Downregulation of natriuretic peptide C-receptor protein in the hypertrophied ventricle of the aortovenocaval fistula rat.

Objectives: This study examined the expression of the C-type receptor for the natriuretic peptide family (NPR-C) in the ventricles of normal and aortovenocaval (AV)-fistula rats, the latter a model of cardiac volume overload producing hypertrophy of both ventricles.
Methods: Western blotting with a rabbit anti-NPR-C antibody was used to quantify NPR-C levels in ventricular membranes. NPR-C expression was localised anatomically and measured in frozen sections of cardiac tissue by histochemistry and in vitro autoradiography.
Results: Western blot analysis revealed a single band (approximately 120 kDa) in ventricular membranes which was reduced to approximately 60 kDa after treatment with beta-mercaptoethanol. NPR-C immunoreactivity and [125I]rat ANP1-28 binding (displaceable by the NPR-C-specific ligand C-ANP 4-23) were localised to the endocardium. NPR-C protein levels, as measured by all three techniques, were reduced significantly in the hypertrophied ventricles of AV-fistula rats compared to sham-operated animals.
Conclusions: Volume-induced cardiac hypertrophy in the AV-fistula rat is associated with downregulation of endocardial NPR-C. This may be one mechanism by which the endocardium regulates the myocardial response to changes in haemodynamic load.