Body surface area in the infant rat.

Body surface area (SA), one index used to minimize size differences in metabolic studies, was estimated by a coating method in rats aged 1, 7, 14, and 21 days (d) (n = 100-107). Body weights (BW) at each age varied about twofold. Regression equations were calculated for SA (cm2) vs. BW (g) (SA = 8.73 + 2.29 BW, 17.79 + 1.71 BW, -4.92 + 2.16 BW, and 53.68 + .82 BW at 1, 7, 14, and 21 days, respectively) and log SA vs. log BW (SA = 6.71 BW0-667, 9.12 BW0-577, 1.73 BW1-042, and 18.97 BW0-412). All the latter differed significantly from SA = 10 BE2/3, frequently used with adult mammals. Correlation coefficients were approximately 0.6-0.9 and did not differ with mode of expressing results. Regressions, whether linear or logarithmic, differed significantly among ages, apparently reflecting appreciable conformational changes in the rapidly growing and maturing preweanling rat.