Estradiol replacement enhances sweet taste preference in ovariectomized Rats: Interaction with energy intake...

Estrogens exert anorectic and anti-obesity effects via homeostatic regulation. However, their role in hedonic ingestive behavior, particularly in sweet taste preference, remains unclear. We examined the effects of estradiol replacement on the intake of sweetened solutions, water, and total energy in ovariectomized rats with concurrent access to sweetened solutions, water, and a standard rodent chow. Compared with the non-replaced (E2 (-)) group, the estradiol-replaced (E2 (+)) group exhibited a higher intake of various sweetened solutions, including those containing non-caloric artificial sweeteners and natural sugars. Food intake was lower in the E2 (+) group than in the E2 (-) group. Total energy intake was lower in the E2 (+) group than in the E2 (-) group when rats consumed water, sucralose, and fructose, but not when rats consumed glucose or sucrose. To explore the involvement of micro-opioid receptors in the estrogen-induced enhancement of sucrose intake, we chronically infused naltrexone (NTX), a partial micro-opioid receptor antagonist. NTX attenuated sucrose intake in the E2 (+) group but not in the E2 (-) group. By contrast, NTX reduced food intake in the E2 (-) group. Additionally, c-Fos expression in the nucleus accumbens shell was attenuated by NTX in the E2 (+) group during the short-term sucrose preference test. These findings suggest that estrogen enhances sweet taste preference and that available palatable glucose or sucrose diminishes the estrogen-induced attenuation of homeostatic energy intake. Moreover, micro-opioid receptors possibly play a role in the estrogen-induced enhancement of hedonic sweet taste preference, while they are involved in the enhancement of homeostatic food/energy intake in the absence of estrogen.