Determining the Metabolic Effects of Adrenalectomy and Glycemic Parameters on Caloric Efficiency and Adiposity in the Congenic LA/Ntul//-cp (Corpulent) Rat

By 6 weeks of age, the obese phenotype of the congenic LA/Ntul/-cp (corpulent) rat strain has developed obesity. To learn more about the role of adrenal cortical secretions in the expression of obesity in this strain's obese phenotype, congenic male lean and obese LA/Ntul/-cp (corpulent) rats were fed an ad libitum standardised Purina chow diet (CHOW) from 6 to 12 weeks of age, and subgroups (n=6 rats / subgroup) were overfed with a highly palatable cafeteria diet (CAFÉ (WOA). At 6 WOA, a subgroup of obese rats (n=6) underwent bilateral adrenalectomy (ADX) and were given the same dietary and treatment regimen. BW of lean and obese animals were comparable at 6 WOA and increased by 88 percent in the lean phenotype and 281 percent in the obese phenotype over the course of the 6 weeks study, whereas BW of ADX obese rats were similar at 6 and 9 WOA but continued to increase to 2.5-fold above starting weights and 1.8-fold above 9-week weights between 9 and 12 WOA. The CAFE supplement had no influence on ultimate body weights in the lean phenotypes, but was linked with significantly higher body weights in the obese phenotype (p=0.05) at ages 9 and 12 WOA, as well as in the obese-ADX at 12 WOA. CE (kcal/gram gain of BW per day) remained relatively constant in lean and obese-ADX rats throughout the study, but CE was more efficient in the obese phenotype at all ages studied and was more efficient with the CAFE supplement feeding regimen. Fasting I:G ratios at 12 weeks of age were 4.2-fold greater in obese than lean and were partially normalized in obese-ADX to 1.7-fold increase at 12 WOA. Obese rats had a 3.8-fold higher relative adiposity than lean rats, with the SQ depot showing the largest increase. At each age studied, obese rats had lower resting VO2 (RMR) than lean rats, which was enhanced by ADX. Obese and obese-ADX rats have more thermogenic interscapular brown adipose tissue (IBAT) than lean rats. In conclusion, the findings of this study show that CE is associated with a predisposition for the expression and development of adiposity in this strain's obese phenotype, as well as an increased I:G ratio and IBAT mass, which are consistent with reduced insulin sensitivity and an impaired capacity for energy expenditure, and that CE became normalised on the Chow diet but not the CAFE diet after ADX. These findings point to a number of metabolic variables that contribute to better energy storage, utilisation, and/or conservation efficiency in the obesity phenotype of this strain than in the lean phenotype, and which were partially rectified in the obese phenotype by ADX.