Abstracts

A standard burn model using rats¹ 1 . From the INCIS (UNINCOR) and School of Medicine (UFMG). 2 . Professor Titular da Disciplina de Anatomia, INCIS (Instituto de Ciências da Saúde), UNINCOR (Universidade do Vale do Rio Verde) - Três Corações/MG. 3 . Professor Titular da Disciplina de Cirurgia, Faculdade de Medicina da Universidade Federal de Minas Gerais e Coordenador do Curso de Pós-Graduação em Cirurgia, UFMG. Belo Horizonte/MG.

Tufi Neder Meyer² 1 . From the INCIS (UNINCOR) and School of Medicine (UFMG). 2 . Professor Titular da Disciplina de Anatomia, INCIS (Instituto de Ciências da Saúde), UNINCOR (Universidade do Vale do Rio Verde) - Três Corações/MG. 3 . Professor Titular da Disciplina de Cirurgia, Faculdade de Medicina da Universidade Federal de Minas Gerais e Coordenador do Curso de Pós-Graduação em Cirurgia, UFMG. Belo Horizonte/MG.

Alcino Lázaro da Silva³ 1 . From the INCIS (UNINCOR) and School of Medicine (UFMG). 2 . Professor Titular da Disciplina de Anatomia, INCIS (Instituto de Ciências da Saúde), UNINCOR (Universidade do Vale do Rio Verde) - Três Corações/MG. 3 . Professor Titular da Disciplina de Cirurgia, Faculdade de Medicina da Universidade Federal de Minas Gerais e Coordenador do Curso de Pós-Graduação em Cirurgia, UFMG. Belo Horizonte/MG.

Meyer TN, Silva AL. A standard burn model using rats. Acta Cir Bras [serial online] 1999 Oct-Dec;14(4). Available from: URL: http://www.scielo.br/acb.

SUMMARY: Experimental burn models are always needed, being essential for burn research. In the present study, we describe a standard Fischer F-344 rat burn model, in which burns are produced with a heated brass bar. The animals were anesthetized with ketamine (90 mg/kg). After the burns, they were resuscitated with saline. Burns ranging from 26% to 30% of total body surface area resulted in a 62.5 % mortality rate after 25 days. This model is an additional option for those interested in burn research.

SUBJECT HEADINGS: Burns. Disease Models, Animal.

INTRODUCTION

Vertebrate models are essential for burn research since new therapeutic modalities must first be investigated at the experimental level before clinical use². Many animals have been used in experimental burn models: dogs^5,22,9, sheep^6,21,14, rabbits^18,15,12, guinea pigs^20,11,16, hamsters¹, pigs^17,23,19,7, and primates²⁷. By far, rats and mice have been the most frequently used species in burn models. Experimental burns can be inflicted by various means, scalding being the most usual²⁴. Other means have been: flame^5,22,9, metal probes^13,15,19, molten wax³, scalding plus irradiation¹⁰, nitrogen mustard⁸, hydrofluoric acid⁷, microwave radiation²³, smoke inhalation¹⁴, liquid propane⁴, NaOH²⁵, HCl²⁶, and electric energy²⁷. The rat model of Walker and Mason²⁴ has been extensively used, being also adapted to mice. In the present study we have developed another standard rat model in which burns are produced with a heated brass bar. This is an additional option for those interested in experimental burn research, especially mortality studies.

METHOD

The animal experiments carried out in the present study were performed in accordance to Institutional Review Board (UNINCOR) norms and to those contained in the Guide for the care and use of laboratory animals (NIH – National Institutes of Health, 1996).

Forty six adult male Fischer F-344 rats weighing 218-381 g ( mean: 293,5 g) and with total body surface area of 363 to 527 cm² were used in this study. Forty animals were assigned to the burn group and six were used as controls. All animals were anesthetized with intraperitoneal ketamine (90 mg/kg) and were shaved on the dorsum from neck to tail longitudinally and transversally in such a way as to spare the ventral surface of thorax and abdomen. After these procedures, controls were placed in individual cages for recovery. Burns were then produced in the other forty animals by means of a brass bar measuring 5.5 x 2.0 x 2.0 cm. A screwdriver with a plastic handle was prepared and screwed to the brass bar (Fig.1). The bar was heated in boiling water, so that its temperature reached 100^o C as measured with a thermometer. The bar was held in contact with the shaved animal skin for 20 seconds, producing third-degree burns (as previously determined in a pilot study). The number of burns per animal was such that 26%-30% of the total body surface area was burnt (see Table 1). Body surface was calculated by Meeh’s formula ²⁴: A = 10 x W^2/3, where: A= area in cm², 10 is a constant and W=weight in grams. After the burns, the animals received intraperitoneal injections of saline (0.1 l/kg) and were placed in individual cages for recovery. All animals from both groups had free access to laboratory chow and tap water. They were kept in an experimental room whose temperature was maintained between 25^o and 28^o C, with natural light and dark cycles and observed for mortality at 12-hour intervals for 25 days. Mortality rates were summarized at 3, 7, 15 and 25 days. Surviving animals were sacrificed after this period with lethal doses of intraperitoneal ketamine.

RESULTS

All animals survived in the control group. For the burn group, the following mortality data were obtained: 16 animals died after 3 days (40%); 21 animals died after 7 days (52.5%); 23 animals died after 15 days (57.5%) and 25 animals died after 25 days (62.5%) (Figure 2).

DISCUSSION

Rats and mice are frequently used for experimental burns since they are readily available, inexpensive and easy to manage. Besides, homogenous strains can be another factor in standardization. So far, the time-honored scalding model described more than 30 years ago by Walker and Mason ²⁴ has been predominantly used by burn researchers. In this model, heat-resistant burn devices, or templates, must be constructed in such a number as to be adjusted to several animal weights (and body surfaces) and to the desired extent of total body surface area burns. This has been a very useful tool for the experimental study of burns and so it will continue to be used, but other options should be available. Simulating a clinical situation in experimental conditions may require burns inflicted through means other than scalding. A heated metal bar having known dimensions can provide such means. Very few reports about this type of burning model in rats providing standardization, as we have done, have been found in a Medline survey from 1966 to now. The presently described model offers the following advantages: there is no need for manufacturing devices, except for the standard brass bar, which can be easily machined; the bar can be used on rats of any size; it is possible to grade the extent of total body surface area burned just by varying the number of inflicted burns; changing the percentages of burns may be accompanied by variations in mortality, therefore fitting the researcher’s objectives; this is a simple, inexpensive model requiring no specific abilities. As a disadvantage, it may be said that burning the animals will take more time than by scalding. Table 1 has been constructed to permit an easier calculation of how many burns are needed to obtain given percentages of total body surface area burns in rats of different weights. Those interested in burn research may find it useful.

CONCLUSIONS

In this model, burning adult male Fischer F-344 rats with a brass bar to the extent of 26%-30% of total body surface area caused mortality rates of 40% after 3 days, 52.5% after 7 days, 57.5% after 15 days and 62.5% after 25 days. This is a reproducible, potentially useful rat burn model.

ACKNOWLEDGMENTS

The technical assistance of Regina de Fátima Lopes (INCIS-UNINCOR) is gratefully acknowledged.

Meyer TN, Silva AL. Um modelo padronizado de queimaduras em ratos. Acta Cir Bras [serial online] 1999 Oct-Dec;14(4). Available from: URL: http://www.scielo.br/acb.

RESUMO: Modelos experimentais de queimaduras são sempre necessários, sendo essenciais para pesquisas em queimaduras. No presente trabalho, os autores descrevem um modelo padronizado de queimaduras em ratos Fischer F-344, no qual as lesões térmicas foram produzidas com uma barra de bronze aquecida. Os animais foram anestesiados com cetamina (90mg/kg). Após as queimaduras, foram ressuscitados com salina. Queimaduras variando de 26% à 30% da superfície corporal resultaram em uma taxa de mortalidade de 62,5% após 25 dias. Este modelo é uma opção a mais para aqueles interessados na pesquisa em queimaduras.

DESCRITORES: Queimaduras. Modelos animais de doenças.

Address for correspondence:

Tufi Neder Meyer

R. Desembargador Alberto Luz, 129

37410-000 Três Corações – MG

Tel/Fax: 55 35 231-2147

e-mail: tufi@unincor.br

Data do recebimento: 05/06/99

Data da revisão: 10/07/99

Data da aprovação: 20/08/99

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History