Intraluminal micromanometry: an evaluation of the dynamic performance of micro-extrusions and sleeve sensors

Mechanisms of gastro-oesophageal reflux in the ferret

Transient lower oesophageal sphincter (LOS) relaxation is the major mechanism of gastro-oesophageal reflux in humans--an event unassociated with swallowing. Mechanisms involved in triggering transient LOS relaxation are poorly understood, and their further study requires a small animal model. In this study we aimed to establish methods for prolonged ambulant oesophageal manometry in ferrets, and to determine motor events associated with reflux episodes and their triggering by different gastric nutrient loads. Forty-two studies were performed on nine ferrets with chronic cervical oesophagostomies, through which a manometric assembly was introduced and secured to a collar, which incorporated a microphone for detection of swallows. The assembly included a gastric feeding channel, one gastric and four oesophageal manometric sideholes, a 2.5-cm-long LOS sleeve sensor, and an oesophageal pH electrode. Intragastric infusions were given over 2 min, the first after a 30-min control recording period, and in 29/42 studies, a second infusion was given 60 min later. Infusions were either 25 mL 10% dextrose solution, pH 3.5 (22 studies), 25 mL triglyceride emulsion (Intralipid) pH 3.5 (11 studies), or 25 mL air (nine studies). Episodes of oesophageal acidification were absent before gastric infusions. After infusion, 2.1 +/- 0.2 episodes occurred over the first 30 min. After glucose infusion, 15/18 acidification episodes (83%) occurred during transient LOS relaxation, and 3/18 (17%) occurred after gradual (< 1 mmHg sec-1) downward drifts in basal LOSP to < 2 mmHg. After lipid infusion two acidification episodes occurred, both during transient LOS relaxation. Mean duration of transient LOS relaxation was 8.0 +/- 0.4 sec. All infusions increased occurrence of transient LOS relaxation to a similar extent, each of which ended with primary peristalsis. We conclude that gastric infusion of glucose, lipid and gas are all effective in provoking gastro-oesophageal reflux in ferrets. Reflux occurs through similar mechanisms to those seen in humans, i.e. increased triggering of transient LOS relaxation. The conscious ferret is therefore an appropriate model for future studies of manipulation of mechanisms giving rise to gastro-oesophageal reflux.

Vagal and sympathetic influences on the ferret lower oesophageal sphincter

This study has investigated the relative involvement of cholinergic, adrenergic, nitric oxide and tachykininergic transmission in extrinsic neural influences on the lower oesophageal sphincter (LOS) in urethane anaesthetized ferrets. A micromanometric assembly (OD 1.75 mm) incorporating a sleeve sensor was used for high-fidelity oesophageal, LOS and gastric pressure measurement at low perfusion rates (< 0.1 ml/min). The LOS response to vagal and splanchnic nerve stimulation (0.5 ms pulse width, 10 s duration) was frequency- and voltage-dependent. LOS responses to stimulation at 20 V, 10 Hz were investigated in separate groups of animals with either L-NAME (100 mg/kg), hexamethonium (15 mg/kg), guanethidine (5 mg/kg), CP96,345 (NK-1 antagonist, 4 mg/kg), atropine (0.4 mg/kg) or propranolol (1 mg/kg). Propranolol treatment was followed by yohimbine (1 mg/kg) and prazosin (0.25 mg/kg). Vagal stimulation caused an immediate decrease in LOS pressure, followed by increase on cessation of stimulation, followed by a prolonged decrease (77 +/- 2%) for up to 5 min. L-NAME did not affect inhibition, but increased excitation 4-fold (p < 0.001). Guanethidine and CP96,345 had no major effect. Hexamethonium decreased the inhibitory (p < 0.05) and excitatory (p < 0.01) responses. Atropine reduced the excitatory response (p < 0.05). Some inhibition still remained if all treatments were combined. Splanchnic stimulation reduced LOS pressure by 70 +/- 6% for 101 +/- 17 s. L-NAME, guanethidine, hexamethonium and CP96,345 all independently significantly reduced inhibition. The combination of guanethidine and CP96,345 usually abolished splanchnic-induced inhibition. Atropine was without effect. Propranolol (1 mg/kg) changed the splanchnic-induced response from mainly inhibition to excitation (100 +/- 44% increase). LOS responses to noradrenaline (1-10 micrograms close IA) showed similar features to responses to splanchnic stimulation. We conclude that vagal stimulation evokes LOS relaxation via activation of established cholinergic and NANC mechanisms and other, unidentified mechanisms. Splanchnic stimulation activates adrenergic neurones probably via nicotinic and non-nicotinic ganglionic mechanisms, which in turn elicit beta adrenergic inhibitory effects on the LOS. Splanchnic stimulation also antidromically activates spinal afferent fibres. These may release substance P from peripheral myenteric plexus and prevertebral ganglionic endings causing activation of myenteric NANC inhibitory neurones and sympathetic neurones, respectively.

Effects of fractionated abdominal irradiation on small intestinal motility--studies in a novel in vitro animal model

Disordered small intestinal motility occurs frequently during acute radiation enteritis. However, the characteristics and time course of the motor dysfunction are poorly defined. These parameters were assessed in a novel animal model of radiation enteritis. Ileal pressures were recorded in vitro with perfused micromanometric catheter using an arterially perfused ileal loop in 22 ferrets following fractionated abdominal irradiation (9 doses 2.50 Gy thrice weekly for 3 weeks). Tissue damage was graded histologically. Studies were performed 3 to 29 days after irradiation. Tissue from 7 control animals was also studied. All treated animals developed diarrhoea. Histology showed changes consistent with mild to moderate radiation enteritis. Following irradiation, there was an initial increase in frequency followed by a non-significant reduction in the frequency, but not the amplitude of ileal pressure waves. The frequency of pressure waves showed an inverse relationship with time after radiation (r = -0.634, p < 0.002). There was no relationship between motility and histology. We conclude that abdominal irradiation is associated with a time-dependent reduction in ileal motility which does not correlate with light microscopic changes.