Allergy Asthma Immunol Res.  2013 Nov;5(6):389-396. 10.4168/aair.2013.5.6.389.

MRI Reveals Edema in Larynx (But Not in Brain) During Anaphylactic Hypotension in Anesthetized Rats

• Toyota I
• Tanida M
• Shibamoto
• Wang M
• Kurata Y
• Tonami H

• KMID: 2260283
• DOI: http://doi.org/10.4168/aair.2013.5.6.389

Abstract

PURPOSE
Anaphylactic shock is sometimes accompanied by local interstitial edema due to increased vascular permeability. We performed magnetic resonance imaging (MRI) to compare edema in the larynx and brain of anesthetized rats during anaphylactic hypotension versus vasodilator-induced hypotension.
METHODS
Male Sprague Dawley rats were subjected to hypotension induced by the ovalbumin antigen (n=7) or a vasodilator sodium nitroprusside (SNP; n=7). Apparent diffusion coefficient (ADC) and T2-relaxation time (T2RT) were quantified on MRI performed repeatedly for up to 68 min after the injection of either agent. The presence of laryngeal edema was also examined by histological examination. Separately, the occurrence of brain edema was assessed by measuring brain water content using the wet/dry method in rats with anaphylaxis (n=5) or SNP (n=5) and the non-hypotensive control rats (n=5). Mast cells in hypothalamus were morphologically examined.
RESULTS
Mean arterial blood pressure similarly decreased to 35 mmHg after an injection of the antigen or SNP. Hyperintensity on T2-weighted images (as reflected by elevated T2RT) was found in the larynx as early as 13 min after an injection of the antigen, but not SNP. A postmortem histological examination revealed epiglottic edema in the rats with anaphylaxis, but not SNP. In contrast, no significant changes in T2RT or ADC were detectable in the brains of any rats studied. In separate experiments, the quantified brain water content did not increase in either anaphylaxis or SNP rats, as compared with the non-hypotensive control rats. The numbers of mast cells with metachromatic granules in the hypothalamus were not different between rats with anaphylaxis and SNP, suggesting the absence of anaphylactic reaction in hypothalamus.
CONCLUSION
Edema was detected using the MRI technique in the larynx during rat anaphylaxis, but not in the brain.

Keyword

Anaphylactic shock; brain edema; laryngeal edema; mast cell

MeSH Terms

Anaphylaxis
Animals
Arterial Pressure
Brain
Brain Edema
Capillary Permeability
Diffusion
Edema
Hypotension
Hypothalamus
Laryngeal Edema
Larynx
Magnetic Resonance Imaging
Male
Mast Cells
Nitroprusside
Ovalbumin
Rats
Rats, Sprague-Dawley
Nitroprusside
Ovalbumin

Figure

• 

  Fig. 1 The schema of the time course of MRI examinations. T1WI, a sagittal T1-weighted image; T2WI, a sagittal T2-weighted image; T2WI for T2 map, a sagittal T2-weighted image for the quantitative T2 map; DWI, a coronal diffusion-weighted image.

• 

  Fig. 2 Time course changes in the mean arterial blood pressure in the anaphylaxis (black circle; n=7) and SNP (white circle; n=7) groups. Mean±SD; *P<0.05 vs. baseline.

• 

  Fig. 3 Diffusion-weighted images in a rat of the anaphylaxis group at baseline (A and B), and the first (C), second (D), third (E) and fourth (F) examinations after an injection of the antigen. Panel A shows a magnified image of the brain in Panel B. ADC was quantified in regions of interest (white circles) in Panel A. No significant changes in the brain diffusion-weighted images were found after injection (C, D, E, and F) versus baseline (B).

• 

  Fig. 4 The sagittal T2 weighted images in the anaphylaxis (A, B, and C) and SNP (D, E, and F) groups at baseline (A, D), first examination (B, E) and fourth examination (C, F). T2 weighted images in the anaphylaxis group showed increased signal intensity in the larynx (red arrows) at the first (B) and fourth (C) examination. In contrast, in the SNP group, no changes were found in the larynx (red arrow heads) at the first (E) and fourth (F) examination.

• 

  Fig. 5 Time course changes in T2RT, a parameter that represents the amount of protons within tissue and thus correlates well with the brain water content, at baseline and at the first, second, third and fourth examination after injections of the antigen (black circle; n=7) or SNP (white circle; n=7). (A) cortex, (B) basal ganglion, (C) hypothalamus, (D) larynx. Mean±SD; *P<0.05 vs. baseline; #P<0.05 vs. the SNP group.

• 

  Fig. 6 Staining with hematoxylin and eosin of the epiglottis of the anaphylaxis (A, B) and SNP (C, D) group rat; ×20 for A and C, ×100 for B and D. The double-headed arrows shown in Panels B and D indicate the length between the epithelium and the cartilage for evaluation of thickness of the subepithelial space.

• 

  Fig. 7 Toluidine blue staining of the hypothalamus of the anaphylaxis (A, B) and SNP (C, D) group. The areas indicated by the rectangles in Panel A and C are shown at higher magnification in Panel B and D, respectively. The arrows indicate mast cells containing numerous metachromatic red-purple granules stained with toluidine blue. 3V, the third ventricle; ME, median eminence. Scale bars=200 µm.

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