Natriuresis of fasting: the possible role of leptin-neuropeptide Y system

We developed a new hypothesis claiming that natriuresis of fasting is not o nly caused by diminished insulin resistance and hyperinsulinaemia with the subsequent reduction of renal sodium retention but it can also be attribute d to the function of the leptin-NPY system. Each element of this concept ha s been substantiated by convincing experimental evidences as follows: 1. Leptin, the adipocyte-derived peptide hormone conveys information to the central nervous system about the size of body energy stores and it recipro cally regulates the hypothalamic expression of NPY, the major mediator of i ts metabolic and neuroendocrine actions. 2. NPY has been demonstrated to be intimately involved in the regulation of renal functions; under various experimental conditions it increased urine flow rate and urinary sodium excretion presumably through stimulating the s ynthesis and/or release of other natriuretic factors. 3. Fasting-induced suppression of tissue expression of leptin mRNA and circ ulating plasma leptin levels is associated with simultaneous activation of NPY system. 4. This sequence of events implies that NPY contributes to natriuresis that occurs in response to fasting. (C) 2001 Harcourt Publishers Ltd.