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Biomedical subjects

T R Koch

Publications and source records attributed to T R Koch.

At least 19 recordsLinked to original sources
PubMed1998

Distribution of muscarinic receptor subtypes in rat small intestine.

Despite its great promise, small intestinal transplantation in some patients is complicated by difficult postoperative management. The reasons for this are complex. In a rat model of small intestinal transplantation, frequencies of migrating myoelectric complexes during fasting are reduced in ileal isografts and muscarinic receptor density is decreased. We hypothesized that the distribution of muscarinic 1 receptors localized to enteric neurons is altered after small intestinal transplantation. Distal small intestine was orthotopically transplanted in Lewis-to-Lewis donor-recipient combinations. At 3 months, transplanted and normal ileum was obtained to prepare membrane fractions. [N-methyl-3H]Scopolamine served as ligand, while scopolamine methylbromide, pirenzepine, and methoctramine were used in competitive homologous and heterologous displacement experiments. Receptor subtype models were examined by nonlinear regression analysis. In normal and transplanted ileum, heterologous displacement was consistent with three site models (P < 0.05). In normals, the muscarinic 1 receptor subtype was most abundant, with a relative distribution of 69 to 78%. There was a relative distribution of 13 to 16% for muscarinic 3 receptor subtype. After transplantation, the muscarinic 1 subtype decreased to a mean of 45% but the muscarinic 3 subtype increased to a mean of 42%. Using pirenzepine, mean pKD values were not different between the two groups. It is concluded that the decrease in muscarinic 1 receptor subtype after transplantation could be related to neuronal cell loss or to downregulation of the expression of muscarinic 1 receptors. The results did not support defective posttranslational processing of receptor proteins.

Animals↗
PubMed1997

Chronic glutathione depletion alters expression of enteric inhibitory neurochemicals in the mouse.

Antioxidants may delay or prevent neural diseases. Depletion of the non-enzymatic antioxidant, glutathione, in a mouse model was produced by inhibiting its rate-limiting enzyme, gamma-glutamylcysteine synthetase, for 7 weeks. Ileum and colon were obtained from treated and control (saline) mice. Glutathione levels and nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity were determined by spectrophotometric assays; vasoactive intestinal peptide (VIP) levels were measured by radioimmunoassay. Glutathione levels were higher in ileum than colon. Colonic glutathione was decreased in treated mice compared to controls; there were no differences in ileal glutathione levels. VIP was decreased in ileum compared to controls, while NADPH diaphorase activity was decreased in colon compared to controls. In this chronic mouse model, glutathione appeared to regulate expression of enteric inhibitory nerve cell products.

Animals↗
PubMed1996

Expression of mRNA for vasoactive intestinal peptide in rat small intestine.

Transplantation of small intestine is a neural model that permits studies of expression of the neuropeptide, vasoactive intestinal peptide, following extrinsic denervation, transection of intrinsic neural pathways, and an ischemic interval. Tissue levels of vasoactive intestinal peptide were examined at 3 months in ileum from a sham operation, in ileum after resection of proximal small intestine, in ileum after resection of proximal small intestine and extrinsic denervation, in ileum after resection of proximal small intestine and 30 min of ischemia, and in ileum obtained 3 months after ileal isografting in Lewis-to-Lewis combinations. Vasoactive intestinal peptide levels were increased in transplanted rat ileum, resection controls, denervation controls, and ischemic controls compared to sham-operated ileum (pANOVA < 0.01). The increased levels of this peptide were highest in denervation controls and lowest in ischemic controls. Northern blot analysis using rat vasoactive intestinal peptide cDNA identified a single 1.7-kb transcript in normal and transplanted rat ileum. The density of vasoactive intestinal peptide transcripts was increased in transplanted ileum (8450 +/- 540) compared to normal ileum (5790 +/- 620) (P < 0.01), and the ratio of this transcript to glyceraldehyde-3-phosphate dehydrogenase density units was also increased in transplanted ileum (0.81 +/- 0.08) compared to normal ileum (0.40 +/- 0.07; P < 0.01). Enhanced transcriptional regulation was the likely mechanism for increased tissue vasoactive intestinal peptide. The increased tissue levels appeared to be a response to extrinsic denervation and transection of intrinsic neural pathways, while an ischemic interval appeared to decrease tissue levels of the peptide.

Animals↗
PubMed1996

Decreased vasoactive intestinal peptide levels and glutathione depletion in acquired megacolon.

We reported decreased vasoactive intestinal peptide levels in acquired megacolon. The origin of altered neuropeptide levels is unknown, but recent work suggested that tissue antioxidants may function as neuroprotectants. Our hypothesis was that altered levels of inhibitory neurotransmitters in human colon are associated with depletion of the tripeptide thiol, glutathione. Normal colon samples (N = 10; from patients 41-80 years old) and acquired megacolon samples (N = 10; from patients 31-98 years old) were obtained at surgery. Vasoactive intestinal peptide levels were decreased in muscularis externa from acquired megacolon (P = 0.01), while there was a modest increase in NADPH diaphorase activity in muscularis externa from megacolon (P = 0.10). Glutathione in acquired megacolon was detectable in muscularis externa from only five specimens (P < 0.05), but was not significantly different (P > 0.05) in the mucosal-submucosal layer. The results supported the presence of vasoactive intestinal peptide and NADPH diaphorase in distinct subpopulations of nerves in human colon. The results also supported the hypothesis that glutathione functions as a neuroprotectant in a subset of patients with acquired megacolon.

Adult↗
PubMed1995

Expression of mRNA for vasoactive intestinal peptide in normal human colon and during inflammation.

The availability of colon provides a ready source of human neurons. Among the products of nerve cell bodies, vasoactive intestinal peptide is a neuropeptide that serves as a marker of non-adrenergic, non-cholinergic inhibitory nerves in colon. These nerves have been proposed to be involved in regulation of immune function, secretion, and smooth muscle function. In previous work, we identified decreased tissue levels of vasoactive intestinal peptide in a disorder of chronic colonic mucosal inflammation, ulcerative colitis. We hypothesized that diminished gene expression of vasoactive intestinal peptide could result in decreased tissue levels of this neuropeptide. Sigmoid colon was obtained at surgery from controls (n = 6) and patients with ulcerative colitis (n = 6). Vasoactive intestinal peptide mRNA was quantified by Northern blot hybridization and tissue levels of vasoactive intestinal peptide were determined by radioimmunoassay. Tissue vasoactive intestinal peptide was decreased only in the mucosal-submucosal layer of ulcerative colitis (p = .02). There was a single 1.7 kbase vasoactive intestinal peptide transcript identified in both control colon and ulcerative colitis. Normalized vasoactive intestinal peptide mRNA levels were increased by 260% in ulcerative colitis compared to controls (p < .01). These observations suggest that decreased vasoactive intestinal peptide gene expression or abnormal post-transcriptional processing are not primary defects in this disorder of chronic inflammation. The findings support the alternative hypothesis that axonal degeneration in ulcerative colitis could result in increased expression of neuronal vasoactive intestinal peptide mRNA.

Adult↗
PubMed1995

Fractionated irradiation alters enteric neuroendocrine products.

Radiation profoundly alters the contractile activity of the small intestine and colon. We hypothesized that some motor changes of the gut might be secondary to impaired neural input to smooth muscle or abnormal release of gut endocrine peptides. The density of products within peptidergic and cholinergic nerves and gut endocrine cells was estimated in six normal controls and six dogs who had received 1500 cGy in six equal fractions of 250 cGy. Choline acetyltransferase, acetylcholinesterase, vasoactive intestinal peptide (VIP), substance P, peptide YY (PYY), and motilin were measured in tissue specimens divided into mucosal-submucosal (MS) and muscularis externa (ME) layers. Tissue samples were obtained from the duodenum, jejunum, ileum, and proximal and distal colon. In addition, serum levels of motilin and PYY were determined before and during the administration of 1500 cGy in four separate dogs instrumented to record upper gut contractile activity. Intrinsic cholinergic activity as estimated by choline acetyltransferase activity was unchanged, while acetylcholinesterase activity increased in the MS layers of distal small bowel and colon. VIP was increased in the MS layers of jejunum and proximal colon as well as in the ME layers the jejunum and ileum. By contrast, substance P increased in the jejunal and proximal colonic MS layers and in the ME layers of the jejunum and ileum. Duodenal and jejunal motilin levels markedly decreased after radiation exposure, while serum motilin levels continued to cycle at a decreased peak level with migrating motor complexes. Colonic PYY remained unchanged but serum PYY levels decreased after irradiation. Increased neuronal synthesis and inhibition of neurotransmitter release are potential explanations for elevated tissue concentrations of VIP, substance P, and acetylcholinesterase. There appeared to be differences in the sensitivity of gut endocrine cells to irradiation. Changes in gut regulatory peptides and cholinergic enzyme activity occur with fractionated doses of abdominal irradiation, while the same schedule of irradiation produces striking changes in the canine small intestinal and colonic motor activity. It is therefore likely that alterations of contractile events may be produced by changes in gut neuroendocrine products.

Acetylcholinesterase↗
PubMed1995

Altered neuropeptide content and cholinergic enzymatic activity in the inflamed guinea pig jejunum during parasitism.

We investigated the effects of an enteric infection with the parasitic nematode, Trichinella spiralis, on peptidergic and cholinergic neural pathways of the guinea pig jejunum. The content of the enteric neuropeptides, substance P (SP) and vasoactive intestinal peptide (VIP), and the activities of the key cholinergic enzymes, acetylcholinesterase (AChE) and choline acetyltransferase (ChAT), were measured and compared in extracts of jejunal muscularis externa (ME) obtained from uninfected jejunum and T. spiralis-inflamed jejunum. Significant decreases were detected in both SP immunoreactivity and AChE activity on days 6 and 10 postinfection (PI) in nematode-infected guinea pig jejunum compared to uninfected controls. The maximum changes observed for SP and AChE both occurred on day 10 PI and were evident as decreases of 37% and 48%, respectively, from the mean uninfected control values for SP and AChE. In contrast, VIP immunoreactivity and ChAT activity showed no significant changes during the enteric phase of T. spiralis infection. Nematode-evoked histopathological changes in jejunal tissues from infected animals were associated with significant increases in myeloperoxidase (MPO) activity, an index of inflammation intensity, which occurred on day 6 PI (885% of mean control) and day 10 PI (469% of mean control) coinciding temporally with the significant decrease in SP content and AChE activity during infection. Thus, intestinal motor disturbances observed in mammalian hosts during enteric nematode infections involve inflammation-generated changes in the neurohumoral control of smooth muscle function.

Acetylcholinesterase↗
PubMed1993

Gene expression and transcript size of the prepro-peptide VIP/PHM-27 in normal human tissue.

The transcript size of VIP/PHM-27 mRNA (vasoactive intestinal peptide/peptide histidine methionine) and the relative distribution of VIP/PHM-27 gene expression in 10 normal human tissues was examined. After mRNA extraction from tissue, VIP/PHM-27 transcript size and relative abundance of mRNA was determined by Northern blot analysis and densitometry of the autoradiograms. VIP/PHM-27 mRNA was detectable in brain, pancreas, colon, ileum and striated muscle while no hybridization signal was observed in liver, kidney, lung, heart, prostate and placental tissue. VIP/PHM-27 transcript in human brain and gut was a single band of 1.7 kb; by contrast, a 7.0-kb transcript was detected in striated skeletal muscle. The highest relative levels of mRNA were observed in brain and pancreas.

Animals↗
PubMed1993

Acquired megacolon is associated with alteration of vasoactive intestinal peptide levels and acetylcholinesterase activity.

Based upon previous morphologic studies, we hypothesized that the development of acquired megacolon was associated with abnormalities of enteric neurotransmitter concentrations and enzymatic activities. Specimens were obtained at surgery from patients with normal descending-sigmoid colon (n = 13) and patients with sigmoid megacolon (n = 6; defined by radiologic measurement). Radioimmunoassays were used to measure the non-adrenergic, non-cholinergic inhibitory neuropeptide, vasoactive intestinal peptide, and the non-adrenergic, non-cholinergic excitatory neuropeptide, substance P, while spectrophotometric assays were used to quantitate acetylcholinesterase activity and choline acetyltransferase activity. There were significantly decreased concentrations of vasoactive intestinal peptide and decreased acetylcholinesterase activity in muscularis externa from patients with acquired megacolon. In megacolon, vasoactive intestinal peptide-containing nerve fibers appeared to be diminished in circular and longitudinal smooth muscle, and immunostaining of nerve cell bodies in the plexus submucosus externus appeared diminished. These results suggest the hypothesis that production of vasoactive intestinal peptide is altered allowing secondary colonic hypertrophy to develop from prolonged cholinergic nerve-mediated contractions of circular smooth muscle. As a corollary to this hypothesis, colonic dilatation might result from prolonged contraction of longitudinal smooth muscle.

Acetylcholinesterase↗
PubMed1993

Characterization of neuropeptides extracted from canine intestine.

Quantitative determination of neuropeptides in biologic tissues by radioimmunoassay requires both an efficient extraction of neuropeptides as well as maintenance of immunochemical reactivity. Vasoactive intestinal peptide, substance P, and met5-enkephalin were chosen for this study because they are neuropeptides which appear to be involved in multiple physiologic systems. Since all three neuropeptides have a methionine residue within their amino acid sequence, oxidation of methionine to methionine-sulfoxide during the extraction process could diminish their immunochemical reactivity. Multiple factors that might be important in extracting these neuropeptides from canine intestine, including pH of the solvent, tissue homogenization, heating, and addition of enzyme inhibitors, were examined. Concentrations of vasoactive intestinal peptide-like immunoreactivity and substance P-like immunoreactivity were significantly higher in acidic solvents, and tissue homogenization appeared to increase the concentrations of these two neuropeptides. Substance P-like immunoreactivity was increased by heating after tissue homogenization, suggesting heat-induced denaturation of tissue enzymes liberated by homogenization. Separation of acidic tissue extracts by high performance liquid chromatography followed by radioimmunoassay for all three neuropeptides revealed minor acid-induced oxidation of substance P. These results should be useful for planning the extraction of these three neuropeptides from other tissues.

Acetates↗
PubMed1993

Muscarinic cholinergic receptor density following small intestinal transplantation in rats.

After small intestinal transplantation, intestinal isografts can organize migrating myoelectric complexes, and we have shown that migrating myoelectric complex frequency in the fasted state was reduced compared with controls after transplantation of the distal 50% of small intestine. We hypothesized that changes in motor activity after transplantation were related to alteration of cholinergic nerve activity or receptor density. With use of standard microsurgical techniques, the distal 50% of small intestine was orthotopically transplanted in a Lewis-to-Lewis donor-recipient combination. Resection controls were prepared by resecting the proximal 50% of small intestine, and sham controls were prepared by performing a sham laparotomy. Two months after surgery, small intestine was harvested. Choline acetyltransferase activity among the three groups was similar, suggesting that intrinsic cholinergic nerves remained intact. There was a strong trend toward decreased acetylcholinesterase activity [analysis of variance (ANOVA), P = 0.16] after transplantation, consistent with loss of extrinsic vagal nerve fibers. There were no differences in histochemical distribution of acetylcholinesterase among these groups. Muscarinic receptor density, as determined by binding to [N-methyl-3H]scopolamine, was decreased after transplantation (ANOVA, P = 0.02). There was a trend toward decreased receptor density in animals with resected small intestine. Surgical interruption of intrinsic nerve pathways rather than ischemia or extrinsic denervation might be the mechanism for diminished receptor density after transplantation, and reduced small bowel motor activity may be related to decreased density of muscarinic cholinergic receptors.

Acetylcholine↗
PubMed1992

Association of constipation with neurologic diseases.

To investigate possible etiologic influences on the development of constipation, the present study examines the concordant occurrence of constipation with other diseases. Using 8.8 million Medicare patients hospitalized in the United States during 1987, the frequency distribution of all three-digit International Classification of Diseases (ICD) codes was compared in constipated patients and patients without constipation. Most associations and the closest associations were observed between constipation and neurologic diseases, the majority of which resulted from damage to the central nervous system. Associations between constipation and disorders of the spine also involved neuronal damage. The influence of potential confounding factors such as immobility or pain on the development of constipation was assessed and found to be minimal. The frequent association of constipation with disorders involving neuronal malfunction suggests that disruption of the neural modulation of colonic motility may play an important role in the development of constipation.

Aged↗
PubMed1992

Enterohepatic circulation is essential for regular cycling of duodenal migrating motor complexes in dogs.

The role of enterohepatic circulation and specific bile acids in the initiation and caudad migration of duodenal migrating motor complexes (MMCs) was investigated in conscious dogs. All dogs had spontaneous duodenal MMCs that migrated to the terminal ileum when bile flow was intact. During the first 3 days after total external biliary diversion, no MMCs originated in the duodenum. Instead, all MMCs originated in the jejunum and migrated to the ileum. During the next 4 days of total external biliary diversion, 81% of the MMCs originated in the jejunum and 19% in the duodenum. When normal bile flow was restored after 9 days of total external biliary diversion, regular duodenal MMCs resumed after a delay of 126 +/- 27 minutes. Perfusion of individual bile acids or dogs' own bile, but not saline or alkaline solution, into the duodenum or perfusion of dogs' own bile directly into the ileum during total external biliary diversion restarted duodenal MMCs with a time lag of about 2 hours. The authors conclude that intact enterohepatic circulation is essential for the initiation of regular duodenal MMCs.

Animals↗