Rectal lactate levels in endoluminal microdialysate during routine coronary surgery

The aim of this prospective study was to determine the feasibility of intestinal endoluminal microdialysis as a new method for clinical monitoring of the adequacy of splanchnic perfusion in the large bowel. A microdialysis catheter for continuous lactate, glycerol, glucose and pyruvate measurements attached to a tonometric catheter was placed into the lumen of the recto-sigmoid junction prior to surgery in 13 patients undergoing elective cardiac surgery with cardiopulmonary bypass (CPB). Lactate was also measured in blood and muscle. CPB was associated with a 10-fold increase in luminal lactate from 0.16 (0.01) to 1.67 (0.38) mmol x l(-1) (p < 0.001). Muscular lactate increased from baseline levels 1.20 (0.21) to 1.77 (0.36) mmol x l(-1) during CPB (p = 0.01), but the muscular lactate-pyruvate ratio remained unchanged. Arterial lactate increased only slightly from 0.9 (0.05) to 1.1 (0.06) mmol x l(-1) (p = 0.027) during CPB. Increased lactate concentrations in the large bowel during CPB are suggestive of local lactate production consistent with impaired oxygen delivery. Intestinal endoluminal microdialysis is a potential clinically applicable method for monitoring intestinal metabolism. Combined with tonometry, microdialysis provides the opportunity to monitor both circulation and metabolism in the rectal mucosa.

Long-term serotonin administration leads to higher bone mineral density, affects bone architecture, and leads to higher femoral bone stiffness in rats

New evidence suggests a control of bone mass by the central nervous system. We have previously shown that functional serotonin receptors are present in bone cells and that serotonin stimulates proliferation of osteoblast precursor cells in vitro. In the present study we investigated the effects of serotonin on bone tissue in vivo. Ten, 2-month-old female Sprague-Dawley rats were injected with serotonin subcutaneously (s.c.) (5 mg/kg) once daily for 3 months, controls received saline. Using microdialysis and HPLC, free circulating serotonin levels were measured. DXA scans were made after 3 months of serotonin administration. Bone architecture and mechanical properties were investigated by micro-computed tomography (microCT), histomorphometry, and mechanical testing. A long-lasting hyperserotoninemia with a >10-fold increase in serotonin appeared. Total body BMD was significantly higher (0.1976+/-0.0015 vs. 0.1913+/-0.0012 g/cm2) in rats receiving serotonin. Cortical thickness (Ct.Th) measured by microCT analysis was also higher, whereas trabecular bone volume (BV) was lower. Interestingly, the perimeter and cross-sectional moment of inertia (MOI), a proxy for geometrical bone strength, were the same in both groups. These data suggest that serotonin reduces resorption or/and increases apposition of endosteal bone. Mechanical testing showed that femoral stiffness was higher in serotonin-dosed animals. The energy absorption also seemed slightly, but not significantly higher. In conclusion, hyperserotoninemia led to a higher BMD, altered bone architecture and higher femural bone stiffness in growing rats, demonstrating that serotonin may have important effects on bone in vivo.

ECL cell histamine mobilization and parietal cell stimulation in the rat stomach studied by microdialysis and electron microscopy

AIM

Gastrin stimulates acid secretion by mobilizing histamine from enterochromaffin-like (ECL) cells that occur predominantly at the base of the gastric glands. The parietal cells occur higher up in the glands nearer to the gastric lumen. The present study was performed to assess whether histamine is transported from the ECL cell via the microcirculation (endocrine route) or local diffusion (paracrine route).

METHODS

Totally isolated, vascularly perfused, rat stomachs were examined both in basal and gastrin-stimulated state. Histamine concentrations, determined by radioimmunoassay in venous effluent and microdialysate from an indwelling probe in the submucosa, were monitored over a period of 240 min. Gastrin-17 was infused through an arterial catheter for 120 min. The parietal cells were examined by electron microscopy, and the percentage of actively secreting parietal cells (displaying secretory canaliculi) in four regions along the glands (basal to surface, zones I-IV) was determined.

RESULTS

Gastrin stimulated acid secretion and histamine release as well as parietal cell activation. Upon gastrin stimulation, histamine concentration in the microdialysate was 2.5-fold higher than in the venous effluent (P = 0.008). The parietal cells in the upper part of the gland (zone III) were found to be activated the most.

CONCLUSION

As the histamine concentrations were higher in the tissue (microdialysate) than in blood, histamine seems to reach the parietal cells via the paracrine route. The fraction of active parietal cells seems to depend more on the age of the parietal cells than on the distance from the ECL cell.

Gut luminal microdialysis of glycerol as a marker of intestinal ischemic injury and recovery

OBJECTIVE

To evaluate microdialysis as a method to assess different degrees of intestinal damage and recovery during ischemia and reperfusion; to evaluate information obtained from microdialysis catheters in the peritoneum, the gut wall, and the gut lumen.

DESIGN

Randomized, controlled animal experiment.

SETTING

University laboratory animal center.

SUBJECTS

Twenty-seven domestic pigs.

INTERVENTIONS

The superior mesenteric artery was cross-clamped for 60 mins (n = 14) or 120 mins (n = 10) followed by 2 or 4 hrs of reperfusion. Three pigs served as controls.

MEASUREMENTS AND MAIN RESULTS

Intestinal mucosal integrity was assessed by morphometry, adenosine triphosphate in the gut wall, and permeability of C-polyethylene glycol. Lactate, glycerol, pyruvate, and glucose were measured by microdialysis. Changes in adenosine triphosphate, permeability, or lactate did not correlate to different extents of intestinal damage caused by 60 or 120 mins of ischemia. During the reperfusion period, pigs with 60 mins of intestinal ischemia showed a faster recovery of these variables than pigs with 120 mins of intestinal ischemia. Glycerol increased with increasing duration of the ischemic insult. After 60 mins of intestinal ischemia, glycerol in the gut lumen decreased toward baseline but remained high after 120 mins of intestinal ischemia. There was a good correlation between gut luminal glycerol and recovery of mucosal damage throughout the reperfusion period. In the peritoneal cavity, both glycerol and lactate decreased to baseline relatively shortly after onset of reperfusion independent of the duration of intestinal ischemia.

CONCLUSIONS

Microdialysis of glycerol provides information about the extent and severity of intestinal damage after ischemia and about the ensuing recovery. The gut lumen is to be preferred as a site for placement of microdialysis catheters.

Long-term serotonin administration induces heart valve disease in rats

BACKGROUND

The purpose of this study was to investigate whether rats dosed with serotonin develop changes similar to those seen in human carcinoid heart disease.

METHODS AND RESULTS

Ten Sprague-Dawley rats were given serotonin injections subcutaneously once daily for 3 months; controls were given saline. A long-lasting hyperserotoninemia with a >10-fold increase in both platelet-poor plasma and dialysate from the femoral muscles appeared. The animals developed clinical signs such as flushing and loose stools. After 3 months, 6 of 10 rats given serotonin had pathological echocardiographs. Two animals had a combination of aortic and pulmonary valve insufficiency, 1 had isolated aortic valve insufficiency, and 3 had isolated pulmonary valve insufficiency. Histopathological examination revealed shortened and thickened aortic cusps and carcinoidlike plaques characterized by a collection of myofibroblasts within an extracellular matrix of collagen ground substance. Immunostaining for Ki-67 demonstrated an increased number of proliferating subendocardial cells. In the control group, no pathological changes were seen. With the use of reverse-transcription polymerase chain reaction, normal rat aortic cusps were shown to express mRNA for serotonin receptors 5-HT1A, 5-HT2A, and 5-HT2B and the serotonin transporter 5-HTT.

CONCLUSIONS

For the first time, long-term serotonin administration was performed in rats. Morphological and echocardiographic changes similar to those seen in human carcinoid heart disease developed. This study demonstrates that serotonin most likely is involved in the pathogenesis of carcinoid heart disease.

Intestinal injury after thoracic aortic cross-clamping in the pig

BACKGROUND

The mucosal surface epithelium is an essential part of the functional intestinal barrier, but its structural response to ischemia/reperfusion is only partly characterized. The purpose of this study was to provide a detailed morphological evaluation of intestinal surface epithelium after aortic cross-clamping.

MATERIAL AND METHODS

Pigs were subjected to thoracic aortic cross-clamping for 60 min and subsequent reperfusion for 120 min. Tissue blood flow and high-energy phosphates were measured with microspheres and HPLC, respectively. Urinary excretion of (14)C polyethylene glycol (MW 4000 Da) (PEG-4000), loaded into an intestinal loop, provided an index of intestinal permeability.

RESULTS

Jejunal blood flow was restored at 10 min after aortic declamping. Denudation of the basement membrane of the intestinal villi tips, as a consequence of epithelial shedding, increased markedly during the initial 60 min of reperfusion (P = 0.002). During the following 45 min, the denuded basement membrane was partly covered with low cuboidal and squamous-shaped cells extending lamellipodia over a wavy basement membrane. Restoration of ATP at 60 min after aortic declamping correlated inversely to the extent of denuded basement membrane (r = 0.75, P = 0.032). Permeability of PEG-4000 increased markedly after aortic declamping and was linearly correlated to the area of denuded basement membrane (r = 0.87, P = 0.01).

CONCLUSIONS

Reperfusion for 2 h after aortic cross-clamping is associated with initial aggravation of ischemia-induced injury in the porcine jejunum, but thereafter with restitution of the surface epithelium. Restoration of ATP may be important to avoid intestinal injury after ischemia. Increased permeability of a macromolecule in response to reperfusion is closely correlated to injury of the surface epithelium.

Gut barrier dysfunction as detected by intestinal luminal microdialysis

OBJECTIVE

To evaluate the use of gut luminal microdialysis as a tool for monitoring ischaemic metabolites, particularly glycerol, as markers of intestinal dysfunction during and after intestinal ischaemia.

DESIGN

A randomised, controlled animal experiment.

SETTING

National laboratory animal centre.

INTERVENTIONS

In seven pigs the thoracic aorta was cross-clamped for 60 min followed by 2 h of reperfusion, while five pigs served as controls.

MEASUREMENTS AND RESULTS

Glycerol, lactate and glucose in the intestinal lumen and mucosa were measured by microdialysis. Intestinal tissue blood flow was determined by means of colour-labelled microspheres. To assess intestinal permeability, (14)C-polyethylene glycol 4000 (PEG-4000) was instilled in a jejunal segment and then measured in venous blood. Intestinal blood flow was reduced to 10% of baseline by aortic cross-clamping ( p=0.001) and returned to baseline during reperfusion. Intestinal luminal lactate increased during ischaemia and further increased during reperfusion. The increase was paralleled by augmented intestinal permeability; there was a significant correlation between luminal lactate and venous PEG-4000 ( r=0.89, p<0.01). Aortic cross-clamping caused a marked increase in intestinal mucosal glycerol concentrations, which correlated with luminal glycerol during both ischaemia and reperfusion ( r=0.85, p<0.01).

CONCLUSION

Microdialysis of lactate may be useful for monitoring intestinal ischaemia and reperfusion. Release of lactate into the intestinal lumen appears to be related to increased permeability. Intestinal luminal glycerol closely mirrored glycerol concentrations in the intestinal wall.

Arterial air embolism after venous air infusion in newborn piglets

In the newborn period, decreased right atrial pressure results in functional closure of the foramen ovale (FO). The objective of this study was to investigate whether air bubbles infused in the vena cava will pass through the FO into the arterial circulation in a newborn animal. Since air tends to rise to the highest point in a fluid, the study also investigated whether the animal's position could influence arterialization of air. Twelve 1-3-d-old piglets were anaesthetized and mechanically ventilated, and had catheters placed in the vena cava for infusion of air, in the aorta for blood gas and blood pressure measurements, and in the pulmonary artery for pressure measurements. After stabilization, 0.05 ml kg(-1) per minute of air was infused for 25 min followed by a 3 h observation period. Six piglets were placed in the left, and six in the right lateral recumbent position. Air bubbles in the left atrium or ventricle was monitored by echocardiography. Ultrasound Doppler probes were placed on both carotid arteries for detection of air embolism. Gas bubbles were detected in the left ventricle within 45 s of air infusion in 11 of 12 piglets. Eight piglets had air bubbles in the carotid arteries. Mean pulmonary arterial pressure (PAP) increased significantly after 1 min of air infusion, whereas mean systemic arterial pressure remained unchanged. When arterial air embolism occurred, PAP had not increased significantly. The time to reach maximum PAP with the animals in the left recumbent position was significantly shorter than in the right.

CONCLUSION

This study shows that venous gas bubbles enter the arterial circulation through the FO in newborn piglets and that body position may influence the haemodynamic effect of these bubbles.