Biphasic relaxation of the opossum lower esophageal sphincter: roles of NO., VIP, and CGRP.
Vasoactive intestinal polypeptide (VIP) and nitric oxide (NO.) are thought to mediate lower esophageal sphincter (LES) relaxation. Transverse muscle strips from the opossum LES were used to test this hypothesis. Electrical field stimulation (EFS) produced a biphasic LES relaxation: a rapid component during the stimulus was more prominent at lower stimulus frequencies, and a sustained component was more prominent at higher frequencies. N(omega)-nitro-L-arginine and hemoglobin inhibited the rapid component but affected the sustained component less. Exogenous VIP decreased LES tone. A number of purported VIP antagonists blocked neither VIP-induced nor EFS-induced relaxation of the LES. The calcitonin gene-related peptide (CGRP) antagonist CGRP-(8-37) did not alter EFS-induced LES relaxation. EFS-induced relaxation of opossum LES muscle is biphasic, and the initial, rapid component of the relaxation is mediated primarily by NO. The mediator of the sustained component was not identified.
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Department of Pediatrics, University of Iowa College of Medicine and Department of Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.
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Murray
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Clark
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Conklin
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D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000037:antagonists & inhibitors / Q000502:physiology*; D004558:Electric Stimulation; D004943:Esophagogastric Junction / Q000502:physiology*; D005260:Female; D006454:Hemoglobins / Q000494:pharmacology; D007106:Immune Sera / Q000494:pharmacology; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology; D009893:Opossums; D014660:Vasoactive Intestinal Peptide / Q000037:antagonists & inhibitors / Q000276:immunology / Q000494:pharmacology / Q000502:physiology*
D006454:Hemoglobins; D007106:Immune Sera; D019335:Nitroarginine; D009569:Nitric Oxide; D014660:Vasoactive Intestinal Peptide; D015740:Calcitonin Gene-Related Peptide