receptors are evident in this preparation.

Smooth muscle relaxing effects of NO, nitrosothiols and a nerve-induced relaxing factor released in guinea-pig colon.

1 The aim of the present study was to compare the biological activity of S‐nitroso‐L‐cysteine (CYSNO), S‐nitrosoglutathione (GSNO), S‐nitroso‐N‐acetyl‐D, L‐penicillamine (SNAP) and hydrox‐ylamine to that of nitric oxide (NO) and a vascular relaxing factor released by nerve stimulation in the guinea‐pig intestine. The biological activity was examined in a bioassay system with guinea‐pig colon as donor tissue and a series of spiral strips of rabbit aorta without endothelium as detector tissues. 2 Electrical stimulation of the guinea‐pig colon released a vascular relaxing factor. The half‐life of the relaxing factor down the bioassay cascade was the same as exogenously applied NO. Nω‐nitro‐L‐arginine (L‐NOARG) inhibited the release of bioactivity. 3 The relaxations of the assay tissues caused by exogenous CYSNO also declined during the passage down the cascade. However, in the presence of L‐cysteine (10−5 m) the half‐life of CYSNO increased and there was no significant breakdown through the cascade. In contrast, the half‐life of applied NO and the vascular relaxing factor released by nerve stimulation was unaffected by the presence of L‐cysteine. 4 Exogenously applied GSNO (20–50 nm), SNAP (2–4 nm) and hydroxylamine (300–600 nm) caused relaxations that did not decline during the passage down the cascade. 5 In summary, the relaxation of the bioassay tissues during nerve stimulation was indistinguishable from the relaxation induced by NO, whereas relaxations induced by CYSNO, GSNO, SNAP and hydroxylamine showed different pharmacological profiles. The released bioactivity is thus likely to be NO itself.

Inhibitors of phosphodiesterase 5 (PDE 5) inhibit the nerve‐induced release of nitric oxide from the rabbit corpus cavernosum

Nitrergic neurons are important for erectile responses in the corpus cavernosum and impaired signalling results in erectile dysfunction, today treated successfully by oral administration of the selective phosphodiesterase 5 (PDE 5) inhibitors sildenafil, tadalafil and vardenafil. Although the importance of nitrergic neurons in urogenital function has become evident, it has not been investigated if the PDE 5 inhibitors affect the nerve‐induced release of nitric oxide (NO). In a previous study we found that the soluble guanylate cyclase (sGC)/cyclic guanosine 3’,5’–monophosphate (cGMP) pathway might modulate nerve‐induced release of NO in isolated cavernous tissue.