Functional innervation of the aganglionic segment in Hirschsprung's disease--a comparison of the short- and long-segment type

Intracellular calcium mobilization of the aganglionic intestine in the endothelin B receptor gene-deficient rat

BACKGROUND AND AIM

Up to now, numerous reports have analyzed the pathogenesis of Hirschsprung's disease (HD) by means of physiologic, pathologic, or molecular biologic methods. However, very little is still known about the smooth muscle cell itself. The endothelin B receptor gene-deficient (EDNRB(-/-)) rat, which is suitable for research of HD, has an aganglionic segment of the total colon. Our purpose is to investigate the myogenic mechanisms using simultaneous measurements of the intracellular Ca2+ concentration ([Ca2+]i) and tension and reverse transcriptase polymerase chain reaction for L-type Ca2+ channel (L-VOC) expression.

METHODS

The muscle strips of the rat distal colon were loaded with a Ca2+ indicator dye, fura-PE3/AM, for 3 to 4 hours. The changes in the fluorescence intensity of Ca2+-fura-PE3 complex of the strips were monitored with a front surface fluorometer (CAM-230). The fluorescence intensities at 340- and 380-nm excitation and their ratio (F340/F380) were recorded as the level of [Ca2+]i. The comparison of L-VOC alpha1c subunit messenger RNA (mRNA) expression in both wild and homozygous rat was performed by reverse transcriptase polymerase chain reaction.

RESULTS

The peak levels of force development induced by carbachol were 139.1% +/- 5.0% in EDNRB(-/-) rat, whereas the peak levels were 242.1% +/- 27.7% in EDNRB(+/+) rat. The changes in the [Ca2+]i elevation induced by carbachol were 101.7% +/- 12.2% in the homozygous rat, whereas these were 143.8% +/- 8.9% in the wild-type rat. Both results in the homozygous rat significantly decreased in comparison with those of the wild rat (P < .05). The expression of the L-VOC channel mRNA also decreased in the homozygous rat.

CONCLUSIONS

This is the first report to show the [Ca2+]i mobilization in the smooth muscles of the rat model of HD. The decrease in both [Ca2+]i and force development was thus considered to be due to the decrease in the Ca2+ channel expression.

Increased smooth muscle contractility of intestine in the genetic null of the endothelin ETB receptor: a rat model for long segment Hirschsprung's disease

BACKGROUND AND AIMS

The endothelin ETB receptor null rat (ETB(-/-)R) has an intestinal segment without ganglia, and this rat is characterised by intestinal obstruction similar to that observed in human Hirschsprung's disease. In the present study, we have examined the myogenic mechanism responsible for obstruction in the ETB(-/-)R.

RESULTS

The ETB(-/-)R had an enlarged belly and the average lifespan was 18.1 days. The bowel from the rectum to the lower part of the small ileum was constricted whereas the upper region was dilated with faecal stasis and thus presented as megaileum. The constricted muscle segments without ganglia had a greater increase in absolute force when stimulated by carbachol, high K+, and endothelin-1 compared with that of normal siblings. In contrast, in the dilated part with ganglia, the absolute contractile force due to these stimulants in the ETB(-/-)R was not different from that in the ETB(+/+)R. Such a functional hypertrophy of the musculature was observed in parts of the colon, caecum, and distal ileum without ganglia but not in the part of the proximal ileum and jejunum with ganglia. Morphological study demonstrated that the thickness of the circular and longitudinal muscle layers was greater in the constricted part of the intestine in the ETB(-/-)R, and these changes were associated with an increase in the number of smooth muscle cells.

CONCLUSIONS

Our findings suggest that both increased contractility of smooth muscle and increased thickness of the intestinal muscular wall may contribute to the intestinal obstruction in the ETB(-/-)R.

Electrophysiological properties of the aganglionic segment in Hirschsprung's disease

BACKGROUND

In Hirschsprung's disease, the severity of bowel obstruction varies among those patients who have the affected colon of a similar length, suggesting that there is more than a simple aperistaltic obstruction in the pathophysiology of Hirschsprung's disease.

METHODS

A series of our electrophysiological studies of the aganglionic segments from human specimens and rat models were reviewed to obtain an overview of Hirschsprung's disease.

RESULTS

In human studies, a generation of regular spontaneous activity was recorded in both the dilated ganglionic segment and transitional aganglionic region, while the smooth muscle cells of the narrow aganglionic segment were electrically quiescent. According to a pattern of innervation, in the dilated ganglionic segment inhibitory junction potentials associated with or without excitatory junction potentials were observed in all of the examined cells, and these intrinsic nervous inputs were gradually decreased in the transitional region. In the narrow aganglionic segment, only excitatory junction potentials of the extrinsic nervous origin were found in about 20% of the examined cells In rat models, distally increasing tendency of the excitatory nervous inputs was observed in the narrow aganglionic segment.

CONCLUSION

A bowel obstruction in Hirschsprung's disease might be generated due to complex mechanisms involving myogenic and neurogenic abnormalities.

The role of nitrergic system on the contractility of colonic circular smooth muscle in Hirschsprung's disease

The contribution of nitrergic tone on the contractility of colonic smooth muscle in Hirschsprung's disease (HD) was investigated.

METHODS

Ganglionic and aganglionic bowel specimens were taken from 8 patients with HD during pull-through operations and electrical field stimulation (EFS)-induced isometric contractions of the circular smooth muscle were recorded in vitro. Isolated circular muscle strips prepared from colonic segments of sex- and age-matched patients (n = 3) who underwent surgery for nonmotility-related colonic diseases formed the control group. Statistical analysis was performed by two way analysis of variance and unpaired Student's ttest.

RESULTS

The amplitude of spontaneous rhythmic activity was lower in aganglionic segments than in ganglionic ones. The amplitudes of contractile responses were significantly greater in aganglionic segments. In ganglionic preparations, N(omega)-nitro-L-arginine (L-NNA) addition into the medium increased the contractile responses to the level of aganglionic preparations. This increase was completely blocked by L-arginine application. Neither L-NNA nor L-arginine produced any change in aganglionic segments. A relaxation phase was detected in both ganglionic and aganglionic segments. In ganglionic preparations, this relaxation phase was completely inhibited by L-NNA and restored by L-arginine, whereas no effect was detected in aganglionic ones. Responses obtained from the control group were similar to the ganglionic segments of HD patients.

CONCLUSIONS

In normal colon and as well as in ganglionic segments of HD, the evoked contractile activity and relaxations are under the tonic influence of the nitrergic system. Aganglionic segments totally lack the nitrergic activity in both evoked contraction and relaxation responses, while still maintaining an inefficient relaxation capacity under unknown mechanisms.