Nitric oxide as modulator of cholinergic neurotransmission in gastric muscle of rabbits.
The effects of the nitric oxide (NO) synthesis inhibitors, NG-nitro-L-arginine (L-NNA) and NG-nitro-L-arginine methyl ester (L-NAME), on the electrical field stimulation (EFS)-induced inhibitory responses were investigated. EFS caused, in strips contracted by means of substance P (SP), prostaglandin F2 alpha (PGF2 alpha), or carbachol (CCh), a fast relaxant response that, depending on stimulation frequency and strip tension, could be followed by a slower, sustained relaxation. The NO synthesis inhibitors blocked the EFS-induced fast relaxations and often reversed them into contractions; these effects were greatly counteracted in SP- or PGF2 alpha-treated strips by scopolamine or atropine. In CCh-precontracted strips, either L-NNA or L-NAME became progressively unable to block the EFS-induced fast relaxations as the CCh concentration was increased. The NO synthesis inhibitors greatly reduced the sustained relaxant responses elicited either by EFS or exogenous vasoactive intestinal polypeptide (VIP). The results indicate that the NO synthesis inhibitors abolish the neurally induced fast relaxation by interfering with the cholinergic excitatory pathway. The involvement of both VIP and NO in sustained relaxations is also suggested.
Baccari
M C
MC
Department of Physiology, University of Florence, Italy.
Iacoviello
C
C
Calamai
F
F
D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009433:Neural Inhibition / Q000187:drug effects; D009569:Nitric Oxide / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000502:physiology*; D011817:Rabbits; D013270:Stomach / Q000187:drug effects / Q000502:physiology*; D013373:Substance P / Q000494:pharmacology; D009435:Synaptic Transmission; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D004791:Enzyme Inhibitors; D019335:Nitroarginine; D009569:Nitric Oxide; D013373:Substance P; D014660:Vasoactive Intestinal Peptide; D002217:Carbachol; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester