Objective: To characterize the interactive effects of amylin with phentermine or sibutramine on food intake, body weight/composition and gene expression in diet-induced obese (DIO) rats.
Design: DIO rats were intraperitoneally injected with a single dose of amylin (10 microg kg(-1)) and/or phentermine (1 mg kg(-1)) or chronically infused with amylin (100 microg kg(-1) d(-1)) or vehicle with or without phentermine (0.5-10 mg kg(-1) d(-1)) or sibutramine (3 mg kg(-1) d(-1)) using two surgically implanted subcutaneous osmotic mini-pumps.
Measurements: Twenty-four hour food intake, locomotor activity and components of meal microstructure (meal size, latency, duration and intermeal interval) were measured following acute administration (amylin, phentermine or amylin+phentermine). Body weight and composition (for amylin and/or sibutramine or phentermine) and metabolism-related gene mRNA expression in the liver (fatty acid synthase, stearoyl-CoA desaturase-1 and carnitine palmitoyltransferase-1) and brown fat (beta-adrenergic receptors and uncoupling protein-1) were measured (for amylin and/or phentermine) after sustained infusion (2 weeks).
Results: Acute co-administration of amylin (10 microg kg(-1)) and phentermine (1 mg kg(-1)) reduced acute food intake (up to 19 h) more than either monotherapy. In two studies, sustained subcutaneous infusion of amylin for 2 weeks decreased cumulative food intake (22%) and vehicle-corrected body weight gain ( approximately 4-8%). Phentermine's anorexigenic (10-17%) and weight-reducing effects ( approximately 0-5%) were only evident at the highest dose tested (10 mg kg(-1) d(-1)). Combination of amylin (100 microg kg(-1) d(-1)) and phentermine reduced food intake (30-43%), body weight (8-12%) and adiposity to a greater extent than either monotherapy. Amylin prevented phentermine-induced reductions in UCP-1 mRNA in brown adipose tissue. When amylin+sibutramine were infused, mathematically additive decreases in food intake (up to 45%) and body weight (up to 12%) were evident. Similar to amylin+phentermine treatment, amylin+sibutramine mediated weight loss was attributable to significant reductions in fat mass.
Conclusions: Combined treatment of DIO rats with the pancreatic beta-cell hormone amylin and phentermine or sibutramine resulted in additive anorexigenic, weight- and fat-reducing effects.