Publications

BACKGROUND

Obese Zucker rats demonstrate increased susceptibility to hepatic ischemia-reperfusion injury. This study evaluates the effect of mild systemic hypothermia on ischemia-induced acute fulminant necrosis during warm ischemia and reperfusion, and investigates blood metabolic profiles under normothermic and mildly hypothermic conditions.

METHODS

The left and median hepatic lobes of male, obese, Zucker rats were exposed to 75 minutes of ischemia under either normothermic (36.9 +/- 0.3 degrees C) or mildly hypothermic (33.3 +/- 0.1 degrees C) conditions followed by 8 hours of reperfusion. Animals were killed and tissue and blood were harvested for analysis of histology, liver enzymes, and metabolic 1H-NMR spectroscopy.

RESULTS

Liver enzyme activities were significantly higher in the normothermic group when compared with mildly hypothermic animals. Histologic analysis showed greater than 75% necrosis in the normothermic group, whereas in the mildly hypothermic group necrosis was less than 25%. Blood from normothermic animals contained greater concentrations of lactate (190%, P = .001) and lower concentrations of glucose (60%, P = .01) than hypothermic animals; hepatic osmolyte betaine was also increased in blood from the normothermic group (220%, P = .0002). In addition, normothermic rats had increased concentrations of circulating fatty acids, triglycerides, glutamate, succinate, and acetate when compared with the hypothermic.

CONCLUSION

Mild hypothermia decreased hepatic necrosis in obese rats. NMR blood profiles indicate that hypothermia protects hepatic metabolism.

Several animal models of atrial fibrillation (AF) have been developed that demonstrate either atrial structural remodeling or atrial electrical remodeling, but the characteristics and spatiotemporal organization of the AF between the models have not been compared. Thirty-nine dogs were divided into five groups: rapid atrial pacing (RAP), chronic mitral regurgitation (MR), congestive heart failure (CHF), methylcholine (Meth), and control. Right and left atria (RA and LA, respectively) were simultaneously mapped during episodes of AF in each animal using high-density (240 electrodes) epicardial arrays. Multiple 30-s AF epochs were recorded in each dog. Fast Fourier transform was calculated every 1 s over a sliding 2-s window, and dominant frequency (DF) was determined. Stable, discrete, high-frequency areas were seen in none of the RAP or control dogs, four of nine MR dogs, four of six CHF dogs, and seven of nine Meth dogs in either the RA or LA or both. Average DFs in the Meth model were significantly greater than in all other models in both LA and RA except LA DFs in the RAP model. The RAP model was the only one with a consistent LA-to-RA DF gradient (9.5 +/- 0.2 vs. 8.3 +/- 0.3 Hz, P < 0.00005). The Meth model had a higher spatial and temporal variance of DFs and lower measured organization levels compared with the other AF models, and it was the only model to show a linear relationship between the highest DF and dispersion (R(2) = 0.86). These data indicate that structural remodeling of atria (models known to have predominantly altered conduction) leads to an AF characterized by a stable high-frequency area, whereas electrical remodeling of atria (models known to have predominantly shortened refractoriness without significant conduction abnormalities) leads to an AF characterized by multiple high-frequency areas and multiple wavelets.

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been fully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (HV(T)) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of HV(T) (P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of HV(T) (P < 0.05). BAL fluid from rats exposed to 20 min of HV(T) increased nitric oxide synthase activity nearly threefold in naïve primary alveolar macrophages (P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 min of stretch in vitro also significantly increased nitrite production in naïve macrophages (P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI.

Primary canine oral mucosal epithelial cells were cultured on temperature-responsive dishes and cell culture inserts to fabricate transplantable epithelial cell sheets. When 3T3 feeder layers and fetal bovine serum were eliminated from dish culture, the harvested cell sheets became significantly more fragile. In contrast, when epithelial cells were cultured on inserts having submicron-scale pores, cell sheet fragility was eliminated. Keratin expression profiles showed no differences among the harvested cell sheets, but the expression of p63, a putative stem/progenitor marker, was strongly dependent on the presence of 3T3 feeder layers and serum. These results suggest that the maintenance of stem/progenitor cells is influenced by the apical/basal supply of nutrients as well as culture supplements.