Opioid involvement in regulating the intake of highly palatable diets was studied by examining the effect of feeding either a corn- starch-based diet (CHO) or a high fat diet containing sucrose (Fat/Sucrose) on hypothalamic opioid levels. Rats received either CHO ad libitum, Fat/Sucrose ad libitum, Fat/Sucrose pair-fed to the caloric intake of CHO, or Fat/Sucrose at 60% of ad libitum Fat/Sucrose intake. Animals receiving Fat/Sucrose ad libitum consumed more calories and gained more weight than animals receiving CHO (P < 0.001). Relative to CHO, ad libitum intake of Fat/Sucrose elevated proDynorphin mRNA levels in the arcuate and Dynorphin A1-17 levels in the paraventricular nucleus (PVN) (P < 0.05), but did not affect arcuate mRNA levels of proEnkephalin or proOpiomelanocortin (POMC), or PVN levels of Met-Enkephalin or β-Endorphin. Pair-feeding the Fat/Sucrose diet to the level of intake of the CHO diet resulted in levels of proDynorphin and Dynorphin A1-17 that were similar in the two diet groups. Pair- feeding Fat/Sucrose reduced mRNA levels of proDynorphin, proEnkephalin and POMC, and Dynorphin A1-17 levels, relative to ad libitum feeding of Fat/Sucrose. Met-Enkephalin and β- Endorphin were not affected by dietary treatment. Feeding Fat/Sucrose at 60% of ad libitum intake resulted in mRNA levels of proDynorphin, proEnkephalin and POMC, and Dynorphin A1-17 levels that were similar to those observed in CHO group, Hypothalamic Dynorphin A1-'17 and proDynorphin mRNA levels are stimulated by feeding a highly palatable diet rich in fat and sucrose. The increased synthesis may be due in part to a palatability-induced overconsumption of calories. Calorie restriction of the same diet decreases mRNA levels of proDynorphin, proEnkephalin and POMC, as well as levels of Dynorphin A1-17.
Bibliographical noteFunding Information:
The authors are grateful to J.O. Douglass for generously providing the transformed cell stocks needed to produce the cDNA probes for proDynorphin, proEnkephalin and POMC. This work was supported by General Research Funds of the Department of Veterans Affairs (VA) Medical Center and by National Institutes of Health Grants DA-03999, DA-07097 and DK-42698.
- Highly palatable diet
- Opioid mRNA
- Opioid peptide