Effect of endotoxin on opossum gallbladder motility: a model of acalculous cholecystitis

Abstract

Objective: To determine whether endotoxin causes histologic changes in the gallbladder consistent with acalculous cholecystitis, and to determine the effects of endotoxin on gallbladder motility.

Summary background data: Acute acalculous cholecystitis is frequently seen in critically ill, septic patients, after prolonged fasting and gallbladder stasis. The pathogenesis of acalculous cholecystitis is unknown; however, previous studies have suggested that ischemia may play a role.

Methods: Adult opossums received Escherichia coli lipopolysaccharide. The gallbladder was removed for histologic examination or for physiologic studies 4 hours to 2 weeks later. For histologic examination, gallbladder strips underwent standard hematoxylin-and-eosin processing. For physiologic studies, they were mounted in a tissue bath to determine responses to cholecystokinin octapeptide or electrical field stimulation.

Results: Intravenous endotoxin at a dose of 0.005 mg/kg resulted in disrupted mucosal surfaces and areas of hemorrhage; higher doses of endotoxin resulted in coagulation necrosis, hemorrhage, areas of fibrin deposition, and extensive mucosal loss, consistent with an acute ischemic insult. Endotoxin abolished the contractile response to cholecystokinin octapeptide in gallbladder strips 4 hours after endotoxin administration. The 0.005-mg/kg dose of endotoxin decreased the contractile response to cholecystokinin octapeptide for up to 96 hours after endotoxin administration and decreased the contractile response to electrical field stimulation for 48 hours after administration. Inhibition of nitric oxide synthase reversed the decreased contractile response to cholecystokinin octapeptide.

Conclusions: Endotoxin causes an ischemic insult to the gallbladder similar to that seen in acalculous cholecystitis. Also, endotoxin may lead to gallbladder stasis by decreasing gallbladder contractile responses to hormonal and neural stimuli.

Figure 1. Transverse sections of opossum gallbladder before and after administration of Escherichia coli lipopolysaccharide (×50). (S, serosa; SM, smooth muscle; M, mucosa.) (A) Control. (B) Four hours after administration of 0.005 mg/kg. Areas of hemorrhage are seen in the smooth muscle layer, but the mucosal layer is relatively intact. (C) Four hours after administration of 0.05 mg/kg. There are increased areas of coagulation necrosis and hemorrhage in the serosal, muscle, and mucosal layers, as well as areas of fibrin deposition and increased mucosal loss. (D) Four hours after administration of 0.5 mg/kg. Abundant areas of hemorrhage and coagulation necrosis are seen. There is extensive mucosal loss and edema in all layers of the gallbladder wall.

Figure 2. Effect of cholecystokinin-8 (1.5 × 10⁻⁸ mol/L) on gallbladder isometric tension before and after administration of 0.005 mg/kg endotoxin). Controls, n = 16; 4 to 96 hours, n = 8; 2 weeks, n = 4. (*P < .05 vs. control, Wilcoxon rank-sum test.)

Figure 3. Effect of cholecystokinin-8 (CCK-8) on gallbladder isometric tension before and after endotoxin administration. First tracing: gallbladder smooth muscle response to CCK-8 (1.5 × 10⁻⁶ mol/L). Second tracing: blunted gallbladder contractile response to CCK-8 48 hours after endotoxin administration (0.005 mg/kg). Third tracing: effect of N^G-nitro-L-arginine (L-NNA) (1 mol/L) on the baseline tone of the gallbladder strip during endotoxemia. Fourth tracing: reversal of the blunted contractile response to CCK-8 during endotoxemia by pretreating the strips with L-NNA.

Figure 4. Effect of electrical field stimulation-induced gallbladder contractions after endotoxin administration (0.005 mg/kg). Electrical field stimulation parameters: 8 Hz, 0.1-msec pulses, 5-second duration, 1-minute intervals, 70 V. Controls, n = 16; 4 to 96 hours, n = 8; 2 weeks, n = 4. (*P < .05 vs. control, Wilcoxon rank-sum test.)