Amber Ledlow

The effects of recombinant human hemoglobin on esophageal motor function in humans

Abstract Background & Aims: Nitric oxide controls lower esophageal sphincter (LES) relaxation and esophageal peristalsis in opossums, but its role in the control of esophageal motility in humans is not defined. Hemoglobin inactivates NO by binding it. Recombinant human hemoglobin (rHb1.1) was used to test the hypothesis that NO mediates esophageal motor functions in humans. Methods: rHb1.1 or human serum albumin was administered intravenously to fasting male volunteers. Esophageal manometric studies were performed before, during, and up to 6 hours after the infusion. Results: rHb1.1 increased the velocities of peristaltic contractions to produce simultaneous contractions in 6 of 9 subjects. It increased the amplitude and duration of contractile waves in the esophagus. There was no consistent effect on the resting tone of the LES, but LES relaxation was inhibited. Spontaneous, simultaneous high-pressure contractions occurred in 8 of 9 subjects. Lower retrosternal chest pain during swallowing was observed in 4 subjects. Conclusions: rHb1.1 interfered with esophageal peristalsis and LES relaxation. It precipitated esophageal spasm in some subjects. These data support the hypothesis that the timing of smooth muscle esophageal peristalsis and LES relaxation are mediated by NO. They suggest that some disorders of esophageal motor function may result from defects in NO neuromuscular communication.

Effects of recombinant human hemoglobin on opossum sphincter of Oddi motor function in vivo and in vitro.

Nitric oxide (NO) acts as a nonadrenergic, noncholinergic inhibitor neurotransmitter that regulates sphincter of Oddi (SO) motor function. Hemoglobin blocks NO activity by binding it after it is synthesized. We hypothesized that recombinant human hemoglobin (rHb1.1) affects SO motor function by scavenging NO. Under anesthesia, 12 opossums underwent biliary tract manometry. Following a stabilization period, six animals were given rHb1.1 (0.28 g/kg over 30 min), while six received bovine albumin (0.28 g/kg over 30 min). Recordings were made during the infusion and for 3 hr after the infusion. In anin vitro preparation, force transducers were used to record spontaneous contractions at two sites along the sphincter segment. After a control period, rHb1.1 (0.1 mM) or cyanomethemologbin (0.1 mM) was added to the tissue bath and recordings continued for another 2 hr. Recombinant human hemoglobin decreased the frequency of contractions, increased resting tone, and blocked the relaxation phase of contractionin vivo. It increased the baseline amplitude, the frequency, and the peak amplitudes of contractionsin vitro. Albumin or cyanomethoglobin, which are unable to bind NO, had little effect on SO motor activity. We conclude that rHb1.1 may alter SO motor function by binding endogenous NO.

Vasoactive intestinal contractor: Localization in the opossum esophagus and effects on motor functions

BACKGROUND/AIMS Vasoactive intestinal contractor (VIC), an endothelinlike peptide and a putative gastrointestinal hormone, contracts gastrointestinal smooth muscle. The aim was to study VIC in relation to esophageal function. METHODS Intramural nerves in opossum esophageal smooth muscle strips were stimulated in the presence of various concentrations of VIC and were stained for VIC immunoreactivity. RESULTS VIC caused an atropine-resistant increase in the amplitude of nerve-induced contractions of the circular muscle. VIC alone contracted longitudinal muscle, and this effect was nearly eliminated by 1 mmol/L atropine. VIC caused an atropine-resistant increase in the resting tone of the lower esophageal sphincter muscle, but it did not affect nerve-induced relaxation of that muscle. VIC-immunoreactive nerve fibers occurred in the longitudinal muscle layer, in the muscularis mucosae, and around the ducts of esophageal glands. A few such fibers were found in the circular muscle layer. Nerve fibers and cell bodies of the myenteric plexus showed VIC immunoreactivity. In the stomach, immunoreactive nerve fibers occurred in muscularis mucosae and circular muscle but not in longitudinal muscle. CONCLUSIONS VIC is localized in neuronal elements of the opossum esophagus and excites contractions in esophageal smooth muscle.

Effect of Hydroxyl Radical (OH•) on Sphincter of Oddi Motility

Antioxidant enzymes are present in sphincter of Oddi nerves and regulate sphincter of Oddi motor function mediated by NO-releasing nerves. Oxygen free radicals (O2-.) produce hydrogen peroxide (H2O2) by the action of superoxide dismutase (SOD). Hydroxyl radical (OH.) has been shown to play an important role as a mediator of H2O2 toxicity. The aims of our study were to determine the effects of H2O2 on sphincter of Oddi motility and if these effects are mediated by OH.. Adult opossums were sacrificed and the sphincter of Oddi removed and placed in a tissue bath containing oxygenated Krebs solution. Force transducers recorded tension in a transverse orientation at two sites along the sphincter of Oddi specimen. H2O2 was added into the tissue bath at concentrations from 0.01 to 0.5%. O2-. radicals were inhibited by the addition of SOD, while OH. was scavenged by the addition of alcohol (ETOH) or dimethyl sulfoxide (DMSO). H2O2 produced a dose-dependent increase in baseline amplitude, frequency, and peak amplitude of contractions. The effect of 0.01% H2O2 on sphincter of Oddi contractile frequency was inhibited by 0.2% ETOH and DMSO, but not by SOD. We conclude that H2O2 has profound effects on sphincter of Oddi motility and that the actions of H2O2 are probably mediated through OH..

Effects of recombinant human hemoglobin on opossum sphincter of oddi motor function in vivo and in vitro

Nitric oxide (NO) acts as a nonadrenergic, noncholinergic inhibitor neurotransmitter that regulates sphincter of Oddi (SO) motor function. Hemoglobin blocks NO activity by binding it after it is synthesized. We hypothesized that recombinant human hemoglobin (rHb1.1) affects SO motor function by scavenging NO. Under anesthesia, 12 opossums underwent biliary tract manometry. Following a stabilization period, six animals were given rHb1.1 (0.28 g/kg over 30 min), while six received bovine albumin (0.28 g/kg over 30 min). Recordings were made during the infusion and for 3 hr after the infusion. In an in vitro preparation, force transducers were used to record spontaneous contractions at two sites along the sphincter segment. After a control period, rHb1.1 (0.1 mM) or cyanomethemoglobin (0.1 mM) was added to the tissue bath and recordings continued for another 2 hr. Recombinant human hemoglobin decreased the frequency of contractions, increased resting tone, and blocked the relaxation phase of contraction in vivo. It increased the baseline amplitude, the frequency, and the peak amplitudes of contractions in vitro. Albumin or cyanomethoglobin, which are unable to bind NO, had little effect on SO motor activity. We conclude that rHb1.1 may alter SO motor function by binding endogenous NO.