Divergence of mucosal and motor effects of insulin-like growth factor (IGF)-I and LR3IGF-I on rat isolated ileum following abdominal irradiation

Roles of muscarinic receptor subtypes in small intestinal motor dysfunction in acute radiation enteritis

Administration of abdominal radiotherapy results in small intestinal motor dysfunction. We have developed a rat radiation enteritis model that, after exposure in vivo, shows high-amplitude, long-duration (HALD) pressure waves in ex vivo ileal segments. These resemble in vivo dysmotility where giant contractions migrate both antegradely and retrogradely. Mediation of these motor patterns is unclear, although enteric neural components are implicated. After the induction of acute radiation enteritis in vivo, ileal segments were isolated and arterially perfused. TTX, hexamethonium, atropine, or the selective muscarinic antagonists pirenzepine (M(1)), methoctramine (M(2)), and 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP; M(3)) were added to the perfusate. The baseline mean rate per minute per channel of HALD pressure waves was 0.35 +/- 0.047. This was significantly reduced by TTX (83.3%, P < 0.01), hexamethonium (90.3%, P < 0.03), and atropine (98.4%, P < 0.01). The HALD pressure wave mean rate per minute per channel was significantly reduced by pirenzepine (81.1%, P < 0.03), methoctramine (96.8%, P < 0.001), and 4-DAMP (93.1%, P < 0.03) compared with predrug baseline data. As an indicator of normal motility patterns, the frequency of low-amplitude, short-duration pressure waves was also assessed. The mean rate per minute per channel of 5.15 +/- 0.98 was significantly increased by TTX (19%, P < 0.05) but significantly reduced by pirenzepine (35.1%, P < 0.02) and methoctramine (75%, P < 0.0003). However, the rate of small-amplitude pressure waves was not affected by hexamethonium, atropine, or the M(3) antagonist 4-DAMP. The data indicate a role for neuronal mechanisms and the specific involvement of cholinergic receptors in generating dysmotility in acute radiation enteritis. The effect of selective M(3) receptor antagonism suggests that M(3) receptors may provide specific therapeutic targets in acute radiation enteritis.

Radiation therapy-induced mucositis: Relationships between fractionated radiation, NF-κB, COX-1, and COX-2

Radiation therapy is one of the three major treatment modalities used in eradicating malignant tumours. When ionising radiation is used to treat abdominal tumours, severe side effects largely due to mucosal damage in the alimentary tract are common, particularly when it is combined with chemotherapy. Radiation-induced mucositis may not only limit the therapeutic doses of combined treatment but also adversely affect the quality of life of the patient. Treatment strategies to treat and prevent radiation-induced mucositis have been reviewed and published in the Clinical Practice Guidelines, 2004. However evidence supporting an effective treatment approach is tenuous, probably because the mechanistic evolution of radiation-induced mucositis is poorly understood. Several animal models have been used to examine the various effects of radiation but no single animal model has been able to effectively capture the effects of radiation on the alimentary tract at the molecular level before symptoms begin. This review will outline the events which occur following radiation exposure; from chromosomal aberrations in the mucosal cells leading to apoptotic and mitotic death, to the evolution of mucositis involving changes in gene activations and signaling. A better understanding of the mechanisms of radiation therapy-induced mucositis is necessary as it will allow for future pharmaceutical interventions to alleviate if not eliminate the debilitating side effects.

IGF-I mediated survival pathways in normal and malignant cells

The type-I and -II insulin-like growth factors (IGF-I, II) are now established as survival- or proliferation-factors in many in vitro systems. Of note IGFs provide trophic support for multiple cell types or organ cultures explanted from various species, and delay the onset of programmed cell death (apoptosis) through the mitochondrial (intrinsic pathway) or by antagonizing activation of cytotoxic cytokine signaling (extrinsic pathway). In some instances, IGFs protect against other forms of death such as necrosis or autophagy. The effect of IGFs on cell survival appears to be context specific, being determined both by the cell origin (tissue specific) and the cellular stress that induces loss of cellular viability. In many human cancers, there is a strong association with dysregulated IGF signaling, and this association has been extensively reviewed recently. IGF-regulation is also disrupted in childhood cancers as a consequence of chromosomal translocations. IGFs are implicated also in acute renal failure, traumatic injury to brain tissue, and cardiac disease. This article focuses on the role of IGFs and their cellular signaling pathways that provide survival signals in stressed cells.

Small bowel motility

The publications relevant to small bowel motility have been concentrated during the past year in several main areas: further characterization of normal patterns of small bowel motor activity and transit, physiologic control mechanisms, visceral hypersensitivity, inflammation and motility, disease processes and dysmotility, and novel pharmacologic approaches to altered sensorimotor activity.