Effect of Nitric Oxide Synthase Inhibitor Nitro-L-Arginine on NADPH-d Staining in Myenteric Nerves of stimulated Guinea Pig Ileum and Monse Colon
Schwartz, Eric J.
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Relaxation of smooth muscle in the gastrointestinal tract is regulated by the release of nonadrenergic noncholinergic (NANC) neurotransmitters from enteric inhibitory nerves. Nitric oxide synthase (NOS) synthesizes nitric oxide (NO) which acts as a NANC inhibitory transmitter. In hind-limb vasculature of the rat it has been shown that nerve mediated increases in blood flow are due to vasodilation caused by the release of NO from pre-formed stores. The stores could be depleted by repeated nerve stimulation in the presence of a NOS inhibitor. These stores of NO are believed to be labeled by nicotinamide adenine dinuecleotide phosphatase diaphorase (NADPH-d) staining. In the present studies we tested the possibility of NO being held as a stored form within the terminals of enteric inhibitory nerves through attempting to deplete NO stores by stimulating the release of NO in the presence of NOS inhibitor nitro-L-arginine (NLA). Longitudinal muscle myenteric plexus (LMMP) or mouse colon tissues were prepared on tissue racks containing platinum electrodes and placed in tissue baths (37 °C). Tonal contractions were induced by adding histamine (10 µM), and measured with a force transducer and polygraph chart recorder. Relaxations of LMMPs and mouse colon tissues were achieved by either electrical stimulation (150 V), a high K+Krebs (60 mM) solution, or in the mouse colon with nicotinic agonist dimethylphenylpiperzimium (10 µM). Following stimulation, tissues were stained with NADPH-d. NANC relaxations were blocked by NLA, but no depletion or decrease in NADPH-d staining was observed in the tissues. We conclude, therefore, that myenteric neurons do, not contain NLA depletable preformed stores of NO that can be localized by NADPH-d staining.