Objective and design:

The early phase of weight loss induced by fasting is associated with diuresis, natriuresis and reduction in blood pressure through unclear mechanisms. Atrial natriuretic peptide (ANP) is a cardiac hormone with potent natriuretic, diuretic and hypotensive effects mediated by'biologically active'receptors (NPr-A). A second type of receptor mediates the clearance of ANP (the clearance receptor, NPr-C). Since NPr-C appears to be abundant in adipose tissue, we analysed NPr-C and NPr-A gene expression in white and brown adipose tissue (WAT and BAT) as well as in renal cortex of fasting rats. Plasma ANP, cyclic GMP and aldosterone were also measured.

Methods:

Twelve male Wistar rats were deprived of food for about 50 h, and 12 other rats were fed ad libitum. Periepididymal WAT, interscapular BAT and left renal cortex were used for RNA extraction and northern blot analysis with rat NPr-C and NPr-A complementary DNA probes labelled with 32P-dCTP. Densitometric analysis of hybridization signals was corrected by (3 actin expression before statistical analysis. Blood was drawn for ANP, cyclic GMP (cGMP) and aldosterone radioimmunoassays, which were also measured in a group of six rats deprived of food for 25 h.

Results:

A dramatic decrease in NPr-C steady-state messenger RNA levels was observed both in WAT (about 3.6-fold, P< 0.001) and in BAT (about threefold, P< 0.01), but fasting did not affect the expression of NPr-A in adipose tissues. In the renal cortex NPr-C and NPr-A messenger RNA levels were unaffected by fasting. ANP and aldosterone levels were reduced after fasting whereas cyclic GMP was increased at 25 h, but the differences did not reach statistical significance.

Conclusions:

Fasting exerts a tissue-specific and gene-specific suppression of NPr-C gene expression in adipose tissue that appears to be accompanied by an increased biological activity of ANP. The natriuresis and diuresis and reduction of blood pressure induced by fasting might result from a reduced expression of NPr-C in adipose fat pads.