Hypothalamic neuropeptide Y and plasma leptin after long-term high-fat feeding in the rat

The ingestion of fat by rodents affects the level of neuropeptide Y (NPY) in the hypothalamus and we hypothesized that they might be linked via leptin, the adipose tissue hormone. The influence of fat intake on leptin and NPY levels was studied in rats fed on either a high-fat (HF) or a low fat diet (LF) for 5 months. Ingestion of the HF diet increased fat deposition (+48%; P < 0.01), leptinemia (+189%; P < 0.001) and reduced NPY levels in the arcuate nucleus (-35%; P < 0.01) and in the paraventricular nucleus (-22%; P < 0.01). However, although leptin levels reflected the amount of relative fat deposition (r = 0.62; P < 0.01), we found no evidence for a direct relationship between plasma leptin and NPY levels in the hypothalamus. These results suggest that the long-term effects of fat intake on NPY concentrations in the hypothalamus and plasma leptin are associated with different regulatory mechanisms.