1992) for which the measurement of the body surface area of these ... Calculations to determine the body surface area in Wistar rats have been available for.
J. Anim. Physiol. a. Anim. Nutr. 77 (1997), 61-65 0 1997 Blackwell Wissenschafts-Verlag, Berlin ISSN 0931-2439
Eingang des Ms.: 5. 11. 1996
‘3. Grisolia’ Research Unit and 2Preventive Medicine Department, Hospitals Vall d’Hebron, Passeig Vall d’Hebron, Barcelona, Spain
Body surface area in Sprague-Dawley rats By M. FARRIOL’, J. ROSSELL~’ and S. SCHWARTZ‘
Introduction Rats are the most extensively used animal species in the experimental laboratory and have been employed in a large number of research fields. As they are relatively inexpensive, Sprague-Dawley and Wistar rats are the most commonly-used in scientific studies and are the best animal model for multiple studies. These studies include work concerning burns et a]. 1994) pharmaceutical studies (REILLY and WORK(ZAPKrA-SIRvEm et al. 1986; FARRIOL MAN 1993; GRAY et al. 1991), investigations in nutrition ( D E M I C H E Lal.E 1989) ~ ~ and ageing 1992) for which the measurement of the body surface area of these (MCCARTER and PALMER animals is essential. A recent work by SMITHet al. (1995), showed that models for predicting dose measure of drugs gave more correct estimations when the dose administered was scaled to body surface area. Using mathematical approaches, different calculations have been devised based o n body weight to estimate the body surface area of experimental rats. Attempts have been made to improve the precision of these estimations by adding other body parameters to the empirical formulas. Calculations to determine the body surface area in Wistar rats have been available for many years and have been reviewed (SANROMAN et al. 1985), and recently data from cotton 1993). However, studies with Spraguerats have been reported (OHWADA and KATAHIRA Dawley rats have not clearly defined this question. The growth curve is different in these rat species and the measurements described for one species are not necessarily applicable to others. The aim of the study was to measure the body surface area of Sprague-Dawley rats and to compare the results with those obtained using four different mathematical formulas, dcscribed by four authors, t o estimate this parameter.
Material and methods Seventy male Sprague Dawley rats weighing 79-674 g were studied. The animals were killed by an overdose of ether anaesthesia. The weight, abdominal length mouth-penis, abdominal length mouth-tail at the juncture or root, tail length, tail perimeter (at juncture) and body surface area (BSA) were measured for each of them. In order to determine the gold standard (GS) surface area, the skin of the animals was dissected completely and measured by the same technical assistant throughout the process. The extremities were severed at the tarso and carpo, pressed on an ink pad and imprinted on paper. The dissected skin was immediately placed on a sheet of filter paper, with the interior side down, and pressed vertically to avoid stretching. The skin form was outlined and photocopied on identical sheets of paper. The total surface image was cut out and weighed. The values obtained were interpolated on a curve
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M. Farriol, J. Rossello and S. Scbwartz
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I.
2 BSA=KxWx3
2.
BSA=KxW
3.
BSA = 6.67 x W0.7x
4.
BSA=
0.34
2.54 x W0.7x L
fi
FLg. 1. Formulas used in this study. K=constant; W = weight; L = length mouth-tail
madc with the same material. The resulting measured surface area values werc considered t o bc the GS. T h e GS of each rat was compared with the BSA obtained using thc four mathematical equations (SANROMANct al. 1985) attributcd to MEEH(I), RUBNEK(2), VALLOIS(3) and SAN ROMAN(4) (Fig. 1). A n intra-class correlation coefficicnt ANOVA (SPSS statistics softwarc) was applied to detcrniinc the degree of concordance betwecn the measured body surfacc area and that calculatcd by the four formulas. In addition, to detcrmine whethcr body mcasurcments other than those used in the formulas could be good indicators of BSA, the Pcarson coefficicnt of correlation was pcrforincd betwcen thc weight of the rats and four body parameters (tail, mouth-tail, mouth-penis, tail perimeter).
Results T h c GS surfacc area obtained in the 70 rats studicd ranged from 177 to 733 cm2 (Table 1 ) . T h c correlations (r) bctween weight and the body lengths described above were: weighthail, r = 0.943; wcight/mouth-tail, r = 0.981; weight/mouth-penis, r = 0.967; weighdtailpcrimctcr, r = 0.895. Thc intra-class corrclation coefficient between the GS and the four Table 1. Number of animals in each range of measured body surface Total body surface (cm’)
100-200 200-300 300-400 400-500 500-600 600-700 700-800
Number of animals
2
17
6
13
9
18
5
Body surface in Sprague-Dawley rats
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formulas showed excellent reproducibility: formula 1 (MEEH), r = 0.837; formula 2 (RUBNER),r = 0.941; formula 3 (VALLOIS),r = 0.993; and formula 4 (SANROMAN),r = 0.961. Statistically significant differences (p < 0.05) were found between the GS and formula 1, formula 2, and formula 4. The intra-class correlation coefficient obtained using VALLOIS’ formula was closest to perfect reproducibility (r = I), with no significant differences. T o evaluate the degree to which the various estimated values approached the GS, the mcan of the deviation in percentages (absolute value) was calculated. It was confirmed that for the entire sample, the VALLOISformula offered the smallest mcan deviation: 3.65%, as compared to formula 1 (22.25%), formula 2 (12.18%) and formula 4 (9.4%). In light of these findings, a further study that compared, animal by animal, the BSA data obtained with the VALLOISformula and the GS was performed. The body surface area obtained with the formula was subtracted from the measured body surface results. There were positive differences (lower results) in 28/44 rats, and negative differences (higher results) in 21/26 rats. When the animals were evaluated according to positive or negative differences, we found that the point of inflection of these differences was at a body weight of 300 g. The GS and data from the VALLOISformula were classified into two groups according to the inflection point (GSl and V1: < 300g; GS2 and V2 > 300g). The mean values of the groups were: GSl = 260.6 61.5; GS2 = 585.9 f 95.1; V1 = 253.4 & 63.3 and V2 = 597.2 f 94.6. No statistically significant differences between the GS and data from VALLOIS’ formula were found with this new classification. At the cut-off point of 300 g, the means of the differences were, once again, less for the VALLOISformula (3.96% for animals over 300 g and 5.09% for those under). Thus, in the small animals (under 300 g) the body surface was underestimated and in the large animals (over 300g) it was overestimated with VALLOIS’ calculation, by a mean of 20 cm‘. When the results from the formula were adjusted according to body weight of the animal by adding o r subtracting this figure, the intra-class coefficient of correlation improved by five-thousandths of a point, from 0.993 to 0.998.
Discussion The effort to define a simple method for determining body surface area in animals and humans has a long history. In 1879, a formula was devised by MEEH to estimate this parameter in rats used for experimentation. In this calculation, animal weight was the only measurable factor taken into account to estimate surface area, and this was added t o a constant depending on each animal species. Since body weight is a variable that depends on sex and age, this method did not produce a precise estimation for the different species of animals. Over the years, attempts have been made to improve on this initial approach and to optimize the system of calculation. It is known that adult land mammals exhibit geometric similarity over a substantial weight range and relatively constant partitioning of body weight and surface area among the body 1992). The shape of animals has been traditionally modelled as a series segments (PROTHERO of cylindrical sections. If the animal has a form close to a regular geometric shape, as is the case of the snake, it is very easy to estimate surface area by simple arithmetic, without taking the weight into account. However, when the animal has a more irregular form, other empirical considerations must be included to arrive at an accurate estimation. Thus, investigators attempting to find a more precise estimation of body surface area in animals have introduced other measurements in their formulas. It is clear that the body segments comprising the longitudinal axis determine a large 1992) has shown proportion of total body weight. A recently-published study (PROTI-IERO that the head-trunk body segment constitutes some 70% of the body weight for a given
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M . Farriol, J . Rossello’ and S. Schwartz
species. W o r k i n g w i t h t h e dog, VALLOIS i n t r o d u c e d ‘abdominal length’ (mouth-tail) in his calculations. T h i s parameter, directly related t o t h e f o r m of t h e animal, proved t o b e a good choice. T h e weight of t h e animal, w h i c h c o r r e s p o n d s t o its age, is t h e m o s t reliable indicator of n o r m a l g r o w t h a n d a satisfactory state of health. I t has been described (GOLDSPINK and KELLY1984) i n rats t h a t t h e body weight increased approximately 3550-fold from t h e fetal age of 14 d a y s to senility (105 weeks). After 6 m o n t h s , thc weight of t h e rats reaches a plateau a n d a change in t h e g r o w t h c u r v e is p r o d u c e d . T h e c o m p a r i s o n of t h e measured surface of t h e animals studied a n d t h e d a t a obtained w i t h t h e VALLOIS f o r m u l a s h o w s that this calculation is a very accurate s y s t e m f o r estimating t h e surface area of Sprague-Dawly rats. T h e slight e r r o r s t h a t arose in t h e measurements of animals a t both extremes of the weight range studied do n o t imply a serious flaw in t h e system. T h e fact of measuring t h e length of t h e animal, although a simple act, w a s translated i n t o great precision i n t h e formula.
Summary A study was designed to measure the body surface area of Spraguc-Dawley rats and to compare thc results with those obtained using the mathematical formulas described by four authors to estimate this parameter. The animals were killed by an overdose of ether anaesthesia. To determine the gold standard body surface area, the skin of the animals was dissected completely and measured. The gold standard was compared with the body surface area obtained in the same rats using the mathematical equations proposed by MEEI-I,RUHNEK, VALLOIS and SAN ROMAN.Analysis of variance showed statistically significant differences (p < 0.05) in body surface area results between the gold standard and MEEH’S, RUBNIX’S,and SAN ROMAN’Sequations. However, no significant differences were found with VALLOIS’S formula, indicating that results with this calculation were similar to the measured body surface. Further statistical analysis showed that in the small animals the body surface area was undercstimatcd and in thc large animals it was ovcrestimated by a mcan of 20cm’ using the Vallois formula.
*
Zusammenfassung Die Messung der Korperoberjlache bei Sprague-Dawley Ratten In der vorliegenden Untcrsuchung wurde die Korperobcrflache von Sprague-Dawley Ratten gemessen und mit Resultaten aus mathematischcn Formeln von vier verschiedenen Autoren verglichen. Die Tiere wurdcn durch eine Uberdosis von Ether getotet, um dann mit Hilfe des Umrisses der Haut die Korpcroberflachc zu messen. Die Ergebnisse aus der Hautoberflachen-Messung wurde mit den Gleichungen von MEEH,RUBNER,VALLOISund SANROMANverglichen. Die Varianzanalyse zeigt deutlichc statistische Unterschiede (p < 0,05) zwischen dem ermittelten Wert und den mathematischen Ableitungcn bzw. Gleichungen von MEEH,RUBNERund SANROMAN.Es wurden keine statistischen Unterschiede zwischen den vorliegenden Messungen und der Formel von VALLOIS gefunden. Das zeigt, da8 dic Ergebnisse dieser Berechnung in ihrcr Genauigkeit ubereinstimmen. Zusatzliche Analysen zeigcn, da8 die Anwcndung der VAL1201s’schenFormel die Korperoberflache kleiner Tierc unterschatzt und die gro8er Tierc um einen durchschnittlichen Wert von 20 cmz uberschatzt.
References DEMICHELI?, S.J.; KAKLSTAD, D.; BKISTIAN, B. R.; ISTFAN,N.; BAIMYAN, V. G.; BLACKBURN, G . L., 1989: Am. J. Clin. Nutr. 50, 1295. FARKIOI., M.; SCHWAKIZ,S.; ROSSELI-0,J.; GALAKD, R.; CATALAN, R.; HUGUI:T,P., 1994: Burns 20, 496. GOLDSPINK, D. F.; KEILY‘, F. J., 1984: Biochem. J. 217, 507. , A,; FORBES,M.; GERMAN,E.; ROBERTS,F. J.; SNELIANG, C. F. T., 1991: GRAY,J. H.; H E N R Y D. Burns 17, 37. MCCARTEK, R. 1.; P A L M E R , J., 1992: Am. J. Physiol. Endocrinol. Met. 263, E448.
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K., 1993: Jik. Dob. 42, 635. OHWADA,K.; KATAHIRA, PROTHERO,J., 1992: Am. J. Physio. 262, 492. REILLY,J. J.; WORKMAN,P., 1993: Can. Chem. Pharmacol. 32, 411. M. A,; BONAFONTE,J. I.; SANCHEZ-VALVEKDE, B.. 1985: Sci. SANROMAN,F.; SANCHEZ-VALVERDE, Tec. Anim. Lab. 10, 181. SMITH,A. E.; GRAY,G. M.; EVANS,J. S., 1995: Reg. Toxicol .Pharmacol. 21, 339. ZAPATA-SIRVENT, R. L.; HANSBROUGH, J. F.; BENDER,E. M.; BARTLE,E. 1.; MANSOUK,M. A,; CARTER, W. H., 1986: Surgery 99, 53. Authors’ address: M. FAKRIOL and S. SCHWARTZ, ‘S. Grisolia’ Research Unit, Hospitals Val1 d’Hebron, Passeig Val1 d’Hebron 119-129, Barcelona (08035), and J. R O S S E L L Department ~, of Preventive Medicine, Hospitals Val1 d’Hebron, Passeig Val1 d’Hebron 1 19-129, Barcelona (08035), Spain.
