Misoprostol, a synthetic PGE1 analog, in the treatment of duodenal ulcers. A multicenter double-blind study.

Misoprostol, a synthetic analog of prostaglandin E1, inhibits gastric acid production and is cytoprotective at doses well tolerated by patients in preliminary trials. This multicenter double-blind study was performed in out-patients with endoscopically demonstrated duodenal ulcers, to compare the efficacy in ulcer healing and the safety of two dosages of misoprostol and placebo. Up to six antacid tablets daily were permitted for pain. 308 patients enrolled and were randomized to three treatment groups: placebo, misoprostol 50 micrograms and misoprostol 200 micrograms. After two weeks of treatment, the three groups had similar percentages of patients with complete ulcer healing. However, after four weeks, 76.6% of patients taking misoprostol 200 micrograms q.i.d. had complete healing, compared with 42.6% on misoprostol 50 micrograms q.i.d. and 51% on placebo (P less than 0.001, 200 micrograms versus placebo). Patients taking misoprostol 200 micrograms used less antacid than the others. Diarrhea, mild and self-limiting, was present in 13% of the 200 micrograms group versus 5% on placebo. We conclude that misoprostol 200 micrograms q.i.d. is effective, safe and well tolerated in the treatment of duodenal ulcers.

Effects of sulfodeoxycholate on rat and rabbit small intestine.

To determine how sulfation alters the biological properties of dihydroxy bile acids, we compared the effects of 3-sulfodeoxycholate (SDC) and deoxycholate (DC) in the rat and rabbit intestine. While 5 mM DC induced water and electrolyte secretion and inhibited glucose absorption in the rat, SDC enhanced jejunal and ileal water and solute absorption. SDC had no effect in the rabbit ileum. In the rat jejunum DC caused mucosal injury and enhanced mucosal permeability while SDC had no effect. In vitro in the rabbit ileum, 10 mM SDC enhanced net sodium flux and decreased net residual flux, while 0.5 mM DC reduced net sodium flux and induced Cl- secretion. Both bile acids increased short-circuit current and potential difference and decreased tissue conductance. During reversed-phase, high-performance liquid chromatography SDC was more polar than DC. Sulfation reduced the ability of DC to destroy large unilamellar liposomes by a factor of 10. Thus, sulfation abolishes the effects of DC on the intestine by enhancing the polarity of this molecule. The enhancement of intestinal solute and water absorption by SDC requires further study.

Prospective trial of proximal gastric vagotomy.

Forty men who were to have elective operation for nonobstructive duodenal or pyloric channel ulcer were randomized prospectively to undergo either proximal gastric vagotomy without drainage (PGV, n = 18) or selective vagotomy, antrectomy, and gastroduodenostomy (SVA, n = 22). Gastric acid analyses were accomplished before and 3 and 12 months after operation. Clinical interviews were conducted yearly. Thirty-nine patients were evaluable at 2 years, 25 at 4 years, and 15 at 5 years. No operative deaths occurred. Recovery was more rapid and the incidence of serious operative morbidity was lower after PGV than after SVA. Reduction of basal and stimulated gastric secretion was greater after SVA than PGV. Significant long-term sequelae other than recurrent ulcer were less frequent after PGV compared to SVA. Recurrent ulcer may occur more often after PGV; 3-month gastric secretory studies may be helpful in anticipating recurrence. Patients who undergo PGV have a particularly increased risk of developing pyloric channel ulcer disease, and low secretory values indicating an adequate vagotomy do not assure future protection from pyloric channel ulcer recurrence. Long-term sequelae after SVA, particularly dumping, do not have dependable reoperative options, whereas antrectomy should be a reliable reoperative solution to ulcer recurrence after PGV. PGV, performed correctly with a 5 to 7 cm vagal-esophageal separation, is preferable to vagotomy and resection for elective treatment of nonobstructing duodenal ulcer disease.

Local modulation of intestinal ion transport by enteric neurons.

Principles of autonomic nervous system control of intestinal ion transport need to include the newer concepts of the enteric nervous system (ENS). Based on studies of nervous control of the myenteric plexus, it is likely that ENS control of intestinal transport occurs through local mechanisms. In vitro transport studies and a limited number of radioreceptor-binding studies in mucosal cells support the notion that putative neurotransmitters alter transport by acting directly with mucosal receptors. In vivo and in vitro studies cannot alone uncover the indirect transport effects that neurotransmitters may have when they interact with enteric neurons. Studies focused on uptake and release of neurotransmitters suggest that norepinephrine (NE)-induced absorption may be modulated by local NE presynaptic neuronal mechanisms. Endogenous NE release may be enhanced by nicotinic and angiotensin II agents but decreased by muscarinic and alpha-adrenergic agents or prostaglandins. Presynaptic neuronal mechanisms that modulate endogenous acetylcholine (ACh) release and ACh-induced secretion are less well defined. Intestinal transport may be controlled by negative feedback, interneuronal, or transsynaptic presynaptic mechanisms. We propose that transport is controlled by a balance between the principal neurotransmitters NE and ACh. These neurotransmitters may be modulated by neuroactive peptides located either in neurons or in enteroendocrine cells. Efferent neurons may modulate release of neuropeptides from enteroendocrine cells into the luminal or antiluminal sides of mucosal cells. Intestinal transport also may be controlled by luminal factors that cause neuropeptide release from enteroendocrine cells or by specialized luminal receptors acting on sensory afferent neurons and intrinsic neuronal reflexes. Therefore, local modulation of intestinal transport by the ENS represents a finely tuned neuronal system with complex interrelations similar to many found in the central nervous system.

Endogenous norepinephrine release induced by tyramine modulates intestinal ion transport.

To study the effects of endogenous norepinephrine on intestinal ion transport, we tested the actions of an indirect sympathomimetic agent, tyramine, on electrolyte fluxes in the short-circuited rabbit ileum in vitro. Tyramine (10(-5) M) alone had no effect on short-circuit current or Na transport but increased Cl absorption. Tyramine decreased the short-circuit current, stimulated both Na and Cl absorption, and increased tissue conductance when its breakdown by endogenous monoamine oxidase enzymes was inhibited by pretreatment with pargyline (10(-4) M). Pargyline alone had no effect on short-circuit current and NaCl transport. The effect of norepinephrine on NaCl transport was inhibited by the alpha-adrenergic receptor antagonist, phentolamine (10(-7) M). This response was also prevented when animals were chemically sympathectomized with 6-hydroxydopamine. Although sympathectomy decreased measurable tissue norepinephrine by 80%, it did not alter basal short-circuit current, Na and Cl absorption, and the short-circuit current response to glucose-stimulated Na transport and to exogenous norepinephrine. Thus, a pool of norepinephrine in intestinal adrenergic neurons released by tyramine affects intestinal ion transport but does not alter basal ion transport. These data suggest close neuropharmacologic similarities between the adrenergic nervous system in the intestine and other organs.

Aspirin-stimulated intestinal electrolyte transport in rabbit ileum in vitro.

Because aspirin and the heavy metal salts of related anions have effects on intestinal ion transport and on diarrheal states, we have studied the effect of aspirin (ASA) on the in vitro rabbit ileum in an attempt to understand its mechanism of action. Ten millimolar of aspirin increased the conductance of rabbit ileum by 10--50% but did not change the permselectivity of the shunt path as determined by measurement of diffusion potentials. In Cl-free and HCO3-free solutions, aspirin reduced both Na absorption and the short-circuit current (Isc), which suggests an effect on electrogenic Na transport. Such an effect was not unexpected, since aspirin interferes with ATP production. However, in Ringer solution, aspirin in concentrations as little as 1 mM in the serosal solution reduced the Isc as before but also stimulated Na and Cl absorption and reduced JRnet (? HCO3 secretion) to zero. Aspirin had no effect on Na transport in the absence of Cl and no effect on Cl transport in the absence of Na, which suggests that aspirin stimulated a coupled transport process. Although these effects of ASA resemble those of alpha-adrenergic agents, ASA's effect was not blocked by alpha-adrenergic blockers such as phentolamine or phenoxybenzamine. The exact mechanism of ASA-stimulated NaCl absorption remains to be determined.

Cholinergic-adrenergic interactions on intestinal ion transport.

The autonomic control of intestinal electrolyte transport has been investigated in the in vitro, short-circuited rabbit ileum with varying doses of carbachol and with neuroeffector blocking agents. Low-dose carbachol (less than 10(-6) M) and high-dose carbachol (greater than 10(-4) M) had different effects on Na and Cl transport. Low-dose carbachol caused a transient increase in the potential difference and short-circult current, stimulated Cl secretion, and inhibited the residual flux (probably HCO3 secretion). This is a muscarinic response since it is inhibited by atropine (10(-6) M). After an initial increase of the potential difference and short-circuit current, high-dose carbachol reduced these electrical parameters, stimulated Na and Cl absorption, and abolished the residual flux. This is a nicotinic response since it is inhibited by hexamethonium (10(-5) M). This nicotinic response is identical to that reported by others with alpha-adrenergic agents and it was inhibited also by phentolamine (10(-7) M). We propose that high-dose carbachol stimulates nicotinic receptors on postganglionic sympathetic fibers present in our preparations causing a release of catecholamines and a resulting alpha-adrenergic response by the intestinal epithelial cell. The physiological significance of this response in the gut remains to be determined.

Effect of aspirin on normal and cholera toxin-stimulated intestinal electrolyte transport.

The effect of aspirin on normal and cholera toxin-stimulated electrolyte transport has been investigated in vitro, because this drug appears to inhibit cholera toxin-induced intestinal secretion in in vivo animal models. In the Ussing chamber, 10 mM aspirin decreased the control rabbit ileal potential difference and short-circuit current by 50% and increased conductance by 28%. Bidirectional electrolyte flux determinations showed that aspirin significantly increased both Na and Cl absorption and reduced flux (which probably represents HCO3 secretion) to zero. This effect of aspirin appears to be identical to that reported to others with catecholamines as determined with similar techniques. However, alpha-adrenergic blockers did not prevent the electrical effects of aspirin, suggesting that aspirin does not have its effect through release of tissue stores of catecholamines. In the presence of aspirin, cholera toxin increased the potential difference and short-circuit current, and decreased the conductance of rabbit ileum in a fashion qualitatively similar to control tissues. However, aspirin reversed cholera toxin-stimulated Na transport from secretion to absorption, inhibited cholera toxin, induced Cl secretion by 58% and partially, but not significantly, inhibited HCO3 secretion. Thus, the inhibitory effect of aspirin on cholera toxin-induced electrolyte secretion appears to be due to aspirin-stimulated Na and Cl absorption. Although aspirin reduced tissue cyclic AMP concentrations in normal and cholera toxin-stimulated ileum, it also inhibited the electrolyte secretion induced by exogenous cyclic AMP. Thus, if aspirin's stimulatory effect on sodium and anion absorption in normal tissue and its inhibitory effect on cholera toxin-stimulated sodium and anion secretion involves a cyclic AMP-mediated system, the effect must be a step distal to cyclic AMP production or degradation. The exact mechanism of aspirin's effect on normal and cholera toxin-induced electrolyte transport, and its possible usefulness in the treatment of cholera diarrhea, remains to be determined.