Relationship of Alterations in Energy Metabolism to Hypophagia in Rats Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin

Relationship of Alterations in Energy Metabolism to Hypophagia in Rats Treated with 2,3,7,8-Tetrachlorodibenzo-p-dioxin. POTTER, C. L., MENAHAN, L. A., AND PETERSON, R. E. (1986). Fundam. Appl. Toxicol. 6, 89–97. Efficiency of energy utilization was evaluated temporally in 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 50 μg/kg)-treated male Sprague—Dawley rats (275–300 g), their pair-fed counterparts, and a group with ad libitum access to ground feed. TCDD treated rats exhibited a progressive reduction in feed intake and body weight. The weight loss of vehicle-treated rats, pair-fed to the TCDD-treated group, was comparable to that found in rats receiving TCDD. Following treatment, rats administered TCDD were as efficient in absorbing feed energy from the gut as control rats. This was evidenced by similar relative digestible energy values in TCDD-treated rats, their pair-fed partners, and a group with ad libitum access to feed. Equivalent decreases in oxygen consumption and carbon dioxide production in TCDD-treated rats and their pair-fed counterparts, relative to rats with ad libitum access to feed, suggested that the decrease in both of these parameters in TCDD-treated rats was secondary to hypophagia and/or weight loss. Decline of respiratory quotient (RQ) to almost 0.7 in both TCDD-treated rats and their pair-fed counterparts is indicative of fat combustion. By Day 17 post-treatment, RQ increased significantly in the TCDD-treated and pair-fed groups possibly due to a limitation in the availability of lipid stores. Also, TCDD-treated rats and their pair-fed partners diminished their water intake to a similar extent without reducing urine output. Likewise, urinary excretion of both energy and urea was decreased to the same extent in rats treated with TCDD as it was in their pair-fed counterparts. However, TCDD-treated rats tended to excrete more urinary ammonia than their pair-fed partners on Days 10 and 16 post-treatment. Thus, TCDD treatment does result in a reduction of caloric intake in the rat, yet efficiency of energy utilization is preserved.