Microvascular permeability increases early in the course of acid-induced esophageal injury.

To test the hypothesis that microvascular injury is involved in the pathophysiology of acid-induced esophagitis, the effect of acid perfusion on intraluminal plasma protein loss was studied in relation to histological changes. Four groups of opossums (n = 6 in each) were perfused with either normal saline control) or 10, 20, or 100 mmol/L isoosmolar hydrochloric acid at 2 mL/min for 90 minutes using a midesophageal catheter. The distal esophagus was cannulated via a gastrostomy, and the effluent was collected and measured for intraluminal loss of IV injected 125I-bovine serum albumin. Plasma protein loss in the control group was constant with a total loss of 3.40 +/- 0.69 mg/g dry wt. Perfusion of 10, 20, and 100 mmol/L hydrochloric acid increased total protein loss to 8.06 +/- 2.62, 13.94 +/- 2.72, and 27.34 +/- 4.34 mg/g dry wt, respectively. The protein loss was not associated with intraluminal blood loss, as measured by previously injected 51Cr-labeled autologous red blood cells. Histological changes, scored by a blinded observer, were significant only between control animals and those perfused with 100 mmol/L hydrochloric acid. Separate studies using the vascular tracer monastral blue B demonstrated an increase in labeling of lamina propria blood vessels that varied directly with the concentration of acid perfusate, thereby providing direct morphological evidence of microvascular injury. These studies suggest that increased microvascular permeability occurs early in the course of acid-induced esophageal injury.

The microvascular anatomy of the canine stomach. A comparison between the body and the antrum.

To investigate whether there is a difference in the microvascular architecture between the body and the antrum of the canine stomach, these two locations were compared with respect to microsphere entrapment and the microvascular architecture and diameter in relation to histology by corrosion casting and by intraarterial injection of india ink. There was 63% shunting of 9-micron microspheres in the antrum, but none in the body. Corrosion cast and Indian ink studies showed that in the body there was a single microvascular network of capillaries that appeared to originate from the arterioles in the submucosa and were in close apposition to the epithelial cells of the gastric glands. The diameter of these capillaries was 8.6 +/- 0.2 microns. In contrast, there were two distinct capillary networks in the antrum: a basal and a superficial. The capillaries of the basal network of the antrum originated from the arterioles at the level of the muscularis mucosa and drained into the capillaries of the superficial mucosa. The capillaries of the superficial network had a significantly larger diameter (10.8 +/- 0.4 microns) than those of the basal network (7.3 +/- 0.2 microns). In many instances the capillaries of the superficial network originated directly from the ascending arterioles passing through the basal network. These direct arteriocapillary connections may have permitted the shunting of 9-microns spheres in the antrum.

Effect of intraesophageal location and muscarinic blockade on balloon distension-induced chest pain.

Intraesophageal balloon distension has been introduced recently as a provocative test in the assessment of patients with noncardiac chest pain. In order to examine the effect of balloon location and muscarinic blockade on distension-induced pain, 10 asymptomatic male volunteers were studied on two separate days using a low-compliance perfused manometry system that incorporated a silicone rubber balloon. Five-second-duration balloon distensions using balloon volumes of 2.5, 5, 7.5, and 10 ml of air were performed with the balloon located both 16 cm (proximal site) and 6 cm (distal site) above the lower esophageal sphincter (LES) before and after administration of atropine (10 micrograms/kg intravenously) or placebo in a randomized double-blind fashion. A standardized scoring system was used to assess the balloon distension-induced pain. Pain scores varied directly with balloon volume but were consistently higher with the balloon located at the proximal site versus the distal site. This was not associated with any differences in intraballoon pressures between the two sites; however, contraction amplitude orad to the balloon was greater with balloon distension at the proximal site. Atropine significantly decreased pain sensation scores with the balloon located distally but not proximally. This attenuation was not associated with significant changes in intraballoon pressures; however, contractions orad to the balloon were markedly inhibited by atropine with distal but not with proximal distension. These studies indicate that balloon distension-induced pain varies depending on the location of distension. This difference is not explained by differences in esophageal wall tension at the site of distension.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of primary and secondary esophageal peristalsis in humans: effect of atropine.

To determine whether physiological differences exist between primary (swallow-induced) and secondary (distension-induced) peristalsis in humans, 10 healthy male volunteers underwent esophageal manometry on 2 consecutive days using a perfused intraluminal catheter system that incorporated a latex balloon. Initially the catheter was positioned so that the balloon was centered 16 cm above the lower esophageal sphincter (LES), and intraluminal pressures were recorded 21, 11, 6, and 1 cm above the LES. After a series of wet swallows, dry swallows, and balloon distensions, the catheter was repositioned so that the balloon was 6 cm above the LES and pressures were recorded 1 and 11 cm above the LES. A series of balloon distensions were repeated in this position, and the subject was then given either atropine (10 micrograms/kg iv) or placebo in a double-blind randomized fashion (on consecutive days). The protocol was then repeated in reverse order. Distension-induced responses aboral to the balloon with the balloon located 16 cm above the LES were 1) of lower amplitude, 2) more often nonperistaltic, and 3) less atropine sensitive than swallow-induced contractions at comparable sites. With the balloon located distally (6 cm above LES) contractions induced at the 11-cm site (i.e., orad to the balloon) were much more atropine sensitive than contractions induced at the same site when the balloon was located proximally (i.e., 16 cm above LES). These data suggest that, contrary to previous reports, secondary peristalsis differs significantly from primary peristalsis. Furthermore, atropine differentially effects these two types of peristalsis, suggesting that the neural pathways involved are dissimilar.

Gastrointestinal blood flow in the opossum with special reference to the esophagus.

The opossum esophagus, like that of the human, is composed of striated muscle fibres proximally and smooth muscle fibres distally. Because of this similarity the opossum has been used extensively as an animal model for esophageal studies, but to date no data on esophageal blood flow have been reported in this species. The purpose of this study was to establish the basal blood flow characteristics of different regions of the opossum gastrointestinal tract with particular reference to the esophagus. Intracardiac injection of 15-microns microspheres was used to provide an estimate of blood flow (mL.min-1.g-1 dry tissue) to the whole wall, the combined layer of mucosa plus submucosa, and the muscularis propria. Basal blood flow in the whole tissue and mucosa-submucosa was significantly higher in the lower esophageal sphincter than in the proximal or distal esophagus. The muscularis propria blood flow displayed an aborally increasing gradient with flow to proximal esophagus (striated muscle) less than distal esophagus (smooth muscle) less than lower esophageal sphincter. Regional differences in blood flow to other regions of the gastrointestinal tract were similar to that described in other species. In addition, no changes in basal blood flow occurred despite repeated microsphere injections, suggesting that this species provides a good animal model for the study of gastrointestinal blood flow.