J Neurogastroenterol Motil.  2016 Jan;22(1):141-148. 10.5056/jnm15036.

Three Gaseous Neurotransmitters, Nitric oxide, Carbon Monoxide, and Hydrogen Sulfide, Are Involved in the Neurogenic Relaxation Responses of the Porcine Internal Anal Sphincter

• Folasire O
• Mills KA
• Sellers DJ
• Chess-Williams R

• KMID: 2379713
• DOI: http://doi.org/10.5056/jnm15036

Abstract

BACKGROUND/AIMS
The internal anal sphincter (IAS) plays an important role in maintaining continence and a number of neurotransmitters are known to regulate IAS tone. The aim of this study was to determine the relative importance of the neurotransmitters involved in the relaxant and contractile responses of the porcine IAS.
METHODS
Responses of isolated strips of IAS to electrical field stimulation (EFS) were obtained in the absence and presence of inhibitors of neurotransmitter systems.
RESULTS
Contractile responses of the sphincter to EFS were unaffected by the muscarinic receptor antagonist, atropine (1 muM), but were almost completely abolished by the adrenergic neuron blocker guanethidine (10 muM). Contractile responses were also reduced (by 45% at 5 Hz, P < 0.01) following desensitisation of purinergic receptors with alpha,beta-methylene-ATP (10 muM). In the presence of guanethidine, atropine, and alpha,beta-methylene-ATP, the remaining relaxatory responses to EFS were examined. These responses were not altered by the cyclooxygenase inhibitor, indomethacin (5 muM), the vasoactive intestinal polypeptide receptor antagonist, [D-p-Cl-Phe6,Leu17]-vasoactive intestinal peptide (PheLeu-VIP; 100 nM), or the purinoceptor antagonists, 8-phenyltheophyline (P1 receptors) or suramin (P2 receptors). However, relaxation responses were reduced by Nomega-nitro-L-arginine (L-NNA; 100 muM), an inhibitor of nitric oxide synthesis (40-50% reduction), zinc protoprophyrin IX (10 muM), an inhibitor of carbon monoxide synthesis (20-40% reduction), and also propargylglycine (30 muM) and aminooxyacetic acid (30 muM), inhibitors of hydrogen sulphide synthesis (15-20% reduction).
CONCLUSIONS
Stimulation of IAS efferent nerves releases excitatory and inhibitory neurotransmitters: noradrenaline is the predominant contractile transmitter with a smaller component from ATP, whilst 3 gases mediate relaxation responses to EFS, with the combined contributions being nitric oxide > carbon monoxide > hydrogen sulfide.

Keyword

Anal canal; Autonomic nerves; Carbon monoxide; Hydrogen sulfide; Nitric oxide

MeSH Terms

Adenosine Triphosphate
Adrenergic Neurons
Aminooxyacetic Acid
Anal Canal*
Atropine
Autonomic Pathways
Carbon Monoxide*
Carbon*
Gases
Guanethidine
Hydrogen Sulfide*
Hydrogen*
Indomethacin
Neurotransmitter Agents*
Nitric Oxide*
Norepinephrine
Prostaglandin-Endoperoxide Synthases
Purinergic Antagonists
Receptors, Muscarinic
Receptors, Purinergic
Relaxation*
Suramin
Vasoactive Intestinal Peptide
Zinc
Adenosine Triphosphate
Aminooxyacetic Acid
Atropine
Carbon
Carbon Monoxide
Gases
Guanethidine
Hydrogen
Hydrogen Sulfide
Indomethacin
Neurotransmitter Agents
Nitric Oxide
Norepinephrine
Prostaglandin-Endoperoxide Synthases
Purinergic Antagonists
Receptors, Muscarinic
Receptors, Purinergic
Suramin
Vasoactive Intestinal Peptide
Zinc