Heme oxygenase activity in the internal anal sphincter: effects of nonadrenergic, noncholinergic nerve stimulation.
OBJECTIVE
To date, the exact role of carbon monoxide (CO) in the nonadrenergic, noncholinergic (NANC) relaxation is not known. This is partly related to the lack of an appropriate method to measure heme oxygenase (HO) activity in the gastrointestinal tissues.


METHODS
HO activity of the opossum internal anal sphincter (IAS) smooth muscle was determined using a newly developed assay system that used radiolabeled hemin as a substrate. Enzyme activity of the IAS tissues was measured in the basal state, after electric field stimulation (EFS), ganglionic stimulant dimethyl diphenyl piperazinium iodide (DMPP), and neuropeptide vasoactive intestinal polypeptide (VIP). The presence and localization of HO was examined by Western blot analysis and immunocytochemistry.


RESULTS
NANC nerve stimulation of the IAS smooth muscle by EFS (0.25-5 Hz), DMPP, and VIP caused a significant increase in the HO activity of the IAS. The increase in HO activity by EFS was inhibited by the HO inhibitor Tin protoporphyrin (1 x 10(-4) mol/L). Both HO-1 and HO-2 were present in the IAS tissue extracts, and both enzymes were localized in the neurons of the myenteric plexus. The method for HO activity determination used in the present study was found to be reliable and reproducible.


CONCLUSIONS
The data suggest that the HO pathway may have a role in neurally mediated relaxation of the IAS. The exact site of involvement and the source of HO activity, however, remains to be determined.
Chakder
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S
Division of Gastroenterology and Hepatology, Department of Medicine, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
Cao
G Y
GY
Lynn
R B
RB
Rattan
S
S
D001003:Anal Canal / Q000201:enzymology*; D000818:Animals; D015153:Blotting, Western; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D051547:Heme Oxygenase-1; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008665:Metalloporphyrins / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology / Q000294:innervation / Q000502:physiology; D009197:Myenteric Plexus / Q000166:cytology / Q000201:enzymology; D009424:Nervous System Physiological Phenomena; D009474:Neurons / Q000201:enzymology; D009893:Opossums; D011524:Protoporphyrins / Q000494:pharmacology; D014018:Tissue Distribution; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D007527:Isoenzymes; D008665:Metalloporphyrins; D011524:Protoporphyrins; D014660:Vasoactive Intestinal Peptide; D004246:Dimethylphenylpiperazinium Iodide; C032628:tin protoporphyrin IX; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C105245:heme oxygenase-2