Enhanced Caloric Efficiency Contributes To Adiposity In La/N//-Cp Corpulent Rats

Obesity is readily detected among 25% of the offspring of the congenic LA/Ntul//-cp (corpulent) rat strain by 5 to 6 weeks of age where it occurs as an autosomal recessive trait. The obese phenotype of this strain demonstrates characteristic glucose intolerance and varying degrees of insulin resistance, but typically remains euglycemic following insulinogenic dietary regimens. Groups [n=12-20 rats/phenotype] of female congenic lean and obese LA/Ntul//-cp rats were ad libitum fed standardized Purina #5012 stock diets for 4, 14, or 24 months or the same diet plus a 16% (w/v) sucrose solution (SSOL) supplement from 12 weeks of age, and measures of body weight (BW), caloric intake (CI), and caloric efficiency (CE) determined as outlined by Vedula et al at each age studied. BW of lean animals remained similar at all ages, while BW of obese phenotype were significantly greater than their lean littermates at each age studied. The SSOL supplement was without significant effect on final BW in the lean phenotypes at all ages studied (p=n.s.) but were associated with greater BW at ages 14 and 24 months of age in the obese phenotype (p=<0.05). CE was determined as the ratio of kcal/gram of BW per day remained relatively constant in lean animals throughout the age range, but CE was more efficient in the obese phenotype at all ages studied and became progressively more efficient with the SSOL supplement feeding with increasing age. The results of this study indicate that CE is associated with the predisposition for the development of obesity in the obese phenotype of this strain and likely implicates multiple metabolic factors that contribute to a greater efficiency of energy utilization and or energy conservation in the obese than in the lean phenotype of this strain, and the metabolic impact of added sucrose as a SSOL was associated with an additive impact on the CE of weight gain and adiposity in the obese phenotype of this congenic rodent strain. The implications of the greater adiposity and CE among the obese phenotype when ingesting the insulinogenic SSOL supplement being associated with increasing degrees of insulin resistance is a new finding for this strain of obese rodent and will be discussed. References 1Hansen, CT. The development of the SHR/N- and LA/N-cp Congenic Rat Strains. NIH pub, Div of Res Serv, Vet Res Br, NIH, Bethesda, MD p. 7-10. 1988 2Tulp, OL. Characteristics of thermogenesis, obesity, and longevity in the LA/N–cp rat. ILAR News 32(3), 32-39, 1990. 3Vedula, U, Schnitzer-Polokoff, R and Tulp. OL. The effect of acarbose on the food intake, weight gain, and adiposity of LA/N-cp rats. Comp. Biochem. Physiol. A Comp. Physiol., 100. pp. 477-482, 1991. 4Tulp, O.L. and Brown T. Effect of a Fructan-Chromium Complex on Glycemic Responses of Congenic Obese LA/Ntul/ /-cp Rats. Adv in Obes, Weight Mgmt & Control, 2016. 5Michaelis, OE. IV, Ellwood, KC, Tulp, OL and Greenwood, MRC. Effect of feeding sucrose or starch diets on parameters of glucose tolerance in the LA/N-cp rat. Nutr. Res., 6(2): 95-99, 1986. 6Bukowiecki LJ, Deshaies, Y, Collet, AJ and Tulp, O. “Major thermogenic defect associated with insulin resistance in brown adipose tissue of obese-diabetic SHR/N–cp rats”, Am J Physiol 261 (Endo Metab) E204-213, 1991.