Basic nutritional investigation Postprandial glycogen and lipid synthesis in prednisolone-treated rats maintained on high-protein diets with varied carbohydrate levels Omar A. Obeid, Ph.D.*, Leila K. Boukarim, M.Sc., Rima M. Al Awar, M.Sc., and Nahla Hwalla, Ph.D., R.D. Department of Nutrition and Food Sciences, Faculty of Agricultural and Food Sciences, American University of Beirut, Beirut, Lebanon Manuscript received January 21, 2005; accepted July 25, 2005. Abstract Objective: The present experiment was designed to study the effect of a high-protein, high- carbohydrate diet versus a high-protein, low-carbohydrate diet on in vivo postprandial glycogen and lipid synthesis of rats treated with prednisolone. Methods: Thirty-two 6-wk-old male Sprague-Dawley rats were randomly assigned to one of four equal groups: high-protein, high-carbohydrate; high-protein, high-carbohydrate with prednisolone; high-protein, low-carbohydrate; and high-protein, low-carbohydrate with prednisolone. Rats were sham operated or subcutaneously implanted with prednisolone pellets while being maintained on their respective diets (39% of energy from protein) for 6 wk. Food intake and body weight were monitored throughout the experiment. At the end of the feeding period, overnight-fasted rats were fed a test meal and injected with 3 H 2 O to measure in vivo rates of glycogen and lipid synthesis. Final plasma glucose, insulin, and triacylglycerol concentrations and hepatic glycogen content were also measured. Results: Results showed that hepatic glycogen content (milligrams per gram of liver) was similar across all four experimental groups. Total hepatic glycogen synthesis and its percentage synthesis via pyruvate (indirect pathway) were higher in rats maintained on the high-protein, high-carbohydrate diet compared with those on the high-protein, low-carbohydrate diet and this was not substantially affected by pred- nisolone administration. Hepatic and epididymal fat pad lipid syntheses were not altered by diet or prednisolone treatments. Conclusion: Under long-term high-protein conditions, prednisolone administration does not seem to affect hepatic glycogen synthesis, which was increased with the increased carbohydrate content of the diet. © 2006 Elsevier Inc. All rights reserved. Keywords: Prednisolone; Glucocorticoids; High-protein diet; Glycogen synthesis; Food intake; Energy balance; Rats Introduction The therapeutic use of glucocorticoids (GCs) is associ- ated with weight gain [1] and may play an important role in the initiation of obesity [2]. Weight gain may be useful only in patients who have a terminal illness [3]. However, in other conditions such as asthma and rheumatoid arthritis, this effect is undesirable and detrimental. Further, additional weight gain in obese individuals may aggravate obesity- related medical conditions, in particular glucose intolerance, hypertension, dyslipidemias, cardiovascular diseases, and osteoarthritis [4]. Human studies have shown that administration of thera- peutic doses of GC increases energy expenditure slightly but food intake markedly [1]. This suggests that GCs induce obesity mostly by promoting energy intake, an effect that may be related to the ability of GCs to directly or indirectly affect central regulation of appetite [1]. GC secretion is linked with meal times in normal humans and rodents [5,6], and increased appetite is associated with GC excess induced by Cushing’s disease or GC administration in normal vol- unteers [7]. This work was supported by a grant from the University Research Board, American University of Beirut. * Corresponding author: Tel: +961-1-350-000, ext. 4440; fax: +961- 1-744-460. E-mail address: omar.obeid@aub.edu.lb (O.A. Obeid). Nutrition 22 (2006) 288 –294 www.elsevier.com/locate/nut 0899-9007/06/$ – see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.nut.2005.07.014