Kenneth A. Hubel

Human Ileal Ion Transport In Vitro: Changes With Electrical Field Stimulation and Tetrodotoxin

To determine whether or not nerves lying in the lamina propria and submucosa affect ion transport by the human intestine, we studied the effects of electrical field stimulation on ion transport across the isolated ileum stripped of muscularis propria. Electrical field stimulation increased transmural electrical potential difference and the short-circuit current, and by increasing the serosal to mucosal movement of chloride (JsmCl), reduced the absorption of Cl (JnetCl). The movement of sodium and the residual ion movement (JnetR) were not affected. The neurotoxin, tetrodotoxin prevented all of the changes caused by electrical field stimulation, but did not prevent the responses to aminophylline, implying that tetrodotoxin affected electrically excitable cells rather than epithelial cells. Aminophylline increased the potential difference and shortcircuit current, reduced tissue conductance (G), and eliminated chloride absorption. In tissues treated with tetrodotoxin, aminophylline also reduced JmsNa, JnetNa, and JnetR; while increasing JsmCl, it augmented the reduction in JmsCl and caused chloride secretion. Atropine reduced baseline short-circuit current and reduced the short-circuit current response to electrical field stimulation. It was concluded that acetylcholine and other chemical transmitters that affect ion transport are released in the submucosa or lamina propria of the human ileum. The identity of the noncholinergic transmitters and the sequence of events leading to their liberation remain to be determined.

Ion transport in normal and inflamed human jejunumin vitro

We studied ion transport in human jejunal mucosa under basal conditions and when tissues were stimulated electrically (EFS) and with theophylline 5 mM (N=12 pairs). Tissues were mounted in a flux chamber to measure unidirectional fluxes of22Na,36Cl, shortcircuit current, Isc (μeq/cm2/hr), electrical potential difference, PD (mV), and total ionic conductance, G (mS/cm2). Six pairs of tissues that were normal or less inflamed responded to theophylline by increasing PD and Isc and by reducing JCl(ms), the mucosal to serosal flux of Cl. In six pairs that did not respond to theophylline or to EFS, inflammation was more intense, and in the basal state, G was lower, PD was higher, and unidirectional fluxes of Na and Cl were halved. We conclude: (1) normal jejunum secretes Cl and responds to theophylline or EFS by reducing JCl(ms) thereby increasing Cl secretion; (2) unlike human ileum, neither theophylline nor EFS affect JCl(sm); (3) inflammation eliminates the response to theophylline and to EFS.

Effects of bethanechol on intestinal ion transport in the rat.

Summary In studies of rat jejunum, par-enteral bethanechol increases the transmu-ral PD, and decreases Na and HCO3 absorption, the rate of H secretion, and the final PCO2. In the ileum, it increases the final pH slightly. Bethanechol has no effect on intestinal transport when added to lumenal fluid. The changes in net transport evoked by pilo-carpine are quantitatively similar in jejunum and ileum, whereas the major effect of bethanechol is on the jejunum, implying that the muscarinic receptor of the ileum is less accessible or less responsive to bethanechol. I gratefully acknowledge the skilled assistance of Norman Hunter. This was supported by U. S. Public Health Service Grant Number AM 16488.

Secretory reflexes in ileum and jejunum : absence of remote effects

We have tested the hypothesis that luminal secretagogues initiate neural reflexes that alter ion transport in small intestinal segments proximal or distal to the site of the secretory stimulus. Effects of secretagogues that act by different mechanisms were studied in vitro by measuring short circuit current (ISC) of ileum or jejunum mounted in a unique flux chamber while proximal mucosa in neural continuity with the tissue was perfused with secretagogues (Na deoxycholate. Escherichia coli STa, 5-hydroxytryptamine, theophylline) or was stimulated electrically (EFS). No proximal stimulus affected distal ISC. We also studied in vivo adjacent segments of ileum or jejunum in neural continuity but with unconnected lumens. In anesthetized rabbits, we measured transmural electrical potential difference and fluid movement (Phenol red marker). Stimulation of proximal segments of ileum or jejunum with STa, or of ileum with 5-HT or Na deoxycholate did not affect distal transport. Stimulation of distal segments of ileum and jejunum with STa or 5-HT, or of jejunum with Ha deoxycholate did not affect proximal transport. We conclude that the secretion caused by luminal secretagogues in the rabbit small intestine is limited to the area of stimulation.

Effects of secretin and glucagon on intestinal transport of ions and water in the rat.

Summary Secretin reduced and glucagon enhanced absorption of ions and water from the small intestine of the rat, when administered intravenously in high doses.

Insulin-induced gastric acid secretion in young men. Test reproducibility and correlation with the augmented histamine test.

Summary 1.Duplicate tests of gastric acid secretion following a standard intravenous dose of regular insulin have been made in 25 subjects in order to determine the most reproducible measurement. 2.The 30-min maximal acid output (MAO) and 60-min MAO showed mean differences between the first and second tests of 16.5 and 16.2%. Because of its similarity to the most reproducible measurement of the augmented histamine test and the desirability of using similar measurements in tests of gastric secretion, the 30-min MAO is recommended as the standard for comparison between insulin tests. 3.The insulin 30-min MAO is suggested as a method of evaluating in man changes in gastric secretory function resulting from partial alteration of the vagal efferent network. 4.The acid secretory responses following histamine and those following insulin show a general tendency to parallel.

Mechanisms of the secretory response to luminal propionate in rat descending colon in vitro

Short chain fatty acids stimulate Cl secretion in rat descending colon in vitro via an enteric reflex involving mucosa and cholinergic nerves. We used the short circuit current as the measure of Cl secretion caused by Na propionate (NaP) (0.5 mM) in luminal bath fluid and studied the mechanism of the response. The NaP response was decreased 81% by atropine and 76% by lidocaine. It was unaffected by tetrodotoxin, omega-conotoxin or by tachyphylaxis to capsaicin, CGRP, substance P, histamine or PGE2. It was not reduced by inhibitors of 5-HT2 or 5HT3 receptors or by partial tachyphylaxis to 5-HT. However, superficial mucosal injury with hypertonic Na sulfate (2 M) or xylose (4.5 M) reduced the NaP response by 90% and 86%, respectively, and mucosal concanavalin A (1 mg/ml) reduced it by 73%. Neither piroxicam (10 microM) nor nordihydroguaretic acid (10 microM) affected the NaP response. We hypothesize that NaP stimulates the superficial epithelium to release an unidentified agonist that depolarizes predominantly cholinergic nerve terminals and causes colonic secretion.

Effects of Secretin on Renal Hemodynamics and Excretion

Summary The infusion of secretin directly into a renal artery produced a dose related increase in RBF and CPAH and reduction in RVR. V and TcH2O were unaffected and no increase in U Na V was observed. This is surprising because dilators of renal vasculature produce a natriuresis which correlates with the increase in RBF.

THE EFFECTS OF GASTRIC FREEZING ON VITAMIN B12 ABSORPTION, ACID SECRETION, TISSUE MORPHOLOGY, AND SERUM ENZYMES.

SummaryIn controlled studies to determine the effect of gastric freezing in patients, the following was found:1.Microscopically the gastric mucosa showed mild degenerative changes with minimal reactive inflammation and foveolar hyperplasia. No necrosis was seen.2.Serum amylase, glutamic oxalacetic transaminase, and leucine aminopeptidase did not rise. This suggested that no appreciable injury to the liver or pancreas occurred.3.Vitamin B12 absorption did not decrease. The apparent increase in absorption that occurred was probably experimental artifact.4.Studies of gastric acid secretion using the maximum histamine and maximum insulin responses (maximum 30-min. output) suggested that injury to the mucosal nerve supply played a role in the reduction of acid secretion that follows gastric freezing.

A small strain gage for measuring intestinal motility in rats.

Strain gages are useful for measuring muscular m o v e m e n t in vivo. They interfere minimally with the normal organ functioning and when chronically implanted can remain functional for long periods of time. Along the a l imentary canal strain gages have been used to moni tor motility of the s tomach, small intestine, and colon (1-3). The gages used in these studies have been a t tached to an underlying support of heavy plastic or metal. They have been too large to use in small animals and numerous steps have been required to make them (I , 2). This article describes the construct ion of a small semiconductor strain gage which has been chronically implanted in the rat to measure intestinal motility. The gage is similar to the one described by Nelsen (1) except that it employs a silicon crystal semiconductor sensing element , is smaller and more flexible, and can be constructed in a few relatively simple steps.