The obese phenotype of the congenic LA/Ntul/-cp (corpulent) rat strain has developed obesity by 6 weeks of age. 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) to learn more about the role of adrenal cortical secretions in the expression of obesity in this strain's obese phenotype (WOA). A subset of obese rats (n=6) had bilateral adrenalectomy (ADX) at 6 WOA and were given the same feeding and treatment regimen. BW of lean and obese animals were similar 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-week 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 effect on final body weights in the lean phenotypes, but was associated with significantly greater body weights in the obese phenotype (p=0.05) at ages 9 and 12 WOA, as well as obese-ADX at 12 WOA. CE (kcal/gram gain in BW per day) remained essentially consistent throughout the trial in both lean and obese-ADX rats, however CE was more efficient in the obese phenotype at all ages tested and with the CAFE supplement feeding regimen. At 12 weeks of age, the obese had a 4.2-fold higher fasting I:G ratio than the lean, which was partially corrected in obese-ADX to a 1.7-fold rise at 12 WOA. Obese rats demonstrated a 3.8-fold higher relative adiposity than lean rats, with the highest increase in the SQ depot. Obese rats showed lower resting VO2 (RMR) than lean rats at all ages tested, which was aided by ADX. In comparison to lean rats, obese and obese-ADX rats exhibit higher thermogenic interscapular brown adipose tissue (IBAT). 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 returned to normal after ADX on the Chow diet but not the CAFE diet. These findings point to a variety of metabolic characteristics that contribute to superior energy storage, utilisation, and/or conservation efficiency in the fat phenotype of this strain compared to the lean phenotype, and that ADX partially corrected in the obese phenotype.
Author(S) Details
Orien L. Tulp
University of Science, Arts and Technology, Montserrat, British West Indies and The University of Health and Humanities, Virgin Islands, UK and The Einstein Medical Institute, FL, USA.
Aftab R. Awan
University of Science, Arts and Technology, Montserrat, British West Indies and The University of Health and Humanities, Virgin Islands, UK and The Einstein Medical Institute, FL, USA.
George P. Einstein
University of Science, Arts and Technology, Montserrat, British West Indies and The University of Health and Humanities, Virgin Islands, UK and The Einstein Medical Institute, FL, USA.
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